ttrmitg Division Range Shelf..- Received... A MANUAL or CHEMISTRY, ON THE BASIS OF TURNER'S ELEMENTS OF CHEMISTRY", CONTAINING, IN A CONDENSED FORM, ALL THE MOST IMPORTANT FACTS AND PRINCIPLES OF THE SCIENCE. DESIGNED AS A TEXT-BOOK FOR COLLEGES AND OTHER SEMINARIES OF LEARNING. Titian. REWRITTEN AND RESTEREOTYPED, WITH MANY NEW ILLUSTRATIONS. BY JOHN JOHNSTON, LL. D., PROFESSOR OF NATURAL SCIENCE IN THE WESLEYAN UNIVERSITT. PHILADELPHIA: CHARLES DKSILVEK, 1229 CHESTNUT STREET. BALTIMORE : CUSHINGS & BAILEY. 1863. Entered, according to Act of Congress, in the year 1856, by CHARLES DESILVER, in the Clerk's Office of the District Court of the United States for the Eastern District of Pennsylvania. gTBXOTTPD BY J. PAOAII. TO PARKER CLEAYELAND, LL.D., PROFESSOR OP CHEMISTRY, MINERALOGY, AND NATURAL PHILOSOPHY, IN BOWDOIN COLLEGE, BRUNSWICK, ME.; DISTINGUISHED NO LESS FOR HIS PERSONAL VIRTUES THAN AS THE AUTHOR OF THE FIRST AMERICAN WORK ON MINERALOGY AND GEOLOGY lje follotofnfl 3Paaes are aaespecttullg Enacrflbetr, Dl TOKEN OP THE DEEP SENSE OP OBLIGATION ENTERTAINED BY HIS FRIEND AND FORMER PUPIL, JOHN JOHNSTON. . (itt) PREFACE \ TO THE PRESENT, OR SIXTH REVISED EDITION BY the original contract between the publishers and compiler of this work, provision was made for a periodical revision, in order that new and important discoveries might be introduced without delay, and the work be made to conform as much as possible to the rapidly advancing science. These revisions have been carefully attended to, and considerable alterations in the plates from time to time have been required; the whole of the part on Organic Chemistry, in the last preceding revision, having been rewritten and restereotyped. But the progress of the science is, and has been, still onward ; new and important facts have rapidly been made known, and new views, throwing more or less light on points heretofore considered obscure and doubtful, have 4)een proposed ; so that in the present revision an entire recast of the work has been found necessary. Encouraged by the favor heretofore sKown the work, the publisher has cheerfully incurred the expensed stereotyping it anew, including the preparation of many new illustrations ; and the results of our joint labors are here presented to the public in a book substantially new, though retaining the former title. The changes which have been made are too great and important to be discussed here ; for a knowledge of them i* (v) VI PREFACE. the intelligent reader is referred to the pages of the work itself; they are such only as the new aspects of the science seemed imperatively to demand. The principles which have been followed in its preparation are indicated in the extracts from the advertisements to former editions, which will be found further on. Many of the new cuts have been derived from the profusely illustrated work of Reg- nault ; others are original, or have been obtained from miscellaneous sources. The Grouping of the Elements adopted is nearly the same as that of Gmelin ; it is not free from objection, but is considered the best yet proposed on this difficult point. In preparing the remarks introductory to the part on Organic Chemistry, important aid has been derived from Dr. W. Gibbs' " Report on the Recent Progress of Organic Chemistry," prepared for the American Asso- ciation for the Advancement of Science, and printed in the Proceedings of their ninth Meeting, at Providence, B. L, August, 1855. Many thanks are due to teachers and other kind friends, for judicious suggestions and encouraging words during the preparation of the work ; and it is now offered to the public in the confident expectation that it will be found,, not less adapted for use in the school or lecture-room than preceding editions. MlDDLETOWN, CT., July, 1856. EXTRACT FROM THE ADVERTISEMENT TO THE FIRST EDITION, (1840.) THE preparation of the following pages was undertaken by the advice .of the late lamented President of the Wesleyan University, with the primary design of providing a suitable Text-book on Chemistry, for the use of the annual classes in that institution. There are indeed already before the public many excellent works on this branch of science, the great merits of which the subscriber is happy to acknow- ledge; but he long since became convinced, from his experience in teaching, of the need of a work of a little different character, for the special use of students in our higher seminaries of learning, as a text-book. The object of a great majority of students, even of those who pursue a collegiate course, is, not tt make themselves familiar with minute details of facts or processes of mani- pulation, but to understand the great principles of the science, and the leading facts which serve for its foundation. To facilitate the accomplishment of this purpose is the object of the present work. In preparing it, the excel- lent "Elements of Chemistry" of the late Dr. Turner has been adopted as the basis, and all of that work incorporated in it which was suited to our purpose. Ills arrangement has been uniformly followed, with a few unimportant excep- tions, which it is not necessary here to particularize. This arrangement, on the whole, is considered the best that has ever been proposed. The part of Dr. Turner's work omitted is taken up chiefly with details of facts and discussions of opinions and theories, which indeed is important in a work designed for the general student, but which would be out of place in a book prepared expressly to be used as a text-book. Its place, however, has been in part supplied by matter compiled from various other sources, so that the work is thought to be sufficiently large for the ordinary use of students, as the study of this science is usually pursued in this country. It has constantly been an object, while the work should be true to the science, and present in true proportion all its important features, to make it at the same time as practical as possible ; to lead the student to apply the principles he learns to the solu- tion of natural phenomena, or processes he may witness in the arts. EXTRACT FROM THE ADVERTISEMENT TO THE SECOND EDITION, IN the present edition the work hasjjeen carefully revised, and indeed re- compiled from the seventh edition of Turner's, and many additions made to adapt it to the advancing state of the science. * * * * The extracts from other authors are always introduced in their own lan- guage, except in cases where it was necessary to make some little change to incorporate the extract the better with the passage with which it comes in connection. In a few instances the names of authors are introduced in the text. To avoid the necessity of constantly introducing quotation marks and references, a list of the authors which have been used will be given. To facilitate the acquisition of the science, the text is divided into paragraphs, and numbered; and references to important facts and principles introduced as frequently as they seemed necessary. As in many institutions so much time cannot be devoted to this science as would be requisite for a thorough study of the whole work, the less important parts have been printed in smaller type, which may be omitted on the first reading. The intelligent student, however, it is hoped, will not be satisfied without a perusal, at his hours of leisure, of the whole work. (vii) LIST OF WORKS MADE USE OF, MORE OR LESS, IN THE PREPARATION OF THIS WORK. Elements of Chemistry, by the late Edward Turner, M.D., F.R.S., Ac., edited by J. Liebig, M. D., Ph. D. F. R. S., &c., and Wm. Gregory, M. D., F. R. S. E. Elements of Chemistry, &c., by Robert Kane, M.D., M.R.I.A., &c. Dublin. Chemistry of Organic Bodies, by Thomson. Do. Inorganic Bodies. Two vols. Ure's Dictionary of Chemistry. Two vols. Encyclopedia Metropolitana. Articles, Electro-magnetism, Electricity, Galvanism, Heat, Light, and Chemistry. Library of Useful Knowledge. Articles, Electricity, Galvanism, Magnetism, Electro- magnetism, Chemistry, &c. Thomson's Outlines of the Sciences of Heat and Electricity. Traite de Chimie Appliquee aux Arts, par M. Dumas. Six tomes. Traite de Chimie, par J. J. Berzelius ; traduit par Me. Esslinger. Huit tomes. Abreg6 Eleinentaire de Chimie, par J. L. Lassaigne. Deux tomes. Organic Chemistry in its applications to Agriculture and Physiology, by Liebig, edited by Webster. Animal Chemistry, or Organic Chemistry in its applications to Physiology and Pathology, by Liebig. Lectures on Agricultural Chemistry and Geology, by J. F. W. Johnston. Elements of do. do. Thomson's " First Principles." Two vols. Prof. Silliman's Chemistry. Two vols. Prof. Hare's Compendium of Chemistry. Faraday's Chemical Manipulation, edited by Dr. J. K. Mitchell. Thomson's History of Chemistry. Two vols. A Treatise on Chemistry by Michael Donovan, Esq.; Lardner's Cabinet Cyclopedia. Prof. John W. Webster's Manual of Chemistry, on the basis of Prof. Urande's. United States' Dispensatory, by Drs. Wood and Bache. American Journal of Science and the Arts, conducted by Prof. Sillimaa. Henry's Elements of Chemistry. Three vols. Cleaveland's Mineralogy and Geology. Dana's Mineralogy. Shepherd's Mineralogy. Three vols. Griffin's Chemical Recreations. Journal of the Franklin Institute. Parke's Chemical Catechism. Chaptal's Chemistry applied to Agriculture. Elements of Chemistry, by M. Lavoisier, translated from the French by R. Kerr, F. R. S. Watson's Chemical Essays. Five vols. Noad's Chemical Manipulation and Analysis. Do. Lectures on Electricity. Knapp's Chemical Technology. Vols. I., II. Gibbs' Report on the Recent Progress of Organic Chemistry. Gmelin's (L.) Hand-book of Chemistry, translated by Henry Watts. Vols. I. to IX. Traite de Chimie Elementaire. Theorique et Pratique, par L. J. Thenard. Cinq tomes, Cours de Chimie Elementaire, par A. Bouchardat. Deux tomes. Lemons sur la Philosophie Chimie, professes an College de France, par M. Dumas. Theorie des Proportions Chimiques, et Table Synoptique des Poids Antomiques, etc., par J. J. Berzelius. Trnite de Mineralogie, par M. L'AbbS Haiiy. Quatre tomes. Elements de Physique, etc., par M. Pouillet. do. Lehrbuch der Chimie, von E. Mitscherlich, Berlin, 1844. Orundriss der Chimie, von Professor Dr. F. F. Runge. Cours de Chimie Generale, par J. Pelouze et E. Fremy. Trois tomes, accompagne" d'un Atlas de 46 Planches. Gcrhardt (Ch.), Trait6 Chimio Organique. Regnault, Cours Klementaire do Chimie. The same, translated into English by Dr. T. F. Betton, M. D. Besides the above, reference has often been made to various other works, as Le Diction- naire des Sciences Naturelles, Annales de Chimie et de Physique, the various Encyclopedias, Philosophical Transactions, &c. (viii) CONTENTS. PAET I THE IMPONDERABLE AGENTS. PAOB INTRODUCTION , 13 I. HEAT. Nature and Sources of Heat 17 Expansion of Bodies by Heat ... 18 Thermometers 22 Distribution of Heat 29 Relation of Heat to Changes in the State of Bodies 36 Specific Heat. Capacity of Bodies for Heat 58 II. LIGHT. Nature and Sources of Light 60 Distribution of Light 65 Decomposition of Light 68 III. ELECTRICITY. Nature of Electricity. Electrical Theories 74 Distribution of Electricity 76 Sources of Electricity 81 Galvanism 88 Effects of Galvanic Electricity '102 Electro-magnetism Ill PART II. GENERAL CHEMISTRY. The Elements. Chemical Affinity 137 Laws of Combination. Atomic Theory 143 Nomenclature of Chemistry. Symbols .... v 151 Crystalography 168 ,ale into its centigrade equivalent ? How may we convert centigrade ,ato Farenheit degrees ? Is mercury always used in constructing ther- mometers ? s _212 167 _122 _77 100 75 50 25 _80 40 _20 Different Thermometers. 26 THERMOMETERS. the extremes of temperature that may occur during the absence of the observer. It consists of two thermometers, with the stems bent near the bulb, and placed in a horizontal position, attached to the same frame, as shown in the following figure : i i i i Register Thermometer. The one usually placed uppermost is a mercurial thermometer, having in the tube a small piece of iron or steel wire, which is pushed forward by the mercury as it expands, but does not recede with it when it contracts. The point at which the iron is left, of course shows the maximum temperature attained. The other thermometer is filled with colored alcohol, and contains in the liquid in the stem a similar piece of iron, inclosed in glass to pre- vent oxidation, around which the alco- hol flows while that in the bulb is ex- panding, so as not to be moved, but which is drawn along with it by capil- lary attraction, when it contracts so as to be kept at its surface. It is there- fore left at the lowest point to which the spirit has contracted, and of course shows the minimum temperature. Both pieces of iron or steel, which thus serve as indices, may be brought to any posi- tion in their respective tubes by means of a magnet applied on the outside. j 23, Breguet's Thermometer is made entirely of solids. It consists of ;A very Breguet's Thermometer. thin strip of platinum, soldered to a QUESTIONS. 22. Describe the register thermometer. fitter. BregueVs thermo- THERMOMETERS. 27 similar strip of silver, and coiled in a spiral, as shown in the figure (page 26). The upper end of the coil is then attached to a firm support, and to the other extremity is fixed a pointer or index, which is made to revolve by any change of temperature, by reason of the unequal expansions and contractions of the two metals. Beneath the pointer is placed a circle which may be gra- duated to any scale desired. It is a very delicate instrument. A modification of this instrument is used in the United States' Coast Survey, for determining the temperature of the water in deep soundings, at sea. The Pyrometer (from pur, fire, and metron, a measure,) is an instrument for measuring temperatures too high to admit of the use of the thermo- meter. The only one now in use is Daniel's pyrometer, which is not of sufficient importance to require description here. By it the melting point of cast iron has been shown to be about 2786 F., that of gold to be about 2016 F., copper 1996, silver I860 , and zinc 713 a . 24. Exceptions to the. general Law of Expansion. There is a remarkable exception to the general law (14) concerning the expansion of bodies by heat, as above stated. Water is most dense at the temperature of about 40, and expands, whether it is heated above this point or cooled below it. To show this, fill an ounce vial with water at a tempera- ture of 65 or 70, and adapt to it a cork, through which passes a glass tube of small bore. Then insert the cork and tube, and fill the latter with water one or two inches above the neck of the vial, and expose the whole to the cold atmosphere of winter, or immerse the vial in a freez- ing mixture of snow and salt ; the contraction of the water in the vial will very soon be made evident by the fall of that in the tube ; but the falling will shortly cease, arid an x;pward motion commence, indicating an expansion of the Water in the vial, although its temperature must be all the time falling. The volume of the water has there- fore first been diminished by reduction of its heat, and WaterKxpanrfon again expanded ; and by making use of the thermometer, when Freezing, it is found thatthe change takes place at about 39 or 40. A large tnermometer tube, nearly filled with water, may be used for the same purpose. 25. The most important effects result from this remarkable property of water. If the density of water continued to increase until it arrived at the freezing point, as is the case with mercury QUESTIONS. What is the design of the Pyrometer ? 24. What exceptions are there to the general law of expansion of bodies by heat ? Describe the method of showing the expansion of water by reduction of temperature. 28 THERMOMETERS. and other liquids, ice would be heavier than water, and as soon as formed would subside to the bottom in successive flakes, until the whole of the water, however deep, would become solid. The effects of such an arrangement can be easily conceived. Countries which, in the present state of things, are the delightful abodes of innumerable animated beings, would be rendered uninhabitable, and must inevitably become dreary and desolate wastes. But, since water expands previously to its freezing, as well as during this change, ice is lighter than water, and floats upon its surface, protecting the water, to some extent, from the further influence of frost. The cause of the expansion of water at the moment of freezing is attri- buted to a new and peculiar arrangement of its particles. Ice is in reality crystallized water, and during its formation the particles arrange them- selves in ranks and lines, which cross each other at angles of 60 and 120, and consequently occupy more space than when liquid. This may be seen by examining the surface of water while freezing, and still better by receiving particles of snow as they fall upon a piece of black cloth. They will often be found to be small but beautiful crystals or collections of crystals, presenting a great variety of forms. Some of the more com- mon forms are shown in the figure. Snow Crystals. QUESTIONS. 25. What is said of the importance of this remarkable pro- perty of water ? What is suggested as the cause of this expansion of watt* in freezing ? DISTRIBUTION OF HEAT. 29 26. The view just taken of the cause of the expansion of water when freezing is sustained by the facts observed in the formation of anchor ice, or ground ice, as it is often called. This ice is found in certain circumstances at the bottom of bodies of water, and not at the top, as with ordinary ice. It has little tenacity, and may be supposed to consist of the primary crystals of water. Separately, they are believed to possess a 'higher specific gravity than water, but, when aggregated according to the law stated above, at angles of 60 and 120 to form common ice, on account of the insterstices necessarily left among them, the volume is so increased as to diminish the specific gravity to the point we usually witness. Manuseript Notes of Professor Cleaveland's lectures in Bowdoin College, 1832. DISTRIBUTION OF HEAT. Heat constantly tends to diffuse itself, and its distribution is effected by Conduction, Convection, Radiation, Reflection, and Transmission. 27, Conduction of Heat. Heat is said to be conducted, when it is transmitted from particle to particle through a body, as when one end of a metallic bar is held in the fire until the whole becomes heated. The passage of the heat in such cases is evidently progressive, as may be shown in the following hianner. Take a small bar of copper, 18 or 20 inches in .. length, and cement to it several small bullets, or mar- bles, about two inches from each other, by means of wax, as shvwn in the figure, and then apply the heat of a lamp to one end. As the heat progresses along the Conduction of Heat. bar, it will melt the wax^ and the balls will drop off in succession, QUESTIONS. 26. What is said of anchor ice in this connection ? What ave some of the modes by which heat tends to diffuse itself? 27. When is heat said to be conducted? How may the conduction of heat along a bar of copper be shown ? 3* 30 DISTRIBUTION OF HEAT. the one nearest the lamp falling first, and the one farthest from it last. Substances differ greatly in their power of conducting heat; a rod of glass, or a piece of charcoal, an inch long, may be heated to redness at one extremity, and yet be held in the fingers by the other extremity; but it cannot be done with a similar piece of metal, because, on account of its better conducting power, thj whole very soon becomes too much heated. The apparent temperature of a body, as determined by the hand, will often depend upon its conducting power. Thus, if on a cold morning of winter, the hand is placed upon a piece of metal, and then upon a piece of woollen cloth, the former will feel much colder than the latter, because the metal in equal times conveys away from the hand more heat than the cloth. 28. Substances are divided into two classes in reference to their ability to conduct heat, called conductors and non-conductors. There are, however, no absolute non-conductors; heat penetrates the substance of all bodies ; the only difference in them, in this respect, is in the rapidity with which the process takes place. Gold is usu- ally considered the best conducting substance known; and very porous solids, the interstices of which are filled with air, as cotton, or sheep's wool, and fur, are the poorest con- ductors. A convenient method to determine the relative conducting power of dif- ferent substances, is, to have them made into cylinders of equal diame- ter, and set in a thin piece of wood at sufficient distances from each other, both extremities of each piece projecting a little from the wood. If the board be held in QUESTIONS. Do substances differ from each other in their power to con- duct heat? Why will some substances feel colder than others, when it is known that all must be at the same temperature ? 28. Into what two classes are substances divided in reference to their conducting powers ? What is usually considered as the best conductor known ? What method for determining the relative conducting power of several substances is pointed out ! DISTRIBUTION OF HEAT. 31 a horizontal position, a small piece of phosphorus may be placed upon the upper extremity of each of the substances experimented upon, and the lower ends exposed to the same temperature by plunging them in heated oil or sand : and the times that elapse before the ignition of the phosphorus upon the several substances, will indicate with some accuracy their relative conducting powers. The following table exhibits the relative conducting power of several metals and other substances : Gold 1000 Silver 973 Copper 898 Platinum 381 Ion 374 Zinc 363 304 180 23 12 Fine Clay 11 Tin Lead Marble..., Porcelain. In the arts, advantage is taken of the imperfect conducting powers of bodies, to prevent the passage of heat in any direction, particularly in confining it. Hence furnaces are generally lined with " fire-brick," or a thick coating of clay and sand. Wooden handles are fitted to metallic vessels, or a stratum of wood or ivory is interposed between the hot vessel and the metal handle. Ice-houses are constructed with double walls, which have their interstices filled with fine charcoal, saw-dust, or some other non-conducting substance, to prevent the influx of heat from without. The design of clothing is to retain the heat produced by the system : and hence the warmest clothing will be that which possesses the least conducting power. In winter, the poorest* conductors are selected, and in summer the best, as it is then desirable that the superfluous heat maybe permitted at once to escape. If, in summer, the temperature of the atmosphere should rise considerably above that of the system, it would be found advantageous to use the same clothing as in cold weather. Snow, in consequence of its imperfect conducting power, serves as clothing to the .earth, and prevents its surface from being cooled down as low as it would otherwise be. Liquids of all kinds, except mercury, are poor conductors of heat. This may be shown by ce- menting a thermometer tube in a glass funnel, inverting it, and filling it with water, so as to cover t-he bulb about a quarter of an inch, or eve '^.,as shown in the figure. Then pour upon the surface Ether burns on the surface of Watec. Cfe. -iTiONS. What is the use of "fire-brick" in coal-stoves? How are ice-houses constructed? What is the design of clothing? What is said of the benefits of snow in winter? How ia the poor conducting power of liquids shown by the burning of ether ? 82 DISTRIBUTION OF HEAT. of the water a little sulphuric ether, aiid inflame it; the ether will burn brilliantly, but without affecting the thermometer for some time, although the flame is so very near the bulb. In like manner, heated oil, poured upon the surface of water in a tum- bler, can scarcely be made to affect a small thermometer placed at the bottom. If a tube ten or twelve inches long be nearly filled with water and placed in an inclined position, so Water boils in vessel with Ice. r that the heat of a spirit-lamp can be applied near the centre, the water in the upper part of the tube may be made to boil, while the, lower portion will remain per- fectly cold. If, before applying the heat, a piece of ice be con- fined to the bottom, it will remain unmelted while the water above is boiling. Mercury, though liquid, is a Very good conductor of heat. Gases are even poorer conductors than liquids ; and it is for this reason that very hot or very cold air can be endured in contact with a person, though exposure to a liquid of the same temperature would produce intense pain, or perhaps even worse effects. Double windows and double doors, with air between them, are sometimes used to insure the greater warmth of dwellings. 29. Convection of Heat. Though fluids are poor conductors of heat, yet, if the heat be applied to the bottom of the vessel con- taining them, in consequence of the mobility of their particles, it is rapidly diffused through the whole mass. The heated portions are expanded, and becoming, in consequence, specifically lighter than the rest, they rise through the centre of the vessel, the colder portions around the sides at the same time descending to take their place. Thus an upward and a downward current will be at the same time established, which will continue until the whole is heated to the boiling point. This mode of distribution is called the convection of heat. w QUESTIONS. How is the poor conducting power of liquids shown by the boiling of water in a vessel containing ice ? 29. How is the heat dis- tributed through a liquid when it is applied to the bottom of the vessel containing it ? What name is given to this mode of the distribution of heat ? DISTRIBUTION OP HEAT. S3 These currents may readily be shown by filling a flask -with water containing some insoluble powder, as pulverized gum copal, and applying the heat of a small lamp, as represented in the figure. When large quantities of. water are slowly heated, the upper portions will frequently be found quite warm; while that in the lower part of the vessel will remain comparatively cold ; iind this though the fire is applied beneath. Hence it is not unfrequent, in bathing establish- ments, to draw both warm and cold water from the same reservoir. Similar currents are produced in gasea when heated ; and it is on this account that the heated air, with the smoke and other fjases from a fire, ascend in a chim- ney, or the pipe from a stove. 30. Radiation of Heat, A hot body suspended in the air emits heat in all directions in right lines, like Currents formed in vessel oF Water radii drawn from tffe centre to the surface of a sphere. This mode of distribution is termed the radiation of heat. The radiation of heat from hot bodies is singularly influenced by the nature and condition of their surfaces, which is perhaps the most important circumstance connected with the subject. It is probable that every sub- Stance in nature has a radiating power peculiar to itself, but, in any case, very much will depend upon the nature of the surface of the body. By many experiments, it has been proved that bodies with bright polished surfaces retain their heat much longer than when their surfaces are rough and unpolished. Adding even a thin coat of whiting or lampblack to a bright tin vessel greatly increases the radiating power of its surface, so that boiling water or other hot liquid contained in it will be cooled- more rapidly in consequence. The same effect will be produced by scratching its surface with coarse sand-paper. Some important practical considerations will naturally suggest themselves in connection with this subject. Whenever it is desired that the heat of a fluid or <3ther substance should be retained, vessels with bright and polished metallic surfaces should be used, but the reverse if the heat is to be distri- buted. Thus tea and coffee pots are usually made of some bright metal, while stoves and stove-pipes, for the diffusion of heat, are made with dark and rough surfaces. Pipes to convey steam from the boilers in steam- engines to the cylinders, and pipes to convey heated air from furnaces to the different apartments of a building, should be bright, or else they should be protected by some non-conducting covering. QUESTIONS. 30. When is heat said to be radiated? How is the radia- tion of heat affected by the nature of the surface of the hentcd body? What surfaces radiate best ? What practical considerations suggest themselves in view of these principles ? 34 DISTRIBUTION OF HEAT. 31. Reflection of Heat That heat may be reflected, may be shown by standing at the side of a fire in such a position that the heat cannot reach the face directly, and then placing a plate of tinned iron opposite the grate, and at such an inclination as per- mits the observer to see in it the reflection of the fire ; as soon as it is brought to this inclination, a distinct impression of heat will be produced upon the face. If a line be drawn from a radiating substance to the point of a plane surface by which its rays are reflected, and a second line from that point to the spot where its heating power is exerted, the angles which these lines form with a line perpendicular to the reflecting plane are called the angles X)f incidence and reflection, and are invariably equal to each other. Thus, let AB (see figure) be the rejecting surface, and R a ray of heat, which strikes A. D IB this surface at D, in the direction RD; it Reflection of Heat. wil1 be thrown off or reflected in the direction DL If a perpendicular PD be erected at tke point D, the angle RDP will be the angle of incidwace, and IDP the angle of reflection. These principles, which have just been developed concerning heat, apply as well to the invisible rays emitted from a moderately heated substance, as to those accompanied by light from an incandescent body, or the rays of the sun. 32. The Absorption of Seat by bodies sustains an intimate relation both to its radiation and reflection. Bright, and polished* surfaces, it is well known, are the best reflectors j and these are just the ones, we have seen (30), which radiate least. And rough, unpolished surfaces, which radiate heat best, are found to be the best absorbers. Surfaces may therefore be divided into two classes, those which afford an easy passage to heat, and those which do not. The former will be good radiators and absorbers, and the latter good reflectors and retainers. The color of a body influences considerably its absorbing, but not it3 radiating power; surfaces that are black, other things being equal, absorb- ing heat more readily than those of a lighter color. QUESTIONS. 31. How may the reflection of heat be shown ? Define the angles of incidence and reflection. Do these principles apply to rays of heat unaccompanied by light? 32. What surfaces are the best absorbers of heat? Into what two classes may surfaces be divided in reference to their power to transmit heat ? DISTRIBUTION OF HEAT. 35 Both the radiation and the reflection of heat are well shown by placing a heated cannon-ball in the focus of a concave reflector, having another similar reflector facing it at a distance, in the focus of which is placed one Parabolic Reflectors. of the ^ulbs of a differential thermometer. The rays from the ball C are reflected in parallel lines from the reflector A (see figure), and are again concentrated on the thermometer D, by reflection from the second concave mirror B. If a piece of phosphorus be substituted for the thermometer at D, it may often be inflamed, even when the reflectors are ten or twenty feet distant from each other. If a lump of ice is made use of, instead of the heated ball, the thermo- meter in the focus of the other reflector will fall ; in which case the bulb of the thermometer is the radiating body, and its heat is received by the ice. 33, Transmission of Heat, When a ray qf heat is thrown^ipon a body, it must either be reflected ', absorbed, or transmitted by the body. We have already seen the conditions upon which reflection and absorption depend, and it remains only to consider the circum- stances of transmission. In general, transparent substances afford the most ready transmission of heat, but there is a great difference among them in this respect. Even atmospheric air transmits heat but imper- fectly. This is shown conclusively by an experi- ment of Daj-y. He contrived to heat a platinum wire by means of galvanism, within a receiver con- taining two concave reflectors, with a thermometer in the focus of one of them, the heated wire being in the focus of the other. Now, when the air was exhausted to f ^th part of its ordinary density, the thermometer, it was QUESTIONS. Explain the effect of parabolic reflectors in reflecting heat. How is a lump of ice to be used instead of a heated ball ? 33. When a ray of heat falls upon a body, in what three ways may it be disposed of? How does the presence of the air affect the transmission of heat? Transmission of Heat in a Vacuum. 36 RELATION OF HEAT found, -would be raised, by means of the ignited wire, three timw as high as when the air in the receiver was at its natural pressure. Bodies that transmit heat freely are said to be diathermanous (from the two Greek words, dia, through, and thermos, heat), as those which afford a free passage to light are said to be transparent. By experiments made with a very delicate piece of apparatus, called the thermo-multiplier, it has been shown that the most diathermanous sub- stance known is rock-salt, in pure transparent crystals. Of different specimens of glass, some are much more diathermanous than others, though all are equally transparent ; and some colored glasses, and other bodies only partially transparent, afford a ready passage to heat, or aro highly diathermanous. It appears, also, that the ray of heat, like a ray of light, is really com- pound, or composed of rays of heat of different kinds, some of which have a greater penetrating power as regards most diathermanous media, than, others. In this respect heat from an oil-lamp will differ from that of a spirit-lamp, though both are equally intense; and the heat of both will differ from that of heated metal. The rays of heat from the sun possess this penetrating power, as I have called it, in a greater degree than any kind of artificial heat. Thus, a pane of window-glass, held between the face and a coal-fire, is found at once to intercept most of the heat ; but no such effect is produced by holding it before the face when exposed to the direct solar ray. The rays of heat, like those of light, may be^ refracted ; and some of them being more refrangible than others, like the different colors of light, they may be separated from each other by means of the prism. The ray of heat, like a ray of light, may also be polarized, and in a similar manner. See Decomposition and Polarization of Light. RELATION OF HEAT TO CHANGES IN THE STATE OF BODIES. 34. Relation of the Three Forms of Matter to each other. "We have seen above (10), that, omitting the imponderable agents, which are^not known to be material, every substance must be in one of the three forms, or states, solid, liquid, or gaseous; and that the particular form a body assumes will depend upon the relative intensity of the cohesive and repulsive forces existing among its particles. If the repulsive force be comparatively feeble, the particles will adhere 80 firmly together, that they cannot move freely upon one another, thus QUESTIONS. What are diathermanous bodies? Will heat from all sources be transmitted alike ? What is said of the rays of the sun ii this connection? May the rays of heat be refracted? Polarized? 34. Upon what will the particular form or state of a body depend ? TO CHANGES IN BODIES. 37 constituting a solid. If cohesion is so far counteracted by repulsion that the particles move on each other freely, a liquid is formed : and, should the cohesive attraction be entirely overcome, so that the particles not oiily move freely on each other, but would, unless restrained by external pres- sure, separate or expand to an indefinite extent, an aeriform substance will be produced. Now, the property of repulsion is manifestly owing to heat ; and as it ;is easy, within certain limits, to increase or 'diminish the quantity of this ; principle in any substance, it follows that the forms of bodies may bo made to vary at pleasure : that is, by heat sufficiently intense, we have reason to believe, every solid, provided decomposition does not take place, may be converted into a liquid, and every liquid into vapor. The converse ought also to be true; and, accordingly, several of the gases have been condensed into liquids by means of cold, or cold and pressure combined, and the liquids have been solidified. The temperature at which liquefaction takes place is called the melting point, or point of fusion ; and that at which liquids solidify, their freezing point, or point of congelation. Both these points are different for different substances, but usually the same, under similar circumstances, in the same body. 35. Liquefaction, By the liquefaction of a substance, we mean its reduction from either the solid or gaseous to the liquid state; but generally it is the former change which is intended. If, when the temperature of the air is at zero, as is often the case in some parts of our country, a quantity of ice be brought into a room, and placed near a fire, it will be gradually heated, like any other solid, as a thermometer placed in it will indicate, until the temperature reaches 32 ; but it will stand at this point until the whole is melted. The thermometer will then begin again to rise, as it did before. Now, it is plain that it must have been receiving heat as rapidly while the thermometer was stationary, as before and afterwards; but the heat thus communicated did not affect the thermometer, because it was all absorbed by the ice, and was expended in changing the ice into water. It has there- fore become insensible to the thermometer, and is properly called latent heat; and if it was known to be material, we might per- haps, with some propriety, consider water as a compound of ice and heat. The quantity of heat which is thus lost or becomes insensible, during the melting of a mass of ice, is sufficient to raise the tern- QUESTIONS. To what is the property of repulsion owing? What is the melting point of a body ? The freezing 'point ? 35. What is meant by the liquefaction of a body ? Is heat always required to produce lique- faction ? Why cannot ice be heated above 32 ? 4 38 RELATIONOPHEAT perature of an equal weight of water about 140, as may be shown in the following manner : Let a pound of water at 32 be mixed with a pound of water at 172, and the temperature of the mixture will be intermediate between them, or 102. But if a pound of water at 172 be added to a pound of ice at 32, the ice will quickly dissolve, and on placing a 'thermometer in the mixture, it will be found to stand, not at 102, but at 32. In this experiment, the pound of hot water which was originally at 172, actually loses 140 of heat, all of which enters into the ice, and causes its lique- faction, without affecting its temperature. 36. Heat of Fluidity. The heat thus required for the lique- faction of solids is often called their heat of fluidity ; and the quantity necessary for the purpose is not the same in any two substances. While the heat of fluidity of water is, as we have just seen, 140, that of spermaceti is 145, that of lead 162, that of tin 500, and that of bismuth 550. That is, to melt any given weight of one of these substances, an amount of heat is required that would heat the same weight of the substance the number of degrees indicated, provided no change of state should take place during the process. The melting point of nearly all substances is the same as their freezing point ; but this point varies greatly in different substances. Thus, solid mercury melts (and liquid mercury freezes) at 39 ; ice at 32 ; sperma- ceti at 132 ; sulphur at 226 ; tin at 442 ; lead at 612 ; zinc at 773 ; silver at 1873, and gold at 2016. 37. Freezing Mixtures are made of various salts and liquids, which have such an affinity for each other, that rapid liquefaction is produced, without the direct application of heat. But as this agent is always required when this change takes place, it must be absorbed from surrounding objects, which therefore lose their heat, or become cold. A good mixture of this kind is made of snow, or finely broken ice, and common salt, both of which, when mixed together, become rapidly liquid ; and the process is attended with great cold, so that a thermometer immersed in it will fall to zero, QUESTIONS. What is the quantity of heat absorbed by ice when it is melted? How is this shown? 36. What is the heat of fluidity of a sub- stance ? Will it be the same in all substances ? What are the melting points of the several substances mentioned ? 37. What are freezing mixtures ? TO CHANGES IN BODIES. %9 or below. Of course, if a vessel of water be immersed in it, the water will in a short time be frozen. Saltpetre, dissolved in cold spring water, will often reduce the tem- perature to 32, or lower, so that water may be frozen by it ; but the greatest cold is produced in this mode by mixtures of certain of the salts and acids. Thus, powdered sulphate of soda three parts, and diluted nitric acid two parts, mixed at 50, will sink the temperature to 3; and phosphate of soda nine parts, and the same diluted acid four parts, will produce a cold of 12. The greatest cold that can be produced in this way is found to be about 100, but by other means still lower tem- peratures have been obtained. But it is not possible, in the present state of our knowledge, entirely to deprive a body of heat. Since solids, on becoming liquid, absorb heat, as we have seen, it necessarily follows, that when liquids become solid, heat must be given out. The freezing point of water is usually said to be 82; but if it -be contained in a close vessel, and cooled very slowly without agitation, its temperature may be reduced, without freezing, to 20, or lower. Slight agitation will now cause it to freeze sud- denly, and the temperature will rise at once to 32, the ordinary freezing point. The portion that has frozen, therefore, has given out sufficient heat to raise the temperature of the whole mass gome 12. Saturated solutions of several of the salts, made at elevated temperatures, upon being slowly cooled, exhibit the same phenomenon. A beautiful experiment may be performed by making a satu- rated solution of Glauber's salt in warm water, and setting it aside in a closely corked vial till it cools. If now the cork be removed, or the vessel violently agitated, the salt will immediately crystallize, and a thermometer placed in it will rise several 'degrees. 38. Provision of Nature. We cannot but notice here the beautiful and unexpected manner by which nature, to some extent at least, checks the cold of winter, which migh otherwise be destructive. The cold atmosphere causes large quantities of water to cengeal, but at the same time heat is given out, which prevents so great a reduction of temperature as might, but for this circumstance, be experienced. QUESTIONS, What is the greatest cold that can be produced by freezing mixtures ? Is heat given out when liquids become solid ? May water have its temperature reduced below the ordinary freezing point? What is the eifect on the thermometer when freezing at length is produced? Describe the experiment with Glauber's salt. 38. How is the excessive cold of winter 1 to some extent checked ? 40 RELATION OP HEAT The peculiar mode provided by the Creator to check the heat of summer, which might otherwise become excessive, will be noticed hereafter. 39. Vaporization. By the term vaporization is meant the conversion of solids or liquids into gases. Aeriform bodies are often divided into vapors and gases, accord- ing to the relative force with which they resist condensation ; but the distinction is of little consequence. Heat is always required to convert a solid or liquid into a gas ; usually, it is communicated directly, as when water is made to boil over a fire, but if not applied directly, it will always be absorbed from surrounding bodies. In most cases, when heat is applied to solids, they first melt, or become liquid, and afterwards, by a continuance of the heat, are converted into vapor; but some, as metallic arsenic, and certain salts, pass at once, when heated, from the solid to the gaseous state. Gases occupy considerably more space than the liquids from which they are formed. Water, when converted into steam, expands about ] 700 times, so that a cubic inch of water forma nearly a cubic foot of steam ; but most liquids expand much less than this. Alcohol, for instance, is expanded, when converted into vapor, only 659 times its original volume, and sulphuric ether 443 times. Volatile substances are such as are readily converted into vapor by heat or at ordinary temperatures, while those that are incapable of this change are often called fixed substances. Two or more gases, whatever may be their density, when brought in contact, readily intermix with each other, and become equally diffused through the vessel that may contain them. This is seen in the atmosphere, which is composed of gases differing in density, but they remain uniformly diffused. If -we fill two bottles with gases of different densities, as hydrogen and carbonic acid, and connect them by a narrow tube, as shown in the figure on p. 41, the lower containing the most dense gas, in a short time the two QUKSTIONS. What is meant by vaporization ? Is heat always required when a vapor is formed ? Do gases occupy more space than the solids or liquids from which they are formed? How many times does water expnnd when it takes the form of steam ? Alcohol ? Ether ? TO CHANGES IN BODIES. 41 gases will diffuse themselves equally through the whole space. The mixture of the gases will even take place through thin membranes, whether animal or vegetable ; the least dense of the gases passing the most rapidly. A good method to show this is to fill an ox bladder with carbonic acid, or even atmospheric air, and suspend it with the neck tied, firmly in a large vessel filled with hydrogen. A transfer of the gases through the substance of the bladder will take place, but the hydrogen entering more rapidly than the denser gas escapes, the bladder will after a time be burst. 40. Ebullition Boiling Point. When a liquid in an open vessel is exposed to any source of heat, the temperature gradually rises, like that of any other sub- stance in similar circumstances, until a certain point Diffusion of "is attained, when a violent motion commences in it, called ebullition or boiling; and no heat can then cause any further increase of temperature. If the heat be continued, the quantity of liquid gradually diminishes, or, as we familiarly sa,y, is boiled away, until the whole is gone. The commotion in the liquid is occasioned by portions of it at the bottom, where the heat is applied, being converted into vapor, and rising in bubbles to the surface. Ordinarily it will be found that water boils at 212, which is therefore called its boiling point ; but the tempeMture at which other liquids boil is not necessarily the same, every liquid having a boiling point peculiar to itself. Thus, the boiling point of alco- hol is only 173, and that of sulphuric ether 96, while that of sulphuric acid is 620, and that of mercury 662. 41. Boiling Point dependent upon Circumstances. But the boiling point of a liquid is not to be considered as perfectly con- stant; it depends upon several circumstances, the most important of which is the pressure of the atmosphere upon the surface of the liquid. By heating a small vessel q water to about 200, and placing it under the receiver of an air-pump, it begins to boil when the air is very moderately exhausted. So, on ascending a mountain, by QUESTIONS. What is said of the diffusion of gases of different densi- ties ? Describe the experiment with the ox bladder. 40. What is ebulli- tion or boiling ? What is the effect of continuing the heat ? What is the boiling point of water ? Is this point in other liquids the same ? 41. What are the circumstances which affect the boiling point of a liquid ? Describe the experiment with the air-pump. 4* 42 RELATION OF II EAT which a part of the atmospheric pressure is avoided, the boiling point falls in proportion to the ascent. At the hospital of St. Bernard, situated upon a point on the Alps, about 8400 feet above the sea, water boils at 196 ; and on the top of Mount Blanc it was observed by Sausure to boil at 184. This is just as we should expect, for the expansion of the vapoi has to take place directly against the pressure of the atmosphere, on the surface of the liquid; and the degree of heat necessary tx produce the expansion will be to some extent proportional to th expansive force required. The pressure of the atmosphere at the surface of the sea is usually about 15 pounds to each square inch, but it is subject to some variation j and the boiling point of any liquid will of course vary at the same time with the atmospheric pressure. In a perfect vacuum, water boils at 72, and sulphuric ether at 46, or about 140 lower than in the open air. , As migjpt be expected, sulphuric ether may easily be made to boil under an exhausted re- ceiver, without heat, even in the coldest weather. For this purpose let a little good ether, in a wine- glass, be placed under an air-pump receiver, as represented in the figure ; upon working the pump, it will boil violently. The experiment Boiling of Ether. r ri . .. J .. r . will usually succeed best if some small pieces of metal are dropped into the ether, before placing it under the receiver. While the boiling is in progress considerable reduction of tem- perature takes place, and water contained in a small vial placed in the ether will be frozen. 42, Other circumstances affecting the boiling point are, the nature of the containing vessel, and the presence of soluble sub- stances in the liquid. Thus water boils in metallic vessels at 212, but in a clear glass vessel one or two degrees more are QUESTIONS. What is said of the boiling point upon high mountains? What is the boiling point of water in a vacuum ? Describe the experi- ment with ether under the exhausted receiver of the air-pump ? While the ether boils how is the thermometer in it affected ? 42. What other circumstances are mentioned as affecting the boiling point ? TO CHANGES IN BODIES 43 required; so any substance, as a salt, held in solution in the water, causes a rise of the boiling point. Water saturated with common salt bolls at 224 ; saturated with saltpetre at 238, and with chloride of calcium at 264. 43. Effect of increased Pressure. If water or other liquids boil at a lower temperature by diminishing the pressure upon the surface, so a higher temperature is re- quired for this purpose when the pres- sure is increased, as in a steam boiler. Water cannot be heated above 212 in the open air, because any additional heat is expended in converting a portion of it into steam, which at once makes its escape into the air; but if it be confined in a strong vessel, it may be heated to any temperature even to redness. The rise of the boiling point under increasing pressure is well illustrated and proved by Marcet's steam apparatus, which is represented in the accompany- ing figure. A is a hollow brass globe, supported on a stand, and in it is con- tained a little mercury, and a small quan- tity of water. Through an air-tight collar, a graduated glass tube, C, is inserted, so as to reach very nearly to the bottom, both ends of it being open. B is a ther- mometer, having its bulb in the water or mercury. Now, by applying a lamp the water is heated, and when the tempera- ture hag risen to 212, the steam will begin to issue freely through the faucet, F; but, by closing the faucet, the escape of the steam, will be prevented, and the temperature witt rise ; the mercury at the same time by the pres- sure of the steam within, being forced up the tube C. And the ^ QUESTIONS. 43. Why cannot water be heated above 212 in the open air ? What, if the steam be confined ? Describe Marcet's steam apparatus. Marcet's Apparatus. 44 RELATION OP *IEAT height to which it may rise will always show the exact amount of the pressure. By this means it has been determined that, at a heat of 250, the tension of steam, thus confined in a boiler, is equal to two atmospheres, or 30 pounds to the square inch ; at 275 its tension is equal to three atmospheres; and four atmospheres, or 60 pounds to the square inch, at 294. The expansive force of steam confined in this manner is the propelling power in the steam engine. (See author's Nat. Philo- sophy, p. 173.) 44. Evaporation. But it is not only when a liquid is heated, and made to boil, that it is changed in to" vapor; this change, in most, and probably in all liquids, and many solids, is ever taking place, whatever may be their temperature, when they are con- tained in open vessels. This slow formation of vapor is termed evaporation. It is seen in the drying of clothes, when wet with water or alcohol, and in the gradual diminution of a quantity of either of these liquids, when left in an open vessel. Even in the forms of ice and snow water gradually evaporates. Evaporation is much more rapid in some liquids than in others ; and it is always found that those which have the lowest boiling point evaporate with the greatest rapidity. Thus, alcohol, which boils at a lower temperature than water, evaporates also more freely ; and ether, whose point of ebullition is yet lower than that of alcohol, evaporates with still greater rapidity. The chief circumstances that influence the process of evapora- tion, are extent of surface, and the state of the air as to temperature, dryness, stillness, and density. The same quantity of liquid, exposed in a shallow vessel, wil evaporate more rapidly than in one of a different form, because of the large amount of surface in contact with the air; so, also currents in the air increase evaporation by removing the vapo* as fast as it is formed. Increased pressure of the atmosphere diminishes evaporation. QUESTIONS. What is the tension of steam at 250 ? 44. Do water and other liquids take the form of vapor without ebullition ? Do all liquids evaporate with the same facility? What are the chief circumstances which influence evaporation? TO CHANGES IN BODIES. .45 45. Heat is absorbed by the Formation of Vapor. During the slow evaporation of water, or other liquids, as well as when they arc evaporated by boiling, a large amount of heat is absorbed, and becomes latent in the vapor produced. It is on this account that ether, alcohol, or even water, though at the same temperature as the air, always feels cold when a little is dropped upoa the hand. The natural heat of the hand is absorbed and carried off in the vapor that is formed. The evaporation of good sulphuric ether may easily be made to freeze water, even in the warmest weather. For this purpose let a very small glass vial, covered with muslin, be filled with water, and suspended by the neck from some convenient support; then drop slowly upon the muslin good sulphuric ether, from the mouth of a vial, or by means of a dropping tube. In a few minutes, ice will begin to form ; and if the operation be continued, the whole of the water will be frozen, perhaps breaking the vial containing it. Porous earthen vessels are often used in hotels and other places, in warm weather, to contain water for drinking. A portion of the water gradually exudes through the vessels, and eva- porates from the surface, by which that within is kept several degrees colder than the tem- perature of the atmosphere. Such vessels are said to be much used in Spain, where they are called alcarrazas. People crossing the deserts of Arabia in caravans, are said sometimes to load camels with earthenware bottles filled with water, Freezing of Water byEvapo- which is kept cool by wrapping the jars with ration of Ether, linen cloths, and keeping them moist with water. 46. The freezing of water by its own evaporation under the receiver of an air-pump, is a common experiment. A shallow dish containing strong oil of vitriol is first placed upon the plate of the machine, and over it, supported by a tripod of wire, is placed a small capsule filled with water. The receiver being now put in its place* covering the whole, by working the pump the QUESTIONS. 45. Is heat absorbed during the slow evaporation of & liquid? Describe the mode of freezing of water by the evaporation of ether. 46. Describe the experiment with water and sulphuric acid under the receiver of the air-pump. 46 RELATION OF HEAT Freezing Water under Ex- hausted Receiver with Oil of Vitriol. air is exhausted, rapid evaporation from the surface of the water commences, which is continued because of the absorption of the vapor by the acid beneath, until the water is frozen. Without the acid, or other substance to produce the same effect, the receiver would soon be filled with vapor, and no further evaporation take place; the vapor of water, at ordinary temperatures, not having sufficient tension to lift the valves of the pump, as it is worked. Indeed, a small drop of water may be frozen under the receiver of an air-pump by its own evaporation, without the use of any substance to absorb the vapor. Let a single drop of water, on a piece of charred cork, hol- lowed a little on its upper surface, be placed under the air-pump receiver, and by working the pump a few seconds, it will be frozen by the rapid evaporation which takes place from its surface. The burnt cork capsule is preferable to one of glass or metal, since, as the water does not adhere to its surface, not so much heat is received from it. 47. Latent Heat of Vapors. It is not easy to determine with precision the amount of latent heat in vapors, or the relative quantify of heat absorbed as they are formed. The results obtained by different experimenters, therefore, are not uniform. It is believed that water, in taking the form of vapor, absorbs nearly 1000 of heat, or heat enough to raise the temperature of an equal weight of water 1000, if it could be confined. The amount of heat in different vapors varies QUESTIONS What purpose docs the acid serve? Explain the method of freezing a drop of water upon a piece of burnt cork under an receiver. 47. What is the amount of latent heat in steam ? Freezing Water by its own Evaporation. TO CHANGES IN BODIES. 47 withlheir nature; in no two vapors is it the same. Thus, while the latent heat of watery vapor is, as we have seen, about 1000, that of vapor of alcohol is only 373, that of vapor of ether 163, vapor of oil of turpentine 138, and of sulphide of carbon 144. The heat which is absorbed when water or other liquid is con- verted into vapor, wilf, as a matter of course, be given out again when this vapor is condensed into the liquid form. On this prin- ciple, steam is often used for warming buildings, being conveyed in pipes through the different apartments. As it passes along the pipes, it is condensed, giving out its heat; and the water that is formed runs back again into the boiler. 48, Distillation, The process of distillation consists simply in evaporating a substance, and again condensing the vapor, by causing it to come in contact with a cold surface. This is usually accomplished by having a tube of considerable length, leading from the top of a close boiler, and passing in the form of a spiral through a vessel which is kept filled with cold water. In the laboratory, the apparatus figured below answers well for distilling small quantities of any liquid. A retort, R, con- tains the liquid to be distilled, and the vapor is received into a flask, F, the mouth of which is slipped on the neck of the retort, but .the joint not made perfectly air-tight. The flask should be kept cold by being immersed in cold water, or by having a small stream of water constantly falling upon it from a vessel above. For larger operations, a Lei- big's condenser is indispensable. Distillation. It consists of a glass flask, for a boiler, which may be heated in a small furnace, as represented in the figure on page 48, or by means of a spirit-lamp, and a metallic case, a,, in which is inserted, through perforated corks, a glass tube, dd, designed QUESTIONS. Describe the mode of warming buildings by the use of steam. 48. In what does the process of distillation consist ? 48 RELATION Or II EAT to be kept constantly surrounded with c'old water. From the vessel, i, o stream of cold water enters the funnel, c, and, as it is heated, escapes at the highest part by the tube, //., and is collected in a basin, b. The glass tube, dd, is connected at one end, by means of a smaller tube, with th boiler, and at the other end, with the receiving-vessel, e, in which is col Distillation. lected the distilled liquid condensed in passing through the tube, dd. The crooked funnel in the boiler serves to introduce the liquid to be distilled. By the process of distillation volatile substances, whether liquid or Bolid, may be separated from those that are fixed, or even from such as are less volatile than themselves Water is distilled to purify it from salts or other substances it may contain in solution or suspension ; and alcohol, by distillation, is separated from water, which is' less volatile than itself, as well as from fixed substances. The application of this process to solids is usually termed their sub- limation. 49. Boiling produced by Cold. We have seen above (41) the effects of diminishing or removing the atmospheric pressure in promoting ebullition, and we are now prepared to understand another ingenious method of accomplishing this object. Let a flask, with a cork well fitted to its mouth, be partly filled with water, and made to boil briskly by means of a spirit-lamp ; then suddenly insert the cork and remove the lamp : the water will QUESTIONS. Describe Leibig's condenser. How is it that substances may be separated from one another by distillation ? 49. Describe the experiment of boiling water by the application of cold. TO CHANGES IN BODIEB. 49 Boiling by Cold. continue to boil, and by immersing it in cold water, as shown in the figure, the boiling will become violent. The same effect will be pro- duced by in-verting the flask and applying snow or even cold water to the bottom. But if the flask be held again a moment over the lamp, the boiling will instantly cease. The reason of this is, because the upper part of the flask, when the cork is inserted, is filled with steam, which is condensed by the appli- cation of cold to the outside, and a vacuum produced, The warm water within then boils, as in a vacuum produced by any other means; but if heat be applied, steam will be again formed, and fill. the upper part of the flask, and, by its pressure upon the surface of the water, prevent further boiling. If the flask is firmly corked, so as to exclude the air perfectly, when it has becom^ cold the water within, as the flask is handled, will fall from side to side, almost like masses of ice, and producing a similar sound to the ear. This is because there being no air within to break up the water as it is thrown in any direction, it falls in a mass and strikes against the sides of the glass with much the same effect as a solid. A small toy of this kind, made of glass tube, and hermetically sealed , is called a water- hammer. 50, The Cryophoms. The cryophorus, or frost-bearer (from the two Greek words, cruos, frost, and pTiero, I bear), is an instrument for freezing water by its own evaporation, whicb beautifully illustrates some of the foregoing principles. It consists of a tube, half an inch or more in diameter, with a bulb blown at each end, one of them having a small aper- ture, A, by which a small quantity of water is introduced, sufficient only partly to fill one of the bulbs. This water is first all collected in the lower bulb, and the heat of a lamp / applied, so as to cause it to boil briskly; and Cryophorus. while the interior is filled with steam, the aperture at A is quickly QUESTIONS. What will be the effect of holding the flask over a lamp ? What is the effect if, when cold, the flask is shaken ? 60, Describe the cryophorus, 5 50 RELATION OF II EAT sealed hermetically, and the lamp removed. When it has become cold, the water is passed to the upper bulb, as represented in the figure (p. 49), and the instrument supported on a stand, with the lower bulb in a beaker glass. All the interior is now filled with vapor of water, except a part of the upper bulb, but no evapora- tion of the water can take place, because of the presence of this vapor. But by removing the vapor, which is accomplished by sur- rounding the lower bulb with a freezing mixture of salt and snow, to condense it rapidly, evaporation of the water is produced, attended with cold sufficient to freeze the most of it, even in the warmest weather. The pulse-glasS, as it is called, is a very similar instrument, and ^ is made in the same manner, except that ether is used in it, instead of water. By grasping one of the bulbs firmly in the hand, the vapor, by its Pulse-glass. expansion, will immediately force all the liquid into the other; and the moment it has all passed through the stem, an^ appearance of vio- lent ebullition is produced, atterded by a- 'distinct sensation of cold in the hand which grasps the bulb. This is occasioned by the rapid evaporation of the film of liquid lining the inside of the bulb. 51, Effect of Perspiration upon the Animal System. The effect of evaporation in withdrawing heat is admirably illustrated by the process of perspiration. The natural temperature of the human body is about 98, but when we take active exercise, or are exposed to a great degree of heat, there is a tendency to a rise of tempera- ture above that which is conducive to health ; and the most injurious effects would ensue, if they were not prevented by the rapid evaporation which takes place from all parts of the surface of the system. Examples of the power of the human body to sustain great and apparently even dangerous elevations of temperature, are on record- It is well known that individuals have voluntarily exposed thcm- QUESTIONS. Describe the pulse-glass. 51. What is the effect of perspira- tion upon the animal system ? Will the human body sustain high tern- peratures for a time without injury? TO CHANGES IN BODIES. 51 selves for several minutes, in ovens, to temperatures even a hun- dred degrees above that of boiling water, without suffering any injury. The very rapid perspiration that takes place in such cir- cumstances, prevents the destructive elevation of temperature in the system which would otherwise take place. 52. Temperature of the Seasons Modified. The heat of sum- mer is always greatly modified by the evaporation which take place from the sur^ce of the earth, and the stalks and leaves of plants and trees. When a stalk of Indian corn (zea maize), or other plant, is -cut down in midsummer, or a brsfach removed from a tree, the leaves soon begin to wither, because of the eva- poration of the moisture in them. But the evaporation is no more rapid from them after being cut than before, but now the supply of water from 'the earth, received by the roots, ceases, and the withering we notice is a necessary consequence. We see therefore that vegetation in warm weather is sending forth into the atmosphere immense quantities of water by evaporation, besides that which rises from the surface of the earth itself; and as a result, the temperature of the atmospheretis more or less cooled. In other words, the heat is thus prevented from becoming as_ excessive as it would be but for this arrangement. We have seen above (38) that heat given out by the freezing of water in winter, prevents the low reduction of temperature that would otherwise be .experienced; and we cannot here less admire the wonderful provision of providence, by which, on the other hand, the excessive heat of summer is, to some extent, limited. 53. Liquids upon very Hot Surfaces. Liquids, as water, thrown upon metallic surfaces, heated nearly to redness, instead of adhering to the surface and rapidly evaporating, will sometimes be seen to roll around in globules, apparently 'without touching, until at length they gradually disappear. This is occasioned by an atmosphere of vapor that is formed around the globules of liquid, by its rapid formation preventing the tem- perature from rising as high as the boiling point, and also by its elasti- city preventing the liquid from coming in contact with the metallic plate. Alcohol dropped upon the surface of. heated oil of vitriol, exhibits a like phenomenon. This has been called the spheroidal stale of liquids. QUESTIONS. 52. How is the heat of summer modified ? Why does a plant-stalk, separated from its root, so rapidly wilt iu warm weather ? Is water constantly evaporating from the leaves and stalks of plants? 63. Describe the action of a drop of water upon a very hot surface. 62 RELATION OF HEAT 54, Dew. Dew is a deposit of moisture from the atmosphere upon a cold surface in contact with it. If, in the summer, a ves- sel is left but a few minutes filled with ice-water, or even cold spring-water, dew soon collects upon it, and after a time, the water thus condensed trickles down the surface in drops. A surface upon which dew is seen to form will always be found colder than the surrounding air; and the particular temperature at which it begins to form is called the dew-point. When the air is very dry, this point will always be considerably below the temperature of the air j but when there is much moisture present this will not be the case. In fair weather, during the summer season, there is usually seen, in the morning, a copious deposit of dew upon the leaves of plants, and upon other substances exposed to the open air. This is occasioned by the radiation of heat from bodies at the surface of the earth, which takes place rapidly during the night, cooling them down considerably below the temperature of the air. Substances, therefore, which radiate slowly (30), as polished metallic surfaces, seldom have any dew upon them, while good radiating surfaces near them will be abundantly covered with it. In cloudy weather (without rain), there is generally little dew, because the heat radiated from the earth is reflected back by the clouds ; and by suspending even a small handkerchief by the four corners, a few inches from the earth, the deposition of dew on substances under it is, for the same reason, prevented. In some warm countries, water is said to be frozen during the night by the rapid radiation which takes place from its surface. The water for this purpose is poured into shallow pans, so situated as to receive as little heat as possible from the earth. 55, Hygrometers. Hygrometers are instruments for determin- it<$ the relative quantity of watery vapor present at any time in thfe atmosphere. Daniel's hygrometer (represented in the figure on p. 53) is much in use. It consists of a tube, A, with a bulb at each end, and is formed in the same manner as the cryophorus QUESTIONS. 54. What is dew? Under what circumstances is it de- posited? How do the leaves of plants and other bodies at the earth's surface become colder than the air ? Why is there usually little dew in cloudy weather ? 55. What are hygrometers 1 TO CHANGES IN BODIES. Hygrometer. (50), except that it contains ether instead of water. The tube is supported by a stand j and the lower bulb, which is usually made of colored glass, .is about half filled with the ether, having in it the bulb of a very deli- cate thermometer, with its stem extending upward in the tube. The other bulb is empty, or contains only "the vapor of ether, and is covered with muslin. To the stand B is attached a small thermometer, to -indi- cate the temperature of the air. By pour- ing a little ether upon the muslin, the bulb is cooled, and the vapor of ether within condensed, and a rapid evaporation of the ether in the bulb produced, as in the cryo- phorus. This occasions a cooling of the colored bulb, and a deposition of dew upon its surface, the small thermometer within showing the exact temperature at which the process commences, which is taken as the* dew-point. Properly, however, it is the difference between the temperature thus obtained, and the tem- perature of the air, which shows the real state of the air as to moisture. A decided objection to the use of this instrument is found in the fact, that it is extremely difficult to determine accurately the moment when the formation of dew upon the bulb actually commences. Its indications, therefore, cannot always be fully relied on. The wet-bulb thermometer is now mostly used to determine the hygrometric state of the atmosphere. Two thermometers are attached to the same support, as shown in the figure on p. 54, one of them having a piece of muslin wrapped around its bulb, which is kept wet by a string leading to it from a small fountain of water, attached also to the support between the thermometers. Now, as the evaporation from the muslin necessarily reduces the temperature, this thermometer will always stand a little lower than the other, the bulb of which is dry; and, moreover, as the QUESTIONS. Describe Daniel's hygrometer, thermometer. 5* Describe the wet-bulb 54 RELATION OF HEAT rapidity of the evaporation from the muslin will depend upon the dryness of the air, the difference between the readings of the thermometers will indicate its true hygrometric condition. 56. Watery vapor exists in three different states : 1. As transparent, invisible steam, as it rises from boiling water, and before it comes in contact with the air; 2. As it appears partially condensed, after escaping into the air; and 3. As it exists in the atmosphere at all temperatures, but invisible to the eye. That steam, before coming in contact with the atmosphere, is perfectly transparent and invisible, is shown by partly filling a glass vessel with water and causing it to boil rapidly. The steam within, above the water, cannot be seen until it escapes into the air, and becomes partially condensed,*as stated above. Clouds are collections of watery vapor, in this partially con- densed state, in the upper regions of the atmosphere, and differ from fog only in their more elevated position. The moisture that constitutes clouds, when fully condensed, falls in rain upon the earth, or is solidified and falls in beautiful crystals (25), as snow. If the drops of rain are frozen after they are formed, hail is produced. If in warm weather a quantity of air be forced into a large glass receiver, so as to produce a pressure of at least two atmospheres, a slight mistiness will usually be seen within, occasioned by a partial con- densation of the watery vapor forced in with the air. If the process is several times repeated, drops of water may be obtained, forming a kind of artificial rain. In the manner stated above, all the water upon the surface of the earth is subjected to a constant natural distillation ; pure water, in the form of vapor, rises in the air from the leaves of plants, from the earth, and from the surface of the ocean, rivers, and lakes, to be again diffused, in rain and snow, over the earth, producing everywhere vigor and life, both in the vegetable and animal world. 57. Liquefaction and Congelation of Gases. By great pres- sure, or by pressure and a low reduction of temperature, many of QUESTIONS. 56. In what three states does watery vapor exist ? What mre clouds ? What is rain ? 57. How may many of the gases be reduced to the liquid state ? TO CHANGES IN BODIES. 55 the gases may be reduced to the liquid state, and the liquids thus formed solidified or frozen. Indeed, all gases may be considered as the vapors of extremely volatile liquids. Some of them, how- ever, have never yet been reduced to th0 liquid state. The usual method to liquefy a gas, is to put the materials from which it is to be formed into a strong glass tube, bent in the middle, as represented in the figure, and hermetically -,. ., A ,v Liquefaction of Gases. sealing it. As the gas is ^^ evolved the pressure of course increases, but at length a point is attained, depending upon the temperature and the nature of the gas, when it begins to condense as 3 liquid, the quantity of which is in- creased by the further evolution of gas from the materials, without any increase of pressure, if the temperature is kept uniform. The bent tube is particularly adapted for the liquefaction of cyanogen gas. To form this gas, dry cyanide of mercury is used, a portion of it being placed in the closed end of the tube, and the other end hermetically sealed. Moderate heat is then applied to the end containing the cyanide, the other end being cooled by a freezing mixture of snow and salt. As the cyanide is decomposed by the heat, the cyanogen first takes the gaseous form, but is subse- quently condensed by the pressure and cold, and collects in the empty end of the tube. Of the different gases, some require a much greater pressure than others to condense them to the liquid state. At sulphurous acid gas becomes liquid under the ordinary atmospheric pressure, but at 32 it requires a pressure of 2 atmospheres to produce the effect. , Carbonic acid gas at has a tension of 23 atmospheres, and at 32 a tension of 36 atmospheres; at higher temperatures the tension is still more increased. The liquids formed from the gases, in the manner described, may be frozen by the great cold produced by their own evapora- tion, or by exposing them in tubes to intense cold. In the former case, the solids formed will appear like snow, and in the latter, like *lear, transparent ice. QUESTIONS. What is the usual method to liquefy a gas ' Do all gasei require a like pressure to reduce them to the liquid state ? 50 RELA TION OF HEAT M 58. For preparing small quantities of solid carbonic acid, the following apparatus answers well, and is much less expensive than such as are usually purchased of the manufacturers of philoso- phical instruments. \ The generator, A, is made of a common mercury flask, having the aper- ture at the neck a little enlarged, so as to be about an inch and a quarter in diameter. A plug of cast-steel, B, is then made of a bar two inches at least in diameter, and turned with a wide and smooth shoulder so as to fit accurately upon a collar of block-tin, when screwed into its place, as repre- sented in the figure. The valves, which are the most difficult part to construct, on account of the great pressure that is to be overcome, are inserted in the plugs, a second one of which, precisely like the preceding, is made to screw, into the receiver, C. Into the upper end of each plug, a hole an inch in diameter is bored about one inch deep, and terminates in a conical point ; from which an aperture, a tenth of an inch in diameter, is bored quite through the plug. E H is composed of two parts, so constructed that when screwed firmly into the cast-steel plug, and the part H which terminates in a conical point screwed down, all escape of the gas from the generator is effectually prevented. When the part H is screwed upward, the escape of the gas around E is prevented by the firm pressure of the shoulder of E upon the washer I, and a shoulder upon the lower part* H, which presses against the bottom of E, and produces the same effect with regard to the escape of the gas around the thread of the screw H. Instead of the valve described above, the following answers better for the generator, as the passage at the bottom of the plug is not liable, as in the other construction, to be closed by the sulphate of soda which is formed. The part H- extends quite through the plug, having at the lower extremity a nut, P, attached firmly by a screw and soldered. Now when the screw H is turned upward, the thread on which extends from I downward about an inch, the nut P perfectly closes the passage below, but by turning the screw down, the passage through the plug is opened at P, and closed at I, allowing the gas to escape laterally, as in the other Construction, The receiver, C, is made of common boiler iron, and should be about two inches internal diameter, and of the same height as the generator, which will make it of the capacity of QUESTIONS. 58. Describe the apparatus for preparing solid carbonic acid. Solidifying Carbonip Acid. TO CHANGES IN BODIES. 57 about a pint. The tube L should screw into the plug connected with the receiver, having its other extremity terminate in a conical point t'o fit into a cavity prepared for it in the other plug. By means of the stirrup- screws M and N, and the block of wood 0, the receiver may then be firmly screwed in its pl^ce ; and when both the valves are open, there will be a free passage between it and the generator, but no communica- tion of either with the open air. To make use of this apparatus, the generator and receiver are separated, and the plug B being removed, 2 pounds of bicarbonate of soda, made into a paste with the same weight of water, are introduced into A, and 21 J ounces of strong sulphuric acid are poured into several copper ves- sels, made a little shorter than the length internally of tfce generator, arid of such a diameter that they will just pass the aperture. These being nearly filled with acid are dropped into the generator, which, after the plug B is inserted, is allowed to lie on one side for fifteen or twenty minutes, and several times rolled over, to mix the acid with the soda. The receiver is then attached to it as seen in the figure, by means of the stirrup-screws M and N ; and, if kept sufficiently cool by means of ice, the liquid carbonic acid formed in A will shortly be distilled over into C, the passage between them being of course previously opened. The valves are now to be closed, and the receiver, which contains the liquid carbonic acid, separated from the generator. A small tin cup (not represented in the figure) is then to be attached to the tube L, to receive the jet of acid from the receiver. It is essential that the liquid acid should escape into this cup, which is effected by having a small tube pass from the steel plug nearly to the bottom of the receiver, or by inverting the receiver before opening the valve. The apparatus should be well tested, at least three times, before run- ning any risk by venturing to handle it while charged. This is best done by means of a hydraulic press ; but the same object may be accomplished very effectually by standing the apparatus when charged in a tub of water heated to about 150, so that when the apparatus and water have attained the same temperature, it shall not be lower than 130. If a more severe test is desired, the water may be made still warmer. In constructing an apparatus, care should always be taken to make the receiver of not more than one-fifth the capacity of the generator. The quantity of materials used should also be just sufficienf very nearly to fill the generator. In using this apparatus, when the liquid is received in the cup, it hisses and boils with the greatest violence ; and the cold produced by the evaporation of a part of it is so great as to freeze the rest, which is retained in the cup as a fine white snow. By rolling this in balls, and wrapping it in cotton, it may be kept some time ; but in the open air it evaporates rapidly, and intense cold is produced, equal, it is said, to 148. By moistening the solid with ether, and placing it in an exhausted receiver, it is claimed that a temperature as low as 175 or 180 below zero has been produced. The solid does not mix with water when immersed in it; a ball of it thrown upon the surface of water floats about lightly, and at QUESTIONS. How is the freezing of the liquid accomplished ? At what temperature is the solid formed ? 58 SPECIFIC II EAT. length a portion of water in contact with it is frozen by the intense cold. With sulphuric ether or chloroform it mixes readily, and the pasty mass rapidly evaporates, producing intense cold. Mercury which congeals at about 40^ is readily frozen by being kept a short time in contact with the solid, surrounded by some cotton, or by immersing it in a mixture of the solid and ether or chloroform. SPECIFIC HEAT. CAPACITY OF BODIES FOR HE AT . 59. When a body is exposed to any source of heat, its tem- perature rises, and the substance of heat is supposed to accumu- late in it; but the same quantity of heat, imparted to different bodies, will not raise their temperature alike. Thus, if a pound of water and a pound of mercury, in similar vessels, and at the same temperature, be exposed to the same source of heat, the temperature of the mercury will rise about 80, while that of the water rises only 1. It appears, therefore, that it requires 30 times as much heat to raise the temperature of water any given amount, as it does to produce the same effect upon, mercury. This idea is expressed by saying that the specific heats of these substances are as 30 to 1; or we say (as some prefer) that the capacity for heat of water is to that of mercury as 30 to 1. If, instead of comparing equal weights of the two substances, we take equal volumes as a pint of each and expose them to the same uniform source of heat, we shall find that while the water gains 1 of heat, the mercury will gain 2, or a little more. To express this relation we use the term relative heat; and we say therefore that water has more than twice the relative heat of mercury. Other methods of determining the specific heat of bodies* have been devised, one or two examples of which will be given. If a QUESTIONS. What is said of the solution of the solid in chloroform and ether ? How may mercury be frozen by use of the solid acid ? 59. Will the same quantity of heat imparted to different bodies heat them alike? If like quantities of water and mercury are exposed to the same source of heat will they in the same time be heated alike? SPECIFIC HEAT. 59 pound of olive-oil and a pound of water be heated to some given temperature, say 80, and then placed in a cold room, and the number of minutes noted which is required for each to cool an equal number of degrees, say to 50, it will be found that the oil will cool in less than half the time required by th*e Water; but as both substances must be supposed to lose equal quantities of heat in equal times, it follows that the water must have contained more than twice as much as the oil ; or the capacity of water for heat is more than twice that of this oil. If a piece of copper, of a pound weight, be heated to 300, by holding it a few minutes in mercury at this temperature, and then immersed in a pound of water at 50, the copper wiU give out heat to the water until the temperature of both will be at 72. Now, the copper has lost 228 of heat, and the water has acquired 22. The specific heat of water, therefore, is to that of copper as 228 to 22. It is usual to make water the standard in comparing the specific heats of bodies, considering its specific heat as 1-000; we shall then have the specific heat of mercury 1 '|-g=-033, and that of copper 2 aa 5 =-096. No two substances have the same specific heat, but every sub- stance has a specific heat peculiar to itself, and which is to be considered as one of its own peculiar properties. The following table exhibits the specific heats of several well- known substances : Water 1-000 Iron 0-114 Copper 0-096 Lead 0-031 Sulphur 0--203 Phosphorus 0-188 Diamond 0-119 Graphite 0202 Charcoal 0-201 Gold 0-032 Silver 0-057 Alcohol 0-645 Tin 0-056 Platinum 0-032 Zinc 0-095 Mercury.. ., 0-033 Oil of Turpentine 0-467 Ether 0-503 The specific heat of a body depends to some extent upon its tempera* ture, being greater as the temperature is higher. Change of density in a body is usually attended by a correspond- ing change in its specific heat, which is increased as the density is QUESTIONS. What is the ratio of their capacities for heat, or their specific hetts ? What is taken as the standard for the specific heat of bodies ? 60 NATURE AND SOURCES OF LIGHT. diminished, and diminished as the density is increased. This ia seen in solids, as when a piece of iron is heated by hammering, which increases its density and causes a portion of its latent heat to be given out, thus raising its temperature ; but is best illus- trated by the gjases, the densities of which are more easily made to vary at pleasure. Thus, if we suddenly compress a portion of a gas, its temperature is sensibly raised; but, on the other hand, if we diminish its density, it becomes colder by the absorp- tion of heat occasioned by its increased capacity for heat. A delicate thermometer placed under the receiver of an air-pump falls as the air is exhausted. 60. The Fire Syringe is an instrument by which dry tinder or spunk may be ignited by the heat pro- duced by the sudden compression of a portion of at- mospheric air. It consists of a hollow cylinder, closed at one end, and a solid piston fitting it accurately, and having in its under side a cavity to receive the substance to be ignited. To use it, the tinder or spunk is put in the place fitted for it, and the piston is then plunged forcibly into the cylinder; on removing it, the combustible substance will gene- rally be found ignited. If the cylinder is of glass, a flash of light will often be seen when the air is Fire Syringe. Compressed. II. LIGHT. NATURE AND SOURCES OF LIGHT. 61, Nature of Light. Although innumerable observations and experiments have been made upon light, yet it must be admitted that some doubt and obscurity still remain concerning its real nature. But, in the absence of positive knowledge, two theories of light have been proposed, by each of which nearly all QUESTIONS. How does change of density in a body affect its specific heat? 60. Describe the fire syringe. 61. Do we understand fully the real nature of light ? NATURE AND SOURCES OF L-IGHT. 61 the phenomena attending it may be satisfactorily explained ; and it is admitted that each is also attended with its peculiar difficulties. These are called the Newtonian, or corpuscular, and the undulatory theories. 62. The Newtonian theory supposes light to be material, and to consist of inconceivably minute particles, which, however, are too subtile to exhibit the common properties of matter. These particles, emanating from luminous bodies, -such as the sun, the fixed stars, and incandescent substances, and traveling with im- mense velocity, excite the sensation of light, it is supposed, by passing bodily through the substance of the eye, and striking against the expanded nerve of vision, the retina. The whole language of optics is founded on this theory. 63. The undulatory theory, or theory of Huygens, which is now generally adopted, denies to light a separate material exist- ence, and ascribes its effects to the vibrations or undulations of a subtile ethereal medium, supposed to be universally present in nature, the pulses of which, in some way excited by luminous objects, pass through space and transparent bodies, and give rise to vision by impressing the retina, in the same way as pulsations of air impress the nerve of hearing, to produce the sensation of sound. (See Natural Philosophy, p. 188.) 64. Light is not a homogeneous substance, as might be sup- posed, but the white light of the sun is made up of rays of several different colors, as will be shown when we come to speak of its decomposition, or analysis. So, also, it is capable of producing several distinct classes of effects, which have been attributed to the action of distinct agents; as the colorific rays, or the rays which produce the phenomena of color, the heating, rays, and the chemi- cal rays, or those which are capable of producing chemical changes. Thus it is possible, by causing the solar ray to pass through certain substances, to separate the heat entirely from it; or its illuminating power may be destroyed, and a distinct, invisible ray of heat be obtained. So, also, chemical effects may be produced by rays which seem to be destitute of any heating or illuminating power. QUESTIONS. 62. Describe the Newtonian, or corpuscular, theory of light. 63, Describe the undulatory theory. 64. What colored rays are contained in the white light of the sun ? What other rays ? 62 NATURE AND SOURCES OF LIGHT. 65, Sources of Light. The sun is the great source of light to the earth, and all things upon its surface. As rays of heat always accompany the light of the sun, it is natural to suppose that the sun is an intensely heated mass, which is constantly throwing off both light and heat in every direction, like a red-hot cannon-ball suspended in the air; but this cannot be proved. At the present day, it is generally believed that the body of the sun is a dark, opaque substance, surrounded by luminous clouds, unlike any- thing, perhaps, with which we are acquainted upon the earth, but which are the real source of the sun's rays. These clouds are supposed to be of great thickness; but occasionally they break away in places, showing the body of the sun beneath them, which constitute the spots often seen upon his surface. The great distance of the sun from the earth 95,000,000 of miles very probably will ever prevent us from knowing more with certainty of his real nature. Artificial liyJit is produced by various modes, but chiefly by combustion, by the burning of a lamp or candle, or a mass of charcoal; but it may also be produced by galvanism, in a man- ner. to be hereafter explained, by decaying animal and vegetable substances, called phosphori, and by every means which produce great heat. All bodies begin to emit light when heat is accumulated within them in great quantity ; and the appearance of glowing or shining, which they then assume, is called incandescence. The tempera- ture at which solids in general begin to shine in the dark, is between 600 and 700; but they do not appear luminous in broad daylight till they are heated to about 1000. The color of incandescent bodies varies with the intensity of the heat. The first degree of luminousness is an obscure red. As the heat aug- ments, the redness becomes more and more vivid, till at last it acquires a full red glow. If the temperature still increase, the character of the glow changes, and by degrees it becomes white, shining with increasing brilliancy as the heat augments. Liquids and gases become incandescent when str6ngjy heated ; but a very QUESTIONS. 65. What is the great source of light to the earth ? How is artificial light produced? At what temperature do bodies begin to emit light ? NATURE AND SOURCES OF LIGHT. OU high temperature is required to render a gas luminous, more than is sufficient for heating a solid body even to whiteness. The dif- ferent kinds of flame, as that of a wood-fire, candles, and gas-lights, are instances of incandescent gaseous matter. Artificial lights differ greatly in color, some being of a brilliant white, and others being red, blue, yellow, or green. The chemical agency of artificial light is in general analogous to that from the sun ; but in most cases it is too feeble to produce very decided effects. 66. Many substances have the power of emitting a feeble light, unat- tended by sensible heat, and are called phosphori (from two Greek words, phos, light, and phero, I bear). Certain living animals also possess tho same property, as the glow-worm, and the common fire-fly. This pro- perty of bodies is termed their phosphorescence. Some phosphori, as that prepared by mixing sulphur and oyster-shells, und exposing the mixture for a time to a strong heat, the diamond, fluor- spar, &c., shine only after having been heated, or exposed for a few moments to a strong light ; while others, as moist, decaying wood, and decaying fish, shine without such preparation, even at ordinary tem- peratures. Light sometimes appears during the process of crystallization. This is exemplified by a tepid solution of sulphate of potassa in the act of crystallizing; and it has been likewise witnessed under similar circum- stances in a solution of fluoride of sodium and nitrate of stroutia. . An- other instance of the kind is afforded by the sublimation of benzoic acid. Allied to this phenomenon is the phosphorescence which attends the sud- den conti'action of porous substances. Thus, on decomposing by heat the hydrates of zirconia, peroxide of iron, and green oxide of chromium, the dissipation of the water is followed by a sudden increase of density suited to the changed state of the oxide, and 'a vivid glow appears at the same instant. The essential conditions are that a substance should be naturally denser after decomposition than it was previously, and that the transition from one mechanical state to the other should be abrupt. 67, Photometers are instruments for measuring the comparative intensities of different lights, of which several kinds have been proposed; but it does not enter into our present purpose to describe or discuss their comparative merits. To determine the comparative intensities of two lights, as that from different candles or lamps, the following method, originally proposed by Count Kumford, is perhaps as reliable as any ; and lias the advantage of requiring little and very cheap apparatus. , Let L be a lamp, and C a candle, the lights of which we desire to QUESTIONS. Do artificial lights dift'er in their colors? GO. What are phosphori ? 67. What are photometers ? 64 NATURE AND SOURCES OP LIGHT. compare. Provide a screen, S, of white paper, which is to be put in a frame and properly supported by a stand, as shown in the figure, and also a small cylinder, C, of wood or some opaque sub- stance. Then place this cylinder in an upright position in front of the screen, in such a position that its shadow from both of the lights shall be thrown side by side upon the screen, but not over- lapping-each other, and removing the lights to different distances, until the shadows appear of perfectly equal intensities. The com- parative intensities of the two lights will then be as the squares of the distances of the lights from the screen. In the present case, 17 will be the shadow from the light of the lamp, and C' that from the light of the candle ; and the intensity of the lamp light will be to that of the candle light as LL' 2 is to CO' 2 . If LL' Photometer. is 50 inches and CC' 45 inches, then will the light of the lamp be to that of the candle as 2500 is to 2025, or as 1-234 is to 1. This method is founded upon the fact to be illustrated in the next paragraph, that the intensity of the light from any luminous body, at different distances, will be inversely as the squares of those distances. The experiment must, of course, be conducted in a dark room. QUESTIONS. Describe the method -of determining the comparative intensities of two lights by a comparison of the shadows they produce. DISTRIBUTION OF LIGHT. 65 DISTRIBUTION OF LIGHT. 68. Light is distributed, or diffused abroad, by several modes ; as by radiation, reflection, refraction, &c. Light emanates from every point in the surface of a luminous body, and is equally distributed on all sides, if not intercepted, diverging like radii drawn from the centre to the surface of a sphere. Thus, if a single luminous point were placed in the centre of a hollow sphere, every point of its concavity would be illuminated,, and equal areas would receive equal quantities of light. Each ray,*when not interrupted in its course, and while it remains in the same medium, moves in a straight line, as is obvious by the appearance of shadows cast by the side of a house, or of a sun-beam admitted through a small aperture into a dark room. Owing to these modes of distribution, it follows that the quantity of light which falls upon a given surface decreases as the square of its distance from the luminous object increases the same law which regulates the heating power of a hot body. 69. The passage of light is progressive, time being required for its motion from one place to another. It comes to the earth from the sun in about 8 minutes, a distance of 95,000,000 miles, which shows its rate of progress to be about 195,000 miles a second. Owing to this prodigious velocity, the light caused by the firing of a cannon or a sky-rocket is seen by different specta- tors at the same instant, whatever may be their respective dis- tances from the rocket, the time required for light to travel 100 or 1000 miles being inappreciable to our senses. 70. Reflection of Light. Light is reflected in the same man- ner as heat (31), obeying precisely the same laws. This always takes place when it passes from one medium into another of dif- ferent nature or density, whether the media be solid, liquid, or gaseous. Different media, however, differ much in their power of reflection. Bright metallic surfaces, as polished silver or clean mercury, QUESTIONS. 68. How is light distributed ? Does light emanate from every point of an object? What is said of the course of a ray when not interrupted ? 69. Is the passage of light from point to point instanta- neous? What is its velocity? 70. When is light said to be reflected? G* 66 DISTRIBUTION OF LIGHT. ,"' 'A'. B Iteflection of Light. reflect nearly all the rays which fall upon them ; while those which are dull and rough reflect but a few. The reflection of light, like that of heat, takes place at the surface of bodies, arid appears to be influenced rather by the condition of the surface than by the internal nature or structure of the reflecting body. Let A 15 be the reflecting surface, E C the ray incident at C, and C D the reflected ray, and let P C be perpen dicular to AB. ECP will then be the angle of incidence, and PCD the angle of reflection, both of which will be equal. It is not necessary tiiat the reflecting surface should be a plane, as might be supposed; it may be either concave, as a b, or convex, as A' B', and the same results would follow. Light has precisely the same characters after being reflected a? before, but is less intense, because of the absorption of a part of the rays. 71. Refraction of Light. When a ray of light passes through the same medium, as glass or water, or when it passes perpen- dicularly from one transparent medium to another, it moves in perfectly straight lines ; but wnen it passes obliquely from one medium to another of different density, it is thrown more or less out of its first direction, and is said to be refracted. Thus, a ray of light, R, passing through the air, when ifc comes in contact with a piece of polished glass at A, does not move on in a straight line to R', but is bent downward or refracted, and emerges from the glass at B, where it is again refracted in the opposite direction, and takes the same course, though not precisely the same path, as it had at first. Refraction always takes place when a ray of light passes obliquely from one medium to another of different density, but not always to the same amount; this will depend upon the refracting power of Refraction of Light. QUESTIONS. Describe the angles of incidence and reflection. 71. When is light said to be refracted? DISTRIBUTION OF LIGHT. 67 the two media, and also upon the obliquity of the ray to the sur- faces of the media in contact. When the ray passes from a rare to a dense medium, it is always refracted or bent towards a line perpendicular to the surface at the point of contact, and from this line when it passes in the opposite direction, from a dense to a rare medium. To understand the relative positions of the incident and th refracted ray, in the case of any two media, the following la^v needs to be well studied. Let A B in the figure be the surface of some transparent medium more dense than air, as water, and let I C be a ray of light incident upon it at C } it will not pass on in a straight line, but on entering the water will be bent downward, to E ; I C is then called the incident ray, and C E the refracted ray. Let P P' be a line perpendicular to the surface at C, then angle index of Refraction. ICP will be the angle of incidence, and ECP' the angle of refraction. If now from C as a centre we draw the circle A P B P', and also the lines I a and E c both at right angles to P P', then will I a be the sine of the angle of incidence and E c the sine of the angle of refraction. And for the- same two media these lines will always have the same ratio to each other, whatever may be the angle of % incidence. Thus, if a second ray, i C be incident at C, it will emerge at e; and the sines of the angles of incidence and refraction, that is, the lines i b and e d will have to each other the same ratio as the lines I a and EC; and the same will be true for the same media, whatever may be the angle of the inci- dent ray. The quotient obtained by dividing the sine of the angle of inci- dence by that of the angle of refraction is called the index of refraction for the media used ; for the same media it is always QUESTIONS. What is the course of the ray in passing from a rare to a dense medium ? When from a dense to a rare medium ? Describe the angles of incidence and of refraction. Describe the index of refraction. G8 DECOMPOSITION OF LIGHT. the same, but varies with different media. Usually tho air is taken as one of the media, so that the index of refraction for any substance is the quotient thus obtained in tho case of a ray of light in passing from air into that substance. The index of refraction for water is thus found to be 133, for common flint glass 1-56, for oil of cassia 1-64, for phosphorus 2-22, and for the diamond 2 '43. (For the Polarization of Light, see the author's "Natural Philosophy:') DECOMPOSITION OF LIGHT. 72. The Solar Spectrum. The white light of the sun is not a homogeneous substance, but is capable of being separated into several rays of entirely different colors. This was first effected by Newton, by passing it through a triangular piece of clear, solid glass, called a prism. In the figure following, let S be a ray of light from the sun, admitted into a darkened room through the window- shutter, D E ; it will pass downward to the floor, at a little distance from the wall, producing a circular spot of clear white light, W. Then let the prism A B C. be held in the ray, and at once the fP * at W wil1 disa PP ear > and, in its stead, an elongated and beautifully colored image of the sun will be seen upon a screen hung up in front of the window, or on the wall at the opposite side of the room, if no screen be used. The several colors will appear in the order indicated, the violet being uppermost and the red lowest. QUESTIONS. What is the index of refraction for water? Flint-glass? Diamond ? 72. How may light be decomposed ? Describe the exDeri- ncnt .with the prism. Decomposition of Light. DECOMPOSITION OF LIGHT. 69 It will be seen that the light, in passing the prism, lias been twice refracted, or bent upward, first as it entered the glass, and a . J inductive influence of the excited body, in a manner to be hereafter explained. DISTRIBUTION OP ELECTRICITY. 82. Conduction of Electricity. Some substances allow the electric fluids to pass over them freely, and are therefore called conductors; while others, that do not possess this property, or only imperfectly, are called non-conductors. If electricity be im- parted to one end of a conductor, such as a copper wire, the other extremity of which touches the ground, or is held by a person standing on the ground, the electricity will pass along its whole length and escape in an instant, though the wilfe were several miles long; whereas excited glass and resin, which are non-con- luctors, may be freely handled without losing any electricity except at the parts actually touched. QUESTIONS. "Which of these theories is now generally preferred? When do bodies attract and when repel each other? 81. What are electrometers ? Describe the gold-leaf electrometer. 82. What is said of the conduction of electricity ? What are conductors and non-conductors ? DISTRIBUTION OF ELECTRICITY. 77 % To the class of conductors belong the metals, charcoal, plum- bago, water, and aqueous solutions, and substances generally which are moist, or contain water in its liquid state, such as animals and plants, and the surface of the earth. These, how- ever, differ in their conducting power. Of the metals, silver and copper are found to be the best conductors ; and after these follow gold, zinc, platinum, iron, tin, lead, antimony, and bismuth Aqueous solutions of acids and salts conduct much better than pure water. To the list of non-conductors belong glass, resins, sulphur, diamond, dried wood, precious stones, earth, and most rocks when quite dry, silk, hair, and wool. Air and gases in general are non-conductors if dry, but act as conductors when saturated with moisture. It is not, however, to be understood that any very definite line can be drawn between the two classes of conductors and non-conductors ; but there seems to be a very regular gradation from the most perfect con- ductor to the most imperfect, or most perfect non-conductor. This division of substances is, however, found very convenient, though in some instances individuals might differ with regard to the class to which a particular substance should be assigned. 83. Insulation, When a conductor is supported upon a non- conducting substance, it is said to be insulated, and electricity may be retained upon it for a time; but even then it will be gradually diffused and disappear. This is occasioned in part by the conducting power of the air, which is considerable, except when it is very dry. In damp weather, many electrical experi- ments cannot well be performed, because of the rapid diffusion of the fluid through the air, and the deposition of moisture upon the surfaces of insulators. When two substances are rubbed together, both electricities are always developed, one of them going to one of the substances, and the other "to the other substance ; and both electricities maybe retained, if the" two substances rubbed together are insulated. QUESTIONS. What substances are classed with conductors, and what with non-conductors ? Can any definite line be drawn between the con- ductors and non-conductors ? 83. When is a body said to be insulated ? Why do electrical experiments often fail in damp weather ? Are both electricities always developed by friction? 7* 78 DISTRIBUTION OF ELECTRICITY. -f Induction of Electricity. 84. Induction of Electricity, An electrified body always exerts a peculiar influence on the natural electricity of other bodies in its vicinity, called induction, the nature of which will be seen from the following explanation : Let A be a positively excited glass tube, held near one end of an insulated conductor, B, supposed to be in its natural state; the natural electricity in B will instantly be dis turbed, and, on examination, it will be found ^that the end next the excited glass is negatively electrified, and the other end positively, as shown by the algebraic signs. If, instead of the glass tube, some other substance, negatively electrified, had been used, the elec- tricities of the two ends of the conductor B would have been reversed. In every case, the part of the conductor' next to the excited body will be in the opposite state of excitement, while the other end will be in the same state as the excited body. In the experiment nothing but air is supposed to be between the excited body A, and the conductor B, but the inductive influence is exerted through all non-conductors. Thus, if a clean and dry pane of glass be held between A and B, the result will be the same. Let A and B, in the next figure, be two metallic discs, supported upon pillars of glass, their edges being towards the eye, and let a spark of positive electricity be communicated to one of them, as A; it will immediately act by induction upon the natural electricity of B, causing the side next to A to be negative and the other to be positive. The effect is pre- cisely the same as in the preceding experiment, but the form of the con- ductors different. If now we touch the irailffilB I Induction of Electricity. QUESTIONS. 84. What is meant by induction? Explain the experi- ment described in this paragraph. Explain the experiment described in connection with the next figure. DISTRIBUTION OP ELECTRICITY. 79 back of B with the finger, the positive fluid escapes, and the whole disc becomes negative. The action of the positive body, A, has taken place through the stratum of intervening air; and any other non-conductor may be substituted for it. If, for instance, a plate of glass be interposed, the two plates may then be brought much nearer together, and the same results will follow. Instead of the metallic discs, we may simply apply a metallic coating to the two sides of a pane of glass ; which, if the coating do not reach within one or two inches of the edge, serves as a sufficient insulator. 85. The Leyden Jar. The Leyden jar receives its name from the city of Leyden, in Holland, where it was invented. It is essentially the same thing as just described, except that a glass jar is substituted in the place of the pane. It consists of a glass jar, coated both inside and outside with tin-foil, except a part around the top, as shown in the figure. Through a varnished wooden cover, A, a wire, having a knob at top, is passed, and a chain, 'B, extends to the inside coating. Now, when either positive or negative electricity is communicated to the knob at the top, it is im- mediately diffused over the whole inside coating; and by its inductive influence, the outside coat- ing takes on the opposite kind. When in this . Leyden Jar. state, the two coatings being oppositely elec- trified, the jar is said to be charged; and a discharge takes place when a communication is established between the knob and the outside coating, the equilibrium being restored with a bright flash of light and a sharp report. As the human system is a good conductor, this discharge may take place through it, by grasping the outside coating with one hand, and touching the knob at the top with the other ; or several persons may form a line by grasp- ing hands, the one at one extreme touching the outside coating, while the one at the other extreme touches the knob. All will feel the shock, as it is called, at the same instant. While the jar is receiving the charge, it must not be insulated, that is, the outside must communicate with the earth. As the QUESTIONS. 85. Why is the Leyden jar so called ? Describe its con- struction and use. How is the shock produced in the system i* 80 DISTRIBUTION OF ELECTRICITY. positive fluid collects on the inside, the outside becomes negative by the expulsion of the positive fluid naturally in it, and the accumulation of the negative fluid in its stead, drawn from the earth. But if the outside is insulated these transfers to and from it cannot take place, and therefore the jar cannot become charged. 86, Free Electricity resides in the Surface of Bodies. It has been demonstrated that the electricity of an excited body resides entirely upon its surface. Let A be a sphere of metal, suspended by a silk thread, and excited by receiving a spark of electricity and let BB be two covers of paper, gilt outside and inside, and held by glass handles. Let them now be applied to the excited globe, and then instantly removed; it will be found that the electricity has been entirely removed from the ball to the covers. Resides upon the Surface. The free electricity therefore was entirely accumulated upon the surface of the ball. 87. Distribution over Surface. The fluid will be distributed over the surface of an excited conductor, in a mode dependent upon its form; if it be a perfect sphere, the fluid will be dis- tributed equally over every part, but if it be more or less elongated, as in the prolate spheroid, the fluid accumulates in the ends, where the intensity is greatly increased if the spheroid happens to be very considerably Distribution on Ellipsoid, elongated. QUESTIONS. While receiving the charge must the jar be insulated? Why ? 86. In -what part of an excited conductor does the electricity reside? 87. In what manner is electricity diffused over the surface of a sphere? *How is it diffused over the prolate spheroid? SOURCES OF ELECTRICITY. 81 If the extremity of the conductor is carried out to a point, the fluid at once escapes from it, and all excitement disappears, even though it remains insulated. In the same manner, a sharp point projecting from a conductor receives the fluid silently upon it, and the body becomes excited. The effect of points in discharging or receiving either of the fluids is therefore apparent ; and the circum- stance must always be particularly regarded in the construction of electrical apparatus. The escape of positive electricity from a point in a \\\ //, dark room is always attended by the appearance of a faint blue light in the form of a brush, as represented in A, but the escape of the negative fluid, in the same circumstances, presents the appearance of a star, as shown in B. It is to be noticed, that in such experiments the escape of. either fluid is to be considered as precisely Electricity r J on Points. equivalent to the entrance of the other. SOURCES OP ELECTRICITY. 88. As we have seen above, electricity is believed to be con- tained in all bodies, which are therefore properly its sources; but the earth, as being by far the largest mass to which we have access, is its chief source. We propose, however, under this head, to speak of the different modes of exciting or collecting it, which are friction, change of temperature, and chemical action. 89. Friction. It is believed that electricity is always developed when one substance is rubbed against another, oue of the fluids passing to one of the substances, and the other to the other sub- stance, as" before stated; but, in most cases, neither of the fluids is retained, because the rubbing substances are not insulated. If QUESTIONS. What is the effect if one part of an insulated conductor is extended out to a point ? What is said of the influence of points in receiving the fluid ? 88. What is the great source of electricity ? What are the different modes of exciting electricity ? 89. Is electricity always developed when one substance is rubbed against another? How may both be collected and retained ? 82 SOURCES OP ELECTRICITY. Electrical Machine. both be insulated, both the positive and negative fluids may be retained (83). 90. The electrical machine is an instrument for developing electricity by friction more abundantly than it can be done by the simple means heretofore pointed out, though most of the great principles of the science, as we have seen, may be demon- strated without it. The figure in the margin represents the cylinder machine in its usual form. A is a cylinder of glass, firmly sup- ported, and capable of being turned on its axis by a handle; and R is a conductor, supported on a pillar, having the rubber attached to it, with a flap of silk, S, extend- ing nearly over the cylinder. C is made of sheet-brass, and is called the p*rime con- ductor, because it receives the electricity from the cylinder as it is turned, by means of several pointed wires (87), extending inwards towards the cylinder. It is supported upon a pillar of glass. Now, when the cylinder is turned, electricity is abundantly developed by the friction of the rubber against its surface, and is received by the prime conductor, in which it accumulates. The- use of the flap of silk, S, is to prevent the fluid from escaping in the air, as the cylinder is turned. From the principles heretofore discussed, the learner will readily perceive that it is the positive electricity that will be accumulated in the prime conductor; but the negative (83) will also at the same time accumulate in the rubber, if it be insulated. But no considerable quantity of electricity can usually be collected, unless the rubber communicates with the earth, or, which is the samo thing, with the floor of the room. An elegant plate electrical machine is represented in the next figure (p. 83). A B is a firm base of wood, mounted on castors, so as to allow the machine to be moved around easily upon the floor; CCC the prime conductor, supported upon pillars of glass ; P P two circular plates of QUESTIONS. 90. Describe the electrical machine. Describe the large plate machine. SOURCES OP ELECTRICITY. 83 glass upon the same axis, and turned by the handle H ; R R R R the rubbers, of which there are eight, and F F flaps of silk to prevent the MUMEORD 3 Electrical Machine. escape v, f the fluid before reaching the point from the prime conductor. This mi,-jhine, when put in proper order, developes electricity rapidly, and is decidedly preferable to the cylinder machine. When used, the machine should be dry and warm, and per- fectly clean and free from dust. Its action is also greatly increased by spreading the surface of the rubber, where it presses against the cylinder, with a soft amalgam of zinc, tin, and mercury, or with the yellow sulphide of tin, called aurum musivum, the latter, on the whole, being preferable. QUESTION. What is the substance spread over the rubber? 84 SOURCES OF ELECTRICITY. To prepare the amalgam, melt in a crucible three parts of zinc and one of tin, and, after removing it from the fire, add four or five p^rts of ..ercury. Stir the mass with a stick a few seconds, and pour it out upon a clear marble slab, or plate of metal, and allow it to remain several hours before breaking it up. "When wanted for use, grind it as fine as possible in a mortar, and mix it with sufficient tallow to cause it to adhere well to the rubber. If the aurum musivum is used, it is to be mixed with tallow and spread upon the rubber in the same manner. When the machine operates properly, if the knuckle be pre- sented near the prime conductor, a vivid spark passes between them, and a slight stinging sensation is felt; the same thing also takes place on presenting the knuckle to the rubber, provided it be insulated. In the first case the effect is produced by accu- mulated positive electricity ; in the second, by the negative. 91. The Electrophorus (from electron and phero, I bear) is an instrument for readily obtaining small quantities of electricity. It consists of a plate of resin, A, about 12 inches in diameter, contained in a shallow dish of metal, and a metallic disc, Dj a little smaller than the plate of resin, provided with a glass handle, for removing it from the resin at plea- sure. To operate well, the surface of the resin should be perfectly smooth. Electrophorus. J To charge the electrcpnorus, the disc is removed, and the surface of the resin rubbed briskly with a piece of warm, dry flannel, or 'struck several times with a dry silk handkerchief, folded up for the purpose, by which a negative electricity is excited. If, now, the disc of metal be restored by means of its insulating handle, its lower surface will become posi- tive by induction (84), and its upper surface negative. By touching the upper surface of the disc, when in this position, with the finger, the negative electricity will be discharged ; and if it be then removed carefully by its handle, it will be found highly charged with positive electricity, so that a considerable spark may be obtained from it. As the cake of resin has lost nothing of its electricity by the operation, the process may be repeated any number of times, with the same result. QUESTIONS. How may a spark be obtained from the 91. Describe the electrophorus. SOURCES OF ELECTRICITY. 85 The Hydro-Electric Machine is an instrument for exciting elec- tricity by means of high-pressure steam. The excitement is attri- buted to the friction of the steam, carrying with it drops of water, against the pipes from which it issues. 92. Atmospheric Electricity. The general phenomena of thunder and lightning are well known. They are occasioned, as Franklin first demonstrated, about a century ago, by immense accumulations of electricity in the clouds, between which and objects upon the earth violent discharges are frequently taking place. The discharge is believed to differ in nothing from the discharge of a spark from the conductor of an electrical machine, except what necessarily results from the quantity and intensity of the fluid accumulated. Lightning -rods, which are so common at the present day, are rods of metal erected upon buildings, extending a distance above them at the top, and at the bottom connecting with the moist earth. Being made of metal, which is a good conducting material, any discharge that may happen upon the building will be con- veyed by them without danger to the ground. Often several of them are attached to the same building, at dif- ferent points, but they should always be connected together, and also make two connections, at least, with the moist earth. Any attempts to insulate the rod from the building are, to say the least, useless. Buildings with tin or copper roofs, and metallic water-conductors extending downward, require special electrical conductors only for tbe chimneys or other projecting parts, and also from the water-conductors to the moist earth below. Electricity excited by friction is frequently called statical elec- tricity, to distinguish it from dynamic electricity, which will bo hereafter described, under the head of Galvanism. 93. Thermo -Electricity. If a crystal of tourmaline, the extremities of which are dissimilar, 'is slightly heated in the flame of a spirit-lamp, one end will be found, on examination by a delicate electrometer, to be positive, and the other negative; QUESTIONS. What is the hydro-electric machine ? 92? What is said of lightning and thunder ? Who first explained their cause ? What are lightning-rods ? What is said of buildings with metallic roofs t 93. How may crystals sometimes be electrically excited ? 8 86 SOURCES OP ELECTRICITY. but the excitement is very feeble. Crystals of some other sub- stances may be excited in the same manner. But the more common method of exciting electricity by change of temperature, is to heat slightly the ends of two or more small rods of different metals at their junction, as repre- sented in the figure. Let A be a small rod of antimony, and B another of bismuth, soldered together at one end; and then let the heat of a spirit-lamp be applied, for a moment, at the point where they are soldered ; while the bars are warm- ing, the bismuth will be negative, and the antimony Thermoelectricity P ositive - The bismuth j s ca n e d the positive, and the antimony the negative metal, because, while heating, the positive fluid appears to originate in the former, and flow to the latter; but an electrometer will show the different states of the metals, as above indicated. Other metals and even non-metallic substances may be used, with similar results. German silver and brass answer very well, the former corresponding in its action with the antimony, and the latter with the bismuth. The effect will be considerably increased, if several pairs of the metals, arranged as above, are associated together, as shown in the accompanying figure, the alternate rods, A, being of German silver, and the intermediate ones, B, of brass. When the metals are gently heated at the points of junction at one ex- tremit y of the bars > and ke p fc c o1 at the other, the terminal bars become excited, and a constant current flows over any conducting sub- stance, as a copper wire, connecting the extremities of the series. If the upper ends of the rods be heated, the direction of the cur- rent over the wire will be as shown^by the arrow. If the lower ends be heated, or the upper ends cooled, its direction will be reversed. QUESTIONS. Describe the mode with two metals. How may the effect be increased ? SOURCES OP ELECTRICITY. 87 Thermo-Electric Pile. To render the instrument more compact, the metallic 'bars may be placed side by side, with only a slip of silk between them, the ends being bent a little, so as to admit of being soldered as before. Such an instrument constitutes the thermo-electric pile, which is figured in the margin, P and N being the positive and negative poles. The existence and direction of these cur- rents are best shown by a delicate galvanometer, an instrument to be hereafter described. By reversing the experiment, and passing a current of electricity through the series of bars, they will be heated or cooled, according to the direction in winch the current is made to pass. 94. Chemical Action. Chemical action, as the solution of a metal in an acid, and the combustion of charcoal in an ordinary fire, it is believed, is always attended by the development of elec- tricity. In the combustion of charcoal, the gas arising from the coal is positive, while the coal itself, if insulated, is negative; and when a metal is dissolved in an acid, a current of positive electricity always passes from the metal to the liquid, and any conducting substance, as a plate of copper, contained in it. Let Z*be a zinc plate immersed in water, acidulated with a little sulphuric acid, con- tained in a glass vessel, and C a plate of copper, also immerseU in the same liquid ; the zinc will be gradually corroded, and a current of positive electricity pass from it through the liquid to the copper; and if the plates are connected by a wire, the current. will pass over it in the direction indicated by the arrows. But, although we have, in these and other cases of chemical action, such decided and even powerful developments of electricity, it is admitted, that in very many cases where chemical action really takes place, no indications of electricity have as yet been observed. The action of one salt upon another, of one metal upon another, or QUESTIONS. Describe the thermo-electric pile. 94. Is chemical action always attended by the development of electricity? Describe the simple galvanic circle. Are indications of electrical excitement always observed during chemical action ? Simple Circuit. 88 GALVANISM. of a simple element, as oxygen or sulphur, upon a metal, may be mentioned, as instances in which no electrical excitement is actually known to take place. The electricity of chemical action, sometimes called dynamical electricity (92), properly constitutes the subdivision of the general subject of electricity called GALVANISM; and under this title it will be discussed more at length, as it is this branch of the general subject which more especially concerns the student of chemistry. GALVANISM. 95, The science of Galvanism owes its name and origin to the experiments on animal irritability made by Galvani, professor of anatomy at Bologna, Italy, in the year 1790. In the course of some of his investigations, he discovered the fact that muscular contractions are excited in the leg of a frog recently killed, when two metals, such as zinc and silver, one of which touches the crural nerve, and the other the muscles to which it is distributed, are brought into contact with one another. The experiment with 'the legs of a recently killed frog is easily repeated, in the following manner : After killing the frog, immediately separate the hind-legs, with a small portion of the spine, and remove the skin ; then bind around the part of the spine removed with the legs a piece of tin-foil, F, and, holding it up with the left hand, apply a piece of .silver coin, or a rod of silver, S, bent, if neces- sary, so that it shall touch the tin-foil and the flesh of one of the legs at the same time. At each con- tact of the metals,, the muscles of the leg will be violently contracted, and jerking of the legs pro- duced. The experiment succeeds best when the whole is kept wet with clean water. The irrita- Experlmentwith Frog. QUESTIONS. By what name is the electricity of chemical action gene- rally known? 95. What was the discovery of Galvani? Describe the zperiment v?ith the legs of the frog. GALVANISM 89 Dility of the muscles will gradually subside, but sometimes it will continue more than an hour after the death of the animal. The large legs of some insects, especially those of the grasshopper, may be used for the same purpose. It is necessary only to remove with a sharp penknife a portion of the skin from each Bide of the thick part of one of the leap- ing legs, so as to expose the flesh ; then by laying the under side of the leg upon a small piece of moistened zinc, Z, and bringing a piece of copper, C, in contact Experiment with Grasshopper, with the flesh exposed on the upper side, no motions will be observed until the copper also touches the zinc, when quick movements or jerks of the lower part of the leg, AB, will be seen, each time the contact is made. 96. Simple Galvanic Circles, A simple galvanic circle is formed of three substances, two of which are usually metals, and the third a liquid, as a dilute acid. The arrangement de- scribed in paragraph 94 constitutes such a circle. The zinc is acted upon by the acid, and the electrical disturbance takes place over all that part of its surface covered with the liquid ; and a current of positive electricity flows to the liquid. If, now, a plate of copper, or other metal not capable of being acted upon by the liquid, be introduced, it will become positive by receiving elec- tricity from the liquid ; and, by 4 connecting the two plates by wires, a constant current is established over these wires, as shown by the arrows. It matters not, so far as galvanic action is con- cerned, at what part the plates touch each other. . A current is formed, whether contact between the plates is made below, where covered with liquid, above, where uncovered, or along the whole length of the plates, provided both plates are immersed in the same vessel or diluted acid. But in every case /i circuit must be formed, around which the electricity may traverse, either in a single current, or in many partial currents, into which it ma divide itself, as will be the case when the metals are in contact along their whole surfaces. This last result it is desirable to avoid ; and therefore the metals are always to be kept separate below the liquid, and above it also,' except at the part where the QUESTION s. Describe the experiment with the leg of a grasshopper. 96. What constitutes a simple galvanic circle? When is the electricity excited ? What is the use of the plate of copper ? In what direction does the positive current flow ? Must the circuit always m complete ? 8* * GALVANISM. current is desired to pass. Usually, a wire is connected with each plate, which may, be brought in contact or separated at pleasure. When they are in contact, the circuit is said to be closed; when they are separated, it is said to be broken, or open. 97. As the electricity is developed entirely by the chemical action between the zinc plate and the acid, it is only upon the surface of the zinc covered by the acid that the electric disturbance takes place ; and, other things being equal, the quantity of elec- tricity set in motion will be propor- tional to the extent of zinc surface thus exposed to the acid. And in every case, in order to establish the current, the circuit must be made complete. Thus, if we take two cups of dilute acid, immersing in one a copper, C, and in the other a zinc, Z, plate, and connect the two by a wire, as shown in the figure, though Borne chemical action will take place, no current will be established, for the reason that no circuit has been formed. Chemical action does indeed take place in the cup containing the zinc plate, and its electricity no doubt is disturbed ; but, still no current can be esta- blished. For this it is necessary, further, to add the conducting wire AB, as shown in the next figure; the direction of the current will then be as shown by the arrows. It is to be understood that here, as elsewhere, in using this lan- guage, we have reference to the positive fluid ; but in reality there is just as much reason to believe there is also at the same time a QUESTIONS. When is the circuit, said to be closed? When open? 97. To whsit will the quantity of fluid put in motion be proportional ? Explain the necessity of completing the circuit, as illustrated by the figures in this paragraph. Circuit Complete. GALVANISM. 91 negative current established in the opposite direction. In every case, the direction of the positive current will be from the, metal acted upon to the liquid, and that of the negative, of course, the reverse. The direction of the positive current, therefore, in the apparatus last figured, is from the zinc cell to the copper cell, over the wire connecting the cells, and from the copper to the zinc over the wire connecting the plates, as shown in both cases by the arrows. To break the circuit it matters not which of these wires is inter rupted ; both are equally necessary to complete the circuit. 98. A simple galvanic circle maybe formed of one metal and two liquids, provided the liquids are such that a stronger chemical action is induced on one side than on the other. Nay, even a plate of metal, with two portions of the same liquid, may be made to constitute the simple circuit, provided only the conditions are such that one side of the metal shall be acted upon by the liquid more readily than the other. This will be effected, if one portion of the liquid is warmer or stronger than the other, or if one sur- face of the metal is rough and the other polished. We have above represented the positive current as passing from the zinc, through the liquid, to the copper, and in the opposite direction over the wires connecting the plates above the liquid ; this will always take place wheri*a diluted acid is used, which attacks the zinc more violently than it does the copper ; but if a solution of ammonia be substituted for the acid, the copper will be most acted upon, and the current will move in the opposite direction. It is not necessary that copper and zinc alone should always be used in these experiments; other metals may be adopted, with equal, and, in some cases, with even more decisive resuhs. Nor is it required that the liquid should always contain an acid ; other substances, as solutions of the salts, are often very efficacious in exciting this subtile fluid. The conditions required are, that the metals and liquid used should be such that chemical action will take place more readily between one of them and the liquid than between the other and the liquid ; and that metal is always found positive (below the surface of the liquid) which is most acted upon by it. Other things being equal, the galvanic action will be more intense, the greater the difference between the the two metals QUESTIONS. Is there a current of the negative fluid? What is its direction as compared with that of the positive? 98. How may a simple circle be formed of a single metal and two liquids ? Will the positive current always pass from the zinc to the copper? Why is the direction reversed when aqua ammonia is used ? May other metals besides copper and zinc be used ? What are the conditions required ? 92 GALVANISM. used, as regards their tendency to be acted on by the particular menstruum in which they are immersed. Besides the above arrangement, there are several modifications of the simple galvanic circle, each possessing its own peculiar advantages, which will be described hereafter. 99. Compound Galvanic Circles. Galvanic Batteries. The compound galvanic circle, or galvanic battery, consists of a num- ber of simple circles, so arranged in a series, that the copper of each simple circle is connected with the zinc of the one adjacent. One extreme of the series, it will be evident, will be copper, and the other zinc } they are often called the poles of the battery, the former being positive and the latter negative. The voltaic pile (from the name of its inventor) deserves here to be noticed, as the earliest and simplest instru- ment of this kind, though by no means the most efficient. It is formed of pieces of copper, c, zinc, z, and cloth, the latter being moistened with a solu- tion of salt or acidulated water. Commencing with either of the metals, upon this is placed apiece of cloth, and then a piece of the other metal ; the three, of course, constituting a simple galvanic circle. Upon this circle other simple circles are then formed in the same manner, care being taken to place the metals throughout the series in the Voltaic Pile. j same order. The. series may be extended indefinitely; but, usually, from fifty to one hundred pairs of metallic plates will be found as many as can be employed advantageously. When in action, the extreme zinc plate, which is represented as uppermost in the figure, will be negative, and the extreme copper plate positive ; and if they be sonnected by wires, the current will flow in the direction of the arrows, both through the series, and over the wires. The extremes of the series are called its poles, or electrodes (from "electron) and odos } a way). QUESTIONS. 99. What constitutes the galvanic battery, or compound circle? What constitutes the poles of the arrangement? Describe the voltaic pile. How many pairs of plates are needed ? What are the poles, or electrodes ? GALVANISM. 93 Cruickshank's Battery. The voltaic pile is now rarely employed, because we possess other modes of forming galvanic combinations which are far more powerful and convenient. Cruickshank's battery, one of the earliest invented, consists of a trough of baked wood, about thirty inches long, in which are placed, at equal distances, fifty pairs of zinc and copper plates, pre- viously soldered together, and so arranged that the same metal shall always be on the same side. Each pair is fixed in a groove cut in the sides and bottom of the box, the points of junction being made water-tight by cement. The apparatus thus con- structed is always ready for use, and is brought into action by filling the cells left between the pairs of plates with some conve- nient solution, which serves the same purpose as the moistened cloth in the pile of Volta. An excellent compound circle, or battery, is formed by' com- bining a number of cups like that represented in paragraph 94. Each cup contains a zinc, Z, and copper plate, C, the zinc of one cup being con- nected with the copper of the next, through the whole series, leaving the two extreme plates free ; and the cups are filled with diluted acid, or a solution of salt. The two free plates, constituting the extremities of the series, will be the poles, or electrodes ; and when they are connected by wires, the current will be established in the direction of the arrows. By studying closely this arrangement, it will be seen that the actual quantity of electricity flowing over the wires connecting the electrodes, Is no more than when a single cup only, with a single pair of plates, is used. The same electrical disturbance takes place in each cup, over the whole surface of the zinc plate which is covered with the liquid, the part of this plate above the liquid QUESTIONS. Describe the trough battery.' What is said of the quantity of electricity flowing in the compound circle, or battery ? How docs this appear ? Compound Circuit. 94 GALVANISM. becoming negative, and the liquid becoming equally positive ; the copper plate then serves as a conductor to take up this positive electricity, and convey it to the negative zinc of the next cup, by which it will be exactly neutralized. However extensive the series may be, this will take place with every alternate zinc and copper plate except the extreme ones ; so that the quantity pass ing over the wires connecting the electrodes, will be only that of the single pair of plates constituting the extremes of the series. 100. But although the quantity of electricity developed at the electrodes of the compound circle is no more than we should obtain by using a single pair of plates, yet it will be found to have acquired a very important property, called intensity. By this term is meant its power to overcome resistances which may impede the passage of the current. The current from a single pair of plates, however large they may be, will always be exceed- ingly feeble, and will not flow unless the wires connected with them are in actual contact; but, if the polar wires of "the com- pound circle are once brought in contact, they may be separated at a little distance, and the current will continue to pass between them, with a brilliant flame. The reason is ; because the current from the compound circle possesses sufficient intensity to overcome the resistance of the thin stratum of air between the wires, which is not the case with the current of the simple circle. So, if the polar wires of the simple circle are grasped, one in each hand, by the operator, not the least sensation is felt, because there is not sufficient intensity to impel the current through the system, which is comparatively a poor conductor ; but if the same is done with the polar wires of the compound circle, especially if the series be extensive, the moment the circuit is formed, a pow- erful shock is experienced, similar to that received from the Ley- den jar. This is owing to the increased intensity of the current from the compound circle, enabling it to overcome the resistance which is interposed. QUESTIONS. 100. What benefit then is derived from increasing tho series ? What is meant by intensity ? Why will not any sensation be produced in the system by a single cell ? GALVANISM. 95 101. From the above facts we deduce this important practical principle : that, to produce a current of quantity, a single pair only of large plates is wanted; but to give intensity, a number of simple circles must be combined, in the manner described. Compared with frictional or statical electricity, that of the most powerful galvanic battery has always only a feeble intensity, but the quantity is often immense. The energy of any battery, whether composed of one or many simple circles, will depend very much upon the nature of the liquid used. A solution of common salt, sulphate of soda, nitrate of potassa, alum, or other salt, will answer the purpose, but acids are better. Generally, one of the stronger acids is used, diluted with 15 or 20 times its weight of water. For ordinary purposes, a mixture of equal parts of nitric and sulphuric acids, diluted with 20 times their weight of water, will be found to answer well. 102. Nature of the Chemical Action in the Battery. The development of electricity by the usual galvanic arrangements is attributed chiefly, if not entirely, to the decomposition of water in contact* with the zinc plates. Water is a compound of oxygen and hydrogen, and is incapable of acting upon zinc, unless some acid be also present. But when a piece of this metal, in its usual impure state, is immersed in diluted acid, the water is decom- posed, its oxygen combining with the zinc, forming oxide of zinc, while the hydrogen rises in bubbles and escapes in the air, and at the same time the oxide of zinc is taken up by the acid. If, now, a plate of copper is placed in the diluted acid at a little distance from the zinc, and the two connected by a wire, constituting a simple galvanic circle (97), the bubbles of hydrogen will not rise around the zinc as before, but around the copper j showing that the gas has in some way been transmitted through the liquid between the plates, though not the least appearance of any motion can be observed by the eye. If the connecting wire is removed, the evolution of hydrogen at the copper plate at once ceases with the cessation of the electrical current, but continues to rise slowly QUESTIONS. 101. "What is said of the intensity of the excitement pro- duced by the galvanic battery, as compared with that of statical electricity ? What acids are recommended for use in the battery ? 102. What is said of the chemical action that takes place when a piece of zinc is immersed in a dilute acid ? What is the occasion of the bubbles upon the zinc ? When a copper plate is connected with the zinc where do the bubbles of hydrogen make their appearance? 9t> GALVANISM. around the zinc. This latter effect, however, is occasioned by tha impurity of the zinc. Thus it would seem that the development of the current is occasioned entirely by the decomposition of the water, and the formation of oxide of zinc. When the battery is in active operation, though the hydrogen is rapidly evolved at the copper plates, yet the whole surfaces of these plates will be all the time covered with a film of this gas> which interferes with its conducting power, and prevents the fret passage of the current; at the same time, as a matter of course, diminishing very considerably the energy of the battery. T& remedy this difficulty, several new forms of the battery have recently been invented, which act with great energy, and will here be briefly described. 103. Daniel's Constant Battery. This excellent instrument consists of a cylindrical vessel of copper, C, in which is placed another smaller one, L, made of unoiled leather, or ungjazcd porcelain, through which water will gradually percolate; and in the latter is contained a rod of zinc, Z, about an inch in diameter. To charge it, the inner porous ves- sel, which contains the rod of zinc, is filled with diluted sulphuric acid (acid 1 part, and water 8 parts), and the space around the inner vessel with a saturated solution of blue vitriol, acidulated with sulphuric acid. To the side of the copper vessel, and also to the zinc rod, wires are soldered, with binding screws for holding the polar wires; the one connected with the copper being positive, and the other negative, as shown by the algebraic signs. Usually, the zinc rod is amalgamated with mercury, which is done by rubbing the surface with mercury, while covered with some weak acid. This renders the chemical action over the whole surface more uniform, and the action of the battery more constant; but the same thing may be accomplished with less trouble, by using the zinc in its ordinary state, and substituting, in the porous Daniel's Cell. QUESTIONS. 103. Describe Daniel's battery. How is the zinc amal- GALVANISM. 97 cell, a saturated solution of sulphate of soda (Glauber's salt), instead of the diluted acid. The above arrangement, it is plain, constitutes a simple galvanic circle j and its action is particularly energetic and constant, in consequence of the accumulation of hydrogen gas upon the copper plate (102) being completely avoided. This will appear from th'j following explanation. ^ In this instrument, as in the more common one first described^ the electricity is developed at the surface of the zinc, by the decom- position of the water; the oxygen combining with the zinc, and the hydrogen passing through the porous vessel into the vitriol solution, and thence to the sides of the copper vessel, which con- stitutes the copper plate of the series (98). Here the hydrogen does not make its appearance in bubbles upon the surface of the copper, as in the common arrangement,' but enters into a new combination with the oxygen of the oxide of copper deposited from the vitriol solution. Blue vitriol is a jcompound of sulphuric acid and oxide of copper; and while the battery is in operation, it is all the time decomposing, its acid passing into the pocous cup, to act upon the zinc, while the oxide of copper is itself also decomposed, its oxygen combining with the hydrogen at the sur- face of the outer vessel, which receives a new coating of metallic copper. Any number of these arrangements may be united, by connecting the zinc of one with the copper of the next, as heretofore Described (99); and a battery so constructed has this great advantage, that no action takes place when the circuit is not closed. It is also very constant in its action, affording a uniform current for seve- ral hours in succession. The figure in the margin repre- sents a battery of this kind, of six series. When a'battery of this kind is to be used some time, a quantity of un- dissolved blue vitriol should be kept in the upper part of the copper cell, Daniel's Battery, either upon a shelf provided for the purpose, or in a muslin bag, to keep the solution constantly saturated QUESTIONS. How is the hydrogen disposed of in this arrangement? Why is it called a constant battery ? How are the separate cells to be united to form the compound arrangement? 98 GALVANISM. Grove's Cell. 104. Grove's Cell. This battery, invented, by Professor Grove, of London, is remarkable, not only for the constancy of its action, but also for its great intensity. The construction of this battery is shown in the accompanying figure. A glass or porcelain cup, of a proper * ~~^ size, is used, and in it is placed a hollow cylinder of zinc, Z^.(usually having a slit in one side, to allow a free passage to the liquid), and insi le of this, a small cylindrical cup, C, of porous or unglazed porcelain. The glass cup is then filled with diluted sulphuric acid (of the same strength as is used in Daniel's battery), and the porous cup with strong aquafortis (nitric acid). Lastly, a thin slip of platinum, P, is suspended in the aquafortis, and supported by a piece of wood attached to the side of the glass cup, through which a wire passes, and is bent in the form represented in the figure. A projection upward from the zinc supports a binding screw, shown on the right, and another is soldered to the wire to which the platinum is attached, shown at the left. These, of course, serve as the positive and negative poles of the circle ; and to them the polar wires may be attached, when required. The zinc should be well amalgamated, as heretofore described. The action of this battery is essentially the same as that of Daniel's, except that the hydrogen from the decomposition of the water, passing into the porous cell, is expended in decomposing the nitric acid, which, when the instrument is in action, gives off copious nitrous fumes. To understand this, it is necessary to recollect that nitric acid is a compound of nitrogen and oxygen ; and the hydrogen entering the porous cell takes away a part of its oxygen, forming water; and the binoxide of nitrogen which is liberated rises, and uniting with more oxygen from the air, forms *he nitrous fumes. A battery of twelve series of Grove's arrangement is represented in the following figure. The cups are contained in a box of wood, for the sake of convenience in handling, and between the cups are partitions to QUESTIONS. 104. Describe Grove's cell What in this case becomes of the hydrogen ? GALVANISM. hold them more steadily. The hollow cylinders of zinc, when made for this purpose, are oast with 'arms rising from one side, and then project- Grove's Battery. ing a distance horizontally; -and to the end the platinum plate is firmly soldered, so as to hang directly in the nitric acid cup of the next adjacent series. The whole, it will be observed, forms a connected series ; and the terminal zinc at one extremity, and the platinum at the other, with each of which a binding screw is connected, constitute the negative and positive poles. The terminal platinum plate is supported in its place by a wire passing through a piece of wood attached to the side of the box or the cup, as represented in the figure. When a greater power is required than is afforded by a battery of this size, it is found more con- venient to connect two or more batteries together than to have a larger number united in one series. The Batteries are connected by extending a wire from the positive pole of one to the negative of the next ; they then in reality become a single*series. This is the kind of battery generally used in working the magnetic telegraph, as it excels all others in the constancy and intensity of its action. 105. Smee's Cell, This very efficient arrange- ment is represented in the figure in the mar- gin. Two plates of zinc, well amalgamated, are firmly held together against a piece of wood, W, by means of a brass clamp and screw; and between them is a plate of silver, S, the surface of which has been coated over with metallic platinum, in a state of fine powder, called plati- num black. The zinc and silver plates are then suspended in a glass vessel, the piece of wood resting upon the top. A binding screw, con- stituting the -f- pole, is connected by a wire QUESTIONS. What is said of the character of batteries of this kind t t05. Inscribe Sm&a arrangement. 100 G A L V A X ISM. (which is insulated from the brass clamp through which it passes) with the silver .plate, and another, constituting the pole, is soldered to the clamp which holds the zinc plates in their places. The liquid used in the glass cup is sulphuric acid, diluted with- 10 or 15 times its weight of water. The peculiar advantage possessed by this form of the batter} depends upon the rapid evolution of hydrogen from the platinized silver plate. We have seen above (102) that the accumulation of this gas upon the smooth surface of the copper plate, in the old arrangement, considerably retards the passage of the electric cur- rent, by preventing the liquid in a measure from coming in contact with the plate; but this is avoided, in Smee's arrangement, by the roughened surface of the silver plate, produced by the platinum deposit. Compound circles or batteries are readily formed by combining the simple series of Daniel "with each other, or those of Smee with each other; but the proper mode of doing it will be easily understood without further illustrations. For many purposes, they answer well ; but neither of them possesses the energy of that of Grove above described. As batteries are sometimes constructed, and as they are usually repre- sented in books, the direction of the current appears to be the reverse of that in the simple circuit, but this is in consequence of there being a superfluous plate at each extremity whfbh serves only as a conductor. In the figures in this book, however, these superfluous plates are not represented, and the remarks in the text are made with reference to instruments of this construction. 106. Bunsen's arrangement is constructed on the same principle as Grove's, except that hollow cylinders of carbon surrounding the zinc, are substituted instead of the platinum plates. The carbon cylinders are made of carbon from gas-retorte, by grinding it to a powder, and then kneading it with flour dough, and afterwards baking it in a strong heat. 107. Ohm's Formula. The effective force of a battery of any construction will depend upon a number of conditions, or circumstances, which are well expressed in a formula devised by Prof. Ohm, and therefore generally known by his name. To estimate the effective force of any galvanic arrangement, two t^ngs are to be considered, viz : 1. The electromotive force, or absolute tension of the electric fluid, and 2. The resistance to be overcome. As there must always be some resistance to the passage QUESTION. What is the peculiar advantage of Smee's arrangement? 106. Describe Bunseri's arrangement. 107. What is the design of Glint 1 * formula? To estimate the effective force of a battery what two things must be considered ? GALVANISM. 101 of the fluid, the effective force must always be less than the full electromotive power, if such resistance did not exist. The resist- ance will be occasioned chiefly by the wires connecting the poles, but something is due also to the liquid between the plates. ' In the case of a single cell, let the absolute tension be repre- sented by t, and let r be the resistance of the wire, and / the resistance of the liquid between the plates, and A the effective force; then will A = ,. That is, the effective power of the cell will be directly proportional to the absolute tension of the electric fluid, which will in general depend upon the activity of the chemical action taking place, and inversely as the sum of the resistances of the liquid between the plates, and that of the con- ducting wire. To apply the same law in the case of a compound series or battery, we have the following formula : A = < nr n in which n is used to represent the whole number of cells. We see, therefore, that the effective power will be directly proportional to the elec- tromotive force of each cell, multiplied by the number of cells, and inversely as the resistance, which is made up of the resistance of the wire connecting the poles, and the resistance of the fluid of the cells. The resistance r will be proportional to the length of the wire and inversely as tbe area of its section. The resistance / will be proportional to the thickness of the stratum of liquid, and inversely as its conducting power. 103, Animal Electricity. Several animals, .as the gymnotu* electricus, which is found in the fresh waters of some parts of South America, 'the silurus electricus, found in some African rivers, and the torpedo, a species of which has been taken, though rarely, upon the sea-coast of Massachusetts, possess the power of giving strong shocks of electricity, by means of peculiar galvanic arrangements .with which nature has provided them. The electrical apparatus of these animals is plainly connoted with the nervous system, and is perfectly under, the animal's con- QUESTIONS. That resistance will there always be to the passage of the current? T o what is the effective force of a battery proportional? 108. What animals are mentioned as possessing the power of giving shocks of electricity ". Is their electrical apparatus under control of the will ? 9* 102 EFFECTS OF GALVANIC ELECTRICITY. trol. It is made use of as a defence against enemies, and in paralyzing other small fishes, which are immediately seized for food. The shock given by some of these animals is very powerful. EFFECTS OF GALVANIC ELECTRICITY. 109. Galvanic electricity, as we have seen, differs essentially from ordinary, or statical electricity, in several important particu- lars, as its feeble intensity, its immense quantity, and its flowing in a continuous current ; and, as we should expect, there is a cor- responding difference in the effects which these two kinds of electricity are capable of producing. In consequence of the feeble intensity of the most powerful galvanic battery, it is quite incapable of producing many of the more brilliant effects of the common electrical machine, but others are produced not less important. In fact, in the galvanic battery the. ordinary signs of electrical excitement are almost wholly want- ing, plainly for the reason that these indications depend chiefly upon intensity. Thus, when the circuit of a powerful battery is broken, that is, when the poles or electrodes are disconnected, both of them give signs of electrical excitement, if examined by the ordinary tests; one of them being positive, and the other negative, as before explained; but the indications are exceedingly feeble. A Leyden vial may also be charged by establishing a communi- cation between one of its surfaces and one of the electrodes, while the other surface is connected with the other electrode ; but the charge will always be slight. Either of the electrodes will give a spark to a conductor pre- sented to it, but it is shown best by bringing the two polar wires in close proximity; and on establishing the communication be- t^en the electrodes by the hands, previously moistened, a p werful shock is felt, precisely like that produced by the QUESTIONS. 109. In what respect does galvanic differ from Statical electricity ? In the charged galvanic battery, nre the ordinary signs of electrical excitement apparent? May the Leyden vial be charged by an active battery ? How may a spark be obtained from one of the elec- trodes? How ia the shock produced? EFFECTS OF GALVANIC JSLECTRIOITY. 103 discharge of the Leyden jar. But the shock is felt only at the moment the current is established ; if afterwards the hands be held firmly in their places a peculiar feeling of numbness in the muscles in the line of the current succeeds, and continues until the current is again broken. 110, Heating Effects Deflagration. When the communica- tion between the electrodes of an active battery is established by various substances capable of conducting the current, they often become intensely heated, and sometimes even consumed or dissi- pated in vapor by the heat. Thus a small wire interposed in the circuit will become red-hot in an instant, and gold and silver leaf, in the same circumstances, will take fire and burn with brilliant scintillations. This heating effect of the galvanic current may be produced at a distance from the battery, and gun-powder or gun-cotton and other combustibles ignited. Let W be two copper wires, coated with tarred twine, so as to insulate them perfectly, having their ex- tremities connected by a very small platinum wire soldered to them, as shown through the glass cup C. Let the cup be now filled with gunpow- der 01 gun-cotton, and the other ends of the wires brought in contact with the Gunpowder Exploded, poles of the battery; immediately on the passage of the current, the platinum wire will be heated, and the powder exploded. The wires, if well coated, may be extended under water, and a sub- marine magazine exploded. This method has been used for exploding the powder in the blasting of rocks. A mixture of oxygen and hydrogen may be inflamed in the same manner; for this purpose the mixed gases are contained in a pistol, into which the wires are inserted, as shown in the figure on p. 104. QUESTIONS. Does the shock continue while the current flows ? 110. How may the. heating effects of the current be shown? How may gunpowder be inflamed? Describe the method of exploding a mixture of oxygen and hydrogen. 104 EFFECTS OP GALTANIC ELECTRICITY. Pistol. When pieces of well-burnt charcoal are attached to the polar wires, on bringing them near each other, a most brilliant arc of flame appears between them, and the points appear to be vividly ignited, as Charcoal Points. jf heated by any other means. But the heating effect does not depend upon the combustion of the coal, since it is equally as great when the charcoal points are excluded from the air. To produce the effect, the points must first be brought into contact, but they may afterwards be separated some distance, and the arc of flame will continue. At the same time a por- tion of the carbon point in connection with the positive pole disappears, and the other point is elongated as if by matter transferred from the other side. If the char- coal connected with the positive pole be hollowed out so MetaTvoia- as to receive pieces of metal, as silver, gold, or platinum, taiized. when the current passes the metals will not only be fused, but appear to be even volatilized, and pass off in fames. 111. Chemical Effects, Decomposition. The chemicS^ effects ,of the galvanic current are seen chiefly in the decomposition of compound substances, and in the operations of electro-metallurgy, soon to be explained. Thus, when two gold or platinum wires QUESTIONS. Describe the experiment with the charcoal points. How may the metals, as gold and platinum, be even volatilized? 111. In what are the chemical. effects of galvanism chiefly seen? EFFECTS OF GALVANIC ELECTRICITY. 105 Decomposition of Water. are connected with the opposite ends of a battery, and their free extremities are plunged into the same cup of water, but without touching each other, hydrogen gas is disengaged at the negative, and oxygen at the positive wire, these being, as we have seen (102), the elements of water. If the wires are brought into actual contact in the water the current is conducted directly through without acting upon the water, and if any other metal except gold or platinum is used for the posi- tive pole, it will be rapidly attacked by the liberated oxygen. By using one or the other of the two pieces of apparatus figured in the margin, the oxygen and hydrogen may be collected separately or together, as may be desired. The first piece consists of an open vessel, with a shelf and support for two tubes, N and P, which are closed at the top, and binding screws marked + and which connect with wires passing un- derneath the edge of the glass, and terminating in the mouths of the tubes. After filling the tubes and inserting them in their places, the vessel being previously nearly filled with water, the current from the battery is made to pass through in the ordinary way. Very soon the gases will be seen to collect in the tubes; and as water contains by Decomposition of water. volume twice as much hydrogen as oxygen, the tube N COD- QUESTIONS. How may water be decomposed by the current ? Describe the apparatus for decomposing water and collecting the gases formed in separate tubes. Describe that for collecting the gases together. 100 EFFECTS OF GALVANIC ELECTRICITY. taining it will be found to fill proportionally faster than tho other. When the two wires terminate in the same tube, the two gases will be collected together; and by passing afterwards a spark of common electricity through the mixture they will be again united, with an explosion. In decomposing water, it is well always to add a few drops of oil of vitriol, to increase its conducting power. If other compound bodies, such as some acids and solutions of salts, are exposed to the action of galvanism, they are also decom- posed, one of their elements appearing at one electrode, and the other at the other. An exact uniformity in the circumstances attending the decomposition is also remarked. Thus, in decom- posing water or other compounds, the same kind of body is always disengaged at the same side of the battery. The metals, inflam- mable substances in general, the alkalies, earths, and the oxides of the common metals, are found at the negative electrode ; while oxygen, chlorine, and the acids, go over to th.e positive electrode. 112. Those substances which appear at the positive side have been called electro-negative bodies, while those that are separated at the negative,wire are called electro-positive bodies. The decomposition of a salt, which must be in solution, may be shown in the following manner : Let two wine-glasses be filled with a solution of sulphate of soda, (which is a compound of sulphuric acid and soda,) and let some fibre's of moistened cotton be' extended between them, as shown in the figure. If the current is then transmitted tionofSalt. through tbe cups? the 3&It wi]1 goon bQ decomposed, and the cup in conneotion with'fhe positive electrode will be found to contain weak sulphuric acid, and that in con- nection with the negative electrode a solution of soda. If, now, a little red cabbage-water be poured into each, the acid liquid will become red, and the soda solution green. QUESTIONS. May other compounds also be decomposed ? In de- composing a compound, will the same element always appear at the game electrode? 112. What are electro-negative and electro-positive substances ? EFFECTS OF GALVANIC ELECTRICITY. 107 A compound to be decomposed by the current must be in the i'iquid state, and must of course be a conductor; but all com- pounds answering these conditions are not by this means capable of direct decomposition. Yet compounds, not directly decom- posable by the current, are often decomposed indirectly by the hydrogen derived from the decomposition of water that is present. Thus, sulphuric acid is not directly decomposed by the current, but hydrogen separated from the water present, making its appear- ance at the negative pole, unites with the oxygen of the acid, and causes the evolution of fumes of sulphuric acid. Following the suggestions of Faraday, the term electrolysis (from electron, and luo, I unloose) is now very generally used to express this electro-chemical decomposition ', and the term electrolyte to indicate a compound capable of being thus decom- posed. The positive pole or electrode is also called the anode, and the negative pole the cathode (from ana, upward, Jcata, downward, and odos, a way). But instead of the terms anode and cathode, most writers prefer to say positive or negative electrode, as the case may be. The elements of a compound capable of separation by this mode, are termed ions (from the Greek participle ion, going) ; the anion being the element which appears at the anode, and the cation the element which goes to the cathode. It will at once be seen that the anions are electro-negatives, and the cations electro- positives. It is not to be inferred from the above remarks, that every sub- stance will always make its appearance at the same electrode, whatever may be the other substance from which it is separated by the electrolytic action. Oxygen does indeed always appear at the positive electrode, and potassium at the negative j but in the electrolyses of the compounds of other substances, that element will appear'at the positive electrode which is most electro-negative, and that at the negative which is.most positive. 113. The following table exhibits the electrical relations of several of the more important elements. .It is to be understood that each sub- QUESTIONS. Are all compounds directly decomposable by the current? Define the terms, electrolyte, anode and cathode. What are ions ? what anions and cations ? Will every substance always make its appearance at the same electrode, whatever may be the other from which it is sepa- rated? What is the law in this respect? 108 EFFECTS OF GALVANIC ELECTRICITY. stance in the first column is electro-negative as compared -with each ono below it, but in the second column each substance is negative as com* pared with all above it: Oxygen. Fluorine. Chlorine. Iodine. Sulphur. Nitrogen. Phosphorus. Arsenic. Antimony. Gold. Mercury. Silver. Potassium. Sodium. Calcium. Carbon. Hydrogen. Zinc. Iron. Bismuth. Tin. Lend. Copper. Silver. 114, We have seen that the decomposition of a compound takes place only when the current is made to pass through it then one of the ingredients is collected at one electrode, and the other at the other electrode ; thus in the electrolysis of water, the oxygen is collected at the positive and the hydrogen at the negative elec- trode. But how is it that these effects are produced ? and at what precise point or points ? Are both gases liberated at each elec- trode, but one only, hydrogen (the electro-positive element), col- lecting at the negative electrode, and the other, oxygen (the electro-negative element), collecting at the positive pole? This would require that opposite currents of oxygen and hydrogen should be passing by each other in the liquid between the poles while the battery is in operation, of which we have no evidence. Or, does the decomposition take place along the whole line be- tween the poles traversed by the current ? Other similar inquiries may be made, which cannot be answered positively, but the fol- lowing is believed to be a correct representation of the phenomena witnessed, so far as we are able to determine. Water is a com- pound of hydrogen, which we will represent by II, and oxygen, which we will indicate by 0; and the compound by Jf. A tier or row of particles between the "poles we may then represent thus : H, H, H, H, II, H + 000000 QUESTIONS. 114. When only does the decomposition of a compound take place? Describe the manner in which the decomposition of water is supposed to be effected by the passage of the electric current. EFFECTS OF GALVANIC ELECTRICITY. 109 the sign -f indicating the position of the positive pole, and that of the negative. Instantly as the current begins to pass, oxygen from the decom- position of the water appears on the positive side, and hydrogen from the same decomposition at the negative side, a state of things which may be represented as follows : , H, n, rl, H, H, H + 000000 "We have now one less pa'rticle of water than before, and one of the elements of the decomposed particle is found at one electrode, and the other at the other electrode. To produce this effect, it is only necessary that, by the action of the current, all the particles of hydrogen should be removed one place to the right, or all the particles of oxygen one place to the left. That is, the electrolysis of every particle of water in the track of the current has taken place, but the immediate reunion of all the particles has followed, except the extreme particle of oxygen, on the one hand, and the extreme hydrogen on the other. The oxygen and hydrogen thus liberated, at once make their escape; and the continued action of the current produces a like effect on other particles of water until the action ceases, or all the water is decomposed. 115. The quantity of electricity required to effect the decomposition of any compound is probably always the same, as would be shown if we had means to measure it accurately ; and the relative quantities of several electrolites decomposed by a given quantity of electricity will be represented by the combining numbers of these compounds. We shall hereafter have occasion to allude to this point again, in connection with the subject of combining proportions or equivalents. 116. Electro- Metallurgy is the name applied to the deposition of the metals from their compounds by the chemical agency of the galvanic current. "We have seen above (103), in describing Daniel's battery, that during its action there is a constant depo- sition of metallic copper upon the negative plate. Now, if, for the copper plate in this arrangement, a medal, or coin, or other conducting body be substituted, the deposition of the copper upon it will take place in the same manner, and all its minute pecu- QUESTIONS. 115. Is the quantity of electricity required to effect the came decomposition always the same ? 116. What is electro-metallurgy t 10 110 EFFECTS OF GALVANIC ELECTRICITY. Electrotype. liarities will be copied. An apparatus of this kind, called the electrotype, is figured below. A glass vessel is partly filled with a saturated solution of blue vitriol, and in this is placed a porous vessel, containing dilute sulphuric acid, and a rod of zinc, Z, having- a binding screw at top. The medal or coin to be copied is then suspended in the vitriol solution by means of a wire inserted in the binding screw. The surface of the medal on which the copper is to be de- posited should be perfectly clean, and the other surface should be protected by a coating of wax or varnish. In the figure, two medals, M, M, are supposed to be connected at the same time with the zinc. A better method than the above is to use a regular Smee's battery, and to have trie blue vitriol solution in a separate ves- sel, as in the annexed figure. Then let the article to be copied, A, be connected with the zinc of the battery, and a plate of copper, C, with the silver, both being suspended, at a little distance from each other, in the vitriol solution. By the action of the battery, the piece of copper will be gra- dually dissolved, and a corresponding deposit of metallic copper made upon the medal. In the battery here used, one of the zinc plates is supposed to be removed, presenting clearly to view the plate of silver. 117. Other metals besides copper may be deposited in this manner, but a battery of several cells is in most cases required. The most im- portant application that has been made of this discovery is in depositing silver ami gold in thin laminae upon other metals, called plating or gild- ing. For this purpose a Daniel's or Smee's battery of about four cells answers well, and a fifth, which is called the depositing cell. This is Electrotype. QUESTION. Describe the apparatus called the electrotype. ELECTRO- MAGNETISM. Ill filled with a solution of cyanide of potassium, and used in the same manner as just described for obtaining a deposit of copper, except that silver or gold must be used instead of the copper, C, according as one or the other of these metals is to be precipitated. ELECTRO-MAGNETISM. 118. Natural Magnet, or Loadstone. Among the ores of iron, pieces are often found which, possess the property of attracting and retaining pieces of iron or steel with more or less force, and are called magnets or loadstone. Each magnet always has two points iu which the attractive force appears to be concentrated, which are called the poles. They are always readily found by rolling the magnet in iron filings, which will be collected more at these points than in other places. Gene- ^^^^S^^ir'^^^lfe rally they are nearly opposite to each isS other. (See figure.) If a magnet is broken into several pieces, each always retains the same magnetic properties as the whole mass, but in less degree. Sometimes a magnet has more than two poles. 119. If a magnet be suspended horizontally, by a thread, or placed upon a piece of cork floating in a vessel of water, one of the poles will turn towards the north, and is hence called the north pole, and the other towards the south, and is called the south pole. If two magnets thus suspended are brought near each other, it will be found that like poles repel each other, but unlike poles attract. These attractions and repulsions extend to some dis- tance, and are not affected by the interposition of other bodies, not capable of becoming magnetic. This may easily be shown by interposing a pane of glass, or plate of copper, or a thin piece QUESTIONS, 118. What is the natural magnet, or loadstone? What are the poles ? What is the effect if the magnet be broken in several pieces? 119. What is the north pole? What the south pole ? When two magnets freely suspended are brought near each other, what is observed of like, and what of unlike poles ? 112 ELECTRO-MAGNETISM. of wood between the two magnets, when it will be seen that the action of the magnets upon each other is the same as before, and does not even suffer diminution by the interposed substance, except as the distance between them is increased. 120. Magnets and Diamagnets. It has of late been very satisfactorily determined that all substances may be divided into two classes, the magnetic and the diamagnetic. To the first class belong all substances which, like iron, nickel and cobalt, are attracted by either pole of a magnet when presented near them j and when shaped into bars and free" to move (as when suspended by a thread in the centre) in the vicinity of a magnet, they arrange themselves in the direction of a line uniting its IE -^ **i poles. Two bar magnets best illus- ^T === "s| trate this property; when in the Ma s nets - vicinity of each other, and free to move, they take the position indicated in the figure. The substances alrejady named are the only ones that possess this property in any considerable degree j but others have recently been added to the list, as manganese, chromium, titanium, palla- dium, platinum, oxygen gas, &c., in which the magnetic property is manifested only when a powerful magnet is used. Diamagnetic substances are such as are .repelled by either pole of a magnet, and when made into the form of bars and free to move, in the vicinity of the poles of a magnet, arrange themselves at right angles to a line uniting its poles. This relative position of the magnet and diamagnetic bar is shown in the Magnet and Diarnagnet. accompanying ngure. This diainagnetic property is manifested more powerfully by bismuth than by any other substance, but phosphorus, antimony, zinc, tin, sodium, mercury, copper, gold, glass, ether, alcohol, and nany other bodies, are similarly affected. The experiment can oaly be shown by using very powerful magnets. QUESTION. 120. Into what two classes may all substances he divided ? How do magnetic substances arrange themselves when brought into the vicinity of a magnet ? How do diamagnetic substances ? ELECTRO-MAGNETISM. US 121. Magnetic Induction. When either pole of a magnet is brought in contact with a piece of soft iron, or only very near it, the iron itself becomes magnetic, and remains so until the magnet is removed. The figure following represents several pieces of iron, placed in different positions near the poles of a magnet; on examination, they will all be found to have the magnetic property, their poles being developed as indicated by the letters N and S. Magnetic Induction. This influence of a magnet upon pieces of iron, which extends to a distance around its poles, is called its inductive influence. This influence is exerted by a powerful magnet to a considerable distance from either pole, or even through other bodies (119) which are not themselves capable of becoming magnetic. A piece of iron or other substance which is attracted by either pole of a magnet, is evidently first rendered magnetic by induction, and then the attraction follows as a necessary consequence. But the first piece, as a nail, being rendered magnetic by induction, will act in like manner upon a second, and this upon a third, and so on; so that several pieces may be lifted one after another, as represented in the figure. But it will be found, when the connection with the first magnet is broken, the pieces of iron instantly lose their magnetism, and fall asunder. 122. Pieces of hardened steel will also be affected in a similar manner, but much less readily, and, unlike QUESTIONS. 121. What is the effect when either pole of a magnet is brought near "a piece of soft iron ? What is meant by magnetic induc- tion ? Why is a piece of soft iron attracted by a magnet ? 10* 114 ELECTED- MAGNETISM. iron, they retain the magnetism that has been induced. They therefore become permanently magnetic, and for nearly every purpose are superior to the natural magnet, and may be denomi- nated artificial magnets. The 'same magnet may be used suc- cessively to magnetize any number of steel bars, without losing any of its virtue; from which it follows that the magnet commu- nicates nothing to them, but only by its influence developes some hidden principle already there. Artificial magnets are frequently made in the form of the horse-shoe, and are called horse-shoe magnets. To the poles a short piece of soft iron is usually accurately fitted, called the armature or keeper. 123. The Magnetic Needle Dipping Needle. A slender bar of magnetized steel, suspended upon a pivot, so as to revolve freely, constitutes the magnetic needle. Sometimes it is attached to a circular card, and suspended upon a pivot, as in the mariner's compass. 124. If a steel bar be suspended by its centre of gravity, and afterwards carefully magnetized, it will be found not only to place itself in the magnetic meridian, but to assume a position inclined to the horizon. In northern latitudes, the north pole will be depressed and the south pole elevated, while in southern latitudes the south pole will be depressed. The angle of inclination is generally nearly the same in the same place, and is called the dip of the needle; and a needle nicely balanced and adjusted for showing the dip is called a dipping needle. The dip of the needle is subject to considerable variation, but at the present time it is, at Baltimore, about 71 30'; at Philadelphia, 72 15'; at New York, 73 ; at Middletown, Conn., 73 30' ; and at Boston, 74 24. The magnetic needle does not always point to the true north and south, but deviates more or less from this position at different times and places. This is called its variation. At Philadelphia, in 1840, the variation was 8 52' W., and at Middletown, Conn., about 6 40'. 125. Terrestrial Magnetism. The earth may be considered as a great natural magnet, which, by its action on the needle, in the same manner as any .other magnet, causes it to place itself in QUESTIONS. 122. May magnetism be induced in pieces of tempered steel? What are artificial magnets ? 123. What constitutes the magnetic needle? 124. What is a dipping needle? 125. What may the earth be considered ? ELECTRO-MAGNETISM. 115 the position of north and south. Indeed, it is by the inductive influence of the earth that magnetism is developed in bodies upon its surface. This is shown in bars of iron or steel that have stood long in a vertical position, which are always found to be magnetic. Tongs and pokers, from their being usually kept in an upright position, are almost always found to be magnetic. As it has been agreed to call that pole of the needle which points northward, the north pole, it is evident that' the pole of the earth situated 'north must be a south pole; that is, it must possess southern polarity. So, also, the south pole of the earth must possess northern polarity. 126. Relation between the Electric Current and Magnetism. It has been long known that a discharge of lightning will often affect seriously the magnetic needle, sometimes reversing its poles j but it was not until 1819 that (Ersted made his famous discovery, which has served as the basis of the beautiful science of Electro- Magnetism. He first observed that when the wire, connecting the electrodes of an active galvanic battery, is brought near a magnetic needle, it is made to deviate from its ordinary position, and assume a new one, depending upon the direction of the current and the position of the wire in regard to the needle. Thus, the needle being in its natural position, 1st, if the connecting wire be above the needle and parallel to it, the pole next the negative electrode will move westward; 2d, if the wire be ?*> = beneath the needle, it will move east- " fl J ward ; 3d, if the wire is on the west \ side, this pole will be depressed ; and, 4th, if ifc. be on the east side, it will be elevated. The figure in the margin indicates the motion that will be pro- duced in the first of the above cases. Cnm-nt uua Needle. If the wire be placed under the needle, and the current made QUESTIONS. Why do tongs and pokers become magnetic by standing in a vertical position? What is said of the north >md south poles of the earth? 126. What was the fact first observed by (Ersted as regards the wire conducting a galvanic current and a magnet? 116 ELECTHO- MAGNETISM. Current and Needle. to pass from north to south, the motion of the needle will be the game as indicated in the figure. It follows, therefore, if the wire be bent around the needle, in the form of a rectangle, so as to ~ convey the current in one direction J above the needle, and back again, in the opposite direction beneath it, both parts will conspire to produce the same effect, and the motion of the needle will be much increased. Such an arrangement is represented in the annexed figure. In all these cases, the tendency of the needle is to settle directly across the wire, or at right angles to the direction of the current, while the influence of the earth is exerted to bring it in its first position, parallel with the wire, supposing the experi- ment to be commenced with the needle in its natural position. The position it will ultimately take will therefore be intermediate between these two. 127. To avoid the directive influence of the earth upon the needle, the astatic (from the Greek astatos, unstable) needle has been contrived. It consists of two needles, of nearly equal strength, fixed to the same axis, with their poles reversed in reference to each other, and suspended by a thread, as shown in the figure. One of the needles being a little more highly magnetized than the other, or a little larger, they will have a slight ten- dency to settle in the meridian. If, now, a wire is bent several times around the lower needle, each turn or coil being coated with some insulating sub- stance, when the current is passed around it, its influence on both needles will be to turn them in the same direction; and the Astatic Needle. QUESTIONS. What is the effect if the wire is bent around so as to pass several times around the needle? What is the real tendency of the needle? 127. What is the astatic needle? Describe its con- etruction. ELECTRO-MAGNETISM. 117 Astatic Needle. arrangement becomes a most delicate in- strument for 'indicating the passage of the feeblest currents. Such an instru- ment is called a galvanometer, or gal- vanoscope. To protect it from currents of air, the whole is usually enclosed in a glass case; and beneath the upper needle, and above the coil of wire, a graduated circle is placed, to indicate exactly the comparative deflections of the needle. Such an instrument, in connection with a thermo-electric pile (93), becomes a most delicate thermometer, which is capable of indicating a change of tem- perature of only a very small fraction of a degree. 128, Tangential Force, By a careful inspection of the motions produced in the needle by the current in the several positions of the wire, as described in paragraph 126, it will be evident that the real tendency of each pole is to revolve around the connecting wire in a cir'cle, the plane of which is perpendicular to the wire; around the north pole in one direction and around the south pole in the other. The force which causes tffis motion is exerted in lines which are tangents to the circumference of these circles, and is therefore called a tangential force. The motion of the needle actually produced will of course depend upon the mode in which it is supported, as well as the position of the wire in reference to it. It is to be remarked, too, that the pole is a mere point situated near the extremity of the needle ; between this point and the wire the force is exerted. This point, the magnetic pole cannot exist independent of the needle itself, which must ther fore always move with it; and therefore in order to determine the real motion in any particular* QUESTIONS. Describe the galvanometer, or galvanoscope. 128. What is the real tendency of each pole of a magnet when brought near the wire? What is the force called which produces this motion? Upon what will the motion actually produced depend ? 118 ELECTRO-MAGNETISM. N Pole Revolves. case we are to consider the two circumstances, First, the motion the pole tends to make, and Secondly, the motion*of which the needle is susceptible. Upon these two conditions plainly will depend the actual motion that will result. 129. In order easily to remember the particular motion a pole will tend to make in any given case, take the following example. Let us suppose the conducting wire to be placed in a vertical position, and the current of posi- tive electricity to be descending through it, the tendency of a north pole in the vicinity of the wire will be to move around it in a hori- zontal circle, in the direction indi- cated by the arrows in the figure, or in the direction of the hands of a watch with the dial upward. The tendency of the south pole would be to revolve in the opposite direction. If the direction of the electrical current is reversed, and it is made to pass up- ward, both poles would tend to revolve in the opposite direction from that described above. Whatever may be the position of Jthe conducting wire with reference to the needle, the motions produced will always be in accordance with these statements; and reference being had to this particular position of the conducting wire and the needle, we can always determine by inspection in what direction the needle will move, whatever may be the position of the wire in regard to it. We have here been speaking only of motions produced in the needle by the conducting wire; but it is plain that if the pole of a magnetic needle tends to revolve around a fixed conducting wire, a free wire will have a tendency to revolve around the pole of a fixed needle. The fact is, Jhe influence is mutual, and both fie wire and the pole tend to i Evolve, as we will proceed to show. QUESTIONS. To determine the real motion that will be produced in a given case, what two things are to be considered ? 129. When the cur- rent is descending perpendicularly, what will be the tendency of the north pole of a needle in the vicinity of the wire ? ELECTRO-MAGNETISM. 119 130. Both the revolution of a pole around a fixed wire, and the revolution of a wire around a fixed pole, may be shown by the apparatus, a section of which is seen in the cut in the margin. A and B are two glass vessels, filled nearly to the top with mercury. A wire, supported by a pillar be- tween the vessels, has one end bent down so as to dip into the mer- cury in A; and the other end is bent into a hook, , . , , Both Pole and Connecting Wire revolve. on which a short piece of wire is suspended, so that its lower end shall also dip into the mercury in the vessel B. Conducting wires pass through the bottoms of both vessels, with binding screws, C and D, to connect them with the poles of the battery; and to that in A, a small magnet is attached by a thread, so that one of its poles may be a little above the surface of the mercury; and in the vessel B another small magnet is. firmly fixed, with one pole a little above the mercury. When the current is passed through this apparatus, as indicated by the arrows, the upper pole of the magnet in A will revolve slowly around the conducting wire, and the free con- ducting wire suspended in B will revolve around the fixed pole near it. 131. Further Experiments illustrating the Relation of the Magnet and a Galvanic Current. Experiments to illustrate the relation of a current and the magnet may be multiplied almost indefinitely! De la Rive's Ring is a very beautiful contrivance to show the influence of a magnetic pole upon a conducting wire capable of motion. A copper wire is bent into a circle about an inch in QUESTIONS. 130. Describe the apparatus figured in paragraph 130. What is the point illustrated ? 120 ELECTRO- MAGNETISM. diameter, and the two ends- passed through a piece of wood or ~ cork, and soldered, one to a slip of zinc, Z, and the other to a slip of copper, C. If, now, it be placed in a bowl of water containing a little acid, a current of electricity will cir- culate along the wire, in the direction of the arrows ; and if a bar magnet De la Rive's Ring. be brought near it> Jt W ; U be attracted or repelled, according as one pole or the other of the magnet is presented to it. As represented in the figure, if the north pole of the magnet is -presented to it, it will be attracted ; the south pole will first repel it, but in a little time it will turn around, and will then be attracted. We may, therefore, properly regard it as a flat magnet, having its two poles in the centre of the circle, the one on one side, and the other on the other ; the south pole being in that surface on which, when held before you, the positive cur- rent flows in the direction of the hands of a watch. The apparatus will be more powerful if the conducting wire, covered with silk, to prevent lateral communication, be formed into several circles of the same diameter, on the principle of the multiplier. 132. But what are the forces that have produced these special movements? Giving our attention for the present only to the part of the current upward on one side of the ring and downward on the other, we have seen (129) that the downward current tends to revolve around the north pole of a needle in the direction of the hands of a watch, and the upward current in the opposite direction ; let these facts be kept in mind while the eye rests upon the figure, and it is plain that the effect must be to cause the ring to approach the pole, or apparent attraction ensues. If, now, the magnet be suddenly removed, and the south pole presented, in accordance with the .same laws, the ring recedes, turns around, .. nd again approaches the pole ! QUESTIONS. 131. Describe De la Rive's Ring, and the mode o using it. What may we regard it ? 132. Give the reasons for theso movements. ELECTRO- MAGNETISM. 121 133. The galvanoscope is represented by the next figure N and S are the north and south poles of a permanent horse-shoe magnet, supported upon a stand; and between them, in a small glass tube, is a strip of gold leaf, connected at top and bottom with binding screws, as shown in the figure. Now when the current is passed through the gold leaf, it is made to curve to one side or the other, according as the motion of the current is upward or downward. As the poles are situated in the figure, if the direction of the current is downward, the curving or convexity of the gold leaf will be upward froni the plane of the paper j but if the current is upward the strip of gold leaf will be convex in the opposite direction, or backward from the plane of the 134, The Revolving Spur Wheel, figured in the margin, is made to revolve by the action of a magnet upon the galvanic current. A wheel W mad,e of sheet brass, is supported in such a manner that its rays touch in a globule of mercury in the base beneath, from which a concealed wire extends to the binding screw A, the other binding screw B being connected, in like manner, with the Revolving wheel, wire R which supports the wheel. N S is a magnet placed so QUESTIONS. 13. Describe the galvanoscope. 134. Describe the re- volving spur wheel * and give the reasons for the movement produced. 11 122 ELECTRO-MAGNETISM, that its poles shall be as nearly as possible one on each side of the ray of the wheel which for the time is in contact with the mercury. When the poles of the galvanic battery are connected with the binding screws, a ray of the wheel being in contact with the globule of mercury, the current passes through it ; and he wheel is made to revolve on its axis. A permanent magnet may be used, or an electro-magnet, as represented in the figure (p. 121). 135, Relation of Current to the Earth's Magnetism, The ring described in paragraph 131 is acted upon by the earth's magnetism precisely in the same manner as by the magnet, only that the influence is less in degree. In order that it may be made to move by the magnetism of the earth, it is only necessary that it should be enlarged sufficiently, and a powerful current passed through it. The following modification of it answers a good purpose. Let A and B be two metallic pillars, insulated from each other, provided each with a horizontal arm terminating in a small cup filled with mercury, and connected at the bottom with binding screws. Let a ring R of copper wire, 8 or 10 inches in diameter, be suspended by the ends of the wire from the cups of mercury, and the poles of the battery connected with the binding screws ; the current will pass around the circle of wire, which, by the influence of the earth's magnetism, will be made to move until at length it will take a position with its plane at right angles to the meridian. Supposing the direction of the current to be as indicated by the arrows, and recollecting that the QUESTIONS. 135. Does the earth's magnetism act upon a current in the same manner as a magnet? Describe the movegneuts produced in the ring here figured when conveying the current by virtue of the earth's magnetism. Influence of Earth. ELECTRO-MAGNETISM. 128 north. pole of the earth really possesses southern (125) polarity, let the intelligent student determine which side of the circle of wire will settle to the east and which to the west ! It may afford some aid to reflect that the action on the circle of wire will be the same as if it were square, as shown in the margin, in which it appears there are four parts conveying the current, two on which its motion is horizontal in oppo- site directions and on the same side of the point of support. The influence of these is lost and may not therefore be further con- sidered. On the other two parts the motion of the current is in opposite directions, being on one upward and on the other down- upward and Downward ward and on opposite sides of the point of support. Now the tendency of the part conveying the upward current will be to revolve round the north pole of the earth in one direction, and of the part conveying the downward current to revolve around this pole in the opposite direction; considering then the mode in which the wire is suspended, it is plain that the tendency of the circle of wire will be to settle with its plane due east and west, or at right angles to the meridian. If, then, before passing the current, the plane of the circle of wire is placed in the meridian when the current is made to pass it will turn on its points of support until it takes a position at right angles to the meridian. In every case, the side of the circle conveying the downward current will move towards the east, and the other side of course towards the west. The same movement will be produced if the wire conveying the current is bent several times around, as represented in the first figure on the next page, and supported by its two ends resting in cups of mercury, with which the two poles of the battery are to be connected by binding screws not represented in the figure. The influence of each coil conspires to produce the same effect, and therefore the motions described will foe more readily produced. QUESTIONS. Explain the reasons for the motions which are produced by the earth's magnetism, as illustrated by the preceding figure, and also the two figures on the next page. 124 ELECTRO- MAGNET ISM. But it is not necessary that the dif- ferent coils of the wire should lie in the same plane, the result being the same if it is wound in the form of a helix, Influence of Earth's Magnetism. as represented in the next figure; the helix then truly repre- senting a bar magnet, as will be found by holding either pole of a magnet near either end. By examining the direction of the current in this helix, con- sidering it as a bar magnet, it will be found that is the south pole in which (when it is held up before the eye) the current is moving in the direction of the hands of a watch. It is scarcely necessary to remark that, in the other pole, the direction of the current is the reverse of this. 136. Induction of Magnetism by a Current. Magnetism is induced in a bar of soft iron by the simple passage of a current near it, in a direction at right angles to the bar. Thus, if W I be the ======= conducting wire, and N S a small piece of iron lying under the wire, while the current is pass- ing, magnetic polarity will be induced in the induction of Magnetism -iron, N being a north pole, and S a south by a Current. p ] e? w ^ en t h e curren t passes frpm W tO I; but if the current pass from I to W, the poles will be reversed. f But, if the wire is made to pass around the iron many times, the effect will be greatly increased. This is accomplished by QUESTIONS. When the south pole of the helix is held up before the* face, in what direction is the current found to be moving ? 136. How is magnetism induced in a piece of iron by the galvanic current? ELECTRO- MAGNETISM 125 placing the iron in a helix of wire, as shown in the figure. The current being then made to p pass in the direction of the arrows, the iron becomes strongly magnetic, with its poles as shown by the letters N and S. The cups P and __ * ., ... induction of Magnetism by a Current. N serve to connect it with , the battery. When the current is broken, the iron ceases at once to be magnetic ; but if a piece of hardened steel be substituted for the iron, it retains its magnetism permanently. A magnet formed in this manner, by the passage of a current of electricity around it, is very properly termed an electro-magnet. Magnets of this kind have some- times been made of sufficient strength to sustain a weight of 2000 or even 3000 pounds. For this pur- pose, a bar of iron of considerable size is bent in the form of a horse- shoe, and the conducting wire made to pass many times around it, as represented in the figure. An armature of soft iron (122) is attached to the poles, as with the common magnet, from which the weights are suspended. As stated above, when the current of electricity is interrupted, the magnetism will be im- mediately destroyed, and the weights drop off. 137. The Magic Circle, as it has been termed, possesses too much interest to be here omitted, though no new principle is developed by its action. Two semi-ci*cles, A and B, are made of a stout bar of soft iron, and well fitted together, so as to form a circle, C, and include a small helix of wire, H, the two ends of which are to be connected with the electrodes of a small but active battery. While the current is passing, the semi-circles are made power- folly magnetic, and will adhere with a force which is capable of sustaining a weight of many pounds. Ma^-ic Circle. QUESTIONS. What is the effect when the current is made to pass many- times around the piece of iron ? What constitutes the electro-magnet t 137. Describe the magic circle. 11* 126 ELECTRO- MAGNETISM. The wire need in all these arrangements is supposed to be wound with some insulating substance, as silk or cotton, to prevent the contact of the separate coils, which would permit a lateral discharge of the current, so that it would not pass around the whole length of the wire. 138. To form an effective electro-magnet, the total length of copper wire intended to be used is cut into several portions, each of which, covered with thread, is coiled separately on the iron. The ends of all the wires are then collected into separate parcels, and are made to communicate with the same battery, taking care that the positive current shall pass along each wire in the same direction. The current is thus divided into a number of branches, and has only a short passage from one end of the battery to the other, though it gives energy to a multitude of coils. This was first made known by Prof. Henry, now Secretary of the Smith- sonian Institution. 139. Magnetism of the Earth. We have seen above (125) that the earth may be considered as a great magnet, having its south pole somewhere near its north geographical pole, and its north pole near its south geographical pole; and it has been sug- gested that this may be occasioned by currents of electricity flow- ing around it, beneath its surface, from east to west, or in the direction opposite to that of its motion on its axis. Indeed, it has even been suggested that these currents may have their origin in the heating influence of the sun's rays, as successive portions of the earth's surface come under their influence by its daily motion ; but this is to be regarded as only plausible conjecture. That the needle would be in- fluenced by such a current, precisely as it really is, at different points of the earth's surface, may be shown by winding a covered wire several times around the equator of a common globe, and placing a small magnetic needle upon it while the current is passing, as shown in the QUESTIONS. Why must the wire used for this purpose be wound wither some non-conducting substance? ]88. What is said of the total length of wire used for this purpose? 139. What is said of the earth in refer- ence to this subject? How may the magnetism of the earth be occa- sioned ? Describe the figure in this paragraph. 1; L E C K R *> - MAGNETISM. 127 figure (p. 126). The small needle will uniformly settle in the meridian. 140, Electro-magnetic Engines, All the above motions, it will be observed, whether of the magnetic needle or of the con- ducting wire, have been produced by the tangential force; but various machines have been devised, called electro-magnetic engines, for producing motion by direct influence upon each other of th.. unlike and like poles of two or more magnets ; "one of which a< least must be an electro-magnet. The next figure represents a very simple electro-magnetic machine, which by its motion rings a bell with considerable force. N and S 6re the north and south poles of a common horse- shoe magnet, which stands in a vertical position, with its poles downward. A is a piece of soft iron wound with copper wire and fixed upon a vertical axis, so as to revolve very accurately between the poles of a magnet; and CC are binding screws for connecting the wires from the galvanic battery. The extremities of the wire around the magnet A connect with C, by means of parts not represented in the figure, in such a manner that the current flows in the proper direction to develope north polarity in the further ex- tremity A as it approaches the south pole of the magnet S, and south polarity in the other extremity as it approaches the north pole N : but the momeiit the revolving magnet has arrived at a position between N aiid S, the two poles of the stationary magnet, where it would be held if the Bame polarity remained, the direction of the current is reversed, and, as a neces- sary consequence, the polarity of the re- volving magnet. If its momentum has now carried it a little beyond the point, of greatest attraction, it will be urged on by repulsion until it has made a quarter of a revolution, when it will be attracted as before. At S on the vert : c;il axis is a perpetual Screw which acts upon the teeth of a ratchet wheel, and causes the hammer to strike the bell B The machine may be constructed with more than two magnets, and i.1 a variety of forms, but whether it will ever be made practically useful -, remains to' be 'determined. Electro-magnetic Engine. QUESTIONS. 140. What are electro -magnetic nginesf Describe thf engine represented in the figure. 128 ELECTRO- MAGNET ISM. 141. Mutual Influence of Two Currents. Two currents moving in the same direction in the vicinity of each other are mutually attracted, but if moving in opposite directions they repel each other. Let a helix of slender wire be sus- pended by the top so that the bot- tom may just touch in a cup of mercury; and let a current from a battery be passed through it. In consequence of the attractions be- tween the coils, the spiral will be shortened, and the lower end raised from the mercury, thus breaking the circuit. But when the current ceases the end of the wire again falls so as to touch the mercury, and the cur- Attraction. rent - ls renewe( j w i fc h the same effects as before. Every time the wire touches the mercury a brilliant spark is produced. Two currents therefore in the same direction attract each other. 142, " Electro-Dynamic Induction. A current of electricity passing through a conductor in a given direction, induces a cur- rent in the opposite direction in a second conductor situated parallel to the first. Thus, let A B be a portion of a wire con- + A B necting the poles of a gal- === a ==========^^ vanic battery, and MN a - + portion of a second wire M N parallel, and near to the first; at the moment the circuit is formed and the current passes through the first wire in the direction from -f to a secondary current is induced in the second wire in the opposite direction. This current is but for an instant, but is renewed in the opposite direction when the battery current is again broken. QUESTIONS. 141. How do two currents moving in the same direction affect each other? Describe the experiment illustrated in the annexed figure. 142. How may a current be made to induce another current called a secondary current ? ELECTRO- MAGNETISM. 129 A better method to demonstrate the existence of this secondary current is as follows : Let A be a coil of large copper wire, or, better, of copper ribbon, covered with some non-conducting substance, and having binding screws attached to each end, to receive the polar wires of the battery. Above this is placed a coil, W, of fine covered wire, with a metallic handle at each end; and when the battery current is made to pass through the lower coil, the secondary current will be induced in the upper coil, as will be plainly indicated by grasping the handles with the moist hands. In this case, as before, the secondary current is induced at the moment the battery current is established, in the direction opposite that of the battery current, and again when the battery current ceases in the same direction as this latter current. The former is termed the initial and the latter the terminal secondary current. The effect of the shocks will be increased by rapidly breaking and closing the battery circuit, the feeble intensity of the shocks being compensated by their frequency. Of the two coils above used, it is to be observed, that the one connecting the poles of the battery is made of large wire, or ribbon of metal, and is of moderate length, while the other, in which the secondary current is to be induced, is made of smaller wire, and is of much greater length. The secondary current in this case is one of considerable intensity (100), as is shown by the fact that it can be made to pass through the system ; but if the coil had been made of a large wire, and much shorter than it is, the current induced would have had only a feeble intensity, but would have been much greater in quantity. And, in general, it is found that long coils of small wire give secondary currents of QUESTIONS. Describe the .mode of obtaining a secondary current, as illustrated in the next figure. When only is this secondary current induced? What are the terms used to indicate these currents? What rs their direction as compared with the primary current? What is said of the two coils used in this experiment? 130 ELECTRO-MAGNETISM. great intensity, while, on the other hand, to obtain a current of quantity short coils of large wire or ribbon are required. By arrangements altogether similar to the above, with addi- tional coils, tertiary currents have been produced, and others of gtill higher orders, even up to the seventh or ninth. The following mode of developing the tertiary current will show the method to be pursued to obtain others of still higher orders. A is a ribbon coil through which the battery current revolves as before, and B another ribbon coil in which a secondary current is induced, as already explained. A third ribbon coil, C, is placed at a little distance, but has its two ends connected by means of wires with the two ends of the ribbon of the coil B, so that the same current which is induced in B flows also in C. Above C is placed an intensity coil of small wire, W, with metallic handles connected with its extremities. Now when the battery current is established in the coil, A, a secondary current is induced in B and revolves in the coil, C, by which a tertiary current is induced in the coil W. As the secondary current flows in the opposite Tertiary Current. direction from that of the battery current, so the tertiary takes the opposite direction from that of the secondary ; and the same law holds good through all the series of currents. As the dis- tance from the battery increases, the strength of the current gradually diminishes. QUESTIONS. Describe the mode of obtaining a tertiary current. What is said of the direction of the tertiary current as compared with that of the secondary current ? ELECTRO-MAGNETISM. 131 143. Induction of Electricity by Magnetism Magneto- Electricity. Magneto-electricity, as the term implies, is the reverse of electro-magnetism. The current of galvanic electricity circulating around a bar of soft iron, converts it, as we have seen, into a temporary magnet, and renders a bar of steel permanently magnetic. Now, d priori, it would seem very probable that a magnet placed in the centre of a helix or spiral of metallic wire, would develope in it a current of electricity. This is found to be actually the case ; but the current can be observed only at the moment of inserting the magnet or removing it. The development of electricity by magnetism is shown in a very simple manner, by winding the middle of the keeper or armature AB of a powerful horse- shoe magnet, with copper wire, properly bound, and bringing the two extremities of the wire into contact, one of which should be flattened a little, and amalgamated by dipping it into a solution of nitrate of mercury, and the other filed to a point. If, now, the armature be suddenly placed upon the magnet or removed from it, a spark of elec- tricity will manifest itself every time, at the point of contact, C, of the two extremities of the wire. Magneto-Electricity. The electric current flows in one direction at the moment magnetism is induced in the soft iron enclosed in the coil of wire, and in the other direction, when its magnetism is destroyed. The same thing is accomplished, but in a manner a little different, by the apparatus figured on the next page. Externally a large coil of fine copper wire is seen, terminating in binding screws, to which wires with handles, H, are attached, to be grasped by the hands. Within this is a smaller coil of larger wire, the top of which is seen at B ; the extremities of this wire are soldered to the binding screws A and D, the latter also connecting with the horizontal bar E C, which has an irregular surface, resembling that of a coarse file. Inside of the last coil is a bundle of small iron wires, W. Now when the wires from the battery are con- nected with the binding screws A and D, the current circulating in the QUESTIONS. 143. What is the term ma^ne/o-electricity used to signify? Poscribe' the method of developing electricity by means of a permanent magnet and armature. Describe the apparatus represented by the next figure, aod the mode of using it. 132 ELECTRO- MAGNETISM. Magneto-Electricity. helix B induces magne- tism in the wires W, and this in turn at the mo- ment when the magne- tism is induced, or when it is destroyed, induces a current of electricity in the outer helix, which will be felt in the hands when grasping the handles. To produce the great- est effect, the current from the battery should be foriiicd and broken rapidly; which is accom- plished by connecting one wire with the bind- ing screw A, and draw- ing theTfend of the other over the rough sur- face EC. 144, Magneto-electric machines are now made, which act with great energy, producing all the effects both of quantity and intensity. Magneto-Electric Machine. The above figure* represents a machine of this kind. Several steel magnets, NS, are firmly fixed together upon pillars on a base board; and in front of the poles, an armature, A, in the From Davis's Manual of Magnetism. QUESTION. 144. Describe the magneto-electric machine. ELECTRO- MAGNET ISM. , 133 form of the letter U, having its two arms wound with 2000 or 3000 feet of fine insulated wire, is made to revolve on an axis by means of the multiplying wheel W. As the armature is made to revolve in front of the strong poles of the fixed magnets, mag- netism is induced in it (121), currents of electricity being at the same time made to flow through the coils of wire wound upon its arms, in accordance with the principles just explained, which are communicated by wires, concealed under the base board, to the me- tallic handles, H, by the wires C and D. These currents being in one direction while the magnetism of the armature is increasing that is, during one quarter of each revolution and in the other direction while the magnetism is diminishing, would be scarcely appreciable but for a contrivance by which it is constantly interrupted and renewed. This is accomplished by a toothed wheel placed upon the axis at 0, against which the wire C constantly presses, slip- ping from tooth to tooth as the wheel is turned. At every inter- ruption of the current a powerful shock is felt by any one grasping the handles. 145. The Electro-Magnetic Telegraph. This is an instru- ment for conveying intelligence instantaneously, by means of the galvanic current, to any distance, where metallic wires can be extended and properly insulated. We have seen above (136), that the current, when made to pass around pieces- of soft iron, renders them magnetic while 'the current is passing, but that they lose their magnetism instantly when the current is interrupted. Usually, the experiment is per- formed with the battery and the piece of iron in the same room, and even upon the same table, but this is not necessary. If the battery be in one room, and the piece of iron in another room, or in another building at a distance, the result will be the same, only a little increase in the power of the battery will be neces- sary. All that is required is, that good conducting wires, well insulated, should extend from the battery and form a helix around the iron, and on closing the circuit, whatever may be the distance QUESTIONS. What is the length of the wire upon the revolving arma ture? What is the use of the toothed wheel? 145. What is the electro- magnetic telegraph ? May the current from a battery be made to magnetize a piece of iron at a distance ? What is required for this purpose ? 12 ELECTRO-MAGNETISM. of the iron from the battery, it instantly becomes magnetic, and loses its magnetism again when the circuit is broken. The closing and breaking of the circuit can be performed at any point in the line, but we suppose it to be done at the battery. Morse Telegraph. The above figure, which represents the recording part of Morse's telegraph, will perhaps serve better to illustrate the operation of the instrument than a full figure of it. A piece of soft iron, M, in the form of the letter U, with each arm sur- rounded with a helix of covered wire, is firmly fixed upon a base- board, with the ends upward, and the extremities of the wires of the helix connected with the binding screws, (seen at the right,) with which the wires from the battery are connected. A is an armature of soft iron, fixed to the short arm of a lever, which at the other end carries a blunt point of steel, capable of indenting . characters upon paper when pressed against it. Above the point is a metallic roller, with a groove cut around it, into which the point plays, and a narrow slip of paper is supposed to be drawn along between them by the hand. Now let us suppose this instrument, which we will call the register, to be in New York, and the battery in Washington, with metallic wires, well insulated, extended between them ; when the operator in Washington closes the circuit, the iron M instantly becomes magnetic, drawing down the armature A, and pressing the point at the other extremity of the lever against the paper, producing a dot if the paper is at rest, but a straight line if it is in motion. When the operator in Washington breaks the QUESTIONS. Describe the figure given to illustrate the recording part of Morse's telegraph. How is a mark made upon the paper ? Describe the mode in which an operator in Washington may write in New York. What are the only marks the instrument is capable of making ? ELECTRO- MAGNETISM. 135 circuit, the iron M loses its magnetism, and the lever drops by its own weight, leaving the paper to move along unmarked. When the circuit is again closed, the point is raised again in like man- ner against the paper, and immediately drops when the circuit is broken ; so that the steel point in New York is perfectly under the control of the operator in Washington, for making dots and straight lines, with which an alphabet is easily constructed. Thus a dot and line (. ) is A, a line and three dots ( . . .) B, a single dot ( . ) E, and so on through the alphabet. In the next figure the full instrument of Morse is represented. The paper, P, is carried along by machinery, between two rollers, in the direction indicated by the arrows, the machinery being propelled by a weight. A spiral spring, S, attached to a piece projecting downward from the pen-lever, removes the steel point from the paper when the circuit is broken. W W, the wires of Morse's Telegraph. the magnet. The motion of the machinery is regulated by a fan, which is partly seen in the figure. 146. In order to send communications at the same time from New York to Washington, another arrangement similar to the above is needed, with the register in Washington ; but the sam wires and the same battery may be used to return an answer, after QUESTIONS. How is the alphabet used in this telegraph constructed? 146. May the same battery and the same wires be made use of to send communications between two places in both directions ? 136 ELECTRO-MAGNETISM. the Washington operator has finished, merely by having a second register in the same circuit in Washington, and the operator in New York breaking and closing the circuit in that place, as before explained. Nor is it necessary, if the register is in New York, the battery should be in Washington ; it may be at any point in the circuit. In the above explanation, two wires are supposed to be extended the whole distance between the places connected by the telegraph ; but experiment has shown that only one is really needed, as the earth may be made to form a part- of the circuit. Besides the above, two other electric telegraphs are in use in this country, and one or two of still different construction in Europe. House's telegraph (from the name of the inventor) is a most ingenious instrument, which performs the wonderful operation of printing in dis- iinct capitals the messages transmitted. It is too complex to be under- stood without a close examination of the instrument itself. Bain's telegraph is worked precisely like Morse's, but the marks are made on chemically prepared paper, by transmitting the current of elec- tricity ttirough it. Like Morse's, also, it marks only dots or straight lines. QUESTIONS. Are more than one wire needed to send communications between two places in both directions? Are other telegraphs besides Morse's in use ? , PAKT II. GENERAL CHEMISTRY. 147. THERE are two very distinct sub-divisions of the general science of Chemistry, usually denominated Inorganic Chemistry, and Organic Chemistry; the former of which treats only of the chemical history of the elements and their inorganic compounds, while the latter treats of the chemistry of animal and vegetable bodies. There are, however, certain principles equally applicable to both branches of the science, which we propose first to consider, under the above head. THE ELEMENTS. CHEMICAL AFFINITY, 148. The Elements. We consider all substances as simple, or elementary, that have not been decomposed. Of the exact num- ber of these we cannot speak with certainty, as the existence of two or three, the discovery of which has been announced, has not yet been sufficiently verified. On a following page will be found a list of sixty-two, the existence of which, it is believed, has been established. Some of these, as we shall see hereafter, are found only in very small quantities, while others are abundant, the great mass of the globe we inhabit being made up of the various compounds of some fourteen or sixteen. The elementary substances are usually divided into the two classes of non-metallic and metallic, fifteen being included in the former, and the remainder in the latter class ; but several of each class possess characters so peculiar,* that it is difficult to assign them their proper place. QUESTIONS. 147. What two sub-divisions of the general science of Chemistry are there ? What is the distinction between them ? Of what is it proposed to treat under the head of General Chemistry ? 148. What are simple substances ? How many elements are there-? What is said of the quantities of these afforded by nature ? What two divisions of them do we recognize ? 12 * (137) 138 AFFINITY. 149. Affinity, Affinity, or chemical attraction, has already been mentioned as one of the forces with which the particles of every kind of matter seem to be naturally endow.ed. It is to the action of this force that all chemical changes, and the accompany- ing phenomena, are to be attributed. If two elements unite to form a compound, it is this force which occasions it j and if 'a com pound of two or more substances, already formed, is destroyed by the action of another element, it is to this force we are to look for the cause of the change. Affinity is exerted only between the minutest particles of dif- ferent kinds of matter, causing them to combine so as to form new bodies, endowed with new properties. It acts only at insensible distances ; in other words, apparent contact, or the closest proxi- mity, is necessary to its action. Every thing which prevents such contiguity is an obstacle to combination; and any force *which increases the distance between particles already combined, tends to separate them permanently from each other. It follows, therefore, that, though affinity is regarded as a specific power, dis- tinct from, the other forces which act on matter, its action may be promoted, modified, or counteracted by them j and, consequently, in studying the phenomena produced by affinity, it is necessary to inquire into the conditions that influence its operation. 150. The most simple instance of the exercise of chemical attraction is afforded by the admixture of two substances. Water and sulphuric acid, or water and alcohol, combine readily. On the contrary, water shows little disposition to unite with sulphuric ether, and still less with oil ; for, however intimately their particles may be mixed together, they are no sooner left at rest than the ether separates almost entirely from the water, and a total separa- tion takes place between that fluid and the oil. Sugar dissolves very sparingly in alcohol, but to any extent in water; while camphor is dissolved in a very small degree by water, and abun- dantly by alcohol. It appears, from these examples, that chemical attraction is exerted between different bodies with different degrees QUESTIONS. 149. What is affinity ? Are all chemical changes to be re- ferred to this forqe ? Between what only is it exerted ? Is it influenced in its action by other forces of nature ? 150. Where do we observe the most simple instance of the exertion of this force ? Is it exerted with equal intensity between all bodies? AFFINITY. 189 of force. There is sometimes no proof of its existence; between some substances it acts very feebly, and between others with great energy. Affinity is therefore said to le elective, as, when several sub- stances, capable of combining, are mixed together, a particular compound is always formed, in preference to others. Thus, if sulphuric acid, soda, and lime are at any time mixed together, the acid will always combine with the lime, in preference to the soda. 151. Decomposition of a compound is often effected by present- ing to it a third substance, having a stronger affinity for one of the ingredients of the compound than those ingredients have for each other. Thus, oil has an affinity for the volatile alkali, am- monia, and will unite with it, forming a soapy substance called liniment. But the ammonia has a still greater attraction for sul- phuric acid ; and hence, if this acid be added to the liniment, the alkali will quit the oil, and unite by preference with the acid. If water be poured into a solution of camphor in alcohol, the camphor will be set free, because the alcohol combines with the water. Sulphuric acid, in like manner, separates baryta from nitric acid. Combination and decomposition occur in each of these cases; combination of sulphuric acid with ammonia, of water with alcohol, and of baryta with sulphuric acid ; decom- position of the compounds formed of oil and ammonia, of alcohol and camphor, and of nitric acid and baryta. The action becomes more complex when two compounds are presented to each other, of such a nature that a transfer of elements takes place between them. Thus, in mixing a solu- tion of carbonate of ammonia with another of hydrochlorate of lime, the carbonic acid of the first compound unites with the lime of the second, while the hydrochloric acid of the second com- bines with the ammonia of the first. 152. Action of Affinity Modified by Circumstances. The action of affinity is influenced greatly by various circumstances, only a few of which can be here noticed. QUESTIONS. Why is affinity said to be elective? 151. How is decom. position effected by the exertion of this force? Give an illustration. 152. Is the action of affinity modified by the circumstances in which it is exerted ? 140 AFFINITY. The particular state of a substance, whether solid, liquid, or gaseous, is a very important circumstance, intimately affecting all its chemical relations. It is very rarely the case that two solids are capable of combining ; one of them at least must first be made liquid, either by solution in some solvent, or by melting. Thus, tartaric acid and carbonate of soda, in a dry state, are kept toge- gether for any length of time, without any action taking place between them ; but if a little water be added to dissolve them, chemical action at once ensues, attended with violent effervescence. Phosphorus and iodine, though both are solids, and phosphorus and sulphur, will indeed combine when brought together in their ordinary state j but even in these cases, one or both of the sub- stances are made liquid during the action. 153. Cohesion (for it is this force which unites the particles of a solid) is therefore always opposed to the action of affinity; and whatever tends to diminish it in bodies capable of acting upon each other, facilitates their union. Heated water is therefore usually a more powerful solvent than when cold; and salt in fine powder will be dissolved more rapidly in water, than when in large lumps. 154. The gaseous state 'is also unfavorable to the action of affinity. Gases do indeed, in some cases, combine spontaneously, but, usually, the introduction of an ignited body, the electric spark, or, in some cases, the influence of the sun's rays, is needed to cause the. action to commence. Thus, a mixture of oxygen and hydrogen may be kept for any length of time; but the intro- duction of flame, or the passage of the smallest spark of electricity, will cause them to combine instantly, with a powerful explosion. 155. Contact, with a third Lody sometimes will cause a union of two elements, that would otherwise remain together without combining. Thus, the introduction of a piece of spongy platinum into a mixture of oxygen and hydrogen, produces an explosion in a few seconds, without any change being produced in the metal, QUESTIONS. What is said, in this connection, of the peculiar state of a substance, whether it be solid, liquid, or gaseous? Give an example. ]63. Is cohesion always opposed to affinity? 154. What is said of the gaseous state ? How may gases that remain in mixture without uniting afterwards be made to combine ? 155. What is catalysis ? AFFINITY. 141 except that it becomes intensely heated. This power of some bodies to produce- chemical changes, merely by their presence, is termed catalysis (from the Greek, kata, by, and luo, to unloose). 156. Mechanical action also favors the action of affinity. Thus, if a piece of phosphorus be wrapped, with a few crystals \of chlorate of potash, in a piece of tin foil or strong paper, a \smart blow will cause a violent explosion. Common friction matches are ignited by friction against sand-paper, or other hard substance. 157. Relative quantity of matter is the last circumstance we mention, as affecting the action of this force. What is meant by this may be illustrated by the solution of common salt in water. If equal quantities of the salt are added in succession to the water, the first portion will disappear in less time than the second, the second in less time than the third, and so on. As the relative quantity of salt contained in solution increases, the action of the water becomes enfeebled, until full saturation takes place. If a large quantity of salt had been added at first, the full saturation of the water would have taken place much more speedily. 158. Action of Affinity always accompanied by a Change of Properties. A change of properties, to a greater or less extent, always attends chemical action; but no means are yet known by which we can predict what any of these changes will be in any case, previous to making the trial. Often, when two bodies unite, the characteristic properties of both will disappear, and the bodies are said to neutralize each other. Thus, the acids are usually sour to the taste, and possess the power of changing the blue color of some vegetables to red; while the alkalies are exceedingly caustic to the taste, and change vegetable blues to green. Now, when an acid and an alkali unite, a new substance is formed, called a salt, which is mild to the taste, and produces no eifect whatever upon vegetable colors; QUESTIONS. 156. What is said of mechanical action? Give an illus- tration. 157. What is said of the relative quantities of matter that are brought to act upon each other? Give an illustration. 158. Does a change of properties usually accompany chemical action? Can we from a knowledge of the substances used, predict before trial what the changes will be ? When are substances said to neutralize each other ? Give an illustration. 142 AFFINITY. and, indeed, while it possesses many new properties of its own, it exhibits none of those of either of its ingredients. 159. This change may extend to any or all of the properties of bodies. (1.) Bodies, after combining, do not usually occupy the same space as they did before combination. Generally, a con- traction of volume takes place, but this is not universal. A pint of water, added to a pint of sulphuric acid, will not produce a quart of the mixture; and the same will be found true of water and alcohol. When two gases combine, a very great contraction often takes place ; but the result with different gases is very dif- ferent. (2.) The changes- of form that attend chemical action are exceedingly various. The combination of gases may give rise to a liquid, as in the union of oxygen and hydrogen to form water ; or to a solid, as in the union of carbonic acid gas and ammonia to form solid carbonate of ammonia ; or hydrochloric acid and am- monia, to form hydrochlorate of ammonia. Two solids may, in combining, form a liquid, as is the case when crystals of sulphate of soda and nitrate of ammonia are rubbed together in a mortar, or acetate of lead ajid alum. Solids may also, in combining, form gases, as is the case when gunpowder detonates. Two liquids, by uniting, may form a solid, as may be shown by pouring sulphuric acid into a solution of hydrochlorate of lime. (3.) Chemical action is frequently attended by. change of color. No uniform relation has been traced between the color of a compound and that of its elements. Iodine, whose vapor is of a violet hue, forms a beautiful red compound with mercury, and a yellow one with lead. The black oxide of copper generally gives rise to green and blue-colored salts'; while the salts of the oxide of lead, which is itself yellow, are for the most part colorless. A beautiful instance of the change of color produced by chemical action is seen in mixing solutions of chloride of mercury and iodide of potas- sium. The solutions may be made as perfectly limpid as water, but, upon being mixed, a beautiful vermilion red is produced, by the forma- tion of iodide of mercury. The color shortly disappears, if either Bolution was in excess, by the redissolving of the precipitate. About 27 parts of the chloride should be used with 33 parts of the iodide. QUESTIONS. 159. May the change extend to all the properties of bodies ! Give some illustrations. COMBINATION. 143 LAWS OF COMBINATION. ATOMIC THEORY. 160. Laws of Combination. The relative proportions in which substances unite to fomi the different compounds, is governed by fixed laws. There are, however, some apparent exceptions to this rule, in which bodies seem to unite in all proportions, without reference to any law. Thus, water and alcohol seem to unite in all proportions ; and the same may be said of water and the liquid acids. There are still other substances which seem to combine in any proportion within certain limits. Thus, water dissolves com- mon salt very readily, but the quantity ib is capable of holding in solution cannot exceed about four-tenths of its own weight. Below this limit, the water and salt appear to unite in every proportion. 161. The following are the laws which regulate the composition of such compounds : I. The composition and properties of compound bodies are unchangeable. By this it is meant (1.) that any compound, while it retains its characteristic properties, must contain the samfe elements, united in the same proportions ; and (2.) that while a compound contains the same elements, united in the same proportion, it must also possess the same characteristic properties. Thus, water, a com- pound of 1 part* of hydrogen and 8 parts of oxygen, possesses certain well-known properties; now, whenever and wherever a substance is found, possessing the various properties of water, we know, from this law that it must be a compound of these two sub. stances, united in the above proportion ; and whenever a compound of these substances, in this proportion, is formed, it must possess the peculiar properties of water. A change of properties always necessarily implies a change of composition ; and, conversely, a change of composition necessarily implies a change of properties. This law is of universal applica- tion, except in the case of isomeric compounds, which will be hereafter noticed. * Parts by weight are always intended, unless it is otherwise expressed. QUESTIONS. 160. Are the relative proportions in which bodies com- bine governed by any law? What example is mentioned? 161. State the first law of combination. What is water composed of? Does ft change of properties always imply a change of composition ? 144 COMBINATION. II. When any substances (as _B, C, D, &c.} combine with a given quantity of another substance (J.), then the numbers which represent the proportions in which J3, C, D, &c., combine with A y will also represent the proportions in which they will com- bine with each other, if such combinatiofcbe possible. This law is also of universal application, and examples to illus- trate it arc abundant. Thus, 8-0 parts of oxygen ~| 35-4 " chlorine j 16-0 " sulphur j- combine \vitli 1 p&rt of hydrogen. 127-0 " iodine 80-0 " bromine J It follows, therefore, that if oxygen and chlorine combine, it will be in the ratio of 8 parts of the former to 854 parts of the latter; and if chlorine and iodine combine, the compound will contain 854 parts of the former, and 127 parts of the latter; and so of the other substances mentioned. But it is more common, as oxygen unites with nearly all other substances, to determine the quantities severally of these which combine with 8 parts of this element. Thus, 16-0 parts of sulphur 35-4 1-0 6-0 14-0 39-1 31-0 chlorine hydrogen carbon nitrogen potassium phosphorus > combine with 8 parts of oxygen. Any other substance, having an extensive range of affinity, might also be selected tis the basis of our table, and the results would be the same. The numbers thus obtained for the various substances are called their combining numbers, equivalents, or atomic weights. It will be noticed that the numbers used merely express the relative quantities of the substances they represent, that combine together; it is therefore in itself immaterial what figures are employed to express them. The only essential point s, that the relation should be strictly observed. Thus, the equiva- jtent of hydrogen may be assumed as 10; but then the number for oxygen will be 80; that for chlorine 354, &c. Hydrogen QUESTIONS. State the second law of combination. Give an example in illustration. What are the combining numbers, equivalents, or atomic weights of substances ? C M B I N A T I O N . 14.5 combines with other bodies in a lower proportion than any other known substance, and is therefore, with propriety, made tho unit by most writers in the English language; but on the continent of Europe, oxygen is usually considered as 100, and the tables constructed accordingly. 162. We give below a table of all the known elementary sub- stances, with their combining numbers, or equivalents, the com- bining weight of hydrogen being considered as the unit. To find the corresponding numbers in a table in which the combining weight of oxygen is made 100, it is only necessary to multiply the numbers in this table by 12-5. We insert also, in the table, the symbols by which the elements are represented in chemical formulae, a subject to which the attention of the student will be called in a future paragraph. TABLE OF ELEMENTS, WITH THEIR EQUIVALENTS AND SYMBOLS. Elements. Sym- bols. Equiva- lents. Elements. Sym- bols. Equiva- lents. Al 13-7 Mo 460 Antimony (Stibium) Sb 129-0 Nickel Hi 29-5 Arsenic As 75-0 Nitrogen N 14-0 Ba 68-5 No ? Bismuth Bi 208-0 Os 99-5 ISoron B 10-9 Oxygen 8-0 Br 800 Palladium Pd 53-2 Cd 560 Pe Calcium Ca 200 p 31-0 c 6*0 Platinum Pt 99-0 Ce 47-0 K 39-1 Cl 354 R 52-2 Cr 26-7 Ru 52-2 Cobalt Co 29-5 Se 39-5 Cb ? Silicon Si 21-3 Cu 31-7 Ae 1080 Di 48-0 Na 23'0 E ? Sr 44-0 F 19-0 g 16-0 G 4-7 Tantalum Ta 184-0 Gold (Aurum)" Au 1980 Te 64-1 H ro Tb ? Iodine I 127-Q Th 59.4 Iridium Ir 99-0 Sn 58-0 Fe 280 Titanium Ti 25-0 La 47-0 Tungsten (Wolfram) W 92-0 Pb 103-5 u 60'0 L 6-5 v 68-5 MR 12-0- Yttrium Y 32 2 Mn 28-0 Zinc Zn 32-5 Mercury (Hydrargyrum).. HK 100-0 Zirconium .. Zr 34-0 QUESTIONS. 162. What are contained in the table on this page? What is taken as the unit? How may the numbers given in the table be converted into others, in which the combining weight of oxygen is 100? 13 146 COMBINATION. Besides the preceding sixty-two elements, the existence of which seems to be well established, the discovery of four others has been announced, which are to. be considered as doubtful. The names Ari- dium, Donarium, Ilmenium, and Thalium have been given to them. The equivalents given in the table have been taken chiefly from Dana's table, found in the last edition of his Mineralogy, but are reduced 'to the hydrogen standard. In some few instances preference has been given to Regnault's numbers. III. When two substances combine in more proportions than one, then these different proportions will always sustain some simple ratio to each other. To illustrate this law, let A and B be two substances capable of combining with each other in several proportions ; the lowest proportion in which they combine will be in the ratio of one equivalent of each-, or 1 A + 1 B, The other compounds they form will be of the character, 1 A + 2 B, 1 A + 3 B, 1 A +4 B, &c.; that is, 1 equivalent of one substance will be united with 2 or 3, or some exact number of equivalents of the other substance. The compounds of nitrogen and oxygen afford an excellent illustration of the above law. Thus, the 1st compound contains Nitrogen, 14, and Oxygen, 8. 2d " " Do. 14, " Do. 16. 3d " " Do. 14, " Do. 24. 4th " " Do. 14, Do. 32. 6th " " Do. 14, " Do. 40. The law, however, admits of a more general application than these examples alone would authorize us to expect. Substances may com- bine and instances of the kind are not unfrequent in the ratio of 2 equivalents of the first to 3 or 5, &c., equivalents of the second; and even more complex ratios than these are known, as 3 equivalents of one substance to 4, 5 or 7 of the other, but they are not common. They may be expressed thus, 2 A -f 3 B, 2 A -f 5 B, &c., and 3 A -f 4 B, 3 A -f 5 B, &c. Man'ganese and oxygen combine in five different proporti6ns, as shown below. The second compound, it will be observed, contains 2 equivalents of the metal to 3 equivalents of oxygen, while the fifth contains 2 equiva- lents of the metal to 7 equivalents of oxygen. Thus, the 1st compound contains Manganese, 28, and Oxygen, 8. 2d " " Do. 56, " Do. 24. 3d " " Do. 28, " Do. 16. 4th " " Do. 28, " Do. 24. 5th Do. 56, " Do. 56, QUESTIONS. State the third law of combination. Give an illus- tration. COMBINATION: 147 These complex ratios may be expressed fractionally; thus, the expressions 2 A + 3 B, 2 A + 7 B, and 3 A -f 4 B, are equal respectively to 1 A + 1 B, 1 A + 3 J B, 1 A + | B. In the manganese- series above given one place, it will be seen, is wanting, between the fourth and fifth, which may hereafter be filled by farther research. IV. The equivalent of a compound substance will always & equal to the sum of the equivalents of the substances which compose it. Thus, water is composed of 1 equivalent .of oxygen 8, and 1 equivalent of hydrogen 1; its combining number, or equiva- lent, will therefore be (8 + 1 = ) 9. So, also, sulphuric acid, which contains 1 equivalent of sulphur (16) and 3 equivalents of oxygen (8x3 = 24), has for its equivalent 40. The same is true of all compound bodies, as hydrochloric acid, which contains 1 equivalent of chlorine, 35-4, and 1 equivalent of hydrogen, 1, giving for its equivalent 364. The equivalent of potassium is 39-1, and as this combines with 8 of oxygen to form potassa, the equivalent of the latter is 47'1 = 39-1 + 8. Now, when any compound substances unite with each other, one equivalent of one substance combines with one, two, or three equivalents of the other substance, precisely as in the case of the elements. Thus, the hydrate of potassa r composed of potassa and water, contains exactly 1 equivalent, 47-1 parts of potassa and 1 equivalent, or 9 parts of water; and its equivalent is 56-1 =47-1 + 9. So the sulphate of potassa is composed of 40 parts of sulphuric acid and 47 ! parts of potassa, having for its equivalent 87'1; and the nitrate of potassa, composed of nitric acid and potassa, contains 54 parts of the acid and 47-1 parts of potassa, its equivalent being 101-1. V. The quantities of gaseous substances, estimated by measure, which enter into combination, bpar some simple ratio to each other , and also the quantities of the resulting compounds, con- sidered a* gaseous, bear some simple ratio to the sum of the volume of the ingredients. Water, we have seen, is composed of 1 equivalent (estimated ly weight) of each of its elements, hydrogen and oxygen, which QUESTIONS. State the fourth law. What illustration is given ? 148 COMBINATION. are gases ; but if we measure them before causing them to com- bine, we shall find that 1 pint of oxygen will unite with exactly 2 pints of hydrogen. If we use more oxygen than this iu pro- portion, a part of it will remain after combination ; and if we use less, a part of the hydrogen will be left. So, a pint of chlorine will combine with exactly a pint of hydrogen, and a pint of nitrogen with exactly 3 pints of hydro- gen form ammonia ; and so of other gaseous substances, or any capable of taking this form, as sulphur or mercury. If we represent the combining volume of oxygen by 1, as is usual, then the combining volume of each of the following sub Stances, viz., hydrogen, mercury, nitrogen, chlorine, iodine, and bromine, will be 2. Phosphorus and arsenic have the same combining volume as oxygen, 1 ; while that of sulphur is . These numbers are determined by experiment precisely as the numbers representing the proportion in which substances combine by weight. It follows from the above that there must be a close relation between the atomic weights, the combining volumes, and the densities of gaseous substances. The atomic weights of oxygen and hydrogen, we have seen, are as 8 to 1, while their combining volumes are 1 to 2; it follows, therefore, that the density of oxygen must be to that of hydrogen as 16 to 1. So the atomic weights of chlorine and hydrogen are as 354 to 1, but they com- bine in equal volumes; their comparative densities must there- fore be as their atomic weights, that is, as 354 to 1. In fact, in all cases in which the gases combine in equal volumes, their densities respectively must be as their atomic weights. And in the cases of those which do not combine in equal volume, the simple ratio of the combining volume being observed, it is easy to calculate their relative densities from their atomic weights. Thus the combining volumes of hydrogen and sulphur vapor are, respectively, 2 and -i, and their atomic weights 1 and 16 ; the QUESTIONS. State the fifth law of combination. What illustration is given? Is there any relation between the atomic weights, combining volumes, and densities of gaseous bodies ? How is this illustrated by reference to oxygen and hydrogen? When the combining volume? ;:nd atomic weights of gases are given, may their relative densities be calcu- lated t How is this illustrated by reference to sulphur and hydrogen ? COMBINATION. 149 density of sulphur vapor, compared with that of hydrogen, must therefore be 96, which is very nearly the same as it is found to he* by direct experiment. It is customary to refer the densities of gaseous bodies to that of atmo-. spheric air (at a given temperature and pressure) taken as unity ; and we have then, as the result of very many experiments, the numbers in the table below. These numbers will be of use hereafter. One volume of Air weighs 1-000 " " Hydrogen weighs -069 " Oxygen " 1-106 " " Nitrogen -971 " Chlorine " 2-440 One vol. of Iodine vapor weighs 8-716 . " Bromine " " 5-400 Mercury " 6-976 . " Sulphur " 6-654 " " Phosphorus vapor weighs 4-326 Arsenic " " 10-370 By the second part of the fifth law, as enunciated above, the' combining volumes of compound gases will bear a simple ratio to the sums of the volumes, of their respective ingredients. In some cases, no change of ! volume takes place when gases combine, as in the case of chlorine and hydrogen, where equal volumes combine and produce two volumes of hydrochloric acid ; but more frequently a change of volume is observed, as in the case of vapor of water, which is composed of 1 vol. of oxygen and 2 vols. of hydrogen condensed to 2 vols. of steam. So ammonia is a compound of 1 vol. of nitrogen and 3 vols. of hydrogen condensed into 2 vols. of ammonia. The density of a compound gas may therefore often be calculated from the density of its ingredients and the change of volume known to take place in combination. Thus, in the case of water, which we have seen is composed of 1 vol. of oxygen and 2 vols. of hydrogen condensed into 2 vols. of steam, 1 vol. of Oxygen = 1-106 2 " Hydrogen = 2 X '069 =0-138 Steam 1-244 One-half of this sum, 1-244, or 0-622, is therefore the weight of 1 vol., or, in other words, the density of steam. This is the same as found by direct experiment. So in the case of ammonia, mentioned above, 3 vols. of Hydrogen = 3 x "069 = 0-207 1 " Nitrogen 0*971 Ammonia 1-178 As this forms 2 vols. of ammonia, one-half of the sum, 1-178, or, -589 is the weight of 1 vol., or the density of this compound gas. We add one more instance, by way of illustration. Hydrosulphurio QUESTIONS. Does a change of volume sometimes take place when gases combine ? How is this illustrated in the case of water? May the density of a compound gas be calculated from the densities of its ingre- dients and the change of volume that takes place when they combine ? 13* 150 ATOMIC THEORY. acid is a compound of a single equivalent of hydrogen and sulphur, the Combining volume of the former being 1, and that of sulphur . Now, 1 vol. of Sulphur vapor = 6-654 6 " Hydrogen 6 x 0.069 = -414 6 " Hydrosulphuric acid = 7-068 As the 7 vols. in combining form but 6 vols. of the gas, the sum 7 068 is to be divided by 6, giving us for the density of hydrosulphuri acid, 1-178. Some substances, as carbon, cannot by any means yet known be obtained in a state of vapor ; still we may with some certainty calculate what the density of their vapor would be if vaporization were possible. Thus, in the case of carbon, assuming that carbonic acid is composed of 1 volume of carbon vapor and 2 volumes of oxygen, the whole condensed in 2 volumes, we have 2 vols. of Carbonic Acid = 2 x 1'524 = 3-048 2 " Oxygen (subtract) = 2 X 1*106 = 2-212 1 " Carbon vapor -836 One volume of carbonic acid we know contains 1 volume of oxygen, but whether the carbon vapor should be taken as 1 volume or only $ of a volume, we have no means of determining, except the analogy of other compound gases, and therefore our assumption above may not be correct. It is possible that carbonic acid may have a more complex organization and carbon a very different combining volume. The combining volume of oxygen being taken as 1, those of all the elementary bodies capable of assuming the gaseous form are 1, 2, or 4, except that of sulphur, "which is . Of the very many compound gases whose combining volumes have been determined, that of nearly every one is either 2 or 4. 163. Atomic Theory. It will be observed that nothing theo- retical pertains to the above laws, which are simply the enuncia- tion of well-determined facts; but such striking results, obtained by experiment, naturally incline us to inquire for their cause ; and, in the absence of positive proof, the atomic theory has been proposed for this purpose. This theory assumes that every simple substance is an aggre- gation of atoms (9), by which is meant the particles in their smallest state of division ; and that the atoms of the same sub- stance are all precisely of the same weight. It assumes, also, that when simple substances combine to form compounds, they unite by atoms; that is, one atom of one substance combines with oue, two, three, &c., atoms of the second; or two atoms of the QUESTION. 163. Explain the atomic theory. NOMENCLATURE. 151 first combine with three, five, or seven, &c., atoms of the second, c. As these atoms are supposed to be absolutely indivisible, there can, of course, be no such thing as half an atom ] and all compounds must be of the form 1A + 1B, 1A + 2B, 2A+3B, &c. The absolute weight of an atom of any substance has never been determined, but it is assumed -that the equivalents of the various bodies do actually express their relative weights; the term atomic weight is therefore often used as synonymous with equiva lent. Thus, the atomic weight of oxygen is said to be 8, and that of hydrogen, 1, &c. ; and water is said to be a compound of one atom of oxygen and one atom of hydrogen ; while sulphuric acid is a compound of one atom of sulphur and three atoms of oxygen and so of other compounds. Whether the assumptions of this theory are strictly true, we may never be able to determine experimentally, but, it. is readily seen, that if they are a correct expression of what really takes place in nature, they afford an elegant explanation of the reason of the above demonstrated laws. 164. Specific Heat of Atoms. The quantities of heat required to raise the temperature of equal weights of different bodies by a given number *)f degrees (59), varies greatly, according to their nature ; and the num- bers expi-essing these quantities, having reference usually to-water as the standard, express also the capacities for heat or the specific heats of these bodies. Between these numbers no special relation can be traced ; but if we make the calculation in reference, not to equal weights, but to atomic weights, then in some nine or ten of the elementary bodies the specific heats are found to be the same, while several others have a specific heat twice or four times as great. It has been supposed that the specific heat of the atoms of all bodies may be the same a view which is favored by the facts above men- tioned but most bodies, both elementary and compound, depart so widely from this supposed law that its existence is altogether improbable. NOMENCLATURE OF CHEMISTRY SYMBOLS. 165. Nomenclature. Chemistry possesses a more systematic nomenclature than any other branch of natural science ; and a thorough knowledge of it, at the very beginning of his studies, is QUESTIONS. Does this theory account satisfactorily for the "preceding laws of combination? 164. Is the specific heat of the atoms of all bodies the same? 165. What is said of the nomenclature of chemistry ? 152 NOMENCLATURE. very important to the student. Thjs nomenclature is framed in reference to the composition of compounds, and is so contrived that the names of all compounds shall indicate the substances of which they are composed. 166. Elementary substances being composed of only one kind of particles, of course the above remark does not apply to them : their names are mere names ; that is, mere sounds connected by usage with the things signified. Yet, in the case of newly dis- covered elements, names have in some instances been given that indicate some important property of the substance. Thus, oxygen (from the Greek oxus r acid, and gennao, to produce) was so named, because it was supposed to form a necessary part of all acids ; and hydrogen (from httdor, water, and gennao), because it was known to enter into the composition of water. So chlorine, being of a greenish color, received its name, in consequence, from the Greek chloros, green ; and bromine was so called from its offensive odor, from bromos, fetid. Potassium and sodium are so named, because they form the basis, respectively, of potassa and soda; and glucinum (from glukus, sweet), because of the sweet taste of some of its compounds. Other elementary substances of recent discovery have been named in like manner; but all simple substances which have been long known retain their ancient names. Thus, gold, silver, lead, copper, sulphur, car- .bon, are names of well-known substances, and they are retained in chemistry; but they contain, it is evident, no descriptive meaning. 167. But it is to compound bodies that the nomenclature especially applies; and, as above intimated, its design is to indicate their composition by their names. For this purpose, when two substances only are combined in a compound, a part of the name of one, with the termination ide, is made use of, while the other is expressed in full. Thus, oxygen forms oxides ; chlorine, chlorides ; bromine, bromides ; sulphur, sulphurides, or sulphides; carbon, carbonidcs, or carbides, &c., of the other'sub- stance, the name of which is fully expressed; as oxide of iron, oxide QUESTION. In reference to what is this nomenclature framed ? 166. What is said of elementary substances? 167. How is the tenni< nation ide used ? Give an example. NOMENCLATURE. 153 of sulphur, cnloride of hydrogen, &c. Formerly, usage required us to employ the termination ule for the compounds of all the ele- mentary substances except those of carbon, sulphur and phosphorus, with which, without any apparent reason, another termination, uret, was used. Thus, we have been accustomed to say sulphuret of carbon, and not sulphide ; phosphuret of calcium, and not phos- phide; but a change in this respect has taken place, and the termination ide is alone made use of, as sulphide of carbon, &c. When two elements unite in more than one proportion, numeral prefixes from the Greek or Latin are used to designate them ; as protoxide of copper (from protos, first), and deutoxide (deuteros, second) or binoxide (bis, twice) of copper. The first of these compounds contains one equivalent of oxygen, united with one eq. of copper, while the second contains two eq. of oxygen, com- bined with one of copper. So the teroxide (tertio, third) or tritoxide (tritos, third) of nitrogen, is a compound of three eq. of oxygen and one eq. of nitrogen. The same rule is observed with regard to the- compounds of other substances, as protosulphide and bisulphide of mercuryj bicarbofiide of sulphur, terchloride of gold, c. The prefix per is often used to indicate the highest compound known, as peroxide of lead ) and the prefix sesqui implies that two eq. of one of the substances is combined with three eq. of the other substance ; as sesqirioxide of iron, which contains two eq. of iron and three eq. of oxygen. Generally, the electro-negative element is expressed first, as chloride of sulphur, and not sulphide of chlorine ; but this rule is not universally followed. 168. Most of the compounds above described, which may pro- perly be called binary, or bielementary, as being composed of two elements, are also capable of combining together, and forming other more complex compounds, usually called salts. In con- sidering the relations they sustain to each other, they are usually divided into the two classes of acids and bases. The acids are QUESTIONS. How was the termination uret formerly used? When two elements combine in more than one proportion, how are the different compounds indicated ? For what is the prefix per used ? Which element is usually expressed first? 168. May compounds combine to form other more complex compounds ? 154 NOMENCLATURE. generally more or less sour to the taste, change vegetable blues to red, and are electro-negative in relation to the other class ; while the bases are electro-positive, and restore the blue colors which have been changed* to red by acids. Some of the bases are soluble in. water, and are exceedingly acrid and caustic. A large proportion of all the acids are oxides, and are there- fore called oxygen acids, or oxyacids ; but many contain hydrogen, and are called hydracids. So, when a sulphide possesses acid pro- perties, it is called a sulphur acid. As most of the acids belong to the first class, or are oxyacids, special reference is had to them in-the nomenclature ;. and they are named by using the termination ic or ous in connection with the name of the substance with which the oxygen is combined to form the acid, the termination ic being used for the acid contain- ing most oxygen, when there are more than one formed from the same substance, and the termination ous for the one containing least. Thus we have sulphuric and sulphurous acids, the former of which contains more oxygen, and is a more powerful acid than the latter. When there are more than two acids formed from the same substance, the prefix "hypo (Jiupo, sub, or under) is used in connection with the name of one or the other of the two already described,, as the case may require. Thus, we kave %posulphuric acid, which contains- less oxygen than the sulphuric, and the /i^posulphurous, which contains less oxygen than the sulphurous. When a compound, not containing oxygen, possesses acid pro- perties, a part of the name of one of the substances is used as a prefix to the name of the other substance, to form a name for the . acid. Thus, hydrochloric and hydrosulphuric acids are compounds of hydrogen with chlorine and sulphur respectively. So chloriodic acid is a compound of chloride and iodine, Some writers are particular to take the prefix from the name of the negative ele- ment, and say chlorohydric, sulphydric, &c. ; but there is no good reason for such a distinction If no prefix is used, the acid is understood to be an oxyacid, as nitric acid, which is composed of nitrogen and oxygen. QUESTIONS. How are acids generally characterized ? How are bases ? What are oxyacids ? What hydracids ? How are the oxyacids named ? How is the prefix hypo used? Give examples. When an acid compound does not contain oxygen how is it named ? Give examples. SYMBOLS. 155 169. The salts are compounds of the aeids with bases, as Glauber's salt (sulphate of soda), which is composed of sulphuric acid and soda. Names of the salts are formed by changing the termination of the name of tbe acid from ic into ate, and from ous into lie, and expressing in full the name of the base. Thus, sul- phuric acid, combined with bases, forms sulphates; carbonic acid, carbonates, &c., of the bases with which they may be severally united; al sulphate of lime, phosphate of alumina, h^posulphate of soda, &c. So sulphurous acid forms sulphites ; nitrows acid, nitrites; hyposulphurows acid, hyposulph/tes, &c., of the various bases. . Many of the metallic oxides serve as bases of salts, but in expressing them (the salts), the word oxide is often omitted; thus, sulphate of iron is .the same as sulphate of the oxide of iron. If a higher oxide than the protoxide forms the base of a salt, it is usually expressed in full ; thus, we have the sulphate of the ses^u-oxide of iron. 170. Acid or super salts are such as contain an excess of acid, while basic or sub salts contain an excess of base ; salts that con- tain no excess of either acid or base being called neutral salts. A bisulphate contains twice, and a tersulphate three times as much, acid as a sulphate. Prefixes derived from the Greek numerals are often used to express the excess of base in the subsalts ; as oYnitrate of lead, a salt which contains 1 equivalent of nitric acid and 2 equivalents of oxide of lead. The same thing would be expressed by calling it bibasic nitrate of lead. The above explanations will serve to illustrate the fundamental prin- ciples of the present nomenclature ; but it is admitted that it applies but partially to the more complex chemical compounds, which, however, are not of frequent occurrence. * 171. Chemical Symbols. Instead of writing the full name of substances, it is often convenient to substitute abbreviations, which are called the symbols of these substances. For a simple substance, the first letter of the Latin name is generally used 1 ; but when there are two or more having the same initials, some QUESTIONS. 169. What are salts ? How are the salts named ? What is said of the names of salts which have metallic oxides for their bases ? 170. What are acid or super salts ? What basic or subsalts ? 171. What are chemical symbols ? How are they formed ? 156 SYMBOLS. <* other letter of the name is connected with the initial, in the sym- bols of all except one. Thus, stands for oxygen, and Os for osmium; B for boron, Ba for barium, and Bi for bismuth; P for phosphorus, Pd for palladium, and ft for platinum, &c. In the table on page 145, the symbols in general use for all the simple substances are given. These symbols indicate single equivalents of the substances they respectively represent; and to indicate two, threk, or more equivalents, a figure is placed before the symbol, as the coefficient in Algebra, or a little below it at the right. For instance, S signifies a single equivalent of sulphur, 2 S, 3 >j, or S 2 , S 3 , &c., two, three, &c., eq.; and 40, 5 0, or 4 , C 5 , four eq. of oxygen, five eq. of carbon, c, To indicate that several substances are combined, their symbols are simply written side by side, as HO, or with a comma between them, as H, 0, or with the plus sign ( + ), as H + ; all of which expressions represent a single equivalent of protoxide of hydrogen, or water. The comma and the plus sign are generally made use of only when the expression is somewhat complex; thus, N0 5 , is the symbol for nitric acid, KO that for potassa, and KO, N0 5 , or KO + N0 5 that of nitrate of potassa. Sometimes the plus sign is used when the- substances between which it is placed are not combined, but only mixed. Generally, in writing the symbols of compounds, we express the electro-positive element first, as HO, KO, and not OH, OK, hydrogen and potassium being the positive elements of these compounds. So also we write KO, S0 3 for sulphate of potash, and not S0 3 , KO. It is to be particularly observed that small figures, placed at the right of letters, apply only to the ones to which they are attached ; but large figures, placed at the left, like algebraic coefficients, affect all that follow them to the next comma or plus sign. Thus, P0 5 represents phosphoric acid ; NaO, soda ; NaO,P0 5 , phosphate of soda; 2(NaO,P0 5 ), two equivalents of the game phosphate of soda; but 2NaO,P0 5 indicates a single 5q. of bibasic phosphate of soda, which contains two eq. of soda> united to one of acid. In consequence of the frequent occurrence of the double equiva- lent, it is often expressed by drawing a line under the symbol QUESTIONS. How are compounds expressed by the use of these sym- bols ? How is a double atom often expressed ? SYMBOLS. 157 of the single equivalent, or by a black letter. Thus, Al signifies an eq. of aluminum, and Al or Al, two equivalents. A10 3 or A10 3 is the symbol for the sesquioxide of aluminum or alumina, and means the same as A1 2 3 . As oxygen forms an extensive list of compounds, simple dots are often used to indicate its pre- sence in them ; the above symbol for alumina would then become Al A1 2 3 , ' Other examples follow the same rule. Combinations of these symbols, according to the principles above explained, are called Chemical Formulde ; and the great advantages of their use, in expressing forcibly complicated chemi- cal changes, will be fully seea as we proceed. 172. Isomerism Polymerism. Isomeric compounds (161) are such as have the same ultimate composition, but differ from each other in some or all of their sensible properties. The term is derived from the Greek isos, equal, and meros, part. Thus phosphoric acid, P0 fl , is known in three different conditions, as ordinary, pyro, and metaphosphoric acids, the first of which is capable of saturating 3 eq. of a base, as soda ; the second, 2 eq. of base, and the third only 1 eq. In other properties, also, this acid in its different states exhibits a diversity, but its composition in the different states is the same. There are other examples of the same kind Polymeric compounds have the same ultimate composition, but differ in their properties ; and their equivalents are multiples or sub-mul- tiples of each other. Olefiant gas, C 4 H 4 , oil gas, C 8 H 8 , and cetine, C 3J H 32 , form a series of this kind, having the same elements in the same atomic proportion, but the equivalent of the second being twice that of the first, and one-fourth of that of the third. So, oil of turpentine, C 10 H 8 , and oil of lemons, C 20 H 16 , sustain to each other a similar relation. Many other examples are known. 173. Allotropism. This term is used to designate the different con- ditions in which a substance is sometimes found, as it regards the chemical action of other bodies. Thus, iron, in its ordinary state, is readily dissolved by nitric acid ; but if, before immersing a piece of iron wire in this acid, one end of it be headed to redness, or if it is connected with the positive electrode of a galvanic battery, or if it be immersed in the acid in contact with a piece of platinum, in either of these cases, the acid fails to act upon it. So, if an aqueous solution of chlorine be prepared In the dark, it may be kept in a dark place without change for a long time ; but if the sun is permitted to shine upon it a few seconds, decomposition will commence, hydrochloric acid will be formed in the water, and bubbles of oxygen rise to the surface. Many other substances exhibit similar peculiarities, and are said to exist in different allotropic states. QUESTIONS. 172. What are isomeric compounds? What examples are given ? What are polymeric compounds ? Give an example. 173. What does the term allotropism designate ? 14 CRYSTALOGRAPHY. CRYSTALOGRAPHY. 174, The particles of liquid and gaseous bodies, as they unite _to form solids, sometimes cohere together in an indiscriminate manner, and give rise to irregular, shapeless masses ; but more frequently they attach themselves to each other in a certain order, so as to constitute solids possessed of a regularly limited form. The process by which such a body is produced is called crystalization ;' the solid itself is termed a crystal; and the science, the object of which is to determine and classify the forms of crystals, is crystalograpliy. 175. Mode of producing Crystals. Nature presents us with an abundance of crystals in the mineral kingdom, but they may also be produced artificially by several processes. The essential condition is, that the particles of the substance to be crystalized should be free to move among each other, which is accomplished by bringing it into the liquid state by solution, or by melting it. Alum forms beautiful octahedral crystals, by making a saturated solution in warm water, and allowing it to cool slowly. If a small tree be made of copper wire, and its branches immersed in such a solution while cooling, on removing it, the part immersed will be covered with a multitude of small shining octahe- drons, like fruit. If the solution be allowed to stand after it has become cold, the crystals will gradually in- crease in size as the water evaporates. Common salt, blue and green vitriol, and many other substances may be crystalized in a similar manner. Crystalization by fusion is also very common. If a quantity of sulphur be melted and allowed to cool slowly, upon breaking QUESTIONS. 174. Do the particles of bodies sometimes unite so as to form solids of a regular form ? What are such solids called ? 175. What is the essential condition for the formation of crystals ? What is the form of the crystals of alum ? CRYSTALOGRAPHY. . 159 the crust and pouring out all that remains liquid, a mass' of crystals will be found within, shooting in every direction, as repre- sented in the figure. The crystalization of many substances, as sulphur, corrosiv A e sublimate, iodine, &c., may also be produced by sublimation. Crystalization of Sulphur. 176. Crystalization in Solids. Even in solids, crystalization sometimes takes place. Copper wire which has been long kept is said often to lose its tenacity, in consequence of cubic crystals of the metal gradually forming in it. When sugar is melted and allowed to cool, it forms a hard, transparent mass ; but by keep- ing some time, it gradually becomes opaque, and exhibits the ordinary white color and crystaline structure of refined sugar. Common "lemon candy/' which is usually sold in small flat pieces, an inch wide and four inches long, is beautifully trans- parent when first formed; but after a few hours, crystalization commences in numerous points, and gradually extends through the mass, which now becomes opaque ; and at the same time its flavor is improved. 177. Water of Crystalization. Many substances, in crys- talizing, absorb a large quantity of water, called their water "of crystalization, which is essential to the existence of the crystals. It sometimes amounts to half their weight. When exposed to the air, the water often evaporates, and the crystals fall to powder. They are then said to effloresce. Glauber's salt affords a noted instance of this. All substances are limited in the number of their crystaline forms. Thus, calcareous spar crystalizes in rhbmbohedrons, fluor spar in cubes, and quartz in six-sided, pyramids ; and these forms are so far peculiar to those substances, that fluor spar never crys- talizes in rhombohedrons or six-sided pyramids, nor calcareous spar or quartz in cubes. Crystaline form may, therefore, serve as a ground of distinction between different substances. But the composition of substances having the same form is not necessarily QUESTIONS. How may sulphur be crystalized v ? 176. May crystal! zation take place in solids? Give an example. 177. What is water of crystalization? When does a substance effloresce? Are substances limited in the number of their crystaline forms ? 160 CRTSTALOQRAPHY. the same, nor are the erystaline forms of the same substances always identical. 178. Primary Forms. The total number of erystaline forms is unlimited ; but it is found that all the more complex may be derived from thirteen of the more simple forms, which are there- fore called primary or fundamental forms. These readily arrange themselves (see Dana's excellent work on Mineralogy^ in six classes or systems, which are characterized by the comparative length and position of certain imaginary lines, supposed to be drawn through them, called axes. 1. Monometric System. This system includes the cube, A, the regular octahedron, B, and the rhombic dodecahedron, C ; all of which have three equal axes at riglit angles with each other. Hence the name, from monosj one, and metron, measure. The cube, A, is a solid with six equal square faces : its axes, a, b, c, I a Cube. All are three lines, supposed to connect the centres of opposite faces, its solid angles are similar, as also fts edges. The regular octahedron, B, is contained under eight equilateral triangles, Octahedron. QUESTIONS.' 178. What are primary forms? How many of these are there? In how many classes do they arrange themselves? What are the forms of the monometric system ? What is said of the axes of the forms of this system ? C R Y S T A L O G R A P H Y . 161 and its sixes, a, b, c, connect opposite solid angles. All its angles and edges are similar. The rhombic dodecahedron, C, is bounded by twelve equal rhombs; it has two kinds of solid angtes, one kind, as m, m, which is composed of four acute plain angles, and another kind, as rtfn, which is composed of Dcdehecadron. three obtuse plain angles. The axes, #, b, c, connect the opposite acute solid angles. Comparing these three forms with each other, it will be seen that the axes are the same in all, being equal in length, and making right angles with each other. . If any one of them is supposed to be placed within another, the axes of the two will entirely correspond throughout. 2. Dimetric System. This system includes only two forms, the square prism, and the square octaliedron. These solids have three axes, at right angles to each other, but they are of two kinds, as indicated by the name, from dis, twice, and metron, measure. The square prism, D, is bounded by six faces, two of which, 0, 0, Square Prism. called the bases, are squares, but the four other faces are rectangles, the height of which may be either greater or less than the base. The QUESTIONS. AVhat are the forms of the dimetric system ? How are the axes of the forms of this system characterized ? 14* 162 CRYSTALOGRAPHY. axes, a, b, c, connect the centres of opposite faces, as in the cube ; the two last named, b and c, are always equal, but the other, a, sometimes called the prismatic axis, is variable, and may be either longer or shorter than the others. Its, solid angles are similar to each other, but the edges are of two kinds, the basal and the lateral. The square octahedron, E, has for its faces eigh' equal isosceles triangles. he axes connect oppo site solid angles, and correspond in every respec'- with the axes of the square prism. The tw< therefore properly constitute one system. In de- scribing this solid the variable axis, a, is always supposed to be vertical, the other two being hori- zontal. It has two kinds of edges, and two kinds Square Octahedron. of solid angles. 3. Trimeiric System. The three solids of this system are the rectangular prism, F, the right rhombic prism, Gr, and the rhombic octahedron) H. The name is from tris, trice, and metron, measure. These forms have three axes intersecting at right angles, but all are variable, no two being equal. The rectangular prism, F, has six faces, all of which are rectangles : its three axes, a, b and c, connect the centres of opposite faces, and intersect each other at right angles, and are variable, as to their length. Its solid angles are all similar ; but its edges are of three kinds. Rectangular Prism. Right Rhombic Prism. Rhombic Octahedron. The right rhombic prism, G, has six faces, two of which are equal rhombs, and constitute the bases, while the four lateral faces are rec- tangular. Its three axes, a, b and c, intersect at right angles, and are variable; the first, a, connecting the centres of the bases, but the other two, b and c, being drawn between the centres of opposite lateral edges. Its solid angles are of two kinds and its edges of three. The rhombic octahedron, H, has eight faces, which are scalene tri- angles ; its axes, three in number, a, b and c, unite the apices of oppo- QPESTIONS. What are the forms of the trimetric system? said of their axes ? What ia CRYSTALOGRAPHY. 163 site solid angles, and in every respect correspond to the axes of the two solids last desci-ibed. This solid may be considered as composed of two pyramids with rhombic bases, united base to base. Comparing the three forms of this system, we see that their axes are identical ; comparing the systems now described with each other, we find that' they each have three axes intersecting at right angles in the centre of the solids ; but in the first, or submonometric system, all are equal ; in the second, or dimetric, two are equal, and the third variable ; while in the third, or trimetric, all are variable. 4. Monodinic System. This system includes two forms, the right rhomboidal prism, I, and the oblique rhombic prism, J, which have three axes, a, b and c, two of them making their intersections at right angles, but the third is inclined. The name is from monos, one, and clino, to incline. . The right rhomboidal prism, I, has two rhomboidal bases, upon one of which in this figure it is supposed to stand, the other four being rectangles. The axes connect the centres of opposite faces, of which a and b, a and c, intersect at right angles, but b and c are inclined to each other. . '** Q Right Rhomboidal Prism. Oblique Rhombic Prism. Right Rhomboidal Prism. The oblique rhombic prism, J, has its faces rhombs, and its four lateral faces parallelograms. Its vertical axis, a, connects the centres of the bases, but the two lateral axes, b and c, are drawn between the centres of the lateral edges. The last two intersect at right angles, and the vertical axis, a, makes a right angle with b, but is inclined to c. To compare these two forms, the right rhomboidal prism, I, must be placed upon one of its rectangular faces, as in K, making the axis, a, vertical ; the faces m m and n n, in I, will become respectively m m and n n in K, and all the axes of the two will correspond. If now, when in QUESTION. Comparing now the axes of the forms belonging to the three preceding systems, in what do they differ? What forms are included in the monoclinic system ? What is said of their axes ? 164 CRYSTALOGRAPHY. this position, all the lateral edges are removed, as in E7, we shall have the oblique rhombic prism, represented "within the rhomboid.il, as in. K' L A \=\ ------- - z -y/ to Right Rhomboitlal Prism. Oblique Rhomb'l and Right Rhomb'l Prisms figures K x and L; the crystal in the last figure being supposed in the' same position as in I. 5. Triclinic System. A single form only, the oblique rhom- loidal prism, M, belongs to this system. It is bounded by six faces, but only those directly opposite each other are equal. Its basal faces are rhomboids, and its lateral edges are inclined to the plane of its base. Its three axes are unequal, and no two of them intersect at right angles. The name Oblique Rhomboidai Prism, is from tris, thrice, and clino, to incline. 6. Hexagonal System. This system includes the rhombohe- dron, N and 0, and the hexagonal prism, T. These solids have Rhoinbohedron. Rhombohedron. four axes, one of which, called the vertical axis, is perpendicular QUESTIONS. What solid only belongs to the triclinic system ? What is said of the axes of this form ? What are the forms of the hexagonal system ? How many axes have they, and how are they drawn ? CRYSTALOGR.APHY 165 to the other three, called the lateral axes. These latter intersect each other at angles of 00, and are equal. The rhombohedron is of two kinds, the obtuse, N, and the acute, ; in each all the six faces are equal rhombs, and in each there are two e^lid angles, diagonally opposite, which are formed by three equal plain %ugles. Between these, one axis, a, is drawn, called the vertical axis ; vad in describing the solid this is always supposed to be in a vertical Ehombohedron. position. The other three axes, b, c and d, unite the centres of opposite lateral edges. Of the twelve edges, six (three above and three below) are connected with the extremities of the vertical axis around which they are sym- metrically placed. The other six, called the lateral edges, are also situated around this axis symmetrically, and at equal distances from it. This is readily seen by looking downward upon a crystal of this form when in position, a section through the centre perpendicular to the vertical axis being plainly a regular hexagon, as in the figure P. Section Rhombohedron Secondaries. By replacing the six lateral edges by planes parallel to the vertical axis, a, a hexagonal prism, terminated by three-sided pyramids, is pro- duced, represented in R. Removing in a similar manner the lateral solid angles, we have the form, S, which is essentially the same as the QUESTIONS. How is the hexagonal prism terminated with three-sided pyramids produced from the rhombohedron ? 166 CRYSTALOGRAPHY. last except the terminal pyramids ; and by a removal of the terminal pyramids a regular hexagonal prism, T, will be found. In a similar manner, the rhombo- hedron may be derived from the hex- agonal prism, by a replacement of the alternate basal edges of the prism -, first in the form represented in U ; and the replacement being continued until the faces of the original prism are obliterated, the resulting solid will Hexagonal Prism. be the rhombohedron. 179, Secondary Forms, Secondary forms are derived from the primary, by regular, systematic changes or modifications upon the angles or edges. Their number is unlimited. A general discussion of the laws of these modifications cannot be here introduced, and only a few further illustrations. The connection between the different forms of each of the six systems, it is believed, has been made plain ; and also the modifications by which one form is evolved from another, as the oblique rhombic prism, J, from the right rhom^ boidal, I, in the monoclinic system. By the same process the secondary forms are obtained from the pri- maries ; indeed, in each system containing more than one form, any one in that system may be taken as the primary, of which the others are then to be considered as secondaries. Thus, in the dimetric system, either the square prism, or the square octahedron may be taken as the primary form, from which the other may be derived in the, manner pointed out. There- fore, although it is customary to consider as primary all the thirteen forms mentioned above as belonging to the several systems, yet the whole num- ber necessary for the derivation of all known forms is only six, one for each of the six systems. 180. Laws of Modification of Forms/ The modification of the forms of crystals always takes place in accordance with cer- tain laws, which may be stated as follows, viz : All the similar parts of the crystal will be similarly and simultaneously modi- jied) or half of the similar parts will be similarly modified, independently of the other half. In the forms of the monometric system all the parts are similar, and all will therefore be modified in the same manner; but this is not the QUESTIONS. How may the rhombohedron be produced from the hex- agonal prism? 179. What are secondary forms ? In each of the above systems may all the forms be derived from one ? How many funda- mental forms only are then necessary ? 180. Do the modifications in the forms of crystals always take place according to fixed laws? What is the general law stated ? Are all the parts similar in the forms of the monometric system ? CRTS HA LOGRAPHY, 167 case with the forms of the other systems. In the dimetric system, for instance, the square prism, D, (page 161,) has two kinds of faces, the basal and the lateral, and also two kinds of edges, but only one kind of solid angles. The lateral edges, being formed by the meeting of similar faces, may be truncated, that is, replaced by a plane equally inclined to the two faces ; but the basal edges, being formed by the meeting of dissimilar faces, do not admit of truncation. The new plane replacing one of these edges will always be more inclined to one of the old faces than to the other. The solid angles are all alike, but each being formed by two plane angles that are similar to each other, but unlike the third, they cannot be truncated. The figure V represents a square prism with its lateral W Replacements. edges truncated, and in W, we see one of the same with its basal edges replaced,' but each of the new planes is unequally inclined to the adja- cent basal faces 0, and lateral faces I. In the figure X, the square prism has its angles replaced, the new plane, p, making equal angles with the faces I, but not with 0. By continuing the replacements seen in W, or in X, until the old faces are entirely obliterated, it is evident that we shall have the square octa- Square Octahedron. hedron, Y, which sustains the same relation to the square prism as the regular octahedron does to the cube. QUESTIONS. What is said of the faces of the square prism? What is said of the faces forming the basal edges? Can these edges then be truncated ? May the lateral edges be truncated ? If we replace the basal edges on the angles of the square prism, continuing the replace- ment until the original faces are all obliterated, what form will result ? 168 R Y S T A L O G II A P II Y . * By examining the forms belonging to other systems, and applying the game general law, it becomes apparent that the variety of forms capable of being produced is really unlimited, but the subject cannot be pursued further in this place. 181. Formation of Crystals. When a substance crystalizes in circum stances to admit of observation, a very small crystal is first seen, which gradually increases in size by the deposition of particles on the different faces. If this addition of matter be equal on all the faces the form is continued the same, but if there is more added on some of the faces than on others the crystal becomes more or less irregular. Changes of form, in accordance with the laws above mentioned, we may suppose to be pro- duced in the following manner. Let us suppose a substance crystalizing in the monometric system, as galena, or common salt. A cube is formed and is gradually increasing in size by equal additions upon every face, but at length, from some cause not understood, a change takes place, and regular spaces are left at the angles or edges of the cube. We will sup- pose that at each edge of the cube there is left a deficiency, or decrement, of one row of particles for every addition upon the surface; this will occasion the formation of planes upon the edges, and. if continued, will result in the production of a rhombic dodecahedron. Or let us suppose, as the additions are made, a decrement occurs at the angles only .-this will result in the replacement of the angles. Let A be a small cube on which deposits are taking place, as suggested above, leaving decrements at the angles. After a. time it will have the form B, and by a continuation of the process will become of the form C, and then of D ; but unlike the forms represented in the figures, it will be constantly increasing in size. But the form, D, is evidently that of a Monometric Forms. regular octahedron with all its solid angles replaced by planes ; and we suppose the process continued until the perfect octahedron would be formed. By reversing this process, commencing with the regular octa- hedron, and supposing additions to be made on the faces, with decre- ments at the angles, and continuing the process sufficiently, the cube will eventually be produced. Whether this is the real mode by which the variously modified second- ary forms are produced, we may never be able to determine fully ; but, in the absence of positive proof, this has been presented as theoretically possible. QUESTIONS. 181. Ho'w do crystals increase in size ? Illustrate the mode in which a secondary form may be produced in the crystalization of com- mon salt by a supposed decrement upon the edges ? OEYSTALOGBAPHY. 169 182. Cleavage. Crystals are generally capable of separation in certain directions by natural joints; a property which is denominated cleavage. In the primary forms this usually takes place in planes parallel to the faces, but may also occur in planes paraLel to any of the faces of secondary forms belonging to the species. It will usually be found in crystals that cleavage is much m'>re easy in some directions than in others; and the general rule is that it will take place with equal facility parallel to similar faces, and only in this direction. 183. Isomorphism. Isomorphous substances (from isos, equal, and morphe, form), strictly are substances which crystalize in the same form ; but the term is- generally used to indicate those bodies which, in the compounds they form, are capable of replacing each other, without changing the forms of the crystals of these compounds. Thus magnesia and lime, and the protoxides of iron and manganese, form a group, any one of which may replace another in whole or in part in the compounds they form. So also alumina (sesquioxide of aluminum), and sesquioxide of iron, form another group, and phosphoric and arsenic acids another. In general, isomorphous substances will be found to possess other analogous properties; and the compounds they form will often closely resemble each other in all their leading properties. We have an excellent illustration of this in the alums, of which there are several, but all possessing the same crystaline form, and the' same astringent, sweetish taste, the same solubility in water, &c. Below are the formula representing their composition Common alum KO,S0 3 + AJ 2 3 , 3 S0 3 + 24 HO. Iron alum KO,S0 3 + Fe 2 3 , 3 S0 3 + 24 HO. Chromium alum KO,S0 3 + Cr 2 3 , 3 S0 3 + 24 HO. Soda aHim .NaO,S0 3 -f A1 2 3 , 3 S0 3 + 24 HO. Ammonia alum NH 4 0,S0 3 + A1 2 3 , 3 S0 3 + 24 HO. QUESTION, 182. What is meant by cleavage ? How does this usually take place in primary forms ? Is cleavage made with equal facility in all directions? 183. What are isomorphous substances? Will isomor- phous substances usually be found to possess other analogous properties besides those of form ? What is said of the alums iu this connection ? 15 170 CRYSTALOGRAPHY. Comparing these formulae, one after another, with the first, that of common alum, we perceive that in iron and chromium alums the sesquioxide of aluminum is replaced by the sesquioxides of iron and chromium respectively; and in the soda and ammonia alums, the potash is replaced in one by soda and in the other by ammonia (oxide of ammonium). These several sesquioxides are therefore isomorphous, as are also the potash, soda, and oxide of ammonium which replace each other in the other formula. This list of alums might be still further extended ; and all constitute a single family of compounds formed on the same type and possess- ing very similar properties. Many other similar groups of compounds might be given in which isomorphous substances replace each other, but the above will suffice. The following group of simple substances that are isomorphous, is from Gmelin. 1. Carbon, phosphorus, potassium, titanium, bismuth, cadmium, lead, iron, copper, silver, and. gold. 2. Potassium, sodium, lithium, calcium, zinc, lead, and silver. . 3. Oxygen, sulphur, and chlorine. 4. Arsenic, antimony, and tellurium. 5. Platinum, iridium, and osmium. 184. Dimorphism, Dimorphous substances (c??!s, double, and morphe, form,) are such as are capable of crystalizing in two forms belonging to different systems of crystalization. A few substances are known which, under different circumstances,, crys- talize in three forms, and are therefore called trimorphous. Among the simple substances, carbon, sulphur, and perhaps copper, are . dimorphous. Carbon, as diamond, takes a form belonging to the monometric system, but, as graphite, it is found in the hexagonal system. It is scarcely necessary to remark that in these different forms many of its properties are essentially dif- ferent. As diamond, it is the hardest substance known, and is transparent, but, as graphite, it is comparatively soft, perfectly black, and opake. Sulphur when crystalized by melting and slow cooling (175) QUESTIONS. How do the formula for the different alums compare with each other? 184. What are dimorphous substances? What simple substances are mentioned as being dimorphous ? CRYSTALOGRAPIIY. 171 the crystals take forms belonging to the monoclinic system, but the native crystals, and those obtained by dissolving sulphur in the bisulphide of carbon, belong to the trimetric system. Many compound bodies are found to crystalize in two or more forms ; and sometimes it has been ascertained that the particular form produced will depend in some degree upon the temperature of the-crystalizing solu- tion. Carbonate of lime usually crystalizes in forms of the hexagonal system, but occasionally it forms crystals of the trimetric system, and is then called arragonite. Such researches' as have been made on the sub- ject indicate that it takes the form last mentioned when crystalizing at about 212, but forms crystals of the hexagonal system only at very low or very high temperatures. In some cases a change of the crystaline arrangement of the particles of a body, attended by a change of color, is produced by a mere varia- tion of temperature. Thus protiodide of mercury sublimed at a very gentle heat forms small dimetric crystals of a scarlet color, but if sub- limed at high temperatures the crystals are monoclinic and of a sulphur yellow color. The scarlet crystals become yellow by being heated, but turn red again when cooled. The yellow crystals obtained by sublimation retain this color when cooled, but if scratched or disturbed by some pointed instrument, they at once turn red at the point touched, and the change of color soon extends to the whole mass of crystals in contact. QUESTIONS. Upon what has the form of dimorphous substances some' times been found to depend ? PART III. SPECIAL CHEMISTRY INORGANIC. 185, Classification of Elements. Having discussed under the head of GENERAL CHEMISTRY the important principles pertaining to chemical changes generally, we are now prepared for the exami- nation of the various Simple substances, or elements, found in nature, and their inorganic compounds so far as may cowe within the objects of the present work. And, in accordance with general usage, we shall divide them into the two great classes of non-metallic and metallic elements, called also metalloids and metals. Though this division is universally recognized by writers upon this science, yet it is founded upon properties which are not abso- lute, and are much more distinctly seen in some of the elements than in others; a degree of vagueness therefore attaches to it, and several of the simple substances are not readily determined, being referred to either of the divisions with nearly equal pro- priety. It is however retained' because of its convenience ; and, following the example of Regnault, we shall consider as non-me- tallic the following fifteen elements, which are further arranged in natural groups. Of these, silicon, tellurium, and arsenic have not unfrequently been classed with the metals which they and especially the last two strikingly resemble in some of their pro- perties. Iodine and bromine also, though with less reason, have been sometimes regarded as metals. All the elements may enter into the composition of inorganic compounds, which are produced in the mineral world, and may be formed artificially j but only a few of them more especially carbon, hydrogen, oxygen, and nitrogen form organic compounds, which originate almost exclusively in plants and animals. QUESTIONS. 185. Into what two classes are the elementary substances divided ? How many non-metallic elements are there ? May al) the elements enter into the composition of inorganic or mineral compounds? What four are mentioned as forming most organic compounds ? (172) NON-METAL LIC ELEMENTS. 173 A further discussion of the relations of organic and inorganic bodies will be introduced hereafter. 186. For the sake of convenience we shall arrange the non- metallic elements in the five following groups, and introduce them for description in the order in which their names appear. Among the individuals of some of the groups a striking resemblance -is manifest, but in other groups this is less apparent. Each element will first be described, apd afterwards will be introduced the more important compounds it forms with the other elements previously described. METALLOIDS, OR NON-METALLIC ELEMENTS. GROUP. I. OXYGEN. HYDROGEN. NITROGEN. These substances are brought together in the same group merely for the sake of convenience ; each one properly constitutes a class by itself. The first, oxygen, is more abundant than any other element, constitu- ting from 30 to 50 per cent, of the whole globe, or at least that part of it accessible to man. It forms compounds with nearly all other elements. Hydrogen is a highly electro-positive substance, and in some of its properties resembles the metals. Nitrogen is noted for its very feeble affinity for the other elements, whether electro-positive or electro-negative. It has sometimes been classed with phosphorus and arsenic, to which it has some resemblance. GROUP II. CHLORINE. IODINE. BROMINE. FLUORINE. These electro-negative elements constitute a very distinct natural family : each forms a single acid compound with hydrogen, and all except the last form analogous acid compounds with oxygen. GROUP III. SULPHUR. SELENIUM. TELLURIUM. These elements, especially the first two, closely resemble each other; they also form acid compounds both with oxygen and hydrogen, which Are analogous in their constitution. QUESTIONS. 186. In how many groups are the metalloids arranged? N.me the elements of the first group. Why are these arranged together? Name those of the second group. Name the elements of the third group 15* 174 OXYGEN. GROUP IV. PHOSPHORUS, ARSENIC. Two elements very similar in many of their properties, and forming similar compounds with oxygen and hydrogen. Many of their com- pounds are isomorphous. Antimony also properly belongs to the group. GROUP V. CARBON. SILICON. BORON. Combustible bodies incapable of being volatilized even at the highest temperatures known, and forming feeble acids with oxygen. GROUP I. OXYGEN "| Gaseous at all temperatures ; but having few other points HYDROGEN ) of resemblance. A compound of the first two constitutes NITROGEN J water, a mixture of the first and last, atmospheric air. OXYGEN. Symbol, 0; Equivalent, 8 ', Density, 1-106. 187. History. Oxygen (from oxus, acid, and gennao, to pro- duce) was discovered by Priestly and Scheele, independently of each other, in 1774. It has been called empyreal air, because it supports combustion, and vital air, because necessary to respiration. It is the most abundant of the elementary sub- stances, and constitutes from 30 to 50 per cent of the mass of the globe, or at least that part of it accessible to man ; it forms also an ingredient of nearly all animal and vegetable compounds. 188. Preparation. Oxygen is a gaseous substance, and may be obtained from several sources; but the best method to procure it, when only a small quantity is required, is to heat an ounce or less of chlorate of potash in a green glass flask or retort. This salt is composed of chloric acid, C10 5 , and potash, KO; and, when heated nearly to redness, gives up the whole of its oxygen, as shown by the following formula. Thus, each atom of the salt yielding one atom of chloride of potassium, and six atoms of oxygen. The process succeeds better if, before QUESTIONS. Name the elements of the fourth and fifth groups. 187. What important facts are mentioned in the history of oxygen? 188. Describe the mode of preparing oxygen from chlorate of potash? How is it to be collected? OXYGEN. 175 heating, the salt is intimately mixed with an equal weight of pow- dered peroxide of manganese, or oxide ;>f copper. The accompanying . figure will .serve to illustrate the. arrangement of the apparatus required for the experiment. The salt, contained in a retort, is heated by a spirit-lamp, which produces no smoke, and reparation of Oxygeu. the gas, as it forms, passes under a receiver filled with water, and placed on a shelf in a pneumatic cistern, a section of which is shown in the figure. The receiver is open at the bottom, and it is first filled with water by plunging it in the cistern, and then bringing it to its upright position, and raising it carefully to its place upon the shelf, which is just beneath the surface of the water. The water rises in the receiver, in consequence of the atmospheric pressure (see the author's Natural Philosophy, p. 135) ; and when the gas is forced underneath it, it rises in bubbles, displacing the water, and occupying the highest part of the receiver, the shelf being supposed to have an aperture in it, to allow the gas to pass upward, and the water also to escape. 189. We have in the above equation the first instance that occurs in this work of the use made of symbols to illustrate chemical changes. The expression constitutes a proper equation, but it has peculiar properties, in which it differs from algebraic equations. The separate symbols in the equation, of course, indicate equivalents or atoms of the elements symbolized, and the manner in which they are combined in the first member is also designed to indicate the mode of combination of the several sub- stances expressed, before any change is produced; while the second member of the equation shows the state or mode of combi- nation of the same elements after the change has been produced. There must therefore be found represented in each member of the equation the same elements (and no others), and the same QUESTIONS. 189. What is the design of the equation in the preceding paragraph ? What is expressed in the first member of the equation ? What in the second ? What is required in the two members in equations of this kind ? . 176 OXYGEN. member of atoujs of eaoh element. Thus, in the above equation we have represented in each number 1 eq. of potassium, 1 eq. of chlorine, and 6 eq. of oxygen. Of course, if the sum of these were represented in numbers, it would be the same for each member. These remarks apply in all similar cases. Whj?n a large quantity of oxygen is to be obtained, it is more economical to make use of saltpetre (nitrate of potash) ; but a much greater heat is required to decompose it, and an iron retort must therefore be substituted, instead of glass. The iron retort containing the saltpetre is placed in a furnace, the heat of which ean be easily regulated, and a lead tube is connected with it, leading to the pneumatic cistern. As soon as 'the bottle has attained a full red-heat, the gas begins to come over; and if care is taken to prevent the heat becoming too great, very pure oxygen will be obtained. The changes that take place are illus- trated by the following formula : KO,N0 5 =nKO,N0 3 + 20. Thus, each atom of nitrate of potash yields one atom of hyponi- trite of potash, and two atoms of oxygen. This gas may also be procured from the peroxides of man- ganese, lead, and mercury, and from other substances. A ready method to procure it from the peroxide of manganese is as fol- lows: Let a flask of green glass be partly filled with the per- oxide, and then enough strong oil of vitriol poured upon it to moisten it thoroughly, and then apply the heat of an alcohol lamp. By this process sulphate of protoxide of manganese is formed, and oxygen gas, as shown by the following equation : Mn 2 -f S0 3 = MnO, S0 3 + It is thus seen that every atom of the oxide of manganese will yield one atom of oxygen. To insure purity it is well to pass the gas as it is formed through a weak solution of potassa by means of a three-necked bottle, as shown in the figure on next page. QUESTIONS. May oxygen be prepared from nitrate of potash ? De- scribe the mode of preparing it by the use of peroxide of manganese and sulphuric acid. OXYGEN. 177 Preparation of Oxygen. "Whatever mode of preparing it may be adopted, the first por- tions of gas that come over should always be allowed to escape, as it will be mixed with atmospheric air, contained in the appa- ratus at the beginning of the operation. 190. It is always easy to calculate the quantity of oxygen which any given quantity of materials we may desire to use will afford. We will suppose that 1 oz. of chlorate of potash is to be employed, how many cubic inches of oxygen will it afford ? There are in each equivalent of the chlorate of potash 1 eq. of potash and 1 eq. of chloric acid, composed as follows, viz : KO =47-1 = 122-5 of which 48 parts, or 6 eq., are oxygen. We have then the following proportion : 122-5 : 48 : : 480 : z, whence x == 188 grs. for the weight of the oxygen in 1 oz. of the chlorate. Now 100 cubic inches of oxygen (192) weigh 34-28 grains^ aud we have therefore this proportion : 34-28 : 100 : : 188 : z, or x = 548 cubic inches, or about 2 gallons. QUESTION. 190. Supposing the chlorate of potash used to prepare frhe gas, how may we calculate the quantity that may be produced from an ouilce of the salt ? 178 OXYGEN. 191. Oxygen gas is also given off by plants under the influence of light. Let a sprig of mint be placed in a white glass globe, which ia then to be filled quite full of spring-water, and the mouth inverted in a tumbler of water, as shown in the figure. It is then to be placed in the direct rays of the sun ; and in a short time, bubbles of gas will be seen collecting in the upper Oxygen from Plants, part of the glass, which is nearly pure oxygen. 192. Properties. Pure oxygen is a colorless gas, without odor or taste, and has never yet been reduced to the liquid state by any degree of cold or pressure. It is very slightly absorbed by water, 100 cubic inches of that liquid taking up 3 or 4 of the gas. It is heavier than air, 1 00 cubic inches weighing 34 28 grains, while the same volume of air weighs only 31 grains, the temperature be- ing at 60 F., and the barometric pressure at 30 inches. Its density is therefore 1-106. It has a very extensive range of affinity, enter- ing into combination with all the other elements except fluorine. Oxygen is a powerful supporter of combustion; and all sub- stances that are capable of burning in the open air, burn in it with far greater brilliancy. A piece of wood, on which the least spark of light is visible, bursts into flame the moment it is put into a jar of oxygen ; a recently extinguished candle, with the least spark of fire upon the wick, is relighted ; lighted charcoal emits beautiful scintillations; and phosphorus burns with so powerful and dazzling a light that the eye cannot bear its impression. Even iron and steel, which are not commonly ranked among the inflammables, undergo rapid com- bustion in oxygen gas. The combustion of iron and steel is effected by introducing it in the form of wire or' thin slips, as pieces of watch-spring, into a Combustion of iron. vessel of the gas, as shown in the figure. The QUESTIONS. 191. How may it be shown that plants evolve oxygen under the influence of light? 192. What are some of the properties of oxygen ? ' Why is it called a supporter of combustion ? Why is a candlo recently extinguished relighted when plunged in the gas? OXYQ.EN. 179 combustion is commenced by attaching to the lower extremity a piece" of sp ink or other combustible, which is ignited the moment it is to be introduced into the gas. As the combustion progresses, if the cork is tight, the water contained around the bottom of the receiver in the shallow dish is seen to rise, and more must be poured in, to prevent the entrance of air from without. This is occasioned by the absorption of the oxygen by the iron, to form oxide of iron, which falls in melted globules into the dish. When a lighted candle is let down by a wire into a jar of this gas, as in the figure, the case is different ; the candle burns for a time with in- creased splendor, but soon the flame begins to diminish, and at length entirely disappears, without any diminution of the volume of gas contained within. If the candle be relighted and returned to the receiver, it is now instantly extinguished, the gas having lost entirely its power of supporting combustion. The reason is, that the oxygen has disappeared, and a new gas, carbonic acid, C0 2 , taken its place, which Taper in Oxysen< has exactly the same volume as the oxygen from which it was formed. If a piece of burning charcoal had been used, the result would have been the same. 193. Ordinary combustion consists in the union of combustible matter with oxygen, and is usually attended by the evolution of heat and light. A new substance is also formed, which may be solid, liquid, or gaseous. When iron is burned, a solid product* (oxide of iron) results, which just equals the weight of the iron and oxygen together, that have .disappeared during the opera- tion. It is evident that in every case the product of the com- bustion must be equal in weight to that of the oxygen and other substance which have combined. Combustion may, however, be produced without oxygen; a QUESTIONS, How may iron and steel be made to burn in the gas ? What is produced when iron is burned in this way ? Why does thi water rise in the receiver as the combustion progresses ? Why is not the same effect produced when a candle is made to burn in the gas? 193. What is ordinary combustion? May combustion be producec without oxygen ? 180 OXYGEN. piece of phosphorus or powdered antimony, let/ down into a receiver filled with chlorine, will take fire spontaneously, and burn with the evolution of light and heat; so that ordinary com- bustion can only be considered as a particular case of chemical action. Combustion is the great source of artificial heat and light (13, 65). To produce an intense heat means are contrived to force large quantities of air (one-fifth of which is oxygen) in contact with a mass of ignited coal, the carbonic acid formed being allowed to escape freely. To produce light, we burn oil, tallow, or .other substances which contain a large proportion of the same material as coal, as we shall see hereafter. By sup- plying the burning body witli pure oxygen, the intensity of both the heat and light is greatly increased. A very considerable heat is also produced, simply by blowing with a proper blowpipe through the flame of a lamp or candle, which is sufficient for numerous small operations. A better form of the blowpipe is represented in the next figure. Blowpipe. Mouth Blowpipe. The enlargement at the angle is designed to retain auy moisture that may enter the tube from the mouth. . In using the blowpipe the flame is driven violently to one side, as shown in the figure; and the greatest heat is found just be- yond the point of the inner flame. Blowpipe Flame. If pure oxygen is used with the QUESTIONS. What is the great source of artificial light and heat? "What substances do we use for fuel when light is to be produced ? What is the use of the blowpipe ? At what point in the flame is the heat greatest ? HYDROGEN. 181 blowpipe, instead of atmospheric air, as may easily be done, the heat produced becomes much more intense. 194, Respiration is also supported, by oxygen gas, which is absolufely essential to the process; no animal can live in an atmosphere that does not contain it. A small animal, as a bird, confined in a close box, feels no inconvenience for a time ; but the oxygen gradually is absorbed, carbonic acid gas taking its place, and respiration becomes laborious, until at length the ani- mal dies for the want of oxygen. Pure oxygen, however, does not .answer the purposes of respiration, as it excites the vital action too much, producing various inflammatory symptoms, and at length death, as the result of the over-action. 195. Manipulation of Gases. The general method of collecting oxygen, described above, answers for all the gases that are not absorbed by- water. In the same mode, also, a gas may be transferred from one receiver to another. When a gas is to be collected that is largely ab- sorbed by water, some other liquid must Jbe used, as mercury, or a saturated solution of salt ; or the air may b*e removed by the air-pump, and then the gas admitted. HYDROGEN. Symbol, H; Equivalent, 1; Density, 0- 196. History. This gas was first described by Cavendish in 1766, and received from him the name of inflammable air, be- cause of its combustibility. It has received its present name because it forms a part of water (from Jiudor, water, and gennao, to produce). It is not found free in nature, but constitutes one- niuth part of water, and enters into nearly all animal and vege- table substances. ' 197. Preparation. Hydrogen gas is always procured by the decomposition of water, either directly or indirectly. The direct QUESTIONS. 194. Is oxygen necessary for the support of respiration? Will pure oxygen answer the purpose? 195. What is meant by the rminipulatiori of the gases ? When a gas is to be collected that is largely absorbed by water what is the course to be pursued*? 196. What facts are mentioned in the history of hydrogen? Why has it been called inflammable air? Why is it now called "~hy drogenl 197. From what is this gas always prepared ? 16 182 HYDROGEN. method consists in passing the vapor of water over metallic iron, heated to redness. This is done hy putting iron wire or turnings into a gun-barrel open at hoth ends, to one of which is attached a retort containing pure water, and to the other a bent tube. The gun-barrel is placed in a furnace, and when it has acquired a full red-heat, the water in the retort is made to boil briskly. The gas, which is copiously disengaged as soon as the steam comes in contact with the glowing iron, passes along the bent tube, and may be collected in convenient vessels, by dipping the free extremity of the tube into the water of a pneumatic trough. The arrangement of the apparatus will be seen by the ac- companying figure. A retort, a, con- tains the water, b b is the furnace, with Preparation of Hydrogen. the gun . barrel) c r> in which are the iron turnings to be heated, and at the left is the receiver to collect the gas as it is formed. The second, or indirect method, which is the one usually adopted in practice, consists simply in dropping pieces of zinc (or iron) into sulphuric acid, diluted with five or six times its weight of water, and contained in a convenient re- tort. Action immediately commences, without the aid of heat, and the gas may be collected over water. A jar prepared as in the figure is very con- venient for the purpose. The water and zinc are first introduced, and after Preparation of Hydrogen. ^ CQrk w j th the tubeg j g carefully inserted in its place, the acid is poured in through the long- necked funnel. The gas is collected by means of a tube leading from the cover to a receiver, as before. QUESTIONS. Describe the mode first mentioned of preparing hydrogen gas. Describe the mode by the use of dilute sulphuric acid and zinc- HYDROGEN. 183 Decomposition of Water by Potassium. Hydrogen gas is also very readily procured by the action of metallic potassium or sodium upon water. A small receiver is first filled with water, and then a piece of the metal, wrapped in bibulous paper, is quickly placed under it ; as soon as the paper becomes moistened, violent action takes place, and the hydrogen that is liberated rises to the upper part of the receiver. This method, on account of the high price of potassium and sodium, is very expensive. 198. Properties, Pure hydrogen gas is without color, odor, or taste, and refracts light powerfully. It has never yet been reduced to the liquid state. It does not support respiration, but may be breathed, when mixed with air, without injury. It is the lightest substance known, being sixteen times lighter than oxygen, and more' than fourteen times lighter than atmospheric air, 100 cubic inches weighing only 2-14 grains. Soap- bubbles filled with it rise readily through the air. They may be formed very easily by attaching a common tobacco-pipe by its stem to a gas-bottle filled with the gas, and forcing out the gas slowly, immediately Soa P Bubbles with Hydrogen - after dipping the mouth of the pipe in a strong solution of soap in warm water. Hydrogen gas is eminently combustible, and burns with a feeble yellowish flame. This may be shown by pouring some dilute sulphuric acid upon some pieces of zinc in a vial, and inserting a cork with a small glass tube or pipe-stem, as shown in the accompanying figure. In a short time a jet of hydrogen will issue from the tube, and may be inflamed. This is often described as the philoso- phical candle. QUESTIONS. Describe the mode of preparing hydrogen by the use of metallic potassium. 198. Mention some of the properties of hydrogen. What is the weight of 100 cubic inches of the gas ? What is said of soap- bubbles formed with it ? How may it be shown that the bustible ? Hydrogen Com- bustible. of soap- s is com- 1&4 HYDROGEN. If, now, as the jet continues to burn, a glass tube, half an inch or more in diameter, and one or two ^ Ge * ^ on &> ^6 keld ver it, and properly managed, a clear musical note will be produced, its pitch de- pending upon the length and diameter of the tube. It is occasioned by successive explosions within the tube, which follow each other so rapidly as to cause the air in the tube to vibrate, as in a musical instru- ment. The following is an interesting and instructive ex- periment with this gas. Let a bell-glass receiver be ^ e ^ w i tn ^ in the pneumatic cistern, and then, care- Sound*, fully^lifting it with the left hand, with the right hand paes up into the interior a lighted candle, as re-presented in the annexed figure. As the flame enters the hydrogen, it will take fire with a slight explosion, and continue to burn where it is in contact with the air; but the candle being carried farther upward into the pure hydrogen, will be extinguished. The hy- drogen, being qombustible, is inflamed by the burning candle, but not being a sup- porter of combustion, the candle is extin- guished as soon as it is surrounded by it. The gas is retained in the receiver when lifted from its place, because of its being so Hydrogen not a Supporter, much lighter than air. 199. Hydrogen, being the lightest substance known, is made use of by aeronauts for filling their balloons. The buoyancy of a balloon filled with it is easily calculated. Thus, 100 cubic inches of air weighing 31 grains, the weight of a cubic foot will be 535-68 grains, while the weight of an equal volume of hydrogen will be but 36-98 grains. Now 535-68 36-98 = 498-70 grains. This number multiplied by the number of cubic feet in a balloon, will give in Troy grains the weigh, required to be added to make it of equal weight with the air displaced ; QUESTIONS. Describe the mode of producing musical sounds. How may it be shown that the gas does not support combustion ? Will the hydrogen itself be inflamed in the experiment? 199. Why is hydrogen selected for filling balloons? Describe the method of calculating the weight a tolloon will sustain in the air. . COMPOUNDS OF HYDROGEN AND OXYGEN. 185 and if it is loaded with anything less than this it will ascend. The weight of the balloon itself is of course always to be taken into the account. Coal gas being always on hand where there are gas-works, though much heavier than hydrogen, is now much used in balloons in consequence of its being cheaper, the balloon being of course made proportionally larger. Compounds of Hydrogen and Oxygen. There are only two compounds of these substances known, the protoxide, or water, and the peroxide ; and the latter is alto- gether an artificial product, of difficult formation. 200. Protoxide of Hydrogen, or Water. HO, or Aq. ; eq., (1 -f 8 =) 9, This compound, considered in all its important relations, and absolutely universal diffusion, is probably the most important substance known to man. It is the sole product of the combustion of hydrogen, whether in the open air or mixed with oxygen gas. In the experiment for producing musical sounds, the water that is formed will be seen to condense in considerable quantity on the inside of the glass tube, at the beginning of the process, but it will be evaporated when the tube becomes hot. The affinity of hydrogen for oxygen is very great, but the two gases do not combine spontaneously, even if kept together for any length of time. We have seen above (162) that two measures of hydrogen combine with exactly one measure of oxygen ; and the mixture may be exploded by the approach of flame, by the electric spark, by intensely heated metal, or by the mere presence of spongy platinum, a substance that will be described hereafter. To explode the mixed gases by the electric spark, the spark must ^e made to pass through them. This is accomplished in the following manner. A small metallic vessel, as a miniature cannon, has a metallic wire, W, inserted in one side through a piece of wood or .ivory, so Hydrogen Pistol. AS to extend nearly through to the other side, as shown in the figure. QUESTIONS. Why is coal gas now often used as a substitute foi hydrogen in filling balloons ? How many compounds of hydrogen and oxygen are known? 200. What is protoxide of hydrogen? What is said of the affinity of hydrogen for oxygen ? In what proportion do they combine by measure ? By weight? How may the mixed gases be exploded t 16* 186 COMPOUNDS OF HYDROGEN AND OXYCJEN. The piece is then to be filled with the proper mixture of the gases, and a cork, C, inserted in the muzzle. If, now, a spark of elec- tricity be communicated to the ball of the wire W, in escaping from the other end it ignites the gases, and the cork is forced out with a loud report. If a mixture of equal parts of hydrogen and atmospheric air is used, the effect will be nearly the same. The explosion which accompanies the union of these gases is occasioned by the great expansion of the gases at the rnomen of combination, in consequence of the heat developed. This is the only rational explanation that can be given, and yet it is a fact that this combination is attended by a contraction of one- third of the volume of the mixed gases in forming the vapor of water, (162) to say nothing of the still greater contraction which takes place by the condensation of the steam that is found. This expansion takes place apparently with great violence ; but by using a strong receiver for the mixed gases it may be restrained, and then the combination takes place without any report. The figure in the margin represents a piece of apparatus for this purpose. A strong glass globe three or four inches in diameter has a metallic cap upon the neck, upon which a cover is firmly screwed after the mixed No Explosion. , . _. , . , gases are introduced. From each side of the globe is a projection or neck, with a metallic cap, through which wires are inserted so as nearly to meet in the centre. When the globe is charged with the mixed gases the electric spark is passed between these wires, and the gases at once combine, but without explosion, a slight flame only being seen at the instant. The inside of the glass becomes covered with dew from the moisture produced, and when the cover is unscrewed the rushing in of the air attests the vacuum that has been formed. The ignition of hydrogen by spongy platinum is well shown by holding a small piece of this substance in a jet of the gas, by means of a small wire twisted round it. The platinum must be QUESTIONS. Describe the pistol for exploding the gases by the electric Bpark. What occasions the great expansion that takes place? May the jjases be made to unite without an explosion ? COMPOUNDS OF HYDROGEN AND OXYGEN. 187 Fire Apparatus. perfectly dry. It gradually becomes heated to redness, and soon the jet is inflamed. The common hydrogen Jlre-apparatus actl upon this principle. Its construction is shown in the figure in the margin. A cylindrical glass ves- sel, A, is partly filled with dilute sulphuric acid, and in it is a small glass receiver, B, firmly ce- mented at the top into a cap connected with the brass cover. By the action of the acid upon a piece of zinc, Z, suspended inside of this receiver near the bottom, it is soon filled with hydrogen gas, which, on jurning*lhe faucet F, is forced out by the rise of the liquid upon a piece of platinum sponge, contained in the cup 0. Soon the platinum is heated so as to inflame the jet of hydrogen, from which a candle can be at once lighted. The platinum sponge often loses its property of inflaming hydrogen, but recovers it again by being heated. A metallic cup of half a pint capacity filled with the mixed gases and inverted over a small piece of platinum sponge, sup- ported a little above the table by a wire, will be thrown upward to the ceiling by the explosion produced. 201. The compound blowpipe, which is an invention of Dr. Hare of Philadelphia, is a contrivance by which two jets, one of hydrogen and another of oxygen, are made tc issue together, and are inflamed as they escape. The gases are brought by tubes from separate gas-holders, so as to discharge, as near as may be, two measures of hydrogen to one of oxygen. The heat produced by this instrument is very great, probably exceeding that produced by any other means. Compom]d Blowp . pe> QUKSTIONS. Describe the hydrogen fire apparatus. Describe the -ex periment with the spongy platinum and the metallic cup. 201. Describe the compound blowpipe. What is said of the heat which is produced? Explosion. 188 COMPOUNDS OP HYDROGEN AND OXYGEN. Platinum and other substances incapable of fusion in the hottest furnaces, are melted, and often even volatilized by it. A small piece of lime, held in the flame, becomes intensely heated, and glows with a brilliant light, exceeding any other that can be pro- duced artificially. It is known under the name of the Drum- mond tight, and is much used for practical purposes. 202. Water, at ordinary temperatures, is a transparent, color- less liquid, without taste or smell. In the open air, it boils at a temperature of 212, and freezes at 32. The vapor produced by boiling, familiarly called steam, is perfectly colorless and trans- parent, and has a density of 0-622, air befibg 1 ; 100 cubic inches weighing 19-28 grs. In the form of ice, its density is 0-92. A cubic inch of pure water weighs 252-458 grs., being 814 times as much as an equal volume of air would weigh. A cubic foot weighs 1000 oz., or 62 Ibs. avoirdupois. Water is probably the most powerful solvent known. It is capable of com- bining, in definite proportions, with many substances, forming compounds which yet remain perfectly dry. They are usually called Jiydrates. Substances from which all water has been separated are said to be anhydrous. Water is never found naturally perfectly pure ; that of wells, springs, and rivers always contains carbonic acid and saline matter in solution, obtained while percolating through the soil; and that from rain or snow is impregnated with air and oxygen, and some- times with other gases. It is obtained pure only by distillation ; and even then, by standing for a time, it takes up more or less atmospheric air, which, however, does not unfit it for the ordi- nary operations of the laboratory in which it is required. 203. Water when it solidifies often forms beautiful crystals (25) which are best seen in snow and frost; in ordinary ice they cannot usually be seen, though it is believed there is always QUESTIONS. What is said of the light produced -when a piece of lime is held in the flarne ? By what name is this light known? 202. What is said of wate^ at ordinary temperatures ? What are its freezing and boiling points? What is steam? What is its density? What is the density of ice? What is the weight of a cubic inch of water? How many times is it heavier than air ? What are the chemical compounds of -water called ? Is water ever found perfectly pure in nature * How only is pure water obtained ? 203. When water solidifies does it take the form of crystals ? COMPOUNDS OF. HYDROGEN AND OXYGEN. 189 a proper crystaline arrangement. The primary crystals belong to the hexagonal system (178-6), but they are often grouped to- gether iu various modes, as shown in the figures. Nos. 3, 4, 5, 6 ; 7, Crystals of Ice. and f fire more common than the simple forms Nos. 1 and 2. Thej> ^tter are of more frequent occurrence in hoar-frost than in sno-w. 204. The different processes for procuring hydrogen, given above, require some further explanation, before we dismiss this subject. Ihe first method is founded on the fact that iron, at high temperatures, decomposes water when presented to it in the form of steam, the oxygen combining with the iron to form protoxide of iron, and the hydrogen being set free. The changes are thus represented : HO + Fe = FeO + H. The changes which take place in the second and more common process for piocuring this gas, are more complicated. They are represented in the following formula. Thus, HO,S0 3 + Zn = ZnO,S0 3 + H. In this case it /rill still be seen that it is the water which supplies the hydrogen. The oxygen of the water is transferred to the zinc, forming protoxide of zinc, with which the sulphuric acid immediately combines. When a piece of clean zinc is immersed QUESTIONS. What is said of frost and snow? 204. Explain the several modes of procuring hydrogen, and write the equations illustrating the reactions that take place. t 190 COMPOUNDS OP HYDROGEN AND OXYGEN. in water, little action takes place, because the outside becomes coated with a thin film of oxide of zinc, which is insoluble in water; but if sulphuric acid is present, this oxide is instantly dissolved, and thus a clean surface constantly exposed to the water. In the third process, the metal itself at once decomposes a por- tion of the water, forming a soluble oxide of. the metal, and libe- rating the hydrogen. Thus, Here the affinity of metallic potassium for oxygen is sufficient to separate this element from its union with hydrogen in the water, forming oxide of potassium or potassa. ^ Great heat is produced by the action, and the hydrogen liberated is inflamed if the experiment is made in the open air. To show this all that is necessary is to throw a small piece of potassium Potassium inflamed u P on the surface of some water, as shown in the by water. figure. The mode of decomposing water by the galvanic current has already (111) been explained. 205. Knowing that water is formed by the union of 2 volumes of hy- drogen and 1 volume of oxygen condensed into 2 volumes of steam, it is easy to calculate the density of steam, and also the quantity of each of these elements in a given quantity of water. Thus, One volume of oxygen weighs 1-106 Two " hydrogen" 2x069 = 0-138 Two " steam " 1-244 One-half of this sum, or -622, is then the density of the vapor of water which is formed. To calculate the quantity of each of the elements in 100 parts of water we have 1-244 : 1-106 : : 100 : z, whence x 88-9 = quantity pf oxygen. And 100 89-9 = 11-1 = quantity of hydrogen. QUESTIONS. Is heat produced when water is decomposed by potas- sium? 205. What is the density of steam? Describe the mode of cal- culating it. NITROGEN. 191 208. Peroxide of Hydrogen H0 2 ; eq., (1 -f 16 = ) 17. Thia B ub- tance has been obtained only in the liquid form, and when most con- centrated possesses a specific gravity of 1-452. It is colorless, trans- parent, and without odor. It is sometimes called oxygenized water. ^ Though it differs from water only in containing an additional equiva- lent of oxygen, it acts powerfully upon the skin, producing a prickling sensation, whitening the surface, and destroying the texture, if the appli- cation is long continued. If the temperature is raised as high as 59, it is decomposed and con- verted into water and oxygen gas ; a sudden elevation of temperature even causes an explosion. It is also decomposed by the action of nearly all the metals, and many of the metallic oxides. Diluted with water or mixed with some acid, it is less liable to decomposition than when pure. NITROGEN. Symbol, N; Equivalent, 14; Density, 0-972. 207. History. The existence of this element has been known since 1772 ; and it was recognized as a constituent of the atmo- sphere in 1775. It was first called azote (from a, privitive, and zoe, life), because it does not support respiration ; it receives its pre- sent name from the circumstance that it forms an ingredient of nitre. 208. Preparation. Nitrogen gas is readily prepared, nearly pure, by burning a piece of phosphorus in a receiver over water. A small c-up, C, containing a piece of phosphorus, is placed upon the surface of the water in the pneumatic cistern, the phosphorus ignited, and the receiver then placed over it. The phosphorus continues to burn, absorbing all the oxygen, and the water rises to supply its place, as shown in the figure. The glass will at first be filled with phosphoric acid fumes, which how- ever will soon be absorbed by the water. Some vapor of phosphorus, carbonic acid, and perhaps a trace of other gases, may be contained in the QUESTIONS. 206. What is peroxide of hydrogen? What are some of its properties ? 207. How long has nitrogen been known ? What waa it first called ? ' Why has it received its present name ? 208, Describe the mode of preparing nitrogen. Preparation of Nitrogen. 192 A.T MO SPHERIC AIR. nitrogen thus prepared, but it will be found sufficiently pure for nearly all purposes. Other processes might be described for pro- curing it, as by passing a current of chlorine gas through strong aqua ammonia, but the above is the most speedy and convenient. 209. Properties. Pure nitrogen is a colorless gas, wholly devoid of smell and taste, and is distinguished from other gases more by negative characters than by any striking quality. It is Hot a supporter of\ combustion, but, on the contrary, extinguishes all burning bodies that are immersed in it. A taper immersed in it is extinguished at once. No animal can live in it; but yet it exerts no injurious action either on the lungs or on the system at large, the privation of oxygen gas being the sole- cause of death. It is not inflammable, like hydrogen ; though, under favorable circumstanc.es, it may be made to unite with ox}-gen. It is slightly dis- solved by water, and is sometimes found in the water of mineral springs, as at Lebanon, in the State of New York. 100 cubic inches of the gas Do c e o S mbu8fio P n P . ort weigh 3016 grs., giving a specific gravity of 0-97. Atmospheric Air. 210. The earth is everywhere surrounded by a mass of gaseous matter, .called tbe atmosphere, which is preserved at its surface by the force of gravity, and revolves with it around the sun. It is colorless and invisible, excites neither taste nor x smell when pure, and is not sensible to the touch, unless when it is in motion. It possesses the physical properties of elastic fluids in a high degree. Its specific gravity is unity (1), being the standard with which the density of all gaseous substances is compared. It is 814 times lighter than water, and nearly 11,065 times lighter than mercury, 100 cubic inches weighing 31 grs. QUESTIONS. Is the nitrogen thus obtained pure ? ' 209. What are some of the properties of nitrogen? 210. What is the atmosphere? "What are some of the properties of atmospheric air? What is the weight of 100 cubic inches ? , ATMOSPHERIC AIR. 193 Atmospheric air is composed of nitrogen and oxygen, with a variable proportion of carbonic acid and watery vapor, and usually a trace of ammonia. Besides these, there may occasionally be other substances present, depending upon local causes, as the odoriferous principle of plants, and the miasmata of marshes, which is supposed to be the chief cause of disease in many un- healthy situations ; but they cannot be detected by chemical tests. , Instruments for determining the relative pro- portion of the- gases composing the atmosphere are called eudiometers. The following con- trivance answers the purpose very well. Let a glass tube, closed at one end, and graduated to 100 parts, with a small piece of phosphorus sup- ported in it on a wire near the top, be placed as in the figure, with the open end immersed in a vessel of water. The phosphorus gradually ab- sorbs the oxygen of the air in the tube, and the water rises to supply its' place. In one or two days, depending upon the temperature, the ab- sorption will be complete; and the number of the division of the tube now filled with water will indicate the proportion of oxygen. By the above and other similar modes of analysis, it is found that the atmosphere in 100 parts is composed of By Weight. By Measure. Nitrogen 76-9 79-3 Oxygen 23-1 20-7 100 100 The proportion of carbonic acid varies from 2 to 6 parts in 10,000 of air. A trace of ammonia is not unfrequently found, and also of carbureted hydrogen. The atmosphere is believed to extend to the height of about forty-five miles, becoming continually less and less dense from the QUESTIONS. What is atmospheric air composed of? What other gases are also found in it ? What is the design of eudiometers ? Describe the mode of determining the proportion of oxygen by means of phosphorus. What is thus found to be the quantity of oxygen in 100 parts of air? What is the usual quantity of carbonic acid in 10,000 parts of air! What is the height of the atmosphere ? Eudiometer. 194 ATMOSPHERIC AIR. surface upward ; and presses by its gravity upon the surface with a force equal, ordinarily, to about 15 Ibs. to the square inch. It is capable of supporting a column of water about 34 feet, and. a column of mercury about 30 inches in perpendicular height. 211. Atmospheric air is highly compressible and elastic, so that its particles admit of being approximated to a great extent by compression, and expand to an extreme degree of rarity when the tendency of its particles to separate is not restrained by external force. The volume of air and all other gaseous fluids, so Jong as they retain the elastic state, is inversely as the pressure to which they are exposed. Thus a portion of air which occupies 100 measures when compressed by the ordinary atmospheric pressure, will be diminished to 50 measures when the pressure is doubled, and will expand to 200 measures when the compression is reduced to one-half. But those gases which are susceptible of condensa- tion by pressure into the liquid form, as the pressure approaches this point, vary from the law, the volume diminishing more rapidly than this would indicate. The chief chemical properties of the atmosphere are owing to the presence of oxygen gas. Air from which this principle has been withdrawn, is nearly inert. It can no longer support respi- ration and combustion, and metals are not oxydized by being heated in it. The uses of the nitrogen are in a great measure unknown. It has been supposed to act as a mere diluent to the oxygen ; but it most probably serves some useful purpose in the economy of animals and plants, the exact nature of which has not been discovered. 212. The question has often been discussed, whether the oxygen and nitrogen of the atmosphere are to be considered as chemically combined, or only in a state of mixture ; bu*. the latter opinion now generally prevails. It has been supposed that if they are merely in a state of mixture, oxygen, being the most dense, ought QUESTIONS. To what height will the atmosphere support a column of water? Of mercury? 211. Is atmospheric air compressible and elastic ? What is said of the volume of air and other elastic fluids in relation to the pressure to which they may be subjected ? To what ara the chief chemical properties of atmospheric air owing? 212. Are the oxygen and nitrogen of the air to be considered chemically combined, or only in mixture ? COMPOUNDS OF NITROGEN AND OXYGEN. 195 to settle towards the surface of the earth ; but it is found by experiment that gases, whatever may be their relative density, when brought in contact, mix (89) uniformly with each other. The mixture of the gases will even take place through thin mem- branes, (see author's Nat. Phil.j p. 22,) whether animal or vege- table; the least dense of the gases passing the most rapidly. 213. There is still one circumstance for consideration respecting the atmosphere. Since oxygen is necessary to combustion, to the respiration of animals, and to various other natural operations, by all of which that gas is withdrawn from the air, it is obvious that its quantity would gradually diminish, unless the tendency of these causes were counteracted by some compensating process. This, to some considerable extent, is accomplished by vegetation, as it is found that healthy plants, under the influence of the sun's light, are constantly absorbing carbonic acid from the air, the carbon of which is retained, while the oxygen is returned to the air, as we have before seen (191). Still, it has been calculated that the loss of oxygen employed in respiration, over the whole surface of the globe, in 100 years, would not exceed ^^ part of the whole quantity contained in the atmosphere. Compounds of Nitrogen and Oxygen. 214. Oxygen combines with nitrogen in five different propor- tions, forming the compounds NO, N0 2 , N0 3; N0 4 , and N0 5 ; the last three of which are acids. 215. Protoxide of Nitro- gen, or Nitrous Oxide NO; eq., (14 + 8=) 22. This is a permanent, col- orless gas, of a sweetish taste and smell. 100 cubic inches Of it Weigh 47-22 gr's., and Preparation of Nitrous Oxide. QUESTIONS. 213. Is oxygen constantly absorbed from the atmosphere by combustion and by the respiration of animals ? By what reverse pro- cess is carbonic acid absorbed and oxygen restored to the atmosphere ? 214. How many compounds of nitrogen and oxygen are there ? 215. De- scribe the protoxide of nitrogen. 196 COMPOUNDS OF NITROGEN AND OXYGEN. its density therefore is 1-527. It is best prepared as shown in the figure on the preceding page, by heating nitrate of ammonia, by means of a spirit-lamp, in a glass retort to a temperature of 450 or 480. The sole products of the operation, when carefully conducted, so as not to raise the temperature too high, are water and the gas in question. The composition of nitrate of ammonia is NII 3 ,HO,N0 5 which by heat is converted into 2 atoms of the nitrous oxide in question and 4 atoms of water. Thus, NH 3 , HO, N0 5 = 4 HO + 2 NO. The water of course is condensed and remains with that in the cistern, while the gas is collected as in other cases. It is slightly absorbed by water and should not therefore be allowed to remain in contact with it. Some substances burn in this gas with great brilliancy, as a lighted candle and phosphorus; and sometimes the combustion A of iron wire in it may be effected, but not without difficulty. By a pressure of about 30 atmospheres, at a temperature of 82, it is compressed into a liquid, which freezes or becomes solid at about 150 below zero ; and by the evaporation of this solid, a tempera- ture considerably lower than this has been attained. Its action on the system, when breathed, is very remarkable, producing a species of \ intoxication, which has acquired for it the Nitr Combi d stio 8 n. PPOrt8 name of laughing gas. In a few cases, when it has been inspired, injurious effects have resulted j and it should never be breathed but with caution. 216. The analysis of nitrous oxide is made as follows; in a given quantity of the gas accurately measured introduce a piece of potassium, the gas being contained in a glass tube closed at one end and a little bent, QUESTIONS. How is the protoxide of nitrogen prepared ? Describe the chemical changes that take place, and write the equation illustrating them. Is this gas absorbed by water? Will it support combustion? What is said of its effects upon the system when breathed ? 216. De- scribe the mode of analyzing this gas. COMPOUNDS OF NITROGEN AND OXYGEN. 197 (263) so as to retain the potassium while the open end is immersed in mer- cury. Now apply the heat of a lamp and the potassium takes fire imme- diately, absorbing all the oxygen and leaving the nitrogen. This being returned to the gi'aduated tube in which the gas was first measured, will be found to have the same volume as at first. We learn therefore that the protoxide of nitrogen occupies precisely the same volume as the nitro- gen contained in it would alone occupy. Now, One volume of the protoxide weighs 1-527 One " " nitrogen (subtract) '972 Half oxygen, very nearly, -555 Nitrous oxide is therefore a compound of 1 volume of nitrogen and J volume of oxygen, the whole condensed into 1 volume. The same result is obtained by passing a quantity of the gas through a heated porcelain tube by which it is decomposed, and 1 volume of nitrogen and volume of oxygen obtained. 217. Binoxide of Nitrogen, or Nitric Oxide N0 2 ; eq., (14 + 16 =) 30. This is also a gaseous substance, and is easily obtained by pouring nitric acid upon pieces of copper contained in a glass retort. The arrangement shown in the figure is very convenient for the purpose. Into the glass vessel- a put some clean pieces of metallic copper, and then introduce the cover, through which passes the glass tube b, with a funnel at top, and ex- tending nearly to the bottom of the vessel, and a lead tube, c, bent at right angles, to convey away the gas as it is formed. The cover must fit very accurately, in order to prevent the escape of the gas, which is rapidly formed as soon as a little nitric acid is introduced by the funnel and tube b. It may be collected over water, but a small proportion is absorbed. The changes which take place between the copper and the acid are indicated as follows : 4 N0 5 + 3 Cu-= 3 (CuO,N0 5 ) + N0 2 . Preparation of Nitric Acid QUESTIONS. 217. How is the binoxide of nitrogen prepared? are the chemical changes that take place ? 17* What 198 COMPOUNDS OS 1 NITROGEN AND OXYGEN. Thus, from 4 atoms of nitric acid and 3 of copper, there are formed 3 atoms of nitrate of protoxide of copper, and one of the binoxide of nitrogen. 218. Binoxide of nitrogen is a colorless gas, of a density of 1*039, 100 cubic inches weighing a little more than 32 grs. Its most striking property is its strong affinity for oxygen, although most substances intro- duced into it in a state of combustion are extinguished. Charcoal and phosphorus, however, if well ignited, burn in it with great splendor, though the latter by careful heating may be melted in it without igni- tion. When allowed to escape into the air, it forms, with the oxygen of the air, dense orange fumes of nitrous acid. Thus, if a bell-glass receiver, filled with it over water, be suddenly inverted in the air, the dense orange fumes of nitrous acid formed by its union with the oxygen of the atmo- sphere will rise for a few moments from its interior, like smoke from a chimney. Let a receiver filled with this gas be placed in a basin of pure water, as shown in the figure; and then let a few bubbles of oxygen gas be forced in by a pipe leading from a gasometer, or by means of a gas-bag. As the oxygen mixes with the gas within, nitrous acid fumes are produced, which are immediately absorbed by the water, giving it a slight acidity, as may be determiiied by the usual tests. By continuing to force in the oxygen gradually, and supplying the basin with water, all Experiment -with Nitric Oxide. Nitric Oxide and Oxygen. gas will at length disappear, water as nitrous acid. being entirely absorbed by the QUESTIONS. 218. Describe binoxide of nitrogen. What is produced when it comes in contact with atmospheric air or oxygen? Describe the experiment with a receiver filled with the gas over water and oxygen gas. COMPOUNDS OP NITROGEN AND OXYGEN. 199 Binoxide of nitrogen may be analyzed in the same manner as the protoxide (216), by heating in a small quantity of it, accurately mea- sured, a small piece of potassium or sodium, which absorbs the oxygen, leaving the nitrogen free, the volume of which will be found just one- half of that of the compound gas. The binoxide therefore is composed of 1 vol. of nitrogen, which weighs 0-972 1 oxygen, " * 1-106 2 " binoxide, " 2-078 The weight of 1 vol. or the density is therefore, as above stated, 2 -078 -4- 2 = 1-039. 219. Hyponitrous Acid N0 3 ; eq., (14 + 24=) 38. This acid is formed by mixing 4 measures of binoxide of nitrogen with 1 of oxygen, both perfectly dry, and subjecting the mixture to a cold at least as low as zero. It is a colorless liquid, which is at once decomposed by water into nitric acid and the binoxide. This acid does not combine directly with bases, but its salts may be formed by heating carefully the corresponding nitrates. Thus by heating nitrate of potassa, a part of the oxygen of the nitric acid is expelled, and the nitrate is converted chiefly into hyponitrifce of potassa, as indicated in the following formula : KO,N0 5 = KO,N0 3 + 20. The heat should be carefully applied, and the process arrested, as soon as the oxygen which comes over begins to be mixed with nitrogen By treating the mass after cooling with strong alcohol the hyponitrite is dissolved out, and may be obtained very pure. 220. Nitrous Acid J0 4 ; eq., (14 + 32 =) 46. Tnis sub- stance is formed, as we have seen, whenever binoxide of nitrogen comes in contact with oxygen. It may also, be prepared by heating "dry nitrate of lead in a retort, and passing the vapor formed through a tube surrounded with a freezing mixture to condense it. A piece of apparatus like that represented in the QUESTIONS. What is the effect when a piece of potassium is heated in a tube containing nitric oxide ? What is the volume of nitrogen that is left? 219. What is hyponitrous acid? Does it combine directly with bases? How may the hyponitrites be formed ? 220. How may nitrous acid be formed ? 200 COMPOUNDS OP NITROGEN AND OXYGEN. figure answers the purpose well. It is to be placed in a proper vessel, containing the freezing mixture, and connected with the mouth of the retort. As thus obtained, this acid has a density of 142, and at 60 F. is of an orange color, but becomes yellow when cooled to 32, and is nearly colorless at zero. Though it requires a temperature nearly as low as zero to condense it to the liquid form, the liquid boils at 82. It does not combine with bases, but forms compounds with some of the stronger acids It is decomposed by contact with water. 221. Nitric Acid N0 5 ; eq., (14 + 40 =) 54. Nitric acid, or aquafortis, is usually seen as a liquid, and is best obtained by decomposing nitrate of potash or nitrate of soda by strong sulphuric acid, by the aid of heat. The salt, previously well dried, is placed in a retort of hard glass, A, with an equal weight of strong sul- phuric acid, in a fur- .nace, and surrounded Preparation of Nitri^ Acid. at the bottom with sand. A moderate heat is applied, and the nitric acid, as it is separated, distils over into the receiver, B, where it is condensed. To render the condensation more com- plete, the receiver may be surrounded with a net-work, and cold water from a pipe, i, made to fall constantly upon it. The water escapes by the troughs C C and ed. A furnace is not absolutely necessary; the heat of a lamp is sufficient in all laboratory j operations. Nitric acid, as thus formed, is a dense liquid, of a yellow or orange color, and always contains more or less nitrous acid mixed QUESTIONS. May nitrous acid be obtained in the liquid form ? Does it combine with bases? 221. How is nitric acid obtained ? What is the common or commercial name of this acid ? Describe nitric acid. COMPOUNDS OF NITROGEN AND OXYGEN. 201 with it. In its most condensed state it has a density of 1-52, and boils at 188 ; its composition being then N0 5 ,HO. There is another definite compound of the acid and water, N0 5 ,4HO, which has a specific gravity of 142, and boils at 253. The first contains 14 per cent, of water, and the latter 40 per cent. By decomposing dry nitrate of silver*by dry chlorine, nitrio acid may be obtained as a white crystaline solid, which is readily soluble in water, forming the common aquafortis. Strong nitric acid, when exposed to the atmosphere, emits dense, white fumes, which are exceedingly suffocating. Mixed suddenly with water, it occasions a considerable rise of temperature ; but mixed with snow, it produces cold by the rapid liquefaction which is occasioned. Nitric acid may be frozen by cold. The temperature at which congelation takes place varies with the strength of the acid. The strongest acid freezes at about 58 below zero. When diluted with half its weight of water, it becomes solid at 1^. By the addition of a little more water, its freezing point is lowered to 45. It is one of the most energetic acids known, and oxydizes many substances powerfully. Powdered charcoal and oil of turpentine are ignited by it, and most animal and vegetable bodies disor- ganized. Phosphorus is oxydized so rapidly as to produce an explosion. A small drop on the skin will, in a few seconds, destroy its vitality, and produce a permanent yellow spot. There are two varieties of it in commerce, called single and double aquafortis, the latter of which is much the strongest, and usually is of a deep orange color. 222. This acid is sometimes produced by the union of the oxygen and nitrogen of the atmosphere, as the effect of lightnings, and is found as nitrate of ammonia in rain-water after a shower in summer. The same effect may be produced by the electric spark, but the presence of water and some base to combine immediately with the acid is necessary. Let a tube be bent, as in the figure on next page, and the two ends covered with metallic cups, one of them opening by a screw, so that the tube may be half" filled with a weak solution of potash. Now insert the screw QUESTIONS. Does nitric acid always contain water when in the liquid form ? How may it be obtained in the solid form ? May aquafortis be frozen? What is said of its oxydizing power? 222. How may nitrio acid be formed by the direct union of its elements ? 202 COMPOUNDS OF NITROGEN AND HYDROGEN. Nitric Acid Produced. and divide the solution into two equal parts, as nearly as may be, and connect it with the prime conductor of an electrical machine, and cause a succession of sparks to pass through the portion of air contained in the central part of the tube. Upon examina- tion, the solution will now be found to con- f tain nitrate of potassa; the nitric acid of which has been formed by the union of the constituent gases of the atmosphere, as above explained. 223, Gold-leaf answers well, in most cases, as a test for nitric acid. The substance supposed to contain it is mixed with a little hydrochloric acid, and the mixture, if nitric acid is really present, should then be capable of dissolving the leaf. If it is a salt that is to be tested, it should first be dissolved in water, and the solution treated in the same manner with hydrochloric acid and. gold-leaf. Nitric acid is much used in the arts for etching on copper, as a solvent for the metals, &c., and as a tonic in medicine. In the laboratory of the chemist, it is in constant and most important use in a great variety of operations. Compounds of Nitrogen and Hydrogen. 224. Ammonia NH^ eq., (14 + 3 = ) 17. This gaseous substance is the only compound of nitrogen and hydrogen that is known. It has been called by a variety of names, as hartshorn, spirits of hartshorn, volatile alkali, &c. It has sometimes been de- tected in rain-water, either alone or in com- bination with nitric acid Collection of Ammonia. (222) ; but it is readily QUESTIONS. 223. What test of free nitric acid is mentioned ? 224. What is the composition of ammonia ? By what names is it known ? COMPOUNDS OF NITROGEN AND HYDROGEN. 203 obtained by heating the common solution of ammonia, called aqua ammonise, or a mixture of sal ammonia and recently slaked linie. When the latter substances are mixed the odor of ammonia is at once perceived, but it is evolved freely when the mixture is moderately heated. It is rapidly absorbed by water, and should therefore be collected over mercury. The reaction is as follows : NH 3 ,HC1 + CaO = Ca, Cl + HO + NH 3 . The two gases do not combine directly, but their union often takes place when they are presented to each other in their nascent state (226), in various chemical operations. Thus, during the rusting of iron, when moisture is present a portion of ammonia is frequently produced, and when zinc is dissolved in dilute nitric acid the solution will usually be found to contain a little nitrate of ammonia. Ammonia is also produced during the destructive distillation of animal substances ; and the name hartshorn came into use from the circumstance that deer's horns were made use of for the purpose. 225. Ammonia is a colorless gas, and possesses a very pungent odor, by which it may always be distinguished. By a pressure of six or seven atmospheres it is compressed into a liquid ; it also takes the liquid form by the application of intense cold, under the ordinary atmospheric pressure. A lighted candle plunged into it is extinguished, but a small jet of it burns in oxygen gas. Its density is about 0-59, 100 cubic inches weighing 18-29 grs. Ammonia is composed of one volume of nitrogen and three volumes of hydrogen, condensed into two volumes. 1 vol. of nitrogen weighs 0-972 . 3 " hydrogen " 0-207 2 " ammonia " 1-179 One-half of this, or 0-589, is the weight of one volume, or the theoretical density of the gas. QUESTIONS. How may ammonia be obtained from aqua ammonia? What is said of its absorption by water ? What is said of the formation of ammonia during the rusting of iron? 225. What are some of the properties of ammonia ? <504 COMPOUNDS OF NITROGEN AND HYDROGEN. Thie gas is largely absorbed by water, which at 32 is capable of dissolving 500 or 600 times its own volume of it, and then forms the liquid ammonia, or aqua ammonias of commerce. As the gas is absorbed, the water increases considerably in. volume, so that, when saturated, its density is only 0-87, and it contains 32 per cent, of the gas. Liquid ammonia is be"st prepared by the use of a Woulf's apparatus, which is constructed as follows. First a vessel of Preparation of Aqua Ammonia. glass or metal, A., containing the substances from which the gas is to be evolved, is placed upon a furnace or other source of heat, and connected by a tube with a series of three-necked bottles, B, C, D, &c., each partly filled with water. The first tube from the vessel containing the materials, it will be observed, terminates below the surface of the water, in the bottle B, so that the gas coming through it is made to rise through the water; but the tube connecting this with the next bottle C terminates in B near the top, but extends downward beneath the -surface of the water in C. The same thing will also be observed of the tubes connecting together the other bottles. Now when the gaseous ammonia is evolved it passes over, and rising through the water in C, is absorbed, but any other gas passes on in like manner to the next bottle, and so on until it escapes in the air. If any of the am- monia escapes from the first bottle, as will be the case after the water has become in part saturated, it will be likely to be con- QUESTIONS What is said of the absorption of ammonia by water? Describe the mode of preparing the liquid ammonia. COMPOUNDS OP NITROGEN AND HYDROGEN. 205 densed in the next, or farther on in the series. In the centre of each bottle is a tube, open at both ends, but extending down- ward so as to terminate below the surface of the liquid. It ia designed merely as a safety tube ; it is plain that if, in using the apparatus, any obstruction occurs in one of the tubes, the effect will be to force out the liquid through these central tubes without danger to the apparatus ; so also any external pressure will at once be equalized by the entrance of the air through these tubes. This apparatus is used for many similar purposes. In order to ensure the full saturation of the water in the bottles they must be kept cold by means of ice. Ammonia has all the properties of an alkali in a very marked manner. Thus it has an acrid taste, and gives a brown stain to turmeric paper; though the yellow color soon reappears on ex- posure to the air, owing to the volatility of the alkali. It com- bines also with acids, and neutralizes their properties completely. This substance is used extensively in the laboratory of the chemist, and in medicine. Solution of ammonia, taken inter- nally in considerable quantity, has been known to produce death ; and the gas, if inspired too long, is apt to occasion inflammation in the throat and lungs. 226. Nascent State. This phrase, which occurs above, is used to indi- cate the state of a body as it is evolved from a compound containing it. In the case alluded to, the rusting of iron in the presence of moisture, the oxygen which unites with the iron is mostly supplied by the water ; and the hydrogen, as it is thus set free, is said to be in its nascent state, and just at the moment is capable of combining with the nitrogen of the air to form ammonia, which it will not do under other circumstances. Many other substances, when thus separated from compounds of which they form a part, manifest a disposition to form compounds with bodies with which they will not combine directly. QUESTIONS. What is the design of the central tube in each bottle? What is said of the alkaline properties of ammonia? 226. What is meant by the nascent state of a body ? What is said of the properties possessed by substances in this state ? 18 206 CHLORINE. GROUP II. CHLORINE "| Electro-negative elements, which constitute a very distinct IODINE ! natural family. Each forms a single acid compound with BROMINE | hydrogen ; and all combine with the metals, forming com- FLUORINE j pounds that are similar. CHLORINE. Symbol, 01; Equivalent, 354; Density, 2.44. 227. History, Chlorine was discovered by Scheele, in 1774, and for many years was regarded as a compound, but its true character, as a simple element, is now universally admitted. It is not found uncombined in nature, but is abundant in its com- pounds, especially common salt, which is so generally distributed over the surface of the earth. It receives its name from the Greek chloros, green, because of its yellowish-green color. 228. Preparation, Chlorine gas is easily prepared by pouring strong hydrcchloric acid upon half its weight of peroxide of man- ganese, in a glass retort, and applying a gentle heat. It may be collected over hot water, but not without some being absorbed by it. It should always be collected in bottles with good stoppers, in which it may be kept for some time. The following formula indicates the changes that take place : Mn0 2 + 2HC1 = MnCl + 2110 + Cl. A cheaper process, and nearly as convenient, is to mix, inti- mately, three parts of common salt with one of the peroxide, and pour over it two parts of sulphuric acid, previously diluted with an equal weight of water. In this case, Mn0 2 + NaCl + 2S0 3 = MnO,SO, + NaO,S0 3 + 01. QUESTIONS. What are the substances of the second group ? What is said of them as a group ? 227. What facts are mentioned in the history of chlorine? From what is the name derived? 228. Describe the method first mentioned for preparing chlorine. Why should hot water be used in collecting it ? Describe the mode of preparing it by the uso of common salt. What are the chemical changes that take place ? CHLORINE. 207 The chlorine by this process is evidently sup- plied by the salt (chlo- ride of sodium) and there are formed sul- phate of the protoxide of manganese and sul- phate of soda. 1 * It is afforded also by various other prepara- tions. Preparation of Chlorine 229. Properties, Chlorine is a dense gas, of a yellowish green color, as above stated, and has an astringent taste, and rather disagreeable odor. The weight of 100 cubic inches is 76 grains, which gives a density of 244. By moderate pressure it is converted into a liquid, which has a density of about 1-33. As cold water absorbs the gas readily it cannot be collected over it without great loss; but, in consequence of its great specific gravity, it may be collected in an open vessel, by di- rect displacement of the *ir. Let a be the flask containing the mate- rials, and c a receiver in which the gas is to be collected, the tube from the flask extend- ing nearly to the bot- lom. The chlorine gas being so much heavier than air, fills up the receiver just as water would if conveyed into it in the same manner; and if the process is expeditiously conducted, the chlorine may be collected nearly pure. Collection of Chlorine by Displacement of the Air. QUESTIONS. 229. Describe the- properties of chlorine. How may it be collected by displacement of the air? 208 CHLORINE. Prepared by either of the modes described above the gas is always mixed with watery vapor, from which it is readily separated by passing it through a tube containing lumps of dry chloride of calcium. After being evolved from the materials used it should be made to pass through a bottle containing a small quantity of water, to separate any hydrochloric acid that mai Preparation of Dry Chlorine. have come over, and then through the chloride of calcium tube, which will absorb all the watery vapor; it may then be collected in a bottle by displacement of the air, as just described. The bottle should be provided with a well-ground glass stopper. Chlorine is allied to oxygen in many of its properties; alighted candle continues to burn in it for a time with'a dull red flame, giving off a dense black smoke of uncombined carbon ; and phosphorus takes fire in it spontaneously, burning with great brilliancy. Some of the r vj?w metals also, if in thin leaf or fine powder, take supports combustion, fire in it spontaneously. For this purpose, a QUESTIONS. How may the gas be obtained free from moisture ? Will chlorine support combustion? How is phosphorus affected by it? CHLORINE. 209 cwonne. tall jar should be used, as represented in the figure on the left; and the bottom should be covered with sand, to prevent the breaking of the glass by the heated chloride falling upon it. It has a strong affinity for hydrogen, and a mixture of the gases explodes by the approach of flame, and by the electric spark, precisely as a mixture of oxygen and hydrogen. If a piece of paper, moistened with oil of turpentine, be suspended in a bottle of chlorine, it takes fire spontaneously, by the chlorine combining with the hydrogen turpentine; at the same time the Turpentine In- flamed. carbon of the turpentine is liberated, in a state of minute division, as a dense black smoke. The bottle containing the chlorine should have a large mouth. One of the most important properties of chlorine is its bleaching power, all vegetable and animal coloring matters being speedily destroyed by it. Powdered indigo, slightly moistened and dropped into a bottle containing it, even if it is considerably diluted with air, soon loses its color entirely ; and pieces of calico, of different colors, suspended in it, are affected in the same manner, without, in the least, injuring the texture of the cloth. It is therefore much used in preparing rags for the manufacture of writing- paper, and also in bleaching cotton and linen goods. Writing done with common ink is easily removed by it; but printers' ink, being an oily preparation, is not attacked by it. Chlorine is also a powerful disinfecting agent, removing at once all offensive effluvia from sewers, vaults, and other places where they may have collected. For this purpose, bleaching-powder (to be .described hereafter) is moistened with water, and placed in shallow dishes in the apartments to be fumigated. The aqueous solution of chlorine is best prepared by the use QUESTIONS. What is said of the affinity of chlorine for hydrogen? What. is its effect upon oil of turpentine? What occasions the dense black smoke? What is said of the bleaching properties of chlorine? What is said of it as a disinfecting agent? 18* 210 COMPOUNDS OF CHLORINE AND OXYGEN. of a Woulfe's apparatus (225). The solution readily dissolves gold- leaf, forming trichloride of gold. If one of the bottles is kept cold by means of ice, a crystaline solid will be deposited, which is a compound of one atom of chlo- rine and ten atoms of water. 230. By dexterously putting some of these crystals in a glass tut and sealing it hermetically, liquid chlorine may be obtained. By slight elevation of temperature the solid melts and the water and chlorine separate, the latter of -which, in consequence of the pressure, takes the liquifl form. While sealing the tube the end containing the crystals must be Preparation of Liquid Chlorine, kept cold by means of ice. The aqueous solution, if prepared in the dark and kept constantly from the action of light, undergoes no change (173), but if once exposed for a few moments only to the sun's rays, decomposition of the water commences, hydrochloric acid is formed, and oxygen set free. The proper test of chlorine, either free or in combination, is solution of nitrate of silver ; silver and chlorine always forming a dense white pre- cipitate, quite insoluble in water, but readily soluble in aqua ainmoniae. Compounds of Chlorine and Oxygen 231. The compounds of chlorine and oxygen are five in number, as follows, viz. : C10,C10 3J C10 4 ,C10 5 , and C10 7 , all of which are acids ; but as the affinities of these substances for each other are very feeble, their compounds are all decomposed by slight causes. 232. Hypochlorous Acid CIO; eq., (35-4-f8=) 43-4. This is a gaseous substance, of a yellowish-green color, like that of chlorine, but a shade deeper. It exists in combination with lime in the common bleaching-powder. 233. Chlorous Acid C10 3 ; eq., (35-4 -f 24 =) 59-4 Is prepared by the action of oil of vitriol upon chlorate of potash. 234. Hypochloric Acid C10 4 ; eq., (35-4 -f 32 =) 67-4. This com- pound is also gaseous, and of a deep yellowish 'color. It is formed by the action of sulphuric acid upon chlorate of potash. If a few grains QUESTIONS. How is the aqueous solution of chlorine prepared ? May the compound of chlorine and water be crystalized ? 230. How may these crystals be used to form liquid chlorine ? Can the aqueous solu- tion be long preserved without decomposition? What test for chlorine is mentioned ? 231. What compounds of chlorine and oxygen are there? What is the number of equivalents of oxygen in each of these ? COMPOUNDS OP CHLORINE AND HYDROGEN. 211 of chlorate of potash are placed in a wine-glass, and a little sulphuric acid poured in, the glass will be soon filled with the gas, which will be recognised by its color. If now a rag, wet with oil of turpentine, be pre- sented to it, on the end of a wire or a stick, it will be inflamed, and the gas at the same time exploded. 235. Chloric Acid C10 5 ; eqr, (354 + 40 =) 754. Chloric acid is obtained by passing a current of chlorine through a strong solution of potash, with which it combines as it is formed, pro- ducing chlorate of potash. At the same, time with the chlorate of potash there is also produced much chloride of potassium ; the reaction takes place between 6 equivalents of chlorine and 6 equiva- lents of potash, according to the following equation : 6KO + 6C1 = 5KC1 + KO,C10 5 . % The chlorate being only slightly soluble in water, some separates in crystals by a little evaporation of the water, while the chloride remains in solution. To obtain the acid in a separate state, chlorate of baryta is first produced and then decomposed carefully by sulphuric acid. The BaO,S0 3 whicn forms is separated by nitration, and the chloric acid obtained as a syrupy liquid. It is decomposed at a tem- perature of 104. Perchloric Acid possesses no characters that render it of any special interest. Compounds of Chlorine and Hydrogen. 236. Hydrochloric Acid HC1; eq., (354 + 1=) 364. This is the only known compound of chlorine and hydrogen ; and, in -solution in water, has long been used in the arts, under the names of muriatic acid, and spirit of salt. It is formed by the action of diluted sulphuric acid upon common salt. The sulphuric acid should be diluted with about an equal weight of QUESTIONS. 235. How is chlorate of potassa formed ? How is chloric acid procured from this salt? 236. What is the only compound of chlorine and hydrogen that is known? How is hydrochloric acid prepared ? 212 COMPOUNDS OP CHLORINE AND HYDROGEN. water, and be allowed to cool before being used. The changes which take place are as follows : NaCl + S0 3> HO = NaO,S0 3 + HC1. ,From this it appears that the water of the oil of vitriol ia essential to the process ; it is decomposed, yielding its oxygen to the sodium to form soda, which combines with the acid, and its hydrogen to the chlorine to form the hydrochloric acid. Abundant fumes of the gaseous acid will be given off, which should in no case be allowed to diffuse themselves in a room where there are articles of delicate apparatus made of metal, as they will be sure to be corroded after a little time, if not immediately. It is also formed by the direct union of its elements. When equal measures of chlorine and hydrogen are mixed together, and an electric spark is passed through the mixture, instantaneous combination takes place, heat and light are emitted, and hydro- chloric acid is generated. A similar effect is produced by flame, by a red-hot body, and by spongy platinum. Light also causes them to unite. A mixture of the two gases may be preserved, without change, in a dark place; but if exposed to the diffused light of day, gradual combination ensues, which is completed in the course of twenty-four hours. The direct solar ray, like flame and the electric spark, produces an explosion by a sudden inflam. mation of the whole mixture ; but to insure the success of the experiment, the gases should be very pure, and the chlorine recently prepared over warm water. The glass vial containing the mixed gases, after being filled, should be instantly covered with a black cloth, which can be suddenly removed by a stick, or wire, after it is placed in the sun's rays. Hydrochloric acid is, "of course, a chloride of hydrogen. When pure it is a colorless gas, of which 100 cubic inches weigh 39-38 grains, giving it a density of 1-25. By strong pressure it may QUESTIONS. Explain the equation. Is the presence of water essential to the formation of hydrochloric acid? May it be formed by the direct union of its elements ? What several means are mentioned by which the gases may be made to combine ? What are some of the properties of hydrochloric acid ? COMPOUNDS OF CHLORINE AND HYDROGEN. 213 be compressed into a liquid. It is quite irrespirable, and in- capable of supporting combustion. Water absorbs it with avidity, taking up, under favorable circumstances, no less than 480 times its own volume. During the absorption it increases considerably in volume, and the saturated solution has a density of 1/21, and contains about forty-two per cent, of the acid. In preparing the liquid hydrochloric acid, a Woulfe's apparatus (225) is used, only a very little water being contained in the first bottle, in which most of the impurities mixed with the gaseous acid will be deposited. In the open air, copious fumes of the gas constantly arise from the liquid, which produce a cloud of smoke if any ammonia be present in the air. Thus, let a little aqua ammonias be poured into a glass vessel, A, with a large mouth, and then invert over it a tumbler, the inside of which has been thoroughly moistened with common hydrochloric acid. The two gases, coming in con- tact, unite, and fill both glasses with a dense, white Hydrochloric Acid . ' , and Ammonia. smoke, which is solid hydrocnlorate of ammonia (159), in a finely divided state. The same thing is shown when a glass rod moistened with hydrochloric acid is brought near an open vessel containing aqua ammonias. Gaseous hydrochloric acid is composed of equal volumes of chlorine and hydrogen united without condensation. One volume of chlorine weighs 2 '440 One " hydrogen " 069 Forming two vols. hydrochloric acid 2.509 I The weight of 1 vol., or the theoretical density of the gas, is therefore ^1|L 9 = 1-254. 237. Aqua regia, so called because of its ability to dissolve gold and platinum, is a mixture of two parts of hydrochloric to one of nitric acid. Let a single leaf of gold be placed in a wine QUESTIONS. What is said of the absorption of hydrochloric acid by water ? What is said of the fumes produced by the gas -with ammonia ? What is said of the volumes of chlorine and hydrogen which unite to form this acid ? 237. What is aqua regia ? Why is it so called ? 214 COMPOUNDS OP CHLORINE AND NITROGEN. glass containing a little hydrochloric acid, and another leaf in a separate glass with some nitric acid ; the gold will remain undis- solved in both glasses for any length of time ; but, on mixing the contents of the glasses, the whole of the gold will be speedily dis- solved. The real solvent in this case is the chlorine, which is liberated by the action of the acids upon each other. The reaction is shown by the following equation. Thus, N0 5 + 2HC1 = N0 3 + 2HO + 01. This decomposition, however, proceeds only so far as to saturate the liquid with chlorine, but if heat is applied to expel the chlorine, or a metal placed in the liquid with which it will unite, new quan- tities of the acid are decomposed. Nitrohydrochloric acid, there- fore, is a source of chlorine in a very concentrated state, and is capable of dissolving several substances which are not attached by any single acid. Hydrochloric acid may readily be distinguished by its odor and volatility, and by its giving, with a solution of nitrate of silver (230), a precipitate of the white chloride of silver, which is blackened by exposure to the light. Liquid hydrochloric acid is extensively used for various pur- poses in the arts, and is one of the most important chemical agents of the laboratory. Compounds of Chlorine and Nitrogen. 238. Terchloride of Nitrogen. NC1 3 ; eq., (14 -f 106-2 =) 120-2. There is known only a single compound of these ele- ments, the terchloride of nitrogen. It is prepared by pass- ing a current of chlorine through a solution of the hydrochlorate, or other salt of ammonia, and takes the form of a dense yellow liquid, which is seen in small globules at the bottom of the solu tion. The reaction is expressed in the following equation : NH S ,HC1 + 6C1 = 4HC1 + NC1 3 . QUESTIONS. What compound of gold is formed? How may hydro- chloric acid be known ? 238. What compound of chlorine and nitrogen is there? What is said of it? Explain the equation. I IODINE. 215 The liquid has a density of 1-65, and may be distilled under a pressure less than one atmosphere, but at 212 it explodes with the utmost violence. So also it detonates violently by the mere contact with phosphorus, many of the oils, &c., *and never should be handled but with the greatest care. IODINE. Kymbol, I; Equivalent, 127; Density, 4-95 239. History. Iodine from (iodes, violet color) was discovered in the ashes of sea-plants, from which it is still prepared, by M. Courtois of Paris, in the year 1812. It is found also in certain ores of silver and zinc, in sea-water, and in the water of certain mineral springs. 240. Preparation, As stated above, the iodine of commerce is obtained from the ashes of sea-plants, especially the fucus Preparation of Iodine. palmatus. The ley obtained by lixiviating the ashes is first evaporated, to separate a portion of the carbonate of soda and QUESTIONS. 239. When was iodine discovered ? In what is it found t 240. What is the mode of preparing iodine from the ashes of sea-plants T 216 IODINE. other saline compounds it contains, which are less soluble than the iodine compounds chiefly the iodides of sodium and magne- sium and are therefore first to crystalize out from the solution ; the residue is then mixed with peroxide of manganese and sul- phuric acid, and a gentle heat applied, when the iodine distils over, as a beautiful violet-colored vapor, into a receiver prepared for the purpose, where it is condensed. A simple apparatus like that represented in the figure on the preceding page answers well for the distillation. A good method to show the evolution of iodine, is to heat in a glass globe, over a lamp or ignited charcoal, a small quantity of sulphuric acid, and throw suddenly into it 25 or 30 grains of iodide of potassium. A large quantity of iodine will instantly be set free, and its vapor fill the globe. 241. Properties. Iodine, at ordinary temperatures, is a soft, friable, nearly black solid. Usually it is in small shining crys- tals, which have a metallic lustre, and a density of 4-95. Heated a little above 212, it melts, and is then converted into a beau- tiful violet- colored vapor, which has a density of 8-70 (air being 1), and 100 cubic inches weigh 270-1 grains. Iodine is a non- conductor of electricity and heat, and is allied to oxygen and chlorine in many of its properties. Its odor resembles that of chlorine, but is less offensive. It is sparingly soluble in water, requiring about 7000 times its own weight of this liquid for com- plete solution j but alcohol and ether dissolve it freely, forming a deep brown solution. A few of the crystals pressed upon the skin produce a deep stain, which however soon disappears. Starch affords a delicate test of iodine, forming with it a beau- tiful blue. The starch should be prepared by dissolving it in hot water, and allowing it to cool before using. Let a little hot water be poured upon ashes obtained by burning a piece of sponge, and, after filtering, add a drop or two of solution of starch ; then pour in a few drops of sulphuric or nitric acid, and stir it gently, and almost always the blue color will be observed, indicating the presence of iodine. QUESTIONS. 241. Describe the properties of iodine. What is %aiO of its solubility in vrater? In alcohol and sther? What test of iculin* is mentioned ? How may iodine be detected in sponge ? COMPOUNDS OF IODINE AND OXYGEN, HYDROGEN, ETC. 217 Iodine has not been much used in the arts, but is largely em- ployed in medicine. In the Daguerreotype process (76), it is essential ; and recently it is said to have been employed in dyeing. Compounds of Iodine and Oxygen, Hydrogen, &c. 242. Iodine and oxygen combine in three proportions, pro- ducing iodous I0 4 , iodic I0 5 , and periodic I0 7 , acids ; neither of which however possesses any special interest. 243. Hydriodic Acid, HI, (iodide of hydrogen,) is a gaseous substance, of a specific gravity 4-39, and in many of its properties strongly resembles the corresponding chloride of hydrogen (hydro- chloric acid). It is absorbed by water, and then forms the liquid hydriodic acid. It is best prepared by placing in a glass tube alternate layers of iodine, powdered glass (to prevent too rapid action) and posphorus, slightly mois- tened with water. Iodide of phos- phorus is first formed, which is decomposed by the water, producing i j L j j- ? Preparation of Hydriodic Acid. phosphorous acid and hydriodic acid, the last of which being gaseous makes its escape, and may be collected in a dry bottle by displacement of the air, or it may be condensed in water. 244. Teriodide of Nitrogen NI 3 . From the weak affinity that exists between iodine and nitrogen, these substances cannot be made to unite directly. But when iodine is put into a solution of ammonia, the alkali is decomposed ; its elements unite with different portions of iodine, and thus cause the formation of hydriodic acid and teriodide of nitrogen. The latter subsides in the form of a dark powder, which is characterized, like chloride of nitrogen, by its explosive property. It often detonates spontaneously as soon as it is dry, and even when moist, by the slightest causes. Heat and light are emitted during the explosion, and iodine and nitrogen are set free, the former of which may be seen at the instant in the form of vapor. QUESTIONS. What use is made of iodine? 242. What compounds of iodine and oxygen are mentioned? 243. Describe hydriodic acid How is it formed ? 244. Describe teriodide of nitrogen. 19 218 BROMINE. Chlorine combines "with iodine when made to pass over it in a dry glass tube, or when passed through water in which crystals of iodine are diffused. The two substances form several different compounds, but they are not at present well understood. One of these, probably the proto- chloride, Id, has been used in the Daguerreotype process. BROMINE. Symbol, Br; Equivalent, 80; Density, 2-97. 245. History. Bromine was discovered in 1826, in sea-water; and received its name, bromine (from bromos, offensive odor), in consequence of its exceedingly disagreeable smell. Kecently it has been obtained in large quantities from the waters of some of the salt-springs in Pennsylvania and Virginia. . 246. Preparation. The usual mode of preparing bromine is a little complex. First, the brine from the spring is evaporated, and the common salt removed by crystalization, then the mother- liquor, or bittern, as the uncrystalizable residue is called, is treated with a current of chlorine to decompose the bromides of magne- sium, sodium, &c., and sulphuric ether afterwards added, by which the bromine that has been separated from its compounds by the chlorine is taken up, and rises to the surface as a solution of bromine in ether. Another method is to mix with the solution sulphuric acid and peroxide of manganese, as in the preparation of iodine ; and then distilling with a gentle heat. The same apparatus (240) may be used as in the preparation of iodine, but the receiver must be kept cool by a current of cold water. 247. Properties. Bromine is a liquid of a blackish-red color, and specific gravity 2-97. At a temperature a little below zero it is frozen, and boils at about 117, forming a vapor of a beau- tiful blood-red color, and specific gravity 5-39, air being 1. It QUESTIONS. What is said of the compounds of chloride and nitrogen ? 245. When was bromine discovered ? From what is the name derived ? 246. From what is it obtained? What is the mode of preparing it ? 247. Describe its properties. COMPOUNDS OF BROMINE, WITH OXYGEN, ETC. 219 stains the skin yellow, like iodine, but less intensely. Vapor of bromine ignites phosphorus spontaneously, and a lighted candle burns in it a short time. Bromine, in many of its properties is closely allied to chlorine and iodine. Taken into the system it is highly poisonous, and its vapor possesses considerable bleaching power. With starch it forms a yellow color. Like chlorine, it forms a compound with water, which crys talizes when exposed to the cold of a freezing mixture of salt and snow. The compound is Br,10HO. Bromine is sometimes used in medicine, and much more extensively in photography, especially in the Daguerreotype process. Compounds of Bromine, with Oxygen, Hydrogen^ &c. 248. Bromic Acid, Br0 5 , is the only well determined com- pound of bromine and oxygen. It is a liquid, and may be pro- cured of the consistency of syrup. It is very corrosive, and sour to the taste, and by a temperature of 212 is decomposed. 249 Hydrobromic Acid, HBr, is a colorless gas of a density 2-73. To prepare it, a tube of the form of the letter W is pro- vided, and the part at the left filled with pieces of phosphorus mixed with pounded glass, and the whole moistened with water. Into the end at the right some bromine is then poured, and a cork firmly inserted; and into " p re p ara tion of Hydrobromic Acid. * the other- end a smaller tube is fixed, by means of a perforated cork, to convey away the hydro- bromic acid as it is formed. The whole being ready, a gentle heat is applied to the part containing the bromine; and the vapor as it is formed, attacking the phosphorus, first produces bromide QUESTIONS. What other elements does bromine resemble? Does it combine with water? What use is made of it? 248. Describe bromio cid. 249. Describe hydrobromic acid, and the mode of preparing it 220 FLUORINE. of phosphorus, which is at once decomposed by the water, forming phosphorous and hydrobromic acids, the latter of which, being gaseous, passes off, and may be collected over mercury. The gas is rapidly absorbed by water, like hydrochloric acid, and the concentrated solution gives off fumes in the air. In most of its properties it closely resembles hydrochloric acid. By intense cold and pressure the gas may be condensed to the liquid form. 250. Hydrobromic acid is composed of equal volumes of vapor of bro- mine and hydrogen combined -without condensation. Thus, 1 vol. vapor of bromine weighs 5-390 1 " " hydrogen " 069 2 vols. hydrobromic acid, 5-459 One volume of the acid therefore weighs 2-729. FLUORINE. Symbol, F; Equivalent, 19; Density, 1-29. 251. History and Properties. Fluorine has long been known to exist, but it has not, until recently, been obtained in a separate state. It is found in nature in considerable abundance in the mineral called fluor spar, which is a compound of this substance with calcium, the metallic base of lime. It is a brownish-colored gas, of specific gravity 'about 1-29 (probably), and bleaches like chlorine. Such is its affinity for other substances that it attacks them with violence, even gold and platinum ; and can be prepared and kept only in vessels made of fluor spar, which, being already saturated with the substance, is not acted on by it. QUESTIONS. What is said of the absorption of hydrobromic acid by water? 250. Considered as gaseous, what is its composition ? 251. Give the history and properties of fluorine. What is said of its affinity for other substances ? Of what only can vessels be made to contain it ? Why ig not this substance acted on by it ? COMPOUNDS OF FLUORINE. 221 Compounds of Fluorine. Fluorine seems to be incapable of uniting with oxygen, but combines with hydrogen, forming the acid compound HF. 252. Hydrofluoric Acid HF; pq., (19 + 1=) 20. This acid is formed by subjecting powdered fluor spar, moistened with strong sulphuric acid, to a very gentle heat in a leaden vessel. The acid distils over as a pungent, corrosive, vapor, but may be condensed in a leaden receiver, that is kept surrounded with ice. The reactions are as follows : CaF + S0 3 ,HO = CaO,S0 3 + HF. As thus formed, the acid has a density of 1-07, and manifests a strong affinity for water, with which it combines with great energy. It attacks glass powerfully, combining with its silica, and may therefore be used to etch it. This is done by spreading a thin coat of bees'-wax or varnish upon the glass, and tracing the design upon it, taking care to cut quite through the wax. The liquid acid is now poured over the coated surface, or it is exposed a few minutes to the acid vapor, and the wax afterwards removed ; the design will then be found beautifully traced upon the glass. This acid attacks animal substances powerfully, and, therefore, should always be handled with great care. Fluorine unites also with chlorine, iodine, bromine, and some others of the elements, but the compounds are not important. QUESTIONS. Does fluorine combine with oxygen ? 252. Describe tho mode of preparing hydrofluoric acid. Describe its properties. How may it be used for etching upon glass ? What is said of its action upon ani- mal substances ? Does fluorine combine with chlorine, iodine, &o. ? 19* -22 SULPHUR. GBOUP IIL SULPHUR ) Elements in many of their properties closely resembling SELENIUM > each other, and forming similar acid compounds with TELLURIUM J oxygen and hydrogen. SULPHUR. Symbol, S; Equivalent, 16; Density, 1-99. 253. History and Preparation. Sulphur, called also brim- stone, has been known from the remotest antiquity. It occurs, as a mineral production, in many parts of the world, particularly in volcanic regions, as in the neighborhood of Naples, in some of the Sandwich Islands, and in the island of Sicily. In combination with several of the metals, as iron, lead, copper, &c., it is still more abundant, and is found in almost every place. From one of its compounds with iron, called iron pyrites, it is procured in large quantities, for the purposes of commerce. It is found, also, in many organic bodies, as in eggs, in the hair, horns, and hoofs of animals, and in the seeds of black mustard. The island of Sicily furnishes a large part of all sulphur of commerce ; the native sulphur here occurs in immense beds mixed more or less with gypsum, lime, and other earthy matter. This sulphurous earth is first heated in pots so as to melt the sulphur, which is dipped out with ladles, the earthy matter settling to the bottom. The sulphurous earth remaining as sediment is then heated in earthen pots, which are arranged ia double rows, and entirely inclosed in mason-work, except at the top, where is an opening by which they are charged and emptied. At the sides, in the open air, pots are arranged to receive the sublimed sulphur, which, taking the liquid form, passes finally into buckets situated as shown in the figure on next page. QUESTIONS. AY hat elements constitute group 3d of the metalloids'? 253. Give the history of sulphur. "With what is it found combined? In what erganic bodies is it contained? Describe the mode of separating it from the earthy matter with which it is mixed. SULPHUR 223 Separation of Sulphur. The figure represents a section of the rnason-work with two of the included pots, and also the external receivers with which they are connected, and the buckets. 254. Properties. Sulphur is a brittle solid, of a greenish- yellow color, emits a peculiar odor when rubbed, and has little *taste. It is a rion-conductor of electricity, and is excited nega- tively by friction. It fuses at 226, and becomes nearly as liquid as water; but if the heat be raised as high as 430, it becomes so tenacious that the vessel containing it may be inverted without spilling it, and is then of a dark molasses color. When heated to at least 428, and then poured into water, it becomes a ductile mass, which may be used for taking the impressions of seals. After some time, it changes into its ordinary state. Fused sulphur has a tendency to crystalize in cooling. A crys- taline arrangement is perceptible in the centre of common roll sulphur; and, by good management, regular crystals may be obtained. For this purpose, several pounds of sulphur should be melted in an earthen crucible ; and, when partially cooled, the outer solid crust should be pierced, and the crucible quickly inverted, so that the inner and as yet fluid .parts may gradually flow out. On Sul P bur breaking the solid mass, when quite cold, a confused arrangement of prismatic crystals will be found in the interior. Sulphur is dimorphous (184) ; that is, it is capable of cryt- talizing in two distinct primary forms, the oblique rhombic QUESTIONS. 254. Describe the properties of sulphur. How may it b crystalized ? Why is it said to be dimorphous ? 224 SULPHUR. prism, and the rhombic octahedron-, the first belonging to the monoclinic, and the second to the trimetric system. Sulphur is very volatile, and begins to rise in vapor even before it is completely fused. At about 750, it boils, and the vapor, if in a close vessel, will be condensed on any cold surface, forming fhefloicers of sulphur. The density of its vapor is about 6-65. "When vapor of sulphur is brought in contact with vapor of alco- hol, they unite ; but solid sulphur is quite insoluble in alcohol, or water, but dissolves in boiling oil of turpentine, and in sulphide of carbon. By melting the flowers of sulphur and pouring it into moulds, the roll-sulphur of commerce is formed. In this form it is very brittle, and will sometimes break by the heatf of the hand. It is the only substance known that always becomes negatively excited by friction, whatever may be the nature of the substance used as the rubber. -,J* The vapor of sulphur combines readily with iron and other metals, attended with all the pher nomena of combustion. Let the breech of a gun-barrel be heated to redness, and a lump of sulphur dropped into it, and then let the muzzle be instantly closed by a cork ; a jet of vapor of sulphur will issue violently from the touch-hole, r 4 which will be inflamed as it enters Iron Wire and Vapor of Sulphur. ^ ^ . ^ ft buQch Qf ^j .^ wire, held in it, will burn freely, forming sulphide of iron, which will fall in drops. The sulphur of commerce generally has an acid reaction, pro- bably in consequence of a slight oxidation that is gradually taking place. Organic substances in contact with sulphur are always more or less acted upon by the acid or acids thus produced. QUESTIONS. What is the boiling point of sulphur? What are the flowers of sulphur ? Is it soluble in water or alcohol ? How is roll- Bulphur formed ? What is said of its electrical state when rubbed ? How may iron wire be made to burn in vapor of sulphur ? Why does the sul- phur of commerce usually have an acid reaction ? COMPOUNDS OF SULPHUE AND OXYGEN. 225 Uses of Sulphur. Sulphur is used extensively in the arts, and in medicine. It is employed in the manufacture of gunpowder, sulphuric acid, the different kinds of matches, vermillion, &c., and for taking impressions of seals. In medicine, it is used in cuta- neous diseases, and as a cathartic and alterative Compounds of Sulphur and Oxygen. 255. Sulphur and oxygen form as many as seven different com- pounds, viz. : 1. Hyposulpharous acid S 2 02. 2. Trisulpho-hyposulpliuric acid S 5 5 . 8. Bisuipho-hyposuiphuric acid S 4 5 . 4 . MonSsutpfib-fiy posulphuric acid S 3 5 . 5. Sulphurous acid S0 2 . \ 6. Hyp^iuTphfec acid S 2 5 . 7. Sulphuric acid S0 3 . Of these, the fifth and last are by far the most important ; and only these will be here described. 256. Sulphurous Acid S0 2 ; eq., (16 + 16 =) 82. This substance is gaseous at ordinary temperatures, and is the sole product of the combustion of sulphur in the open air, or in dry oxygen gas. It is more conveniently prepared, however, by heat- ing strong sulphuric acid in contact with mercury or pieces of copper. One equivalent of the sulphuric acid gives up one equivalent of its oxygen to unite with the metal, and the oxide thus formed is immediately dissolved by a second atom of the sulphuric "acid, while the sulphurous acid passes off as a gas. . Thus, Hg + 2SO, = HgO,SO,+ S0 8 . Another very easy method is to heat in a retort a mixture of 6 parts of powdered peroxide .of manganese and 1 part of sulphur. QUESTIONS. What use is made of sulphur in the arts ? 255. How many compounds of sulphur and oxygen are mentioned ? 256. Describe sulphurous acid, and the mode of preparing it. . 226 COMPOUNDS OF SULPHUR AND OXYGEN. Preparation of Sulphurous Acid. By this mode, the peroxide gives up one-half of its oxygen, which unites with sulphur to form the sulphurous acid, and protoxide of manganese remains in the retort. An arrangement like that figured in the mar- gin, answers well for its preparation, by either mode. As the gas forms it is made to pass through a little water, to condense any vapor of sulphuric acid that may have come over, and it may then be collected over mercury. Sulphurous acid is a dense, colorless gas, 100 cubic inches of which weigh 68-55 grains, giving it a specific gravity of 2-24. It is distinguished from all other gases by its suffocating odor, which every one has recognized in burning sulphur. It is absorbed largely by water, and may be condensed into the liquid form by moderate pressure, or by a cold of zero. A little of the liquid may be obtained very easily, by putting a small quantity of mercury and sulphuric acid in a bent tube, as represented in the figure, sealing it hermeti- cally, and supplying heat to the extremity, a, which contains the materials, while the other, b, is kept cool by means of ice, or the evaporation of ether. The liquid will be soon found to collect in the cool part of the tube. Care should be taken not to heat the tube too much, lest it should burst. A better method to procure the liquid is to prepare a tube, (as in the figure on next page,) by closing one end, and drawing out a part in the middle to a capillary bore, and then inserting it in a freezing mixture of snow and salt. If, now, a current of the gas, first dried by passing through a chloride of calcium tube, be made Preparation of Sulphurous Acid in Liquid Form. QUESTIONS. What is said of the odor of sulphurous acid ? How may it be obtained in the liquid form ? COMPOUNDS OF SULPHUR AND OXYGEN. 227 to enter the open end" of the tube, it will be con- densed and collected in the lower part. When this part is nearly filled, still keeping in the freezing mix- ture, the upper part may be separated and the lower part, hermetically sealed, and the liquid preserved for any length of time. Or a tube like that represented in the figure on the right margin may be used. The bulb at the centre part is to be sur- rounded with a freezing mixture "PTfvnnrai'nn of Liquid sui- * n a sulta kk vessel, as a glass Preparation of Liquid Su i. phurous Acid, tumbler j and when a sufficient phurous Acid, quantity of the fluid has accumulated, the two ends of the tube may be hermetically sealed before it is removed from its place in the freezing mixture. Under the ordinary atmospheric pressure it becomes liquid at about 14, but at a temperature of 59 it requires a pressure of about 2 atmospheres. The liquid has a density of 142. When allowed to escape in the open air it eva- porates rapidly, producing a cold of 60 to 76, according to the temperature of the air and other circumstances. By severe cold it may be frozen, and with water it forms a compound (S0 2 9HO) which may be solidified. 257. Sulphurous acid is composed of 1 volume of oxygen and ^ of a volume of vapor of sulphur, condensed into 1 volume. If we burn a small quantity of sulphur in a .glass globe over mercury, the sulphur is converted into sulphurous acid, but after cooling the volume of gases is found to be unchanged. The acid therefore occupies the same space as the oxygen entering into its composition Therefore if we subtract the weight of the volume of oxygen from that of a volume of sulphurous acid, there should remain ^ ounds of sulphur with nitro of little interest, are not here described. The compounds of sulphur with nitrogen, iodine and bromine, being QUESTIONS. Describe the properties of dichloride of sulphur. 267. How is chloride of sulphur formed ? Describe its properties. SELENIUM. 239 SELENIUM. Symbolj Se; Equivalent, 39-5; Density, 4-32. \. History, etc, Selenium was discovered, in 1817, by Berzelius, and received its name from selene, the moon. It is usually found associated with sulphur, in some of its compounds with other substances, especially sulphide of iron (iron pyrites). It is found also in combination with copper, lead, mercury, silver, and other metals. From any of these it is prepared by several different processes. Selenium, at ordinary temperatures, is a solid of a deep brown color, the shade varying a little, according as it is seen in a powder or in a solid mass. When melted and suddenly cooled, it has a vitreous conchoidal fracture, and becomes negatively electrical by friction in very dry air. When heated to 212, it becomes partially fluid, and perfectly so at a temperature a little higher than this. Heated to 700, it sublimes like sulphur, which it closely resembles in many of its properties. At a temperature of 212, or a little higher, especially if it has been heated con- siderably above this and again cooled down, it is viscid, and may be worked like softened sealing-wax, and drawn out into small threads. When heated in the open air, it readily takes fire and burns, exhaling a strong odor not unlike that of decaying horse-radish, a character by which it may always be distinguished. Compounds of Selenium and Oxygen. 269. Selenium forms with oxygen three compounds, SeO, SeO,, and Se0 3 . The latter two are acids, and in many of their properties quite similar to sulphurous and sulphuric acids, to which they correspond in composition. QUESTIONS. 268. In what is selenium found? Describe its pro- perties. 269. What compounds does it form with oxygen ? 240 COMPOUNDS OF SELENIUM AND OXYGEN. TELLURIUM. 270. Selenous Acid Se0 2 ; eq., (39-5 -f- 2 x 8=) 55-5. To prepare this acid, a retort contain ing a mixture of chlorate of potash and peroxide of manganese is connected, as represented in the figure, with a tube bent downward so as to receive a quantity of selenium at the lowest part. Heat is then applied to the chlorate by which oxygen gas is evolved, and also to the selenium in the tube. As the selenium becomes heated, it burns slowly, with a blue flame, and the selenous acid is collected in the upper part of the tube in the form of white acicular crystals, which are very soluble in water. Preparation of SeOa. 271. Selenic Acid-~Se0 3 ; eq., (39-5 -f 3 x 8 =) 63-5. Selenic acid is prepared by burning selenium with nitrate of potash, when seleniate of potash is formed, from which the acid may be .obtained in the liquid form. Its chief interest is found in its close resemblance to the corres- ponding sulphur acid, S0 3 , and in the fact that it is capable of dissolving gold. With hydrogen selenium forms a compound, hydroseleni'c acid, HSe, which is gaseous, and irritating to the eyes, nose and Jungs. It is ab- sorbed by water, like hydrosulphuric acid, and the solution, like that of hydrosulphuric acid, is decomposed by contact with the air. The compounds -of selenium with sulphur, chlorine and bromine are not of sufficient interest to require attention in this work. TELLURIUM. Symbol, Te; Equivalent, 64-5; Density, 6-2. 272. History, etc. Tellurium is a rare substance, which has sometimes been found native, but is usually combined with the metals, as gold, silver, bismuth and lead. It is generally pre- pared from the telluride of bismuth, which is found in Schemintz in Hungary. QUESTIONS. 270. Describe the mode of preparing selenous acid. 271. Describe selenic acid. What compound does selenium form with hydrogen ? 272. Describe tellurium. COMPOUNDS OP TELLURIUM WITH OXYGEN, ETC. 241 Tellurium, in some of its physical properties, closely resembles the metals with which it is often associated ; but in its chemical properties it is more nearly allied to the non-metallic elements, especially sulphur and selenium. When pure, it has a clear white color, and bright metallic lustre j and in its general appearance is not unlike antimony. It melts at a dull red heat, and, by slow and careful cooling, may be obtained in crystals, the primary form of which is the rhombo- hedron. At a very high temperature it becomes gaseous. Compounds of Tellurium with Oxygen, Efc. 273. Tellurium forms with oxygen two acid compounds, viz., tellurous acid, Te0 2 , and telluric acid, Te0 3 , which, as will at once be seen, are similar in composition to the corresponding compounds of sulphur and selenium. With hydrogen, also, like the two elements just named, it forms a single gaseous compound, hydrotelluric acid, HTe, l;he smell of which is even more offensive than that of hydrosulphuric acid. Tellurium combines with chlorine, iodine, bromine, sulphur, sele- nium, etc. GROUP IV. ' ^ Two elements which are solid at ordinary tempera- FHC PHORUS [ tureg ^ and similar ia many other properties. Many of J their compounds are isomorphous. PHOSPHORUS. Symbol, P; Equivalent, 32 ; Density, 1-8 to 2. 274. History. Phosphorus was discovered by an alchemist of Hamburg, in 1669; and received its present name (from phns, light, and pherein, to carry) from the circumstance that, at ordinary temperatures, it always appears luminous in the dark.r QUESTIONS. 273. What is said of the compounds of tellurium with oxygen? 274. Give the history of phosphorus. 21 242 PHOSPHORUS. It is not found in nature in a separate state ; but in combination with oxygen and lime, it is very generally diffused, being con- tained in all fertile soils, without exception, and in many vegetable and animal substances. 275. Preparation, Phosphorus, at the* present time, is pre- pared entirely from bones, which are first heated in the open air until they become white, so as to destroy all the animal matter they contain. More than half their weight remains, which is chiefly phosphate of lime. This is then ground to a fine powder, and digested, for one or two days., with dilute sulphuric acid, in the ratio of, 3 parts of the bone ashes to 2 parts of acid and 15 or 20 parts of water. The action of the sulphuric acid upon the phosphate of lime, is to take away a part of its lime, forming with it sulphate of lime; and as the whole of the phosphoric acid of the original phos- phate is then in combination with only a part of its lime, it is plain that this must now be a super-phosphate of lime. This latter is soluble in water, while the sulphate of lime which has been formed is insoluble ; more water is therefore added, and a clear liquid obtained, which is evi- dently solution of super-phosphate of lime. This liquid is now eva- porated until it begins to be quite thick, when it is mixed intimately with charcoal, in fine powder, and thoroughly dried. It is next in- troduced into an earthern retort, a, which is placed in a proper furnace, as represented in the figure; and to the neck of the Preparation of Phosphorus. attached, which connects with a vessel of water. The heat is then gradually raised, when the phosphorus distils over, and is condensed in the water. Much combustible gaseous matter, also, QUESTION. 275. Describe the mode of preparing phosphorus. PHOSPHORUS. 248 comes over and escapes by the second tube, inserted in the water- vessel. The affinity of charcoal for oxygen at low temperatures is not very considerable, but when highly heated it is intense, and sufficient to abstract the oxygen from the phosphoric acid of the acid phosphate of lime, causing the liberation of the phosphorus. This, taking the gaseous state, distils over and is condensed to the liquid form, and finally solidified. The phosphorus thus procured is still impure, and is to be melted in hot water, and pressed through porous leather. 276, Properties, Pure phosphorus is of a light flesh-color, and nearly transparent. At common temperatures, ifc is a soft solid, of specific gravity about 2, and may easily be cut with la tnife. At 108 it fuses, and at 554 is converted into vapor, which has a density of 4-326. It is soluble, by the aid of heat, in naphtha, in fixed and volatile oils, and in some other liquids. By the fusion and slow cooling of a considerable quantity, it may be crystalized, and also from its solution in bisulphide of carbon. The crystals belong to the monometric system. It is usually seen in long, slender sticks, of a waxy lustre, which are made by melting the phosphorus under water and pouring it into glass tubes. Phosphorus may be distilled without difficulty. For a small operation, fit a green glass retort to a tube bent, as represented in the figure, and having its- extremity drawn out to a fine point, but not closed. Sepa- rate the retort and tube, and put in the first a small quantity of phosphorus, and in the latter a little water ; and again con- .nect them firmly together. If now the retort is carefully heated, the phosphorus will gradually distil over and collect in the water in the lowest part of the tube. QUESTIONS. What is the effect produced by the charcoal ? 276. De- scribe phosphorus. In what is it soluble ? In what form is it usually ml 244 PHOSPHORUS. Combustion of Phos- Phosphorus is exceedingly inflammable. Exposed to the air, at common temperatures, it undergoes slow combustion, emits a white vapor of a peculiar alliaceous odor, appears distinctly luminous in the dark, and is gradually consumed. On this account, phosphorus should always be kept under water. In the open air, even the heat of the hand, aided by the slightest friction, is sufficient to inflame it ; and it should therefore always be handled with the greatest caution. It burns in the air with a brilliant, yellowish-white light and intense heat; but in oxygen gas, its combustion is particularly splendid. A good method for performing the experiment is to place a piece of phosphorus in a small cup on a stand, a few inches high, in a basin of- water, and, having ignited the phosphorus by touching it with a piece of heated wire, dexterously to place over it a large bell-glass, previously filled with oxygen. By careful Oxygen ' management, but little of the oxygen will be lost. It may also be made to burn under warm water, by forcing a current of oxygen upon it by means of a gas-bottle, or a flexible tube, leading from a gasometer. A red suboxide is formed which readily takes fire in the open air. The red crust which forms upon the surface of pieces of phosphorus exposed to the action of light, is believed to be a peculiar isomeric, or Combustion of Phos- allotpopic (173 ) condition of this substance. It Wate U r 8 * ma ? be obtained, by keeping a quantity of phos, phorus for several hours, at a temperature of 460 to 480, in a gas which does not act upon it, as nitrogen or hydrogen. This red or amorphous phosphorus differs essentially from ordinary phosphorus. Its melting point is about 482, and it is non-luminous in the air at ordinary temperatures. Heated to 500, it changes to ordinary phosphorus. QUESTIONS. How is phosphorus affected in the open air ? How is it usually preserved ? May it be distilled ? What is said of its. com- buation in oxygen gas ? How may it be made to burn under water ? COMPOUNDS OF PHOSPHORUS AND OXYGEN. 245 277. Uses. Phosphorus is now used in large quantities in the manufacture of friction-matches, which ignite by slight friction. For this purpose it is made into a paste, with gum or glue, by which it is made to adhere to small pieces. of wood or paper pre- viously dipped in melted sulphur, and is also protected from the action of the air. The paste is sometimes mixed with nitrate or chlorate of potash, or oxide or nitrate of lead, but this is not necessary. Occasionally, fine emory or powdered glass is mixed in the paste, to increase the friction. Phosphorus is of great service in the laboratory, and has been sometimes used in medicine. Compounds of Phosphorus and Oxygen. 278. There are four compounds of phosphorus and oxygen, the atomic constitution of which appears to Be P 2 0,PO,P0 3 and P0 5 . The last three are acids ; but only one of these, the last, will be specially described. 279. Dinoxide of Phosphorus P 2 0. This compound is prepared by the combustion of phosphorus under hot water, as in paragraph 276. Atmo- spheric air may be substituted for the oxygen. The oxide appears as flocculi of a brick-red color. It absorbs oxygen from the air, and mixed with phosphorus it renders it more combustible. 280. Hypophosphorous Acid PO. May be obtained as a syrupy liquid, but cannot be crystalized. It cannot be obtained separate from water. 281. Phosphorous Acid P0 3 . Phospho- rous acid may be prepared by the action of the air upon sticks of phosphorus, at ordinary temperatures. For this purpose, place a few sticks of phosphorus in a funnel under a bell-glass, as represented in the figure. The glass is supported a little above the table, to allow the air to enter. Reg- nault advises to put the sticks of phosphorus in small glass tubes, having capillary aper- "^- :_=^ tures for the acid to pass through a~s it is Preparation of POs. QUESTIONS. 277. What use is made of phosphorus ? How are friction- matches made ? 278. What compounds of phosphorus and oxygen are there ? 279. How may dinoxide of phosphorus be prepared ? 281. How may phosphorous acid be prepared f 246 COMPOUNDS OF PHOSPHORUS AND OXYGEN. formed, but they are not essential. Too large quantities of phosphorus should not be used at once. 282. Phosphoric Acid P0 5 ; eq., (32 -f 40=) 72. This acid is formed by burning phosphorus in air or in oxygen gas, as in the experiment given above (27,6). To prepare it perfectly anhydrous, the receiver should be placed over mercury, and the oxygen or air supplied should be perfectly dry. The acid appears as a dense white vapor, which is gradually precipitated, and may be collected. In the open air it at once absorbs moisture. If the white flakes are collected and ignited, the mass, after cooling, is semi-transparent, and is called glacial phosphoric acid. This acid may also be formed from calcined bones. To prepare the common acid, a very good mode is to digest phosphorus in nitric acid, with the aid of heat. One part of phosphorus, with 13 parts of the acid, of specific gravity 1-20, is placed in a glass retort which connects with a receiver that is kept cold by a stream of cold water, as shown in the figure, and heat applied. Red fumes of nitrous Preparation of POs. acid are given off, and the phosphorus rapidly consumed. The liquid collected in the receiver is now to be poured back into the retort, and heated until the water and any remaining nitric acid are expelled. On cooling it will become solid, and present the same appearance as glacial phosphoric acid just described. The acid thus obtained contains 1 eq. of water for each eq. of the acid, and is called mono- hydrated acid. The anhydrcfus phosphoric acid has a very strong affinity for water, and when thrown into it, unites with it with great energy, often producing slight explosions, in consequence of the heat pro- QUESTIONS. i82. What is the composition of phosphoric acid ? How is it prepared ? How by the use of nitric acid ? What is said of its compounds with water ? COMPOUNDS OP PHOSPHORUS AND HYDROGEN. 247 duced. With water it forms three different compounds, as fol- lows, the first two of which have been called, respectively, meta- phosphoric, and pyrophosphoric acids. Monohydrated, or metaphosphoric acid, P0 5 ,HO. Bihydrated, or pyrophosphoric acid, P0 5 ,2HO, Trihydrated, or common phosphoric acid, P0 5 ,3HO. These three acids, or rather compounds of acid and water, can- not be distinguished from each other by external appearance, but dissolved in water they manifest chemical characteristics which render them quite distinct; they also form salts, which, though much alike in their general properties, are nevertheless easily dis- tinguished from each other by the proper tests. Compounds of Phosphorus and Hydrogen. There are several compounds of phosphorus and hydrogen, but one only will claim attention from us, the common phosphuretted hydrogen, PH 3 . The o'thers are P 2 H, and PH 2 . 283. Phosphide of Hydrogen PH 3 ; eq., (32 + 3 =) 35. This gaseous substance, called also phosphuretted hydrogen, 13 best prepared by heating some sticks of phosphorus in a strong solution of caustic pot- ash, in a small glass retort, which, at the beginning of the opera- tion, should be quite filled with the mate- rials. If, then, the mouth of the retort is made to dip slightly in i . /. , PIIs spontaneously combustible. a basin of water, each bubble of the gas, as it breaks into the air, will burst into a flame, QUESTIONS. 283. What phosphide of hydrogen is mentioned is it prepared ? How 248 COMPOUNDS OF PHOSPHORUS AND HYDROGEN. with the formation of beautiful wreaths of smoke of phosphoric acid, as shown in the figure. In the presence of potash phosphorus has the property of decomposing water, especially if the temperature be raised ; the oxygen and the hydrogen both combining with separate portions of the phosphorus, producing the teroxide of phosphorus (phos- phorous acid) and the terphosphide of hydrogen. Thus, 2P + 3EO + KO = KO,P0 3 + PH 3 . Instead of potash, milk of lime may be used with the same result. Still another method of procuring it is to decompose phosphide of calcium by water, or dilute hydrochloric acid ; but when this acid is used, the gas which is given off is not spon- taneously inflammable. It seemsi to be very well determined that the spontaneous combustion of this gas, in certain cases, is owing to the presence of the vapor of another phosphide of hydrogen con- taining proportionally more phosphorus, which may be separated by passing the gas through a PH 3 gpontane- tube surrounded by a freezing mixture. Q ther com b us tible gases, as hydrogen, are made to inflame spontaneously by receiving a portion of the vapor of this inflammable phosphide. To prepare phosphide of calcium, select a tube of green glass, half an inch in diameter and a foot long ; seal one end hermetically, and bend it a little, as represented in the figure. In the sealed end put some pieces "lam of phosphorus, and^ then, holding the T%& straight part in a horizontal position, ... , n , . introduce some lumps of well burned Preparation of Phosplnde of Calcmm. Ume . g combusti- next to be heated to redness by means of burning charcoal, when heat is also to be applied to the phosphorus sufficient to volatilize it; and the Vapor coming in contact with the heated lime, at once unites with it to form the phosphide of calcium. This should be preserved in bottles with close stoppers ; but even then it gradually undergoes decomposition. Terphosphide of hydrogen is a colorless gas, with a very disagreeable QUESTIONS. Describe some of the properties of phosphide of hydrogen, To what is its spontaneous combustion owing ? OTHER COMPOUNDS OP PHOSPHORUS. 249 odor,* and is irrespirable ; 100 cubic inches of it weigh 36-75 grains, giving it a specific gravity of 1-18. 1 vol. of phosphorus vapor weighs 4-326 6 vols. of hydrogen weigh (-069 X 6) -414 Forming 4 vols. of the terphosphide, 4-740 One volume therefore weighs, or the density of the gas is, 1-186 Other Compounds of Phosphorus. Phosphide of Nitrogen, N 2 P, is a white solid, which is infusible even at a red heat. 284. Chlorides of Phosphorus. There are two chlorides of phosphorus, PC1 3 , and PC1 6 , corresponding in composition to phosphorous and phos- phoric acids. The Terchloride of Phosphorus is formed in the same manner, and by using the same apparatus, as chloride of sulphur (266). The chlorine Preparation of PCR is formed in the flask A, and after being washed in water and dried in the chlorine of calcium tube, is brought in contact with the vapor of phos- * Those who have observed the odor of this gas, and that of the liquid emitted by the American skunk (Mephitis Americana) when disturbed, cannot but have noticed the resemblance between them; which seems to render it probable that the fluid emitted by the skunk contains, in solution, a portion of the gas, or some other nearly-related com- pounds of the same substances. This is rendered still more probable from the fact, that the fluid, when emitted by the animal in the dark, is distinctly phosphorescent. Set Godman's Natural History, vol. 1. 289 : Philadelphia Edition, 1829. QUESTION. 284. What chlorides of phosphorus are mentioned? 250 ARSE NIC. phorus in the retort, D, where the chloride is formed, and afterwards con densed in the receiver E, which is kept cool by a stream of cold water It is a colorless liquid, of a density of l-45j which boils at about 172. 285. Percbloride of Phosphorus is formed by saturating the preceding with chlorine. It is a solid, having its point of fusion, and also its boil- ing point, at about 298. Bromine and sulphur combine readily with phosphorus, but the compounds are not important. Iodide of Phosphorus is formed by bringing the two sub- stances together in a vessel where as little air may have admission as possible. It forms a dark-colored mass. These two substances afford one of the few instances in which reaction takes place between two solids. Let a few crystals of iodine be dropped into a wine-glass, upon a small piece of phosphorus, and immediately place over it a bell-glass. By the heat produced, the phosphorus will be inflamed and a portion of the iodine sublimed ; and the white cloud of phosphoric acid (152), mingling with the dense iodine vapor, presents to the eye a very pleasing appearance. Prep, of Iodide of Phosphorus. ARSENIC. Symbol, As; Equivalent, 75; Density, 5-88. * 286. History and Preparation. Arsenic has very generally been Classed with the metals, chiefly on account of its metallic lustre, and comparatively high specific gravity; but, in its chemical properties, it is much more closely allied to the metal- loids, with which it is here classed. Arsenic sometimes occurs native, but usually it is found in com- bination with the metals, and especially with iron and cobalt. The substance itself, or some of its compounds, seems to have been known from the earliest times. It may readily be prepared by "heating the mineral called mis- pickel, which is a natural compound of arsenic, sulphur and iron, in close vessels, by which the arsenic is expelled and the sulphide QUESTIONS. 285. How is iodide of phosphorus prepared ? What is said of the action of iodine and phosphorus upon each other ? 286. Why has arsenft often been classed with the metals ? Why is it here classed with the metalloids ? With what is it usually found combined ? COMPOUNDS OP ARSENIC AND OXYGEN. 251 of iron remains. By again heating it with black-flux, the arsenic is obtained nearly pure. If the pulverized mineral is well mixed with black-flux at the beginning, and no air admitted into the apparatus, a single operation will afford it in great purity. Let a common Hessian crucible be half filled with the mixture, and then place ano.ther crucible, a size smaller, in an inverted position above it, as shown in the figure, carefully luting them at their junction. A moderate heat should then be applied to the lower crucible and very gradually raised. The arsenic will be sublimed from the mixture and condensed in small crystals in the inverted crucible, which should have a very small aperture in the bottom, to allow the air to escape as the heat is raised. 287. Properties. Arsenic is a brittle substance, of a dark color, and feeble metallic lustre. Heated to about 356, it is sublimed, without first melting, as is the case with most solids. Its vapor has a strong garlic odor, by which its presence may be recognised, and a density of 10-37. Heated in the open air, it readily takes fire and burns with a livid flame. Arsenic is often sold under the very improper names of cobalt and fly -powder. Compounds of Arsenic and Oxygen. 288. Two compounds only of arsenic and oxygen are known, both of which are acids, and in composition correspond to phos- phorous and phosphoric acids. 289. Arsenious Acid As0 3 ; eq., (75 + 3 x 8 =) 99. This compound is the arsenic, or rats' bane, of commerce, well known as a destructive poison. It is always produced when arsenic or its ores are heated in the open air. It is usually sold in a state QUESTIONS. How may arsenic be separated from its compounds? 287. Describe arsenic. What is said of its odor? 288. What com- pounds of arsenic and oxygen are known ? 289. By what names is arsenious acid often known. 252 COMPOUNDS OF ARSENIC AND HYDROGEN. of fine white powder ; but when first sublimed, it is in the form of brittle masses, more or less transparent, colorless, of a vitreous lustre, and conchoidal fracture. This glass, which may also be obtained by fusion, gradually becomes opaque without undergoing any apparent change of constitution, but becomes more soluble in water than before. Its specific gravity is 3-7. At 880 it is volatilized, yielding vapors which do not possess the odor of garlic, and which condense unchanged on cold surfaces. If thrown on burning charcoal, the garlic odor is perceived, because of the reduction of the oxide by the carbon. Destructive as this substance is to the animal system, in minute doses it is sometimes used in medical practice; and in some countries, as in parts of Austria and Hungary, it is habitually used much in the same manner as narcotics, and even administered to horses. The effect is said to be to give a roundness and fulness of form, and clearness and freshness to the complexion. Horses accustomed to receive it in their food, have a fat and plump appearance, and bright and glossy skins. It also improves their breathing. This substance is so frequently used to destroy life, that its detection Ji suspicious cases becomes an important object; but we reserve our remarks on this point until some others of the many compounds of arsenic have been described 290. Arsenic Acid As0 6 ; eq., (75 -f 8 x 5 =) 115. This acid may be formed by dissolving arsenious acid, just described, in nitric acid mixed with a little of the hydrochloric, and evaporating to dryness. It is a powerful acid, much resembling phosphoric acid (247) ; with which it is isomorphous. Its salts are also isomorphous with the salts of phosphoric acid. Compounds of Arsenic and Hydrogen. 291. Two compounds of these elements are known, one of which is solid, and the other gaseous. Of the former, little is known, with cer- tainty, and we therefore do not further allude to it. 292. Arsenido of Hydrogen, Arseniuretted Hydrogen AsH 3 ; eq., (75 _j_ 3 ) 78. This gas is evolved when arsenide of tin or zinc is treated with strong hydrochloric acid, or when sulphuric or hydrochloric acid is made to act upon zinc or iron in the presence of any soluble com- pound of arsenic. To prepare it, pour upon some pieces of zinc diluted sulphuric acid with a few drops of solution of arsenious acid ; the gas, which burns with. a feeble blue flame,,will be at once rapidly evolved. QUESTIONS. Describe arsenious acid. For what purpose is it often used ? 290. To what other acid is arsenic acid analogous ? 292. How is arsenide of hydrogen prepared ? COMPOUNDS OP ARSENIC WITH SULPHUR, *ETC. 253 When thus prepared, the reactions are as indicated in the following formula, the zinc being oxydized at the expense of the oxygen both of the water and the arsenious acid. Thus, ' 6Zn -f 3 HO -f As0 3 -f 6S0 3 = 6 (ZnO,S0 3 ) -f AsH 3 . The gns has a peculiar nauseating odor, and is exceedingly poisonous- Its density is 2-69, and by a cold of 22 it is converted into a liquid under the ordinary atmospheric pressure. By chlorine it is instantly decomposed, chloride of arsenic and hydrochloric acid being formed. By solution of blue vitriol it is rapidly absorbed, and arsenide of copper precipitated. The equivalent "of this gas, AsH 3 , answers to 4 vols., which is thus constituted: 1 vol. of arsenic vapor weighs 10-370 6 " hydrogen " -414 4 vols. arsenide of hydrogen, 10-784 Weight of one vol., or the calculated density of the gas, 2-696. We shall have occasion to speak of this compound again in connection with the detection of arsenic. Compounds of Arsenic with Sulphur and Other Elements. 293. Sulphides of Arsenic. The bisulphide of arsenic, AS 2 , is found native, and called realgar by mineralogists. It may also be fonned by art. It is of a dull red color. The tersulphide, AsS 3 , is the orpiment, or king's yellow of commerce. It is formed artificially by passing a cur- rent of hydrosulphurio acid through an arsenic solution containing a little free acid. It is also found as a natural production, and is of a bright yellow color, and is sometimes called sulpharsenious add. A third compound of these elements, the pentasulphide of arsenic, AsS 5 , called also sulpharsenic acid, is formed by mixing solutions of hydrosulphuric and arsenic acids. It forms slowly, and some days are often required before the whole is precipitated. The compounds of arsenic with chlorine, iodine, phosphorus, &c., will be found described in larger works. QUESTIONS. Describe the reactions which take place in the prepara- tion of arsenide of hydrogen. What are some of the properties of this ' gas ? 293. What is realgar f What is orpimenl? 22 254 DETECTION OP ARSENIC. Detection of Arsenic. 294. Poisoning by arsenious acid is at the present day, .unfor- tunately, very common; and it therefore becomes a matter of special importance to be able with certainty to detect the instru- ment of death. 295. There are as many as ten or twelve different tests for arsenic, but we shall confine our remarks to some of the most important. A single test should never be relied on, but several different ones should always be applied to separate por- tions of the suspected substance. I. Marsh's Test. Put into a two or four ounce vial some pieces of clean zinc, and pour on them a small quantity of dilute oil of vitriol (oil of vitriol 1 part, and water 8 parts), and insert a cork with a small tube, as shown in the figur*e. Very soon hydrogen gas will begin to be evolved, as in the prepara- tion of hydrogen. After a little time the jet of hydrogen may be inflamed ; and if all the materials used were pure, a piece of glass or porcelain held in the flame will receive no stain, but only a deposition of moisture from the com- bustion of the hydrogen. The cork and tube being now removed, introduce some of the suspected substance, or water in which the suspected substance has been digested, with the aid of heat if ueces- Marsh's Test, sary, and immediately replace the cork and tube. In a little time the jet of gas may be relighted ; and if any appre- ciable quantity of arsenious acid is present, a piece of clean glass or porcelain held in the flame will at once receive a black stain upon its surface, caused by a deposition of arsenic. If the quantity of arsenious acid present is large, the flame will be of a pale color, and the blackening of the glass held in the flame will be instantaneous ; but if the quantity be small, the blackening effect will be produced only after a little time. The deposition of arsenic here is from the arsenide of hydrogen, which is formed in the manner heretofore (292) explained. The cold substance held in the flame causes the deposition of the arsenic while the hydrogen is consumed. This is perhaps the most delicate test of arsenic known, but in using it some precautions must always be observed to avoid mistake. In some cases, where organic substances are present, spots similar to those pro- duced by arsenic may be formed, that may be mistaken for arsenic by QUESTIONS. 295. What is said of the number of tests for arsenic? Describe Marsh's test. From what is the arsenic deposited? What is Baid of the delicacy of this test ? DETECTION OF ARSENIC. 255 the inexperienced ; and antimony will form spots very much lite those of arsenic. Means must therefore be adopted to test the material form- ing the dark spot upon the porcelain. For this purpose, it will generally be sufficient to hold the spot a few minutes in the flame of a spirit-lamp ; if the deposite be arsenic it will be volatilized, and disappear, but if pro- duced by antimony or other substances, it will remain. So also arsenic spots, exposed a few minutes, at a moderately elevated temperature, to vapor of iodine, become yellow, and then subsequently disappear by exposure to the air. II. Reinch's Test. In a portion of the suspected liquid, made acid by hydrochloric acid, place a piece of metallic copper, previously filed per- fectly bright, and heat the whole nearly to the boiling point. If any appreciable quantity of arsenious acid be present, the arsenic will be deposited upon it as a gray crust of a metallic lustre. III. Test by Hydrosulphuric Acid. Through a portion of the sus- pected substance, supposed to be in the liquid form, acidulated with muriatic acid, pass a current of hydrosul- phuric acid gas for half an hour, and then boil it a few moments ; if arsenic be pre- sent, a yellow precipitate orpiment (293) will be formed. The mode of passing the current of gas through the liquid will be seen by the accompanying figure. The materials for producing the gas are put into a flask, and a tube, bent twice at right angles, is inserted through a cork, so as to be air-tight ; the other end is then immersed in the liquid, contained in a glass vessel, so Test by Hydrosulphuric Acid, as to reach near the bottom, and the gas, as it escapes, bubbles through the liquid. The mode is the same as before described (263). The precipitate (orpiment) thus formed, is entirely soluble in aqua ammoniae, and in solutions of the alkalies. IV. Test by Ammonia-Nitrate of Silver. Nitrate of silver forms with arsenious acid solutions a precipitate of arsenide of silver, which is of a peculiar canary yellow color, and is soluble in nitric acid. To ensure the formation of this precipitate, the arsenious solution should be Ilightly alkaline, and therefore the ammonia-nitrate of silver is used in preference to the simple nitrate. This is prepared 'by pouring into the nitrate of silver solution aqua ammonia, until the precipitate at first thrown down is nearly all dissolved. A precipitate very similar in its appearance to the above would be produced 'by phosphoric acid in the suspected liquid ; so that the pre- cipitate formed by use of this test should always be further examined, before any reliance is placed upon it. V. Test by Ammonia-Sulphate of Copper. Solution of sulphate of cop- per produces in neutral or alkaline solutions of arsenious compounds a beautiful green precipitate, sometimes called Scheele's green. In making QUESTIONS. Describe Reinch's test. Describe the test with hydro- sulphuric acid. Describe the test with ammonia-nitrate of silver. Describe the mode of Jesting with ammonia-sulphate of copper. What will be the color of the precipitate ? 256 DETECTION OP ARSENIC. the experiment, it is best to use the ammonia-sulphate of copper, which is prepared by pouring into a solution of blue vitriol, aqua ammonise, until the precipitate at first formed is nearly all redissolved, as in the corresponding preparation of ammonia-nitrate of silver. But this test also may form with other substances a precipitate similar in appearance to the above, so that further examination should always be made. VI. Flandin and Danger's Test. Dry the suspected substance (sup- posed to be organic, as sugar or starch,) and treat it with one-fourth of its weight of the strongest oil of vitriol, and apply heat until it is quite dry ; the whole will now be reduced to a black, friable mass, which can easily be pulverized, and is then to be boiled with strong nitric mixed with a little hydrochloric acid. By 1&is process the arsenic, in whatever form it may be,, is converted into arsenic acid, which after the whole has been again evaporated to dryness, to expel any remaining nitric acid, nnd redissolved in pure water, may be examined by the appropriate tests, not for arsenious but for arsenic acid. For this latter purpose, the ammonia-nitrate of silver may be used, which gives with arsenic acid a brick-red precipitate. Or, the arsenic acid being obtained in solution, may be precipitated as arseniate of lime by lime-water, and from this precipitate pure. arsenic with its metallic lustre may be obtained by the process next to be described. VII. Keduction of the Arsenic. "When arsenic is present in any appre- ciable quantity, it may always be obtained in a separate state, so as to be recognised by its peculiar metallic lustre and garlic odor ; and no chemist in any particular case will positively swear to its presence unless he is able thus to procure it ! For this purpose, provide a tube of hard glass, a quarter of an inch in diameter and three or four inches long, with one end hermetically sealed; and fill it to the depth of half an inch with a mixture of the suspected substance, charcoal, and carbonate of soda, the whole being previously well dried at a moderate heat, and ground together to a fine powder. After wiping the inside of thfe tube with a little cotton attached to a wire, to remove any dust, or remaining moisture, a strong heat is applied to the end of the tube containing the mixture, by whiclrthe arsenic will be separated, to be again condensed upon the sides of the tube a little above the heated part. The bright metallic lustre will at once be recognised, and by breaking the tube and heating the part coated, as in the figure, the peculiar garlic odor will be perceived. Other . tests may also be applied to it if desired. This last test may be applied to any of the precipitates obtained by the previous tests. QUESTIONS. Describe Flandin and Danger's test. Describe the mode of testing by reduction of the arsenic. How does the arsenic show itself? May the last mode be applied to the precipitates obtained by the other modes ? CARBON. 257 296. In these directions we are supposed, as a general thing, to be operating with pure ai*senical solutions, but in cases of actual poisoning it will usually be otherwise ; and it often becomes an important object to be able to separate the organic matter contained in the suspected sub- stance. Sometimes the substance will be soluble, as sugar, which will not interfere badly with the operation ; and at others it will be of such a character that it can be removed by passing through it a current of chlorine, or it may be that it can be removed only by heating it with strong oil of vitriol, as heretofore (VI.) described. In any particular ease, the mode of proceeding to be pursued must be adapted to its peculiar circumstances. GROUP V. CARBON J Combustible bodies, and incapable of being volatilized even BORON* N at the hi S hest temperatures. CARBON. Symbol, Cj Equivalent, 6j Density (crystdlizecT), 3 "52. 297. History. Carbon, though rarely met with in nature per- fectly pure and uncombined, is one of the most important of the elements, forming, as it does, an essential ingredient of nearly all vegetable and animal bodies. It is found in a variety of forms j and when uncry^talized and uncombined, its color is always bla.ek. 298. Preparation and Properties. Carbon presents itself to us in a variety of forms, as the diamond, graphite or plum~bayo t mineral coal, charcoal, gas coal, and perhaps we may add lamp- black, though the latter very probably differs from charcoal only in being in a state of fine division. QUESTIONS. 296. In these directions what are we supposed to operate with ? Will this usually be the case in practice ? Will it often be neces-' eary to separate organic matters from the suspected substance ? What elements constitute the fifth group? How are they characterized? 297. Give the history of carbon. 298. What are some of the varieties of carbon ? 22* 258 C A U BON. The diamond is pure crystal ized carbon, and is the hardest substance known in nature. The crystals are of the form of the regular octahedron, but the faces are frequently a little convex, as shown in the figure. Such crys- tals, properly set, are used for cutting glass, a pur- pose for which they are admirably adapted. Heated intensely in the flame of the compound blowpipe, the diamond is entirely consumed, forming carboni acid, just as if the same weight of pure charcoal had been con- eumed. Diamonds are generally very small, the largest ever found weighing less than six ounces. A single diamond has been sold for ; more than half a million of dollars. It is generally found in the same situations as gold and platiaum. A few crys^- tals of little value have been discovered in the vicinity of the gold mines in some of the Soutliern States. It is a powerful refractor of light, and seems to have the faculty of absorbing light, and giving it *out again after a 'time. A diamond held in the sun's rays a. few seconds, and then removed at once to a dark room, phosphoresces very distinctly for a few seconds. Graphite, or plumbago, called also, very improperly, black lead, is a variety of carbon, containing usually a little iron. It is often found crystalized in thin scales" of a hexagonal form. It is not unfrequently formed as an artificial production in iron fur- naces, and is sometimes quite free from iron. It is used for the manufacture of pencils, and in the con- struction of crucibles that are to be exposed to a very intense heat. For this purpose, it is ground to a fine powder, and mixed thoroughly with fire-clay. These crucibles are used chiefly for melting metals. Mineral coal is of two kinds.; the bituminous, and the non- bituminous, or anthracite. Bituminous coal is distinguished by its softening, like wax, when heated, and giving on much gas, which burns with flame.' QUESTIONS. What is the diamond ? What is said of its hardness ? What use is made of it-? What is the effect of the intense heat of the compound blowpipe upon it? What is said of the size of diamonds? What is said of the absorption of light by the diamond ? What is graphite or plumbago ? What use is made of it ? What two kinds of mineral coal are there? How is bituminous coal distinguished ? CARBON. 259 It is also much lighter than anthracite, and more easily ignited. Some of the different varieties of bituminous coal are caking, splint, cherry, and cannel coal. Jet, also, which is used in jewelry, is a bituminous coal ; and in the same family may be included wood or Bovcy coal, sometimes called lignite. ' Anthracite, or stone-coal, differs from the above varieties, in containing no bituminous matter; and, therefore, it yields no inflammable gas by heat. Its sole combustible ingredient is carbon ; and, consequently, it burns without flame. It is found in different countries, but nowhere in such profuse abundance as in the eastern part of the State of Pennsylvania, which supplies most of the northern and eastern parts of the United States with fuel. All the varieties of mineral coal are believed to nave been formed from vegetable substances, which, in the changes the earth's surface has undergone, have become buried beneath it. When bituminous coal is subjected to a high temperature in close vessels,*or with only a limited supply of atmospheric air, the volatile or bituminous manner is expelled, and the remaining porous carbon is called coke. It is used for many important purposes in the arts. Charcoal is prepared by exposing vegetable matter, and espe- cially wood, to a high temperature in close* vessels, or in such circumstances as to avoid the presence of atmospheric air. By the heat a large quantity of water* acetic acid, tar, and other matters, is expelled, and the carbon, with any mineral matter which has been absorbed from the soil, remains. The latter con- stitutes the ashes which remain after the combustion of the coal in the open air. The ueual method of preparing charcoal for ordinary purposes, is to ignite large heaps of wood, which are covered with earth so as to admit only a limited supply of atmospheric air; and the result is to char or convert into coal a large part of the wood, by the heat occasioned by the combustion of the other part. QUESTIONS. What is said of anthracite or stone-coal? Where is it found in this country? What is coke? How is charcoal prepared? What constitutes the ashes ? 260 CARBON. The figure, diminished from Knapp's Technology, represents a section of a coal-pit ready to be ignited. The stake at the centre ^- ' : Preparation of Charcoal serves as a support for beginning the heap ; and by one side of wh^ch space is left to kindle the fire, by dropping in pieces of very dry wood and burning coals. Charcoal is a black, hard, brittle substance, perfectly insoluble in every liquid, but attacked and oxidized by strong nitric acid. It is a good conductor of electricity, but-a non-conductor of heat ; is little acted upon by air and moisture, and is perfectly infusible in the most intense heat that can be applied to it. Heated in the open air, it takes fire and burns freely, especially if in large masses, leaving only a small residue of ashes. 299. Charcoal possesses the property of absorbing a large quantity of air, or other gases, at common temperatures, and of yielding the greater part of them again when it is heated. Recently-burned charcoal absorbs air and moisture so rapidly, for a few days, as materially to increase its weight. Both are absorbed and retained with.such force, that a red heat is required to expel them. This absorption of air may be readily shown in the fol- lowing manner : Let a piece of charcoal, of moderate size, be heated to redness for a few minutes, and then quenched under QUESTIONS. Describe charcoal. 299. What is said of the absorption of gases by charcoal ? How may the absorption of air bo shown ? CARBON. 261 mercury, and placed under a receiver, over the mercurial cistern. The mercury will shortly begin to rise, in consequence, of the absorption of the air within ; and the process will continue for several hours. Charcoal, likewise, absorbs the odoriferous and coloring particles of most animal and vegetable substances. When colored infusions of this kind are digested with a proper quantity of charcoal, a solution is obtained which is nearly, if not quite, colorless. Tainted flesh may be deprived of its odor by this means, and foul water be purified by filtration through charcoal. The sub- stance commonly employed to decolorize fluids is animal charcoal reduced to a fine powder. It loses the property of ^absorbing coloring matters by use, but partially recovers it by being heated to redness. At very high temperatures charcoal has a higher affinity for oxygen than any other substance, and is therefore often heated with oxides of the metals to deoxidize them, or deprive them of their oxygen. Lampblack is minutely divided carbon, prepared by burning rosin or tar in a confined portion of air, so that the hydrogen only of the material is consumed, and the carbon remains as an exceedingly fine powder. It is used as a pigment, and for other purposes. Gas coal -is a deposite of nearly pure carbon upon the inside of the large retorts used in the manufacture of illuminating gas. It is very hard and black, and a good conductor of electricity. Uses. Carbon is used as fuel; in forming gunpowder; as' a pigment) in the formation of steel; as a* polishing-powder ; and in medicine as an antiseptic, &c., &c. QUESTIONS. What is said of the affinity of charcoal for oxygen at high temperatures ? What is lampblack ? What use is made of it ? What is gas coal ? 262 COMPOUNDS OP CARBON AND OXYGEN. Compounds of Carbon and Oxygen. 300. Carbon combines with oxygen in two proportions, form- ing carbonic oxide, CO, and carbonic acid, C0 2 . 301. Carbonic Oxide, Protoxide of Carbon CO; eq., (6 + 8=-) 14. This is a gaseous substance, and is best prepared by heating a mixture of equal parts of dry powdered chalk and iron-filings in a gun-barrel. The chalk, which is carbonate of lime, when heated, gives off its carbonic acid (the compound next to be described) in contact with the heated iron, by which one-half of its oxygen is instantly absorbed, and the carbonic oxide thus produced passes on, and may be collected over water. Thus, CaO,C0 2 -f Fe = CaO -f FeO -f CO. Another method of preparing it, is to heat gently a mixture of oxalic acid and five or six times its weight of oil of vitriol, by which both car- bonic oxide and carbonic acid are produced in equal volumes ; but the Preparation of CO. latter may readily be separated by passing it through a solution of caustic potash or milk of lime, in the three-necked bottle, and collected over water. The changes which take place are as follows, viz : C 2 3 ,3HO + S0 3 ,HO = S0 3 ,4HO -f C0 2 -f CO. The density of the gas is about 0-97; 100 cubic inches weighing 30-20 grains. It is highly combustible, and burns with a beautiful blue flame. QUESTIONS. SOO.^What compounds of carbon and oxygen are there? 301. Describe the mode first mentioned for preparing carbonic oxide. The second mode. Is carbonic oxide combustible ? What is the color of the flame ? / COMPOUNDS OF CARBON AND OXYGEN. 263 It will not support respiration or combustion ; and a lighted candle being immersed in it, as heretofore described in connection with hydrogen (198), is in- stantly extinguished. It is this gas which gives the blue flame seen about the fire of the blacksmith, and in anthracite stoves, when the door is suddenly opened soon after the fire has been kindled, and in furnaces for the reduction of the metals from their ores. Carbonic oxide is believed to be composed of 1 vol. of carbon vapor and 1 vol. of oxygen combined with- out condensation. ' Thus, 1 vol. of carbon vapor weighs -836 1 vol. of oxygen " 1-106 2 vols. of carbonic oxide " 1 vol. of the oxide therefore " 1-942 971 CO is Combustible. 302. Carbonic Acid C0 2 ; eq., (6 + 16 =) 22. Carbonic acid is remarkable as being the first gaseous substance recognise'd, after atmospheric air, which must always have been known. It was first described by Dr. Black, in 1757, and called, by him, fixed air, because he found it fixed in common limestone and magnesia; from which it may be expelled by heat, or by the action of any strong acid. It may be collected over water, but a por- tion will be absorbed. A gas-bottle,, of the form shown in the figure, is con- venient for preparing it. Some frag- ments of marble, and water, are placed in the bottle, and the cover put on, Preparation of co. and then strong hydrochloric acid is poured into, the long-necked funnel. As thus prepared, carbonic acid is a colorless, inodorous gas, of specific gravity 1-52; 100 cubic inches weighing 47-14 grains. It is considered a compound of 1 vol. of carbon vapor and 2 vols. of oxygen condensed to 2 vols. Thus, QUESTIONS. 302. When was carbonic acid discovered ? What was it first caUed? How may it be prepared ? What is its specific gravity? What is it composed of? 264 COMPOUNDS OF CARBON AND OXYOElf. 1 vol. of carbon vapor weighs *836 2 vols. of oxygen. " (1-106 X 2) 2-212 2 vols. of carbonic acid " 3-048 The weight of 1 vol. therefore is 1-524 Or we may consider it a compound of 2 vols. of carbonic oxide and 1 vol. of oxygen, condensed to 2 vols., as follows : 2 vols. of carbonic oxide weigh (-971 X 2) 1-942 1 vol. of oxygen " 1-106 Giving for the weight of 2 vols. of C0 2 , 3 -048 And for the weight of 1 vol., as before, 1-524 Carbonic acid is so much heavier than atmospheric air, that it may be poured from one vessel to another without difficulty. Let a bottle, with a wide mouth, be filled with the gas, and then plunge into it a piece of lighted paper, or other substance, so that some smoke may be mixed with it and render its motions visible. Then hold the bottle in the hand, as if pouring a liquid from it (as represented in the figure), and the motion of the gas, as it is emptied from it, will be made apparent to the eye. Another instructive experiment of the same character may be performed as follows : Provide a glass jar with a large mouth, and place at the bottom a lighted taper, as shown in the figure. Then having filled another jar of about equal capacity with carbonic acid gas, carefully re- move the cover and gradually pour the Contents into the first- Candle Extinguished, mentioned jar; the flame of the taper will first be considerably disturbed by the motion occa- sioned by the descending gas, and will finally be extinguished. QUESTIONS. How may the high specific gravity of carbonic acid be shown by pouring it from a vessel ? How may the flame of a candle be extinguished by it ? C0 a poured from a Vial. COMPOUNDS OF CARBON AND OXYGEN. 265 By a pressure of 36 atmospheres, at 32, it is converted into a beautiful transparent liquid, which may be frozen by intense cold, in the manner already explained. 303. It is capable of supporting neither combustion nor respira- tion; a burning candle plunged into it is instantly extinguished ; - and a living animal, thrown into a vessel containing it, even though considerably diluted with air, soon dies. Carbonic acid is always produced by ordinary combustion j and lives have often been lost by persons placing an open dish of burning charcoal in their bed-rooms before retiring to rest. The oxygen of the air in the room is taken up by the carbon, and the gas in question takes its place, producing the effects described. It is produced, also, by the decay of animal and vegetable substances,' and sometimes is found collected in caves and wells, and is called choke-damp. Though this gas does not support com- bustion, as the experiment is ordinarily made, yet potassium, sodium, and some other of the metals may be made to burn in it. For this purpose, fill a flask with dry carbonic acid gas, and drop into it a small piece of potassium, and apply the heat of a lamp at the point where the metal lies, by means of a blowpipe. When it has become very hot the metal takes fire and burns brilliantly, the carbon of the carbonic acid decomposed being deposited upon it as a black powder. Combustion of Potassium iu COa. 304. Soda-fountains are formed by compressing a large quantity of this gas in water, contained in a strong vessel adapted to the purpose. When the tube leading from the fountain is opened, the water "is forced out by the pressure, and effervesces violently by the escape of the gas. Soda-powders, &c., often used to pro- duce an agreeable drink, in the absence of a soda-fountain, consist of -bicarbonate of soda and tartaric acid, which, when mingled QVESTIONS. May carbonic acid be compressed to the liquid form? 303. Is it always produced in ordinary combustion ? How may potas- sium bo made to burn in it ? What becomes of the carbon of the carbonio acid ? 304. How are soda-fountains formed ? 23 266 COMPOUNDS OP. CARBON AND HYDROGEN. together in solution, produce, by chemical action, tartrate of soda, the carbonic acid passing off into the air with effervescence. So, also, the effervescence which takes place on opening a bottle of beer, cider, or champagne wine, is owing to the escape of this gas, which has been produced by the fermentation of the liquid. All kinds of spring and well-water contain, it in small quantity, and become insipid to the taste by boiling, in consequence of the gas having been expelled. It is also always present in the atmo- sphere, and in some cases accumulates in considerable quantities, as at the Grotto del Cane, in Italy, through which a man may pass without danger, but a dog on entering it is instantly suffo- cated. The carbonic acid here constantly issues from the earth, and accumulates at the bottom, while the air above remains com- paratively pure. 305. Lime-water is an excellent test for carbonic acid; and a vessel of it being al- lowed to stand a few hours, becomes coated with a pellicle of carbonate of lime, by ab- sorbing t this gas from the air. So lime-water becomes milky by blowing into it with a tube from the lungs, for the same reason. A por- tion of the lime is changed into carbonate of lime, which is insoluble, and gives the water its milkiness. Blowing through Lime-water. Compounds of Carbon and Hydrogen. 306. Carbon and hydrogen combine in a number of different proportions, producing compounds, several of which are of special interest, because of their isomeric character; but we shall here describe only two, both of which are gaseous, viz., light carbu- retted hydrogen, C 2 H 4 , and olefiant gas, C 4 H 4 . QUESTIONS. What is said of the Grotto del Cane in Italy ? 305. How is lime-water affected by blowing through it with the mouth? Give the reason for the milkiness produced ? 300. What is said of the com- pounds of carbon and hydrogen ? COMPOUNDS OP CARBON AND HYDROGEN. 267 807. Light Carburetted Hydrogen C 2 H 4 ; eq., (12 + 4=) 16. This gas, called also fire-damp, marsh gas, hydrocarburet, and dicarburet of hydrogen, is formed by the slow decomposition of wood, and woody substances, under water,' especially in warm weather; and may be obtained by stirring the mud and other mattery at the bot- tom of stagnant pools (see figure), and collecting the bubbles of gas in Collecting Marsh Gas. a receiver, as they rise. It some- times accumulates in large quantities in coal mines, where it is formed by the action of water upon the coal. It is best s prepared by heating in a flask, made of hard glass, a mixture of 2 parts of acetate of soda, 3 parts of caustic potash, and 3 of quick-lime. The composition of the acetic acid is C 4 H 4 4 , which, it will be perceived, is precisely equal to 2 eq. of carbonic acid, and 1 of the hydrocarburet in question. Thus, The use of the lime is to protect the gas from the action of the potash. Light carburetted hydrogen is a colorless, transparent gas, 100 cubic inches of which weigh 17*37 grains, giving it a specific gravity of 0-56. One volume contains 2 vols,. of hydrogen, J of a vol. of carbon vapor. Thus, 2 vols. of hydrogen weigh (-069 x 2) -138 \ vol. vapor of carbon ( - 1L 6 ) -418 - . 1 vol. of the hydrocarburet, -556 A burning, candle is extinguished by it, but it is, itself, highly combustible, and burns with a feeble, yellow flame. Mixed with twice its own volume of oxygen, or seven or eight times its volume QUESTIONS'. 307. In what situations is light carburetted hydrogen naturally formed? How may it be collected? How may it be prepared artificially ? 268 COMPOUNDS OF CARBON AND HYDROGEN. of air, it explodes violently by the electric spark, or on the ap- proach of flame. 308. defiant Gas, or Heavy Carburetted Hydrogen C 4 H<; eq., (24 + 4=) 28. This gas was first described in 1796, by some Dutch chemists, who gave it the name, defiant gas, because of its forming with chlorine a peculiar oil-like liquid. It is color- less and tasteless, and but slightly absorbed by water; 100 cubic inches weigh 3041 grains, so that its density is 0-98. Its volume contains 2 vols. of hydrogen, and 1 vol. of vapor of carbon, as follows : 2 vols. of hydrogen weigh (-069 x 2) -138 1 vol. of vapor of carbon, -830 Giving for 1 vol. of olefiant gas, -974 Olefiant gas is prepared by mixing, in a capacious retort, one part of alcohol with four of concentrated sulphuric acid, and heating the mixture, as soon as it is made, by means of a lamp or ignited charcoal. The acid soon acts upon the alcohol, effer- vescence ensues, and olefiant gas passes over, mixed with other substances, chiefly sulphurous acid, from which it may be purified Preparation of Olefiant Gas. by washing it with solution of lime or caustic potassa in several of Woulf s bottles, as shown in the figure. As might be expected, olefiant gas does not support com- bustion ; but a jet of it burns in the air, or in oxygen gas, with a QUESTIONS. Does light carburetted hydrogen form explosive mixtures with oxygen or atmospheric air ? 308. By whom was olefiant gas dis- covered? Why was it so called? Describe it. How is it prepared? What is said of the light produced by its combustion ? COMPOUNDS OF CARBON AND HYDROGEN. 269 brilliant white light. Mixed with oxygen, or air, in proper pro- portions, it explodes violently, like the preceding compound. 309, liluminating Gas is usually a mixture of olefiant and light carburetted hydrogen gases, and is formed by distilling, in large cast-iron retorts, rosin, tar, or other resinous or oily sub- stances, or bituminous coal. Besides the gases mentioned, there are also formed other hydro-carbons, but in less quantity. Illumi- nating gas is used in imtnense quantities in large cities, for lighting the streets, and for fixed lights in stores and other buildings. Illuminating gas is now chiefly prepared from bituminous coal, and as it passes from the retorts is mixed with tar, carbonic acid, sulphuretted hydrogen, salts of ammonia, and other matters, from which it must be freed before being admitted to the burners. For this purpose, it is washed by passing it through water, and then further purified by passing through vats containing recently- slaked lime. If this gas is made to pass through a heated tube it is decom- posed, and a part of its carbon is deposited as a coating upon the inside of the tube. In this way large deposits of jftire carbon are often formed in the retorts of gas-works. It has been de- scribed above (299) as gas carbon. 310. The History of gas manufacture, for illuminating purposes, pos- sesses much interest, as showing the great benefit conferred by science on the arts, and domestic and public economy. In 1680, Mr. Clayton, of Yorkshire, England, observed that a brilliant light -was produced by igniting the gas which issued from a close vessel containing bituminous coal when heated, but it was a century after this before any direct experiments were made with it, with reference to its use in the arts. In 1785, the preparation of gas for illumination, from the destructive distil- lation of wood, was suggested ; but, in 1792, some buildings were actually illuminated .with gas, in Cornwall, England; and the same thing was repeated in 1798, at a foundry in Birmingham. In 1805, some of the cotton-milJs in Manchester were first lighted with gas, by means of permanent fixtures, prepared for the purpose; and this date may be assumed as the beginning of the use of gas-lights for practical purposes. In a half century, therefore, has this manufacture attained its present importance ; and the time is not distant when the quantity annually con- sumed in every civilized country will be greatly increased. QUESTIONS. 809. What is illuminating gas ? How is it usually pre- pared? What is the substance now generally used for producing it' 310. What is said of the history of the use of illuminating gas for prac- tical purposes ? 23* 270 NATURE OP FLAME. THE SAFETY LAMP. Nature of Flame. The Safety Lamp. 311. What we term the combustion of a substance is occasioned by its entering into combination with some other substance, usually the oxygon of the atmosphere, and then taking another form as a compound (193). Of the two substances thus required to produce combustion, one is called the combustible substance, and the other the supporter of the combustion ; but the action is really mutual between them, and neither can burn without the other. The supporter of ordinary combustion, oxygen, is always gaseous, but the combustible may be either solid, liquid, or gaseous. Flame is gaseous matter in a state of combustion, and is made incandescent by the intense heat of the combustion. Two gases are needed to produce it, one of which must be combustible, and the other, of course, a supporter of combustion. The action is mutual between them ;- neither will burn alone ; and a jet of either will burn in the other. In the common lamp or candle, the combustible gases are sup- plied from the oil, or tallow, which is gradually raised, by <;he capillary action of the wick, into the flame, where it is decom- posed by the heat. As these gases, thus produced, escape from the wick, and come in contact with the oxygen of the atmosphere, the two combine, producing the phenomena of light and heat, with which all are familiar. A careful inspection of the flame of a lamp or candle, as it burns quietly, will show, that it is composed of three parts, viz : 1st, a central part, a, surrounding the wick, and extending a little above it, of gaseous matter that has emerged from the wick, and is making its way outward to the atmosphere, which it has not yet reached, and therefore has not yet become ignited; 2d, the bright part of the flame, bb, which, in the form of a conical shell, incloses the part a, and Iliil I iiil'i'i consists of gaseous matter in a state of rapid combustion, the combustible particles, as they reach the air, uniting QUESTIONS. 311. What is ordinarily termed combustion? Must there be two substances to produce combustion ? What are they called ? What is flame? In the common lamp or candle, how are the combustible gases supplied ? Of what several parts is the flame of a candle composed ? What is the dark interior part ? NATURE OF FLAME. THE SAFETY LAMP. 271 with its oxygen, with the evolution of much light and heat ; and, 3d, the part, cc, outside of the part last mentioned, composed chiefly of heated air, and mixed with a small portion of com bustible matter in a state of ignition. That the dark, interior portion, a, is composed of combustible gas, may be shown by inserting, in the , centre of the flame, one end of a small glass tube, as shown in the 'figure, and conveying away a portion, and igniting it as it escapes at the other end. So, when the flame of a candle is suddenly extin- guished, the heat in the wick continues, for a short time, sufficient to decompose the tallow, and the combustible gases Gas'Trom centre of Flame. continue to rise in the form of smoke ; and may often be again relighted by applying the flame of another candle to the ascending smoke, several inches above the wick. In the flame of a jet of gas, precisely the same phenomena, in every particular, will be observed; the dark central cone of unconsumed gas, surrounded by the brilliant hollow cone of flame, and this enveloped in still another less brilliant cone. In the latter case, the gas is previously formed and consumed as it issues into the air, but in the case of the candle or lamp, it is formed in the wick, and instantly consumed as it escapes. 312. That there is really no combustion in the dark central part of the flame, appears from the fact that the wick remains there uncon- sumed, and is even protected by the gas existing there from being attacked by the oxygen of the air. In burning ordinary tallow candles, the wick occasionally becomes too long, and requires to be snuffed but the wicks of the best spermaceti and wax candles, being plaited, QUESTIONS. How may the real character of this gas be shown ? Will the same phenomena be shown in the flame of a jet of gas? 312. Why does not the wick of a candle burn off quite down to the tallow ? Effect of Braided Wick. 272 NATURE OF FLAME. THE SAFETY LAMP. the end curls outward when heated by the flame, and coming in contact with the oxygen of the air, is gradually consumed as the candle burns away. The necessity of snuffing is therefore avoided. The plaited or braided wick, while the candle is burning, will always bend toward that side in which the direction of the separate strands is upward and inward, and of course from the other side in which the direction is upward and outward, Generally the simple braiding of the wick is sufficient, but sometimes a cord or bobbin is braided in with one of the strands, as repre- sented in one of the figures in the margin ; and sometimes, also, a cord is bound to the braided Braided Wicks. ..-. wick, by a thread wound spirally around it. The intensity of the light from any flame, other things being equal, will depend upon the intensity of the combustion, and this will depend in turn upon the regular and abundant supply of the combustible and the supporter.- When the wick of a candle becomes too long, or that of a lamp is too high, only the hydrogen of the gases formed from the decomposed oil is consumed, the carbon escapes in a finely divided state, as a dense, black smoke. This is because of the too rapid supply of the combustible, and the usual remedy is to diminish the length of the wick by snuf- fing or otherwise, but .the same thing would be accomplished by increasing the supply of the supporter, oxygen. This last pur- pose is effected by the use of a glass chimney, by which a current of air is supplied more rapidly to the flame. By the Argand burner (so named from the inventor), a cur- rent of air is also supplied to the centre of the flame, the wick being in the form of a hollow cylinder, as shown in the figure on next page. Both through the centre of the flame and around QUESTIONS. How are the wicks sometimes made to bend outward in th air, so that the end is consumed ? Upon what will the intensity of the light from a flame depend? What occasions the disagreeable smoke sometimes produced by a lamp ? How is the defect usually remedied ? What is the benefit of a chimney to a lamp ? Why . are hollow wicks often used ? . NATURE OF FLAME. THE SAFETY LAMP. 273 the outside strong currents of air are esta- blished, as shown by the arrows. The effect is to produce a perfect combustion of all the oil or other combustible material supplied to the flame. It is found that the intensity of light produced by a flame depends very much upon the amount" of carbon consumed. The flame of pure hydrogen is very feeble, as is also that of the vapor of alcohol and ether ; and these latter contain compara- tively little carbon. But add to alcohol one-fourth of its volume of camphene, which is rich in carbon, and a brilliant flame is produced. This mixture con- stitutes the common burning fluid. Lamp with Hollow Wick and Glass Chimney. Use of Blowpipe. 313, The llowpipe (193) is, as we have seen, simply a con- trivance to supply air to the flame from the lungs. The instrument is usually applied to one side of the flame, and as the current of air is forced through it, it is bent towards the opposite side. By means of this instrument a very intense heat may be produced, sufficient for many im- portant purposes. ' Much will depend in any particular case upon the mode of using the flame ; and the inexperienced student, before commencing, will consult works that treat at length of this subject. 314. Safety-Lamp. The safety-lamp is the invention of Sir M. Davy, to avoid the danger of explosions from mixtures of the above gases with air, which often occur in coal mines, when unprotected lamps are made use of. It consists simply of a com- QUESTIONS. What is the composition of burning fluid? 313. Describe the mouth blowpipe. May a very intense heat be produced by it? 314. For what special purpose was the safety-lamp invented? 274 NATURE OF FLAME. THE SAFETY LAMP. Safety-Lamp. mon lamp, the flame of which is surrounded by wire gauze, through which, it is found, flame will not ordinarily pass. This lamp, as it is usually constructed, is represented in the figure on the left. Its action in arresting flame is easily under- stood when the nature of flame is considered. We have seen that this is simply gaseous matter in a state of combustion, and therefore is intensely heated; now if by any means we can diminish the heat of this gaseous matter, so that it shall fall below the point of ignition, the combustion, and consequently the flame, must cease. And this effect is produced by the wire gauze. To show the effect, let a piece of such gauze, &, be held in the flame of a candle, a-f the flame appears to be cut off by the gauze, and the gases pass through unconsumed, as shown at d, and, by dexterous management, may be relighted. The occurrence of combustible gases in coal mines is occasioned by the action of water upon the coal ; and they often collect in large quantities in places not -properly ventilated, forming mix- tures with the air, ready to explode with excessive violence on the first approach of the unprotected candle of the miner. Before the invention of the safety-lamp, such accidents were of frequent occurrence ; and coal miners lived and worked in .perpetual fear ! All this is avoided by the use of the safety-lamp j and, in view of what has been said above, the mode in which it operates to afford the desired protection is easily understood. When this QUESTIONS. Describe the safety-lamp. What is flame? Will ordi- nary flame pass through wire gauze ? What is the reason given for this fact ? How may this be shown by a lighted candle and a piece o wire gauze ? How are inflammable gases formed in coal mines ? What is the effect when these gases, mixed with atmospheric air, come in contact with -the flame of a lamp ? What is the effect when the safety-lamp is used? Effect of Wire Gauze. COMPOUNDS OP CARBON AND NITROGEN. 275 lamp is carried into an atmosphere containing a considerable pro- portion of fire-damp, this latter immediately takes fire, and burns freely within the gauze, but the flame is not communicated to that without. At first, the flame of the lamp seems to be simply en- larged, but soon it leaves the wick entirely, and the whole space immediately inside the gauze seems filled with flame. When this takes place, the miner is obliged to retire, lest, by the intense heat, the wire of the gauze should be melted or oxydized, and the flame communicated to the mixed gases, without. The same effect might also be produced by strong currents of air, which sometimes occur, forcing the concentrated flame against a particular part of the gauze, and causing it to break, or heating it so as to allow the passage of flame through it. The mode in which the safety-lamp t>pertes may be shown quite well, by pouring a little sulphuric ether into a common glass receiver, which should be inverted and agitated a little, so that it may be filled with a mixture of air and vapor of ether, and then letting the lighted lamp down into it. The mixture of air and vapor of ether entering through the gauze, burns brilliantly within the gauze, but the flame is not com- municated to that without. It should be remarked, that wire gauze serves as a protection a'gainst explosive mixtures of atmospheric air and the carburetted hydrogen only; a mixture of atmospheric air or oxygen with pure hydrogen may be ex- ploded through a very narrow tube of great length. Compounds of Carbon and Nitrogen. 315. There are several compounds of these two substances, but we shall notice only one, the bicarbonide of nitrogen, C 2 N, or cyanogen (from kuanos, blue, and gennao, to produce, because it is an ingredient of Prussian blue). 316. Bicarbonide of Nitrogen, or Cyanogen C 2 N, or Cy ; eq., (12 -f. 14=) 26. This is a gaseous substance,- and is readily formed by heating bicyanide of mercury (to be hereafter described) in a glass retort by a QUESTIONS. Will it answer for the miner to remain with his lamp in the explosive mixture ? Describe the experiment for showing the opera- tion of the safety-lamp. Will wire gauze in this manner prevent the explosifn of mixtures of hydrogen and oxygen? 315. What is said of the compounds of carbon and nitrogen ? From what does cyanogen derive its name ? 316. How is bicarbonide of nitrogen, or cyanogen prepared ? 276 COMPOUND OF CARBON AND SULPHUR. epirit-lamp. It is colorless, has a very pungent odor, and is easily com- pressed into a liquid ; and by the cold produced by a mixture of solid carbonic acid and sulphuric ether, this liquid may be frozen. Of the pure gas, 100 cubic inches weigh 56-47 grains, giving it a density of 1-82. Cyanogen is composed of 1 vol. of vapor of carbon and 1 vol. of nitrogen, as follows, viz. : 1 vol. vapor of carbon weighs 0-836 - 1 nitrogen " 0-972 Weight of 1 vol. of -cyanogen, 1-80H Cyanogen, though a compound, is remarkable for combining with the elementary bodies in the same manner as an element, forming a class of compounds which are called cyanides. Further remarks concerning it will be deferred to Organic Chemistry. Compound of Carbon and Sulphur. 317. These elements combine in only one proportion, forming the following compound : 318. Bisulphide of Carbon CS 2 ; eq., (6 + 32 =) 38. This compound, called also sulplio-carbonic acid, is formed by heating to redness pieces of. charcoal in a porcelain tube or retort, and then causing vapor of sulphur to come in contact with it. The figure on next page represents a good arrangement for the pur- pose, even when a considerable quantity is to be prepared. The retort, R, of stone ware, is first filled with pieces of well-burned charcoal, and the tube T inserted nearly to the bottom, and luted well around the neck, to prevent any escape of gaseous matter. It is then to be placed in a suitable furnace, and con- nected with a Liebig's condenser, C, and this with a receiving vial, V, partly filled with water. A small tube of glass inserted into the cork allows the air to escape as the vial is filled. QUESTIONS. Describe bicarbonide of nitrogen or cyanogen. F6r what is it remarkable? 317. How many compounds of carbon and sulphur are known? 318. Describe the mode of preparing bisulphide of carbon, or sulpho-carbonic acid. COMPOUND 01 CARBON AND SULPHUR. 277 Preparation of CSa. When everything is ready, a fire is kindled in the furnace, and when the retort becomes well heated, pieces of sulphur are occa- sionally dropped into the tube T, and a cork immediately inserted. The sulphur being sublimed by the heat comes in contact with the heated charcoal, with which it combines, producing the com- pound in question. This now passing into the condenser, takes the liquid form, and is collected in the receiver, V. It will be observed that this process is a case of combustion (193), the carbon being the combustible, and the vapor of sul- phur the supporter ; and the compound formed, CS 2 , is analogous to carbonic acid, C0 2 , which is formed when carbon is burned in oxygen. And as carbonic acid combines with oxy bases, to form salts, the composition of which is RO,C0 2 , so sulphide of carbon combines with sulphur bases, to form compounds of the analogous form, RS,CS 2 . The letter B is here used indefinitely, for any element whatever. Bisulphide of carbon is a colorless liquid, which boils at about 112, and has a density of 1-27. It does not mix with water, but dissolves readily in alcohol or ether. Its odor is excessively fetid and nauseous. Both sulphur and phosphorus are dis- solved in it, and may be obtained in crystals by the gradual QUESTIONS. What is said of the relation of bisulphide of carbon to carbonic acid ? May this be considered as a case of combustion ? Which of the substances is to be considered as the combustible body, and which the supporter ? What are some of the properties of bisulphide of carbon ? 24 278 SILICON. evaporation of the solution. By its evaporation iu the open air a very considerable cold is produced, but under the receiver of the air-pump its evaporation is so rapid as to occasion a cold of 76. It burns freely in the open air, producing carbonic and sulphurous acids, and with, oxygen its vapor forms an explosive mixture. SILICON. Symbol, Si; Equivalent, 21-3; Density, ?. 319. History. Silicon was first obtained by Berzelius, in 1824. It was then considered a metal, and named silicium, but is now generally ranked with the non-metallic elements. It is never found in its separate state in nature, although it is really very abundant in every place in silicic acid (silica), and the various siliceous compounds which constitute the rocks and soils. Next to oxygen it is the most abundant element found upon the earth. 320. Preparation. To prepare silicon a, somewhat complex substance is selected, the double fluoride of silicon and potassium, which is a white powder like starch. When this compound is heated in a glass tube with nearly its own weight of potassium, by means of a spirit-lamp, the fluorine combines with the potassium, and the silicon is separated from the mass by washing with water, which dissolves the fluoride of potassium and leaves the silicon very pure. The reactions which take place are represented by the following equation : 3KF,2SiF 3 + 6K = 9KF + 2Si. QUESTIONS. 319. Has silicon sometimes been ranked with the metals ? Is it abundant in nature ? 320. How may it be prepared ? COMPOUND OP SILICON AND OXYGEN. 279 321, Properties. Silicon, as thus obtained, is a powder of a dark, nut-brown color, without metallic lustre, and is a non-con- ductor of heat and electricity. It stains the fingers, and adheres to everything that comes in contact with it ; and when heated in the atmosphere or oxygen gas, it takes fire and burns, with the formation of silicic acid. In close vessels, silicon, like charcoal and boron, is capable of enduring a very high temperature without fusion, but is ren- dered harder and more compact. It is now incombustible, even when highly heated in the air or in oxygen gas, and is unaffected by the blowpipe, even in contact with chlorate of potassa. Compound of Silicon and Oxygen. 322, There is known only a single compound of these elements, the teroxide, Si0 3 . 323. Silicic Acid, or Silica Si0 3 ; eq., (21-3 + 24=) 45-3. This is one of the most abundant compounds in nature, and is found quite pure in quartz, flint, calcedony, agate, &c. ; and, in combination with qther substances, in the material of all soils, and nearly all rocks. Alone, silica is nearly infusible, but may be melted in the intense heat of a compound blow-pipe. It is not acted upon by any acid except the hydrofluoric (252), but, at high temperatures, enters into combination with the alkalies and earths. It is very hard, and has a harsh feeling to the fingers, even in fine powder. In quartz crystals, which are usually six-sided prisms, terminated by six-sided pyramids, it is familiar to every one. By heating silica in fine powder, with four times its weight of carbonate of potash} in a platinum crucible, the carbonic acid is displaced, and silicate of potash formed; which, being treated QUESTIONS. 321. Describe the properties of silicon. 322. What com- pound only of silicon and oxygen is there? 323. What is said of the abundance of silicic acid, or silica ? What is said of its fusibility ? Is it acted upon by any of the acids ? What is the usual form of its crystals ? What is the eifect when silica in fine powder is heated with carbonate of potash ? 2 30 OTHER COMPOUNDS OF SILICON. with diluted hydrochloric acid, yields a gelatinous precipitate of hydrated silica. This is soluble in water, and constitutes soluble glass, or liquor of flints, terms sometimes used. It is some- times found in the waters of hot springs, as the Geysers of Ice- land; and, in fact, in very small quantities, in most natural waters. In this state it is taken up by the rootlets of plants, and is found in their ashes after incineration. It is especially abun- dant in the grasses and the straw of the cereal grains, and in the stalks of rushes and reeds. In the gelatinous state, silica has occasionally been found in the cavities of minerals, when they have been broken. Exposed to the air, and especially if heated, the water evaporates, and dry, tfarsh, insoluble silica only remains. All the different varieties of glass are silicates of different bases, or mixtures of these silicates. This subject will be treated of more at length hereafter. It is in its power thus to combine with the bases, so as perfectly to neutralise them, that this compound, oxide of silicon, or silica, evinces its Claims to be considered as an acid. Other Compounds of Silicon. 324. Terchloride of Silicon SiCl ? ; eq., (21-3 -f 106-2 ==) 127-5. This compound is formed by heating silicon in dry chlorine, or by passing a current of the latter over a mixture of silica and carbon when heated in a porcelain tube. It is a colorless, volatile liquid, which boils at about 138, and has a density of about 1-52. By contact with water it is de- composed, producing silica and hydrochloric acid. 325. Terfluoride of Silicon SiF ? ; eq., (21 <3 -f 57 =) 78-3. This fluoride, called also, fluo- silicic acid, is obtained by gently heating a mix- ture of equal parts of dry and finely-powdered glass and fluor-spar, made into a paste with strong oil of vitriol. The oxygen of the silica and the fluorine of the fluor-spar here exchange places, while the sulphuric acid combines with the lime that is formed, thus, neglecting the water of the sulphuric acid, 3CaF -f Si0 3 -f 3S0 3 = 3(CaO,S0 3 ) -f- SiF 3 . QUESTIONS. Is silica found in nature ? Is it taken up by the roots of plants ? Of what are all the different kinds of glass composed ? 824. How is the terchloride of silicon formed ? Describe its properties. 826. Describe the terfluoride of silicon. BORON. 281 Terfluoride of silicon is a colorless gas, with a pungent, acid odor, and in the open air forms dense white fumes by combining with the moisture it contains. Its density is 3-57. By contact with water it is at once decomposed,* gelatinous silAca is deposited, and the. water is found to contain a peculiar compound, called hydrofluo silicic acid, the composition of which is 3HF, 2SiF 3 . The experiment is best performed by putting the materials in dry retort, A, connected with a receiver, R, partly filled with wata c^itd placed so that it can be gently shaken occasionally, in order that the film of silica forming upon the surface may be broken up, and a fresh surface of water exposed. When hydrofluosilicic acid is saturated with a base, as potassa, the hydrogen is replaced by an equivalent quantity of the metal of the base. Thus, 3HF,,2SiF 3 4- 3KO = 3KF,2SiF 3 -f 3HO. The compound 3KF,2SiF 3 is the double fluoride of silicon and potas- sium (320) used in the preparation of silicon. Silicon is capable also of forming compounds with sulphur and bromine. BORON. Symbol j B; Equivalent, 10-9; Density, 2. 326. History. Boron, in a separate state, was first obtained by Davy, in 1807. It is found in nature only in combination, and in comparatively small quantities. Though it occurs in QUESTIONS. How is terfluoride of silicon affected by contact with water? What is the composition of hydrofluosilic acid? 326. When and by whom was boron discovered ? Is it found naturallv in a separate state? 24* 282 BORON. several minerals, as datholite and boracite, it is obtained chiefly from the waters of certain hot springs, especially in Tuscany and the Lipari Islands, where it occurs in solution, as boracic acid. 327. Preparation. To prepare boron, first make a saturated solution of borax in boiling water, and, while hot, pour in sul- phuric or hydrochloric acid until the solution tastes distinctly sour. As it cools the boracic acid will separate in white, shining scales, which are to be thoroughly washed and dried by fusion in a platinum cru- cible. We thus obtain boracic acid, which is then to be mixed with potassium (or sodium), and heated in a glass tube, as in the preparation of silicon. A part of the boracic acid yields its oxygen to the potassium, and the potassa so formed enters into combination with the rest of the boracic acid to form borate of potassa. By treating the mass with cold water the latter compound is dissolved, and the boron is seen floating in the liquid as a fine powder of a brownish color, and may be collected on a filter. Before filtering, some sal am- monia should be dissolved in the mixture, which has the effect to prevent the escape of the finely-powdered boron through the filter. The mode in which the sal ammonia operates to produce this effect is not understood. 328, Properties. Boron is a dark olive-green powder, without taste or smell, and incapable of fusion in the strongest heat. It is insoluble in water or alcohol. Heated in the open air to about 600, it takes fire and burns brilliantly, forming boracic acid. It is a non-conductor of electricity and heat. * QUESTIONS. 327. How is boron prepared? -Describe the reactions which occur. 328. Describe boron. How is it affected whjen heated ? OTHER COMPOUNDS OP BORON. 283 Compound of Boron and Oxygen. 329. Boracic Acid B<(; eq., (10-9 +24=) 34-9. This acid may be obtained from the common borax of commerce, as just described in the preparation of boron ; it is also produced by the combustion of boron in the air. Boracic acid is slightly soluble in water and in alcohol ; and when the latter solution is inflamed it communicates to the flame a beautiful green tinge, which is characteristic of this substance. To make the experiment, fill a common dropping tube, of the form A B in the figure, with the solution ; and, inserting Green Flame produced by B 8 ' a cork firmly in A, apply the heat of a lamp to the bulb, and inflame the jet of liquid as it issues from the capillary orifice, B. The flame will be of a beautiful green. The color of the flame may also be shown very well simply by moistening one end of a pine stick in the solution, and in- flaming it. Other Compounds of Boron. .330. Terchloride of Boron BC1 3 ; eq., (10-9 + 106-2=) 117-1. This compound is formed by preparing an intimate mixture of boracic acid and carbon, and causing a current of dry chlorine to pass over it in a porcelain tube, kept at a red heat. It is a colorless gas, of a density of 4-03 ; iu the open air it forms dense white fumes with the moisture con- tained therein, and in contact with liquid water it is instantly decom- posed, forming hydrochloric and boracic acids. 331. Terfluoride of Boron BF 3 ; eq., (10-9 -f 57 =) 67-9. Terfluoride of buron,.or fluoboracic acid, is a colorless gas, of specific gravity 2-37. It is prepared by heating in a gun-barrel a mixture of 2 parts of pul- QFESTIONS. 329. How is boracic acid procured from borax ? Describe this acid. What color does it give to the flame of alcohol when dissolved in it ? How may it be shown ? 330. How is the terchloride of boron formed? 331. How is the terfluoride of boron formed? 284 THE METALS. GENERAL PROPERTIES. verized fluor spar (fluoride of calcium), and 1 part of fused boracic acid. It has a strong affinity for water, which dissolves 700 or 800 times its own volume of the gas, and acquires a sour taste and a strong acid reaction, and chars wood like oil of vitriol when brought in contact with it. Boron combines also with sulphur, forming a tersulphide, BS 8 . THE METALS. General Properties. 332. Characteristic Properties, The metals are generally good conductors of electricity and heat, and possess a peculiar lustre called the metallic lustre, which can scarcely be imitated by other substances. When their compounds are decomposed by the galvanic battery, they always make their appearance at the negative electrode (112), and are therefore, without exception, to be considered as electro-positive. But these properties are much more distinct in some metals than in others. Most of the metals are also characterized by their great density, as gold and platinum ; but two at least, potassium and sodium, are lighter than water. All of them except mercury are solid at ordinary temperatures. The ancients were acquainted with only seven metals, viz. : gold, silver, iron, copper, mercury, lead, and tin ; but there are now known, with certainty, forty-seven; and the discovery of several others has been announced, though perhaps not fully proved. 333, Sources of the Metals. Though several o the metals are found in animal and vegetable substances, they seem to form no necessary part of any organic compounds. Most of them, as iron lead, and zinc, are found in the earth in combination with other non-metallic elements, as oxygen, sulphur, or arsenic, and are said to be mineralized, and the compound is called an ore ; but a few, as platinum, gold, and sometimes copper, silver, bis- QUESTIONS. 332. What are some of the characteristic properties of the metals ? How many metals were known to the ancients ? Are all the metals solid at ordinary temperatures ? 333. Do any of the metals form any part of organic compounds ? What constitutes a metallic ore ? THE METALS. GENERAL PROPERTIES. 285 muth, &c., occur in the metallic state, and are said to be found native. Some are found in the form of salts, especially as sili- cates, carbonates, and sulphates. The metals occur sometimes in &er/s, which are more or less parallel with the earthy strata containing them, but more fre- quently in veins or lodes, which traverse the strata in every direction. The veins are more abundant in the older than in the newer rocks ; and their appearance indicates that they are fissures which have been produced in the strata subsequent to their deposition, and then filled by filtration of the metallic matter from above, or by injections from below. Besides the metallic compounds, or ores, these veins always contain other minerals, as quartz, carbonate of lime, heavy spar, and fluor spar, which con- stitute the gangue, or vein-stone. 334. Relations to Li^ht, The relations of the metals to light are in some respects peculiar and interesting. Their peculiar lustre, called the metallic lustre, has already been alluded toj this lustre entirely disappears when they are reduced to a fine powder, but reappears when the substance is rubbed with a burnisher. All the metals except gold are perfectly opake, even when reduced to the thinnest laminae possible. Gold in the form of leaf transmits a feeble green light. The best method to observe this light is to place an un- broken leaf upon a piece of white plate glass, and press it gently with a bunch of cotton to make' it adhere. It may then be preserved for any length of time. The color of most of the metals, seen in mass, is grayish-white, as platinum, iron, lead, and potassium, but seen in powder the color is a deep gray. By burnishing the particles, the original grayish-white is restored. Gold in mass has a beautiful yellow color, and in powder a deep purple, almost black. Copper and titanium i*re red. 335. Malleability and Ductility. Some metals possess the property of malleability, that is, admit of being beaten into thin QUESTIONS. When is a metal said to be found native? 334. What is said of the lustre of the metals ? Is this lustre seen in a metal when it is reduced to .powder ? Are most of the metals opake even when reduced to thin laminae ? What is the color of most of the metals ? What ia said of their color when in fine powder? What metal is yellow? What . metals are red ? 335. What malleable metals are mentioned ? 286 THE METALS. GENERAL PROPERTIES. plates or leaves by hammering. The malleable metals are gold, silver, copper, tin, platinum, palladium, cadmium, lead, zinc, iron, 'nickel, potassium, sodium, aluminum, and frozen mercury. The other metals are either malleable in a very small degree only, or, like antimony and bismuth, are actually brittle. Gold surpasses all the other metals in malleability ; one grain of it may be extended so as to cover about 52 square inches of surface, and the film will have a thickness of only ^-^o^th of an inch. Nearly all malleable metals may be drawn out into wires, a property which is expressed by the term ductility. The only metals which are remarkable in this respect are gold, silver, platinum, iron and copper. The process of wire-drawing consists in drawing the metal through round holes macfe in plates of steel for the purpose. The steel plate is made with a number of holes, of different diameters, through which the rod of metal is made to pass successively, its diameter at each operation being a little reduced andvits length increased. A machine for this purpose is represented by the accompanying figure. AB is the -plate of steel through which the wire is drawn, it is held Wire Drawing. firmly in its place by a support, D. A rod from the rolling mill, in tLo form of a coil, or a coil of wire, is placed upon the reel, F G, which turns QUESTIONS. What metals are mentioned as being brittle ? What is said of the malleability of gold ? Are the malleable metals also ductile ? Describe the process of wire-drawing ? THE METALS. GENERAL PROPERTIES. 287 easily upon its axis ; and the end of the wire, drawn out a little with the h;umnr-r, is passed through the plate and attached to the drum, C, which is turned by machinery, and by its motion winds the wire around itself, at the same time, of course, withdrawing it from the reel. To form small wire it is in this way passed many times through the plate ; and, to prevent its becoming hard and brittle, it is several times annealed during the process. The passage of the wire through the plate is facili- tated by dipping the coils occasionally in a moderately strong solution of sulphate of copper, by which it receives a thin coating of metallic copper. 336. The malleability and ductility of any substance would seem to depend very nearly upon the same properties, but. i* is found in the case of metals that they are not precisely the same. In the following table, in the first column, several of the metals are arranged in the order of their malleability, beginning with the most malleable j in the second column, the same metals are arranged in the order of their ductility. The table is from Regnault. Malleability. 1. Gold. 2. Silver. 3. Copper. 4. Tin. 5. Platinum. 6. Lead. 7. Zinc. 8. Iron. 9. Nickel. Ductility. 1. Gold. 2. Silver. 3. Platinum. 4. Iron. 5. Nickel. 6. Copper. 7. Zinc. 8. Tin. 9. Lead. Both the malleability and ductility of several of the metals vary with the temperature. Thus iron, though partially malle- able and ductile at the ordinary temperature of the atmosphere, is much more so at a red heat ; and zinc is very malleable from 212 to 350, but loses this property if cooled down to 32, or heated to 600. At the latter temperature it is decidedly brittle. When ,a, metal has been hammered or rolled, or drawn out into wire, its hardness as well as density is increased ; and it becomes less malleable. This property, however, is restored by annealing it, which consists in heating it to redness and then cooling it QUESTIONS. 336. Do the malleability and ductility of a substance depend upon the same properties ? Are the malleability and ductility of some of the metals affected by their temperature? What is said of iron and zinc in this connection ? What is meant by the annealing of a metal ? Why is this often necessary in working many of the metals ? 288 THE METALS. GENERAL PROPERTIES. slowly. But the tenacity is often very much diminished by the process, sometimes even more than one-half. 337. The tenacity of a metal is determined by ascertaining the greatest weight a wire made of it, of a given diameter, will sus- tain. The determination is made by attaching one end of the wire to a firm support, and to the other end fixing a pan to receive the weights. Wires 0-787 of a line in diameter (= to about T Jftth of an inch), made of the several metals mentioned below, were loaded gradually until they broke with the weights placed opposite to tfceir names in the following table. These numbers therefore indicate their relative tenacities. Pounds. Iron wire 549 Gold Copper .V 302 Zinc Platinum 274 Tin Silver 187 Lead 27 When a metallic wire is tested in . this manner its length is increased with the weight, but if the load has not been too great it contracts again to the same length as at first, on the removal of the load. If the load be increased beyond a certain point, a permanent elongation is produced ; and usually no great further increase is needed to break the wire. 338. The specific gravity of the metals, like many of their other properties, are very dissimilar. The specific gravities of some of the more important of them are contained in the following Table of the Specific Gravity of Metals Platinum 20-98 Gold 19-02 Tungsten 17-65 Mercury 13-56 Palladium 11-05 Lead 11-35 Silver 10-47 Bismuth 9-82 Uranium 9-00 Copper 8-09 Cadmium 8-60 Molybdenum 8-00 at 60, compared with Water as Unity. Cobalt 8-53 Nickel 8-27 Manganese 8-01 Iron 7-78 Tin 7-29 Zinc 6-86 Antimony 6-70 Chromium 5-09 Titanium 5-03 Aluminum 3-07 Sodium 0-97 Potassium ,.. .. 0-86 QUESTIONS. 33l How is the tenacity of a metal determined? What metal of those mentioned has the greatest tenacity ? What is the second ? 338. What is said of the specific gravity of the metals ? What metal is mentioned as having the greatest specific gravity ? What is the second ? THE METALS. GENERAL PROPERTIES. 289 it 339. Crystaline Characters. Many of the metals have a dis- tinctly cry stall ne texture. Iron, for example, is fibrous; and zi*c, bismuth, and antimony aro lamellated. Metals are some- times obtained also in crystals and most of them, in crystalizing, assume the figure of the cube, the regular octahedron, or some form allied to it. Gold, silver, and copper occur naturally in crystals, while others crystalize when they pass gradually from the liquid to the solid condition. Crystals are most readily pro- cured from those metals which fuse at a low temperature ; and bismuth, from conducting heat less perfectly than other metals, and, therefore, cooling more slowly, is best fitted for the purpose. Several of the metals form small but very beautiful crystals, as they are slowly separated from their solutions by the galvanic current. If in a solution of sulphate of copper we place two plates of copper, and connect them with the two electrodes of a galvanic battery in feeble action, after some time the plate on the negative side will become covered with small crystals of metallic copper, while the other plate will be gradually dissolved. It is believed that some of the metals, in certain peculiar circum- stances, may assume a crystalline structure, even when in the solid state. 340. Alloys. Many of the metals are capable of combining with eachother, forming compounds called alloys, which will be described in their proper places. They possess all the charac- teristic physical properties of the pure metals, and many of them are of great service in the arts. Generally, alloys are more fusible and more oxidable than their constituents separately. Their malleability and ductility usually are much less, and their hardness greater, than those of the metals of which they are composed. Compounds of mercury with other metals are called amalgams. 341. Metallurgy. The reduction of the metals from their ores, and the methods adopted in working them in the arts, con- QUESTIO-NS. 339. Do any of the metals possess a crystaline texture ? What metals are mentioned as being sometimes found in crystals ? De- scribe the mode of obtaining crystals of copper by the galvanic process ? 840. What are alloys ? Do alloys possess the usual physical propertiea of the metals ? What is said of their fusibility ? What of their malle- ability and ductility ? What are amalgams ? 341. What is metallurgy ? 25 290 THE METALS. GENERAL PROPERTIES. * stitutea a distinct branch of chemical science, called by this name. Most of the metals have an extensive range of affinity; many of them form compounds with nearly all the non-metallic elements, and all without exception combine with oxygen. As many of the metallic ores are oxides, the reduction of this class of compounds becomes particularly important. It is effected in several different modes, as, 1. By mere heat. By this method the oxides of gold, silver, mercury, and platinum may be decomposed. 2. By the united agency of heat and combustible matter. Thus, by transmitting a current of hydrogen gas over the oxides of copper or iron heated to redness in a tube of porcelain, water is generated, and the metals are obtained in a pure form. Car- bonaceous matters are likewise used for the purpose with great success. Potassa and soda, for example, may be decomposed by exposing them to a white heat, after being intimately mixed with charcoal in fine powder. A similar process is employed in metallurgy for extracting metals from their ores, the inflammable materials being wood, charcoal, coke, or coal. In the more deli- cate operations of the laboratory, charcoal and Hack flux* are employed. 3. By the galvanic battery. This is a still more powerful agent than the preceding; since some oxides, such as baryta and strontia, which resist the united influences of heat and char- coal, are reduced by the agency of galvanism. 4. By the action of deoxdizing agents on metallic solutions. Phosphorous acid, for example, when added to a liquid containing ' oxide of mercury, deprives the oxide of its oxygen, metallic mer- cury subsides, and phosphoric acid is generated. In like manner one metal may be precipitated by another, provided the affinity of the latter for oxygen exceeds that of the former. Thus, when mercury is added to a solution of nitrate of oxide of silver, metallic silver is thrown down, and oxide of mercury is dissolved > * Black flux is prepared by deflagrating nitre with twice its weight of cream of tartar When equal weights are used, it constitutes white Jlux. QUESTIONS. What is said of the affinity of the metals? What are most of the metallic ores? What are some of the different means by which these ores may be reduced ? SALINE COMPOUNDS, OR SALTS. 291 by the nitric acid. On placing metallic copper in the liquid, pure mercury subsides, and a nitrate of the oxide of copper is formed; and from this solution metallic copper may be precipitated by means of iron. To reduce the other compounds of the metals, other modes are adopted, which cannot here be particularly described. The relations of the various metalloids to the metals will be described as each of these latter elements shall come in review before us, so far as demanded by the special object of the work. 342. Classification of the Metals, The metals have been variously classified by different writers ; but the following arrange- ment into six groups will probably answer our purpose as well as any we can adopt. 1. Metals, the protoxides of which are alkalies. 2. Metals, the protoxides of which are alkaline earths. 3. Metals, the protoxides or sesquioxides of which are earths. 4. Metals which, at a red heat, decompose the vapor of water, but are not actecl upon by liquid water. 5. Metals which are incapable of decomposing water, and whose oxides are not reduced by the mere action of heat. 6. Metals whose oxides are reduced by a red heat. Saline Compounds, or Salts. 343, A salt is a compound of two other binary compounds, which sustain to each other the relation of acid and base ; the former being electro-negative in reference to the latter, which is electro-positive. Thus, sulphate of soda, NaO,S0 3 , is a com- pound of sulphuric acid (teroxide of sulphur) and soda, which is the protoxide of sodium; the former being electro-negative in reference to the latter, which is electro-positive. The acids take their name from the fact that when soluble their taste is very gen-erally sour, but this may not always be QUESTIONS. 342. What are the metals included in the first group? In the second group ? In the third ? In the fourth ? In the fifth ? In the sixth? 343. What is a salt? Illustrate by an example. How are the acids generally characterized ? 292 SALINE COMPOUNDS, OR SALTS. the case; they are mostly combinations of two metalloids, as the sulphuric, nitric, and hydrochloric acids, but sometimes they are formed of a metal and metalloid, as the manganic and chromic- acids, and the sulphides of tin and antimony, which are capable of acting as acids. Most of them have the property of changing the blue solution of litmus to red. The bases, or electro-positive binary compounds, are always formed by the combination of a metal with a metalloid, as the protoxide of potassium (potassa), the protosulphide of potassium, and the protoxides of iron, copper, and silver. 344, Oxysalts. A large majority of all known acids and bases are oxides, called oxacids and oxybases; and the salts formed by their union are therefore called oxysalts. They are therefore double oxides. The metallic oxides, in regard to their disposition to combine with each other as acids and bases, and with the oxides of the metalloids, to form salts (as suggested by Kegnault), may be divided into several very distinct classes, as, 1. Basic oxides, "which combine readily with acids and form definite, crystalizable salts. Most of them are protoxides, as potassa, KO, soda, NaO, protoxide of silver, AgO, and the protoxide of iron, FeO. A few are sesqnioxides or suboxides. , 2. A cid oxides, which, as the name implies, possess acid properties ; they combine with bases to form salts, and very generally change the blue solution of litmus to red. Most of them are bi- or teroxides, as plumbic acid, PB0 2 (binoxide of lead), chromic acid, Cr0 3 , and man- ganic acid, Mn0 3 . "Occasionally they are still higher oxides, as per- manganic acid, Mn 2 7 . 3. Neutral oxides, which may combine with either acids or bases, as alumina, A1 2 0,, and the sesquioxide of antimony, Sb 2 3 ; or with neither, as the binoxides of silver, potassium, barium, and strontium. Some of these, by the action of acids, especially if heated, are decomposed. 4. Saline oxides, which result from the combination of a basic metallic oxide with a higher oxide of the same metal, as the magnetic oxide of iron, Fe 3 4 , which is really a compound of the protoxide, acting as a base, with the sesquioxide, acting as an acid ; and its proper formula is therefore FeO,Fe 2 3 . The oxides of manganese, MngO^ and of chromium, O 8 4 , furnish other examples. QUESTIONS. Are most of the acids formed by combinations of the metalloids ? Do some of the metals form acid compounds ? How do the acids generally affect the blue solution of litmus ? Of what are the Dasea mostly composed? 344. What is said of a majority of all the known acids and bases ? What four classes of metallic oxides are mentioned * SALINE COMPOUNDS, OR SALTS. 293 345. Sulphur Salts. Two sulphides often combine, forming double sulphides, analogous to the double oxides. They possess, in many respects, similar characters to the double oxides or oxy- salts, and are called sulphur salts. Some of the principal sulphur bases are the protosulphides of potassium, sodium, lithium, barium, strontium, calcium, and mag- nesium j and some of the more important sulphur acids are the sulphides of arsenic, antimony, carbon, tin, gold, and hydrogen. The sulphur salts generally are so constituted that if the sul- phur they contain were replaced by an equivalent quantity of oxygen, oxysalts would be produced. Thus, the carbosulphide of potassium, KS,CS 2 , when the 'sulphur is replaced by oxygen, becomes carbonate of potassa, KO,C0 2 ; and, in like manner, the double sulphide of potassium and arsenic, KS,AsS e , by a similar substitution, becomes arseniate of potash, KO,As0 5 . 346. Chlorosalts, The chlorosalts are double chlorides, one of the simple chlorides acting as a chlorobase, and the other as a chloroacid, as the double chloride of gold and potassium, KCl,AuCl 3 , called also aurochlorate of chloride of potassium, and platinochlorate of chloride of sodium, NaCl,PtCl 2 . In the same manner two iodides (an iodobase and an iodoacid) bro- mides, or fluorides, may unite to form in each case a series of salts analogous to the preceding, but not much is known of them. It is to be observed that these combinations take place only between members of the same series, as oxides with oxides, sulphides with sul- phides, &c. ; it is evidently possible that members of different series may unite, as an oxide with a chloride, a chloride with a sulphide, &c. ; but it is a question not fully settled whether such compounds are ever really formed. 347. Haloid Salts. Besides the compounds recognised by the above remarks as salts, the binary compounds of chlorine, iodine, bromine, and fluorine with many of the metals, have been classed with the salts by Berzelius and other eminent chemists, because of their resemblance, in many of their properties, to the salts, QUESTIONS. 345. What are sulphur salts? What is said of the con- stitution of the sulphur salts ? Give an example. 246. What are chloro- salts? May the iodides, bromides, &c., form similar series of salts? Are these combinations always between members of the same series? 347. What are haloid salts, so called ? Are these compounds salts, accord- ing to the definition of a salt adopted above ? 25* 294 SALINE COMPOUNDS, OR SALTB. properly so called. To distinguish them from the salts proper, they have been called haloid salts. But we prefer to limit the definition of a salt, as given above, although in so doing we of course exclude common salt, chloride of sodium, from the class. The elements, chlorine, iodine-, &c., which, by combining with metals, form the so called haloid salts, combine also with hydrogen, forming acid compounds called hydracids (168), as the hydrochloric, hydriodic &c. Now when powerful hydrous acids are brought in contact with the haloid salts, important reactions take place, dependent upon the wate* of the acid. Thus, by the action of oil of vitriol upon chloride of potas- sium, we obtain sulphate of potassa and hydrochloric acid, as shown in the following equation : KC1 -f S0 8 ,HO = KO,S0 3 + HC1. Here the water of the acid is decomposed, yielding its oxygen to the potassium to form potassa, and its hydrogen to the chlorine to form hydro- chloric acid. So, on the other hand, the action of a hydracid on an oxybase results in the production of a haloid salt and water. Thus, KO -f HC1 = KC1 + HO. 348. Neutralization of Acid and Base. When an acid and base combine to form a salt, the peculiar and characteristic pro- perties of each, in a great measure, disappear, the new compound formed not being characterized by the properties of either of its ingredients, but possessing others entirely distinct. Thus, an acid is generally sour to the taste, and changes vegetable blues to red, but the salts it may form with bases possess neither of these properties ; so, also, the alkalies are caustic to the fles.h and taste, and combine with oils to form soaps, but the salts which they form with the acids are entirely destitute of these properties. Most of the other peculiar properties of both acids and bases, when the two combine, are affected in the same manner, and they are therefore said to be neutralized. 349. Salts are often spoken of as divided into the three classes of neutral salts, super or acid salts, and sub or basic salts ; but the distinction QUESTIONS. What is said of the elements chlorine, iodine, &c., which form the so-called haloid salts by combining with the metals? What reactions take place when powerful hydrous acids act upon these salts? Give an illustration. 348. When an acid and base combine do the pecu- liar properties of each disappear ? Give some further illustration. 349. What three classes of salts are mentioned ? SALINE COMPOUNDS, OR SALTS. 295 cannot always be made with accuracy. In general, a neutral salt is formed by the union of a single equivalent of the acid and base, while an acid salt contains two or more equivalents of acid to one of base ; and a sub or basic salt contains two or more equivalents of base to one of acid. But this is to be understood . as liable to many exceptions. Frequently salts denominated neutral contain as many equivalents of acid as there are equivalents of oxygen in the base.- Thus, the neutral sulphate of soda is NaO,S0 3 , and sulphate of the protoxide of iron FeO,S0 8 , but the sulphate of the peroxide of iron is Fe 2 3 ,3S0 3 . Some few acids have the property of combining with bases in such manner- that one equivalent of acid will hold in union with it one, two, three (or even more) equivalents of base, and yet these several salts are considered as neutral ; such acids are called polybasic acids. Phosphoric acid (282) furnishes an instance of the kind. 350. Solubility and Crystalization of the Salts, Nearly all the salts are solid at ordinary temperatures, and very many of them, are susceptible of crystalization. Very generally they are more soluble in warm than in cold water, and often their solubility increases in proportion as the temperature of the water is ele- vated. The following table shows the quantity of nitrate of potash soluble in 100 parts of water at several different tem- peratures : Temperatures. Parts soluble in 100 parts water. 32 13-3 64 , 29-0 113 74-6 207 236-0 In some cases, the solubility rapidly increases as the tempera- ture is raised, up to a certain point, and then diminishes. Sul- phate of soda (Glauber's salt) furnishes an instance of this kind. Of this salt 100 parts of water, at 32, take up 12 parts ; at 77, 99 parts; -at 91, 322 parts; but above this temperature the solubility diminishes, so that at the boiling point only about 212 parts will be held in solution. QUESTIONS. What in general is a neutral salt ? What is a super or acid salt ? What is a sub or basic salt ? Do salts denominated neutral often contain as many equivalents of acid as there are equivalents of oxygen in the base? Give an example. What are polybasic acids? 350. Are the salts usually solid at ordinary temperatures ? Are they more soluble in warm or cold water? What is said of the solubility of nitrate of potash in water at different temperatures? How is the solubility of. sulphate of soda in water affected, as the temperature of the water is raised? 296 SALINE COMPOUNDS, OR SALTS. Crystals of soluble salts may generally be obtained by making a saturated solution at an elevated temperature and allowing it, to cool slowly. Thus, a saturated solution of alum at 100 or 150, on cooling deposits beautiful octahedral crystals; and if a tree or basket made of copper wire is placed in the solution when warm, the crystals will attach themselves to it in various posi- tions, presenting a very beautiful appearance. 351, Salts soluble in water, and even some that are insoluble often retain in their crystals-a portion of water, which is called water of crystalization. Thus sulphate of soda in crystals con- tains JO equivalents of water, and its proper formula is NaO,SO 3 + 10 HO. This is the case however only when the crystalization takes place at a temperature below 92 or 93 ; when it crys- talizes at a higher temperature the crystals are anhydrous. The same salt will often combine with very different quantities of water when deposited from its solution at different temperatures. Sulphate of protoxide of manganese, crystalized from an aqueous solution, at 43, has the formula, MnO,S0 3 + 7HO; when crys- talized between 43 and 68 its formula is MnO,S0 3 -f 6HO; and again when crystalized between 68 and 86, its formula is MnO,S0 3 + 4HO. When a salt of the kind last mentioned is heated in the open air, it gives up its water in successive portions, as the tempera- ture is raised. Sometimes the last equivalent of water is held by a much stronger force than the rest, and can be driven off only by a red heat, and then an entire change in the nature of the salt takes place. The water in such a case is called constitutional water. 352. Sometimes a salt in a dry atmosphere loses a part or all of its water of crystalization, and falls to powder ; it is then said to effloresce. Again, some salts absorb moisture from the air, and are then said to deliquesce. Common pearlash (carbonate of pot- QUESTIONS. How may crystals of salts soluble in water often be ob- tained? 351. What i-s water of crystalization? Give an illustration. Will the quantity of water of crystalization often depend upon the tem- perature of the solutions from which the crystals are deposited ? What will be the effect when a salt of this kind is heated ? 352. When is a salt said to effloresce ? W T hen to deliquesce ? SALINE COMPOUNDS, OR SALTS. 297 ash) is an instance of a deliquescent salt. Left in the open air for a time, it will absorb sufficient water to effect its solution. 353. Water holding a salt in solution invariably has a higher boiling point than pure water. The following table shows the boiling points of saturated solutions of several of the salts. Boiling M* Chlorate of potash ............... 61-5 .............................. 220 Common Salt ...................... 41-0 .............................. 227 Nitrate of potash ................. 335-0 .............................. 241 Nitrate of Lime ................... 362-0 .............................. 304 But the steam from such boiling solutions, as it escapes into the open air (omitting any regard to variations of atmospheric pres- sure), will always be of the same temperature of 212. When a hydracid, as the 'hydrochloric, HC1, acts upon a metal, as zinc, the acid is decomposed, and a chloride of the metal formed, the hydrogen being set free ; thus, Zn -f HC1 ='ZnCl + H. So when liquid hydrochloric acid is poured upon potash, the reactions are KO + HC1,HO == KC1 + HO + H. In both these cases, therefore, as will be seen by an examination of the formulae, the particle of hydrogen of the hydracid has simply been displaced, and a particle of metal substituted. Now all the oxyacids, or nearly all, at least in their active state, contain water, as the sulphuric acid, S0 3 ,HO, and nitric acid, N.OgHQ. They may indeed be obtained free from water, as S0 3 , and N0 5 , but they are then solid and quite inert, possessing none of the active properties of the liquid acids, which, however, they immediately assume on the addition of water. The reaction between zinc and oil of vitriol is Zn + SOs,HO = ZnO,S0 3 + H. QUESTIONS. 353. What is said of the boiling point of water holding a salt in solution ? What is said of the temperature of the steam formed ? When a hydracid acts upon a metal what are the reactions that take place ? What when hydrochloric acid acts upon potash ? In these casea is the hydrogen simply replaced by the metal? Is the result the same when the hydrated oxyacids act upon the metals ? Explain by reference to the action of sulphuric acid upon zinc. 298 SPECIAL DESCRIPTION OP THE METALS. POTASSIUM. Now as hydrated sulphuric acid only, S0 3 HO, is capable of acting upon this metal, and not the dry acid S0 3 , may we not in this case also, in like manner, consider the metal as simply replacing the hydrogen ? If this view be adopted, as it has been by some eminent chemists, then it is required that the formulae of the hydrated acids, the sulphuric, nitric, &c., should be changed accordingly, sulphuric acid being not S0 3 ,HQ, but S0 4 ,H, or, as generally written, H,S0 4 . So also nitric acid is to be considered, not N0 5 ,HO, but H,N0 6 , and so of other acids. We shall not discuss the subject further, but simply give the formulae for several well known salts, according to the old and generally received view, and also according to the new view. Salts. Common Theory. New Theory. Sulphate of Soda NaO,S0 3 Na,S0 4 . Sulphate of Zinc ZnO,SO, Zn,S0 4 . Nitrate of potash KO,N0 5 K,N0 6 . Chlorate of potash KO,C10 6 K,C10 6 . Separate Description of the Metals. 354. The classification of the metals adopted in this work has already been indicated (342). / GROUP I. p *] Metals, the protoxides of which are alkalies. The protoxides I of these metallic elements are very soluble in water, and I possess in an eminent degree the peculiar properties denomi J nated alkaline properties. POTASSIUM. Symbol, K (Kalium); Equivalent, 39*2; Density, 0-865. 355. History. Potassium was first obtained by Sir H. Davy in 1807, from potash, which is the protoxide of the metal. He QUESTIONS. If this view be adopted, how should the formula for com- mon sulphuric acid, or oil of vitriol, be written ? How that for nitric acid ? 354. What metals are included in the first group ? How ar they characterized V 355. By whom was potassium discovered ? POTASSIUM. 299 procured it by subjecting a piece of caustic potash, slightly moistened, to the action of a powerful galvanic current, when oxygen made its appearance at the positive, and the metal potas- sium at the negative, electrode. Previous to this time, potash and the other alkalies and earths had been considered as simple substances. Potassium, in combination with oxygen and other bodies, is very generally diffused in the rocks and soils of every place, but is never found in nature in a separate state. It is contained in most vegetable and many animal substances. 356. Preparation. This metal is best prepared by heating intensely dry carbonate of potash mixed intimately with half its weight of fine charcoal-powder and iron filings. The potash, being an oxide of potassium, at a high temperature yields its oxygen to the charcoal and irqn, and itself distils over into a receiver prepared for the purpose. ^ The following apparatus answers well for the operation. A com- mon mercury bottle, A, covered with an infusible lute, and well dried, is three- fourths filled with cream of tartar that has been previously charred and mixed with one-fourth or one-fifth of its weight of pulverized char- coal, and placed in a proper furnace, with a piece of gun-barrel, B, about a foot in length, extending outward and connect- Jng With a receiver, C. Preparation of Potassium. QUESTIONS. How did Sir H. Davy procure potassium? How were potash and the other alkalies considered previous to this time ? Is pot- ash very generally diffused in nature? 356. How is potassium now usually prepared ? What is the effect produced by the charcoal ? De- Bcribe the apparatus figured in the margin, and the mode of using it. 300 POTASSIUM. A fire of hard coal is then kindled in the furnace (represented in section in figure), which should have a good draft, by con- necting with a chimney, GrF, of sufficient height, in order to produce the greatest heat possible; and the metallic potassium, as it is liberated in the gaseous state, escapes through the iron tube, B, and is condensed and collected in the bottom of the receiver, C. In this receiver some naphtha is placed, to project it from the atmosphere. Charred cream of tartar is used because it furnishes an inti- mate mixture of carbon and carbonate of potassa, but instead of it dry carbonate of potash (pearlash) may be mixed intimately with half its weight of pulverized charcoal. The receiver, C (seen in section), is best made \o of sheet copper, in two parts, M and N, the upper part, N, being without a bottom, and fittiog accu- rately into th lower part, M. The upper part, N, c is also divided into two parts by a vertical partition, as shown in figure j it is also provided with two tubulures, o and^, directly opposite-each other, the one, o, to receive the end of the gun-barrel, B (in Prep. of Potassium. ^ firgt Qf ^ aooompanying fi gures ) 7 and the other, p (corresponding to E in the first figure), to allow the insertion of an iron wire to remove the obstructions that will occasionally collect in the gun-barrel leading from the iron bottle. A small opening is also made for this purpose in the partition of the receiver, N. During the operation much incondensible gaseous matter passes over and escapes by a tube of glass (shown in the first figure) provided for the purpose ; and as it is necessary that the receiver should be kept cold, a small stream of cold water is made to fall upon it constantly, which is prevented from entering the lower part, M, by a rim of metal passing round it, as shown in the figures. The tubulure, p, is to be kept closed by a cork, except as it is necessary to remove it for a moment to insert the iron wire, when obstructions occur in the gun-barrel. The potassium, after the action has ceased, will be found in irregular masses in the naphtha at the bottom of the receiver ; QUESTION. Where will the potassium be found ? BINARY COMPOUNDS OP POTASSIUM. 301 but it will not" be pure. It is now collected in a bag of cloth, through which it is squeezed by compressing the bag with pincers while held in a cup of warm naphtha. If necessary, it may be further distilled in a small iron retort. 357. Properties. Potassium is a solid, in color and lustre much resembling lead. At 150 it melts, and at a dull red heat may be distilled in vessels void of gases capable of combining with it. It is the lightest metal known, having a density of only 0-865, and floats upon the surface of water. At ordinary tem- peratures it is soft like wax, but at 32 it becomes quite hard. But its most characteristic property is its affinity for oxygen ; when 'thrown upon the surface of water it absorbs the oxygen so rapidly as to be inflamed, and burns with a beautiful rose-colored flame. In the open air, the freshly-cut surface absorbs oxygen so rapidly as to be tarnished instantly ; and heated even in carbonic acid (303), it takes fire and burns combustion of by absorbing the oxygen. In consequence of its Potassium upon affinity for oxygen it can be preserved only in tubes hermetically sealed, or under some liquid that does not contain .oxygen, as naphtha, which is found to answer the pur- pose well. Binary Compounds of Potassium. 358. Protoxide of Potassium KO ; eq., (39-2 + 8 =) 47-2. This is potash, or potassa, and is always formed when the metal is exposed in the open air, or oxygen gas, or acted on by water. -In the latter case, the potash formed is immediately dis- solved by the water, as will be found by applying the usual tests. , Pure potash is a white, inodorous substance, with a pungent, , caustic taste, and very soluble in water. It absorbs carbonic acid QUESTIONS. 357. Describe some of the properties of potassium. What is said of its affinity for oxygen ? What is the effect when a small piece of it is thrown upon water? How is it preserved? Why is naphtha selected for this purpose ? 358. What is the common name for protoxide of potassium ? Describe potassa ? Does it usually contain water ? 26 302 BINARY COMPOUNDS OF POTASSIUM. and water rapidly from the air, and should therefore be kept in 'close bottles. When prepared by the slow oxydation of potassium in dry air or oxygen gas it is anhydrous, but when formed by the oxydatiou of the metal in water, or from any of its salts, it is always in the state of a hydrate. Potash forms with water two compounds, the monohydrate, KO,HO, and the pentahydrate, KO,5HO; the former of which is the caustic potash of commerce. To prepare it, pearlash (car- bonate of potash) is dissolved in ten times its own weight of water, and half its weight of recently-slaked lime mingled with it, in successive portions, and the whole boiled briskly for half an jiour. It is then allowed to settle, and the clear liquid is 'drawn off. The lime, in this process, decomposes the carbonate of potassa, and forms insoluble carbonate of lime, which settles to the bottom ; and the clear liquid contains nearly pure potassa. This may be pre- served for use in well-closed bottles, or it may be evaporated to dryness in a vessel of such a form as not to allow any con- siderable accession of air. To insure per- fect purity, it must be again dissolved in absolute alcohol, and the solution filtered and evaporated as before. The hydrate is soluble in alcohol, which is not the case with sul- phate of potash, usually present in pearlash, or carbonate, portions of which may have escaped decomposition by the lime. 359, To prevent the absorption of car- bonic acid from the air while filtering, an apparatus like that figured in the margin is used. It consists of two vessels, A and D, of equal capacity, and connected with each Filtering Apparatus. other. The throat of the upper vessel or QUESTIONS. What hydrates of potash are mentioned? How is pure caustic potash prepared from the carbonate? Why should it be dissolved in alcohol and filtered? 359. Describe the mode of filtering the alcoholic solution. BINARY COMPOUNDS OP POTASSIUM. funnel, A, is obstructed by a piece of coarse linen loosely rolled up, and not pressed down into the pipe through which the solution is filtered. The pipe, c, extending from e to 6, serves for the air to pass from the lower vessel to the upper j and the operation goes quietly on, free from contact with the atmosphere, except the little contained within the apparatus at the beginning of the process. Solution of potassa is highly caustic, and its taste intensely acrid. It possesses alkaline properties in an eminent degree, converting the vegetable blue colors to green, and neutralizing the strongest acids. It absorbs carbonic acid gas rapidly, and is consequently employed for withdrawing that substance from gase- ous mixtures. Potassa is employed as a reagent in detecting the presence of bodies, and in separating them from each other. The solid hydrate, owing to its strong affinity for water, is used for depriving gases of hygrornetric moisture. Caustic potash attacks all animal substances with avidity, and neutralizes all acids. With the fats and oils it combines readily, forming the well-known compound called- soap, of which we shall have occasion to speak again hereafter. This property is charac- teristic of all the alkalies. The pentahydrate possesses no special interest. 360. Peroxide of Potassium, K0 3 , as is shown by the formula, is a teroxide. It is of a dull yellow color, and is formed by burn- ing potassium in an excess of dry oxygen gas. Thrown into water, it gives up two-thirds of its oxygen, and solution of caustic potash is formed. 361. Chloride of Potassium, KC1, is readily obtained by neu- tralizing carbonate of potash, KO, C0 2 , by hydrochloric acid. The reactions which take place have already (347) been explained. Like common salt (chloride of sodium), it crystalizes in cubes, which are anhydrous. i. Iodide of Potassium, KI, is formed by heating potassium in contact with iodine; or, by digesting iodine in a hot solu- QUESTIONS. What is said of the action of potash upon animal sub- stances? What does it form with the fats and oils? 360. What is peroxide of potassium? 361. What is chloride of potassium? How is jodide of potassium formed? 304 SALTS OF POTASH. tion of caustic potash, and exposing the mass, when dry, to a red heat, and subsequently crystalizing from solution in water or alcohol. It is a white solid, very soluble in water, usually seen crystalized in cubes, and is often sold under the name of hydrio- date of potash. Solution of iodide of potassium has the property of dissolving iodine, and becomes of a brown color; it also dissolves other iodides, as the iodides of mercury. Iodide of potassium is much used in medicine, and in certain photographic processes. Bromide, KBr, and fluoride, KF, of potassium, like the chloride and iodide, crystalize in cubes. 362. Sulphides of Potassium. There are at least five sulphides of potas- sium, KS, KS 2 , KS 3 , KS 4 , and KS 5 , which, as shown by their formulae, contain, respectively, 1, 2, 3, 4, and 5 equivalents of sulphur in combina- tion with 1 equivalent of the metal. The most important of these is the pentasulphide, KS 5 , which is easily prepared by heating gently a mixture of carbonate of potash and sul- phur, or by boiling a solution of caustic potash with an excess of sulphur. It is a yellowish-brown solid, very soluble in water, and is used in medicine, especially in cutaneous diseases, under the name of hepar sulphuris, or liver of sulphur. The tersulphide is also used in the same manner. Salts of Potash. 363. Carbonate of Potash, KO,C0 2 . Carbonate of potash, or pearlash j is prepared for the purposes of commerce by leaching the ashes of forest trees, and evaporating the lye thus obtained to dryness, and then heating the dry mass to redness for a time in open vessels, to burn out the combustible matter which is con- tained in it. As thus procured, it is a white spongy mass, very caustic to the taste, and absorbs moisture rapidly from the airj so that it must be kept in close vessels. It is very soluble in water, but insoluble in alcohol, and is easily fused at a red heat. That lound in commerce is very impure, being mixed with silica and o'her substances. It is manufactured in large quantities in the United States, in the Canadas, and in Russia. QUESTIONS. What use is made of iodide of potassium ? 362. What is said of the sulphides of potassium ? 363. What is pearlash ? How is it prepared ? Describe it. What countries furnish it in large quantities ? SALTS OF POTASH. 305 If pure carbonate of potash is required, as is often the case in the laboratory, the tartrate (cream of tartar) or oxylate is heated to redness in the open air, treating the charred mass thus formed with warm water, and filtering. The solution may then be eva- porated to dryness, if the dry salt is desired. By slowly evaporating a solution of carbonate of potash the salt may be crystalized, though not without difficulty. The article sold as potash is the same as pearlash, except that it is not subjected to the last process of calcination. It is a dark- colored mass, and contains much caustic potash, as well as car- bonate, and is used extensively for the manufacture of soap. Pearlash is employed in the manufacture of glass and paints, and for various other purposes. 364, Bicarbonate of Potash, KO,2C0 2 . This salt is pre- pared by subjecting pearlash in solution, for some time, to an atmosphere of carbonic acid, which is absorbed in large quantity. Though less caustic to the taste than pearlash^ it is still highly alka- line. It is less soluble also than pearlash, and less deliquescent. It may be obtained in crystals with less difficulty than the car- oonate, and the crystals contain a single equivalent of water. Their formula may therefore be written KO,C0 2 + HO,C0 2 , that is, the salt may be considered as a double carbonate of potash and water. This salt is extensively used under the name of salseratus. 365. Nitrate of Potash, KO,N0 5 . This salt, the saltpetre, or nitre, of commerce, is formed, in this country, by decomposing the nitrate of lime, which abounds in the caverns of some of the Western StateSj by carbonate of potash, and filtering and eva- porating the solution thus obtained. In some parts of Europe it is prepared in nitre-beds, which are made by heaping together old mortar, refuse animal matter, wood-ashes, &c., in which it gradually forms by the action of the atmosphere. The mass is QUESTIONS. How may pure carbonate of potash be prepared ? What is the article known in commerce as potash ? 364. How is bicarbonate of potash prepared ? May it be obtained in crystals ? By what name ifl it familiarly known ? 365. By what names is nitrate of potash known in commerce ? How is it prepared in this country ? How in some parts of Europe ? 26* 306 SALTS OF POTASH. lixiviated with hot water; and the solution by evaporation yields crude nitre. Nitrate of potash is usually seen in long six-sided prisms. It is a colorless salt, of a cooling saline taste, and is very soluble in water. Its density is about 1-93. Heated to redness, it first melts and is then decomposed, giving off, at first, pure oxygen, and afterwards, if the heat is increased, nitrogen and nitric oxide. Thrown on burning charcoal it is decomposed, producing violent deflagration, by which it may always be distinguished from sul- phate of soda, for which it has sometimes been mistaken. It is a powerful antiseptic, and is used with common salt in the preserva- tion of meat and other substances. But the chief use of nitre in the arts is in the manufacture of gunpowder, which is composed of nitre six parts, and charcoal and sulphur each one part, the whole being moistened and thoroughly ground together, and subsequently pressed and granu- lated. When fired, the nitre, by its decomposition, furnishes oxygen, which combines the carbon, forming carbonic acid, the sulphur at the same time uniting with the potassa. The action of gunpowder depends upon its generating, when decomposed, a large quantity of gaseous matter at a high temperature. The gases are chiefly nitrogen and carbonic acid, which, at the moment of explosion, occupy more than 1000 times the volume of the powder from which they are formed. The formation of the gases is not instantaneous, but occupies a certain time, and the ball is forced from the gun with a velocity due to the ultimate effect of the whole. When made for particular purposes, the proportion of the ingre- dients is sometimes considerably varied. We may, in fact, con- sider gunpowder as of three kinds, which may be called sporting powder, war powder, and blasting powder; the former of which is required to detonate more rapidly and violently than either of the others. The composition of the three kinds is usually about as follows : QUESTIONS. Describe nitrate of potash? How does heat affect it? What is the effect when it is thrown upon burning charcoal? What uses are made of it? What is the composition of gunpowder ? What are the chemical reactions that take .place when it is fired ? Upon what doos the action of gunpowder depend ? What different kinds are mentioned ? SALTS OF POTASH. 307 For sporting powder. For war powder .., Nitre 76-9 parts. Sulphur 9-6 " "^Carbon 13-5 " 100-0 " ...Nitre 75-0 parts. Sulphur 12-5 " Carbon 12-5 " For blasting powder.... 100-0 " .Nitre 62-0 parts, Sulphur 20-0 " Carbon 18-0 " 100-0 " Theoretically, it would seem that the best proportion would be 1 equivalent of nitre, 1 equivalent of sulphur, and 3 equivalents of carbon. Thus, - KO,N0 6 -fS-f3C = KS + N + 3C0 2 . The proportion by weight of the several ingredients would then be as follows : In 100 parts. Nitre, 1 equivalent 101-2... 74-85 Sulphur, 1 16-0 11-84 Carbon, 3 18-0 13-31 100-00 This is very nearly the same proportion as that given for war powder above; but the reactions which take place in the combustion of the powder not being necessarily the same precisely as indicated in the above formula, nor, indeed, in any two cases with the same powder, consider- able variation in the proportion of the ingredients may be allowed. For the best powder, the materials should be freed from all impurities before using them. 366. The comparative force of different specimens of gunpowder, or the initial velocity a given quantity of it will communicate to a ball of a given weight, is determined by several modes, only one of which, called the ballistic pendulum (see figure on next page), will be described, and that very briefly. It is composed of two parts, the ballistic pendulum, P, and the pendulum-gun, G, the former of which, P, consists of a conical box, containing a mass of lead, suspended by an iron rod, inthe manner of a QUESTIONS. What is the difference in the composition of the three kinds of gunpowder ? Is the composition of gunpowder exactly the same as would seem to be required by the chemical formula ? 366. How is the comparative force exerted by different kinds of gunpowder, when fired, determined? Describe the ballistic pendulum. 808 SALTS OF POTASH. Ballistic Pendulum. pendulum, from some very firm support. G- is a common gun-bar- rel supported in an frame, which is also suspended in the man- ner of a pendulum, the gun-barrel, when hanging freely, being made to point to the mass of lead. At m n and op are graduated arcs, each having at- tached to it a slider, which is carried along with the movement of the rod to the furthest point to which it oscil- lates, but does not re- turn with it. The gun-barrel is now charged with the proper quantity of'the powder to be tested, and the ball placed in it, and fired ; and the ball being projected into the mass of lead causes it to move to the left (as the appa- ratus is represented in the figure) to a certain distance, which will be exactly shown by the slide upon the graduated arc, m n. At the same time the gun-barrel will recoil to the right, as will be shown by the slide upon op: The initial velocity of the ball may now be calculated from .the distance either slide has traversed, by means of the proper mathe- matical formulae. To insure accuracy, attention must be paid to several particulars in the adjustment of the apparatus, which are not here alluded to. 367. Sulphate of Potash, KO,S0 3 . This salt is easily pre- pared artificially by neutralizing carbonate of potassa with sul- phuric acid; and it is procured abundantly by neutralizing with carbonate of potassa the residue of the operation for preparing nitric acid (221). Its taste is saline and bitter. It generally crystalizes in six-sided prisms, bounded by pyramids with six sides, but its primary form is the right rhombic prism. The crystals contain no water of crystalization, and suffer no change by exposure to the air. They decrepitate when heated, and enter into fusion at a red heat. They require 16 times their weight of water at 60, and 5 of boiling water for solution. QUESTIONS. 367. How may sulphate of potash be prepared arti- ficially ? What are some of its properties ? SALTS OP POTASH. 309 368. Bisulphate of Potassa, KO,2S0 3 , is easily formed by ex- posing the neutral sulphate with half, its weight of strong sulphuric acid to a heat just below redness, in a platinum crucible, until acid fumes cease to escape. It has a strong sour taste, and reddens litmus paper, and in crystals may be considered a double sulphate of potassa and water, KO,S0 3 -|- HO,S0 3 . It is much more soluble than the neutral sulphate, requiring for solution only twice its weight of water at 60, and less than an equal weight at 212. " It is resolved by heat into sulphuric acid and the neutral sulphate. 369. Chlorate of Potash, KO,C10 5 . This salt is formed, to- gether with chloride of potassium, by passing a current of chlorine through a strong solution of pearlash. The reactions are as follows : 6KO,C0 2 + 6C1 = 5KC1 + KO,C10 6 + 6CO Z . The carbonic acid escapes during the process, and the chloride of potassium being very soluble remains in solution, while the chlorate crystalizes in shining white scales. The chlorine, before entering the potash solution, should be made to pass through a three-necked bottle containing a little Preparation of KO,C10s. water, to separate any sulphuric acid which may pass over with it. The proper arrangement is represented in the figure. QUESTIONS. 368. How is bisulphate of potash formed? 369. Ho-w is chlorate of potash formed ? Describe the reactions that take place. 310 . SODIUM. Its taste is not nnlike that of nitre, but it is much less soluble than that salt. Heated moderately, it melts, and at a red heat is decomposed, giving up the whole of its oxygen. Thrown on burning charcoal, it deflagrates like nitre, but more energetically. A few of the crystals, wrapped in tin-foil, with a piece of phos- phorus, or a little sulphur, explode violently by a blow from the hammer. It was formerly used in the manufacture of Lucifer matches, and has been substituted for nitre in gunpowder; which, however, when thus prepared, is liable to explode from causes so slight that its manufacture is dangerous. The silicates of potash will be described hereafter. 370. Sulphur-Salts of Potassium. Protosulphide of potassium, as the electro-positive element, combines with many other electro-negative sul- phides, forming true salts (345), but we shall here describe only the following two : Hydrosulphate of Potassium, or, more properly, the hydrosulphate of sulphide of potassium, KS,HS, is prepared by passing a current of hydro- sulphuric acid (263) through a solution of potash. When the solution is concentrated the salt may be obtained in crystals. Carbosulphate of potassium, KS,CS 2 , may also be crystalized. It ia prepared by pouring bisulphide of carbon into an alcoholic solution of protosulphide of potassium. SODIUM. Symbol, Na (Natron} ; Equivalent, 23; Density, 0-972. 371, History and Preparation, Sodium was discovered in 1807, by Davy, a few days after the discovery of potassium, The first portions of it were obtained by means of galvanism; but it may be procured in much larger quantity by chemical pro- cesses, precisely similar to those just described for obtaining potassium. Its preparation is less difficult than that of potassium. QUESTIONS. Describe the properties of chlorate of potash. What is the effect when it is thrown on burning charcoal ? What use has been made of it ? Why may it not be used in the formation of gunpowder ? 370. How is hydrosulphate of potassium formed? What is its com- position ? What is the composition of carbosulphato of potassium ? 371 . How is sodium prepared ? BINARY COMPOUNDS OF ODIUM. 311 372. Properties. Sodium has a strong metallic lustre, and in color is very analogous to silver. It is so soft at common tem- peratures, that it may be formed into leaves by the pressure of the lingers. Sodium soon tarnishes on exposure to the air, though less rapidly than potassium. Like that metal it is instantly oxydized by water, hydrogen gas in temporary union with a little sodium being disengaged. When thrown on cold water, it swims on its surface and is rapidly oxydized, though in general without in- flaming } but with hot water it scintillates, or even takes fire, and burns with a beautiful yellow flame, which readily distinguishes it from potassium. . By throwing two pieces, one of sodium and another of potas- sium, at the same time, into a vessel of water, both will usually be inflamed; and the characteristic colors of their flames will be seen together. Sodium is preserved under naphtha in the same manner as potassium. Binary Compounds of Sodium. 373. Protoxide of Sodium NaO; eq., (23 + 8 =) 31. This compound, usually calle.d soda, is formed by the oxydation of sodium, as potassa is from potassium. With water it forms a solid hydrate, which is easily fusible, and very soluble both in water and alcohol. It is a powerful alkali, and very similar in all its properties to potassa. Hydrate of soda is prepared from the carbonate in the same manner as the hydrate of potash. The hydrate is known as caustic soda ; it contains a single equivalent of water, and its formula is therefore NaO,HO. Peroxide of Sodium, Na0 8 , is formed by burning sodium in dry air or oxygen gas. QUESTIONS. 372. Describe the properties of sodium. What is the effect when it is thrown upon water ? How is it preserved ? 373. What is soda ? Describe its properties. By what name is the hydrate of soda known ? What is peroxide of sodium ? 312 BINARY. COM POUNDS OF SODIUM. 374, Chloride of Sodium Nad; eq., (23 + 354 =) 584. This is the common salt of commerce. It may be formed by burning sodium in chlorine, but is obtained in great abundance as a solid deposit, called rock salt, in various parts of the world, as in England, Poland, and at Abingdon in Virginia ; and in solution in the waters of brine springs, which abound in New York, Pennsylvania, Virginia, Kentucky, Ohio, and other States, as well as in other countries. Sea- water contains about 2-7 per cent, of this substance, while the water of the great salt lake in Utah Territory contains about 20 per cent. Around this latter body of water are plains, many miles in extent, which, in the dry season, are covered with incrustations of very pure salt to the depth of more than half an inch. In the rainy season it is more or less dissolved. Rock salt is sometimes mined of sufficient purity for use, and requires only to be pulverized ; but more frequently it is mixed with clay and oxide of iron, and must then be dissolved, and the pure liquid drawn off and evaporated. In 'warm countries, as on the coast of Portugal, in the south of France, and the West India Islands, this substance is obtained by the spontaneous evaporation of sea-water, which is allowed, on the rise of the tide, to flow into shallow basins, being 4 passed from one to another, as it becomes more concentrated; and finally, the evaporation is finished by means of artificial heat. In cold countries, as on the borders of the White Sea, the pro- cess is commenced in a very different manner : the sea-water is exposed to the cold atmosphere, by which a large part of the water is separated in the form of ice, and the remaining liquid portion is drawn off and evaporated. Pure chloride of sodium has an agreeably saline taste. It fuses at a red heat, and becomes a transparent brittle mass on cooling. It deliquesces slightly in a moist atmosphere, but undergoes no change when the air is dry. In pure alcohol it is insoluble. It QUESTIONS. 374. What is the common name for chloride of sodium? Where is it found in the solid state ? What are brine springs ? What is the proportion of it contained in sea-water? In the water of the great salt lake in Utah Territory ? How is this substance procured in certain warm countries ? How in certain cold countries ? Describe some of the properties of common salt ? BINARYCOM POUNDS OF SODIUM. 318 requires twice and a half its weight of water at 60 for solution, and its solubility is not increased by heat. It crystallizes in cubes, which are anhydrous, and have a density of about 2' 13 when its solution is slowly evaporated in the open air hopper-shaped crystals, as figured in the margin, are of common occurrence. Their formation may be explained as fol- lows : first a small cubical crystal forms at H opper-f^m Crystal the surface of the solution, which tends to sink and depress the surface, as shown in the figure A. Soon Cryst. Common Salt. other small crystals form and attach themselves to the first one at its four upper horizontal edges, by which it is a little more de- pressed, as represented in the figure B ; a further addition in the same manner causes a further depression, as seen in C, and SO On. Cryst. Common Salt. A saturated solution of common salt does not freeze even at 0, but hydrated crystals are formed which have the formula, NaCl + 4HO. It fuses at a red heat, and may even be sublimed without change. The uses of this substance are well known. Besides the ordi- nary purposes to which it is applied, in preserving meat from putrefaction, and in seasoning food, it is used extensively in the arts, in glazing pottery-ware, in the manufacture of bleaching- salt, carbonate of soda, hydrochloric acid, &c. The name, salt (Lat., sal), was originally given to this sub- stance alone, but was subsequently extended to an immense class of compounds which have been known as salts. By our present QUESTIONS. Describe the mode in which hopper-formed crystals are sometimes produced. What are the uses of this substance? Does it belong to the family of salts, according to the definition of the werd which we have adopted ? 27 314 SALTS OP SODA. technical arrangement (347), it is entirely excluded from the class. Sodium forms definite compounds with iodine, bromine, fluorine^ sulphur, &c., but they are not described in this work. Saks of Soda. 375, Sulphate of Soda, NaO,S0 3 . Sulphate of soda, or Glau- ber's salt, is sometimes found native in dry situations, but more frequently in solution in the waters of mineral springs. It is also obtained in the manufacture of hydrochloric acid (236). It was first made known by Glauber, from whom it received its name, although he himself called it sal-mirabile. It has a cooling, saline, and somewhat bitter taste ; and is very soluble in water at a temperature 91 or 92, but less so in water that is very cold or very hot (350). The crystals of this salt usually contain more than half their weight of water of crystalization, which escapes when they are exposed to the open air, and they crumble into a white powder. Their proper formula is NaO,S0 3 +10HO. The water therefore constitutes nearly 56 per cent., as will be found by making the calculation. Sulphate of soda is used in medicine as a cathartic, and for the preparation of the carbonates of soda. Bisulphale of Soda may be obtained in crystals which have the formula, NaO,2S0 9 -f 3HO. Deprived of its water of crystalization, it may be used in preparing anhydrous S0 3 (259). 376. Hyposulphite of Soda, NaO,S 2 2 . This salt, which is much used in the daguerreotype process, for removing the sensitive coating from the silver plate, after being taken from the mercurial vapor bath, is prepared by first passing a current of sulphurous acid gas through a solution of car- bonate of soda, to form sulphite of soda, and then dissolving sulphur in a concentrated hot solution of the sulphite. It mjay be obtained in crystals, which, according to some, contain 5, and according to others, 10 equivalents of water. It is also called * dilhionate of soda. QUESTIONS. 375. What is Glauber's salt? What are some of its pro- perties? What is said of its water of crystalization? What use is made of it ? 376. What use is made of hyposulphite of soda ? SALTS OF SODA. 315 377. Carbonate of Soda, NaO,C0 2 . The carbonate of soda of commerce was formerly obtained by lixiviating the ashes of sea-weeds, in the same manner as the carbonate of potassa is obtained from the ashes of land-plants. But it is now manu- factured altogether from .common salt, which is first converted into sulphate of soda by sulphuric acid, and then the sulphate, mixed with charcoal and carbonate of lime, is heated intensely in a wind-furnace. The materials, which consist of about 2 parts of the anhydrous sulphate, 2 parts of chalk (carbonate of lime), and 1 of charcoal, are well ground together, and in- troduced upon the hearth, H H, of a reverbatory furnace, similar to that represented in section in the figure ; and by continued action of the heat, carbonate of soda, NaO,C0 2 , oxysulphide of calcium, CaS,CaO, and carbonic oxide,- CO, are formed : the latter compound being gaseous, of course passes off. The oxysulphide of calcium being insoluble in water, it is now only necessary to digest the black mass which comes from the furnace in warm water, and filter, and a solution of carbonate of soda is obtained. This is now evaporated to dryness. It may be obtained in crystals, which always contain much water of crystalization, and effloresce in dry air. It is the sal soda of commerce. The mixture as taken from the furnace is the soda ash, or British barilla of commerce, and has been sometimes used as a manure. , Carbonate of soda is extensively used in the manufacture of glass and hard soap, and for other purposes. Sesqnicarfoonate of Soda, 2NaO,3C0 2 , called trona, is found in the waters of certain lakes in Egypt, in Hungary, and in this country in springs among the Rocky Mountains. Preparation of Carbonate of Soda. QUESTIONS. 377. From what was carbonate of soda formerly obtained? How is it now manufactured ? Describe the process. 316 8 ALTS OF SODA. 378. Bicarbonate of Soda, NaO,2C0 2 . This salt is formed by exposing the carbonate in solution to an atmosphere of carbonic acid, in the same manner as the bicarbonate of potash. Like the cor- responding salt of potash, it always contains one atom of water, and may be considered a double carbonate of soda and water, according to the formula, NaO,C0 2 + H'0,C0 2 . It is often used by bakers as a substitute for sal-aeratus. 379. Biborate of Soda, NaO,2B0 3 . This salt occurs in solu- tion in the waters of certain lakes in Thibet and the East Indies, from which it is obtained by evaporation, and was formerly im- ported into this country and England under the name of tincal. When refined, by solution and recrystalization, it is sold as borax, a substance well known for its extensive use in the arts in various metallurgic operations. At present, most of the borax of com- merce is obtained from Tuscany, where it is prepared by adding carbonate of soda to the native boracic acid (826) of the hot springs which abound in an extensive volcanic district of th.it country. To obtain it pure, several recrystalizations are required. Ordinary borax crystalizes in right rhombic prisms,- which con- tain 10 equivalents of water ; but when crystal] zed from a hot solution the crystals are octahedrons, and contain only 5 atoms of water. When borax is heated, it first loses its water of crystalization, which causes it to froth up very much ; and at a red heat fuse& into a clear transparent liquid, which on cooling has the appear- ance of glass. At high temperatures, it dissolves most of the metallic oxides, and becomes colored. Borax is used as a flux in metallurgic operations, in the pre- paration of certain kinds of glass, and in medicine. 380. Nitrate of Soda, NaO,N0 5 , resembles nitrate of potassa in many of its properties, but cannot be substituted for it in the manufacture of gunpowder, because of its tendency to absorb QUESTIONS. 378. What is bicarbonate of soda ? What use is made of it ? 379. Where is biborate of soda obtained ? What is it often called ? Where is most of the borax of commerce obtained at the pre- sent time ? What use is made of it ? 380. For what is nitrate of sod\ used? SALTS OF SODA. 317 moisture from the atmosphere. It is used instead of nitrate of potash in the preparation of nitric acid, and sometimes as a manure. 381. Phosphates of Soda. Phosphoric acid forms with soda (and the bases) three series of salts, viz., tribasic or ordinary phosjrfiates, bibasic or pyrophosphates, and monobasic or mcta- phosphates, corresponding to the three states (282) of the acid. ' I. Tribasic Phosphate of Socfa. Of this there are three va rieties, viz. : 1. The salt, 3NaO,P0 5 . 2. The salt, (2NaO + 110) P0 5 . 3. The salt, (NaO + 2HO) P0 5 . The three varieties are tribasic, but the base of the first consists of 3 eq. of soda ; the base of the second of 2 eq. of soda and 1 eq. of water; the base of the third of 1 eq. of soda and 2 eq. of water. The water serving as base in such salts is called basic water. The first two varieties usually crystalize with 24 eq. of water, and the third with 2 eq. of water. If heated, they readily give up their water of crystalization, but a red heat is required to expel the basic water. All of them in solution give a yellow precipitate, 3AgO,P0 6 , with solution of nitrate of silver. II. Bibasic Phosphate of Soda Pt/rophosphate of Soda. This compound furnishes two varieties, viz., 1. The salt, 2NaO,PO 5 ; 2. The salt, (NaO + HO) P0 5 . Both varieties are bibasic, but the base of the first consists of 2 eq. of soda, and that of the second of 1 eq. of soda and 1 eq. of water. Bibasic phosphate of soda crystalizes with 10 eq. of water; the solution of both varieties gives, with nitrate of silver, a white precipitate, 2AgO,P0 5 . III. Monobasic Phosphate of Soda Metdphosphate of Soda NaO,F0 5 . This phosphate in solution gives a white precipitate with solution of nitrate of silver, AgO,P0 5 ; but its composition, it will be observed, differs from that procured from*the bibasic phosphate. Solution of this phosphate also has the property of QUESTIONS. 381. What is said of the salts formed with soda by phos- phoric acid ? What varieties of tribasic phosphate of soda are there ? How may they bo tested when in solution ? What varieties of bibasic phosphate of soda are there ? What is said of the precipitate they give with nitrate of silver f What is metaphosphate of soda ? 27* 818 LITHIUM. coagulating the whites of eggs, an effect not produced by the other phosphates. For the methods of preparing these varieties and sub-varieties of phosphate of soda, the inquiring student will consult larger works on this science, especially the excellent one of Regnault ; the object of the present work not permitting so much minute detail. With other bases phosphoric acid probably forms similar series of salts, but the subject has not been fully investigaged. 382. Characteristics of Potash and Soda Salts. All the salts of potash and soda that are soluble are distinguished from other metallic salts, except the salts of lithia, which are very rare, by giving no precipitate with solutions of the alkaline carbonates. It is therefore sufficient, practically, to be able to distinguish between these two classes of salts ; for which the following tests will suffice. With tartaric acid potassa forms a sparingly soluble salt, which, if the solution is moderately concentrated, appears as a white precipitate ; but with soda no precipitate is formed, as the corresponding salt of soda is very soluble. With potash a strong solution of chloride of platinum forms a yellow precipitate, the double chloride of potassium and platinum, which be- comes more copious by the addition of alcohol ; but in the same circum- stances no precipitate is formed by the salts of soda, because of the solubility of the double chloride of platinum and sodium. LITHIUM.' Symbol, lj ; Equivalent, 6- 4 ; Density, ? 383. History,. Etc. Lithium is a very rare substance, and is found only in a few minerals, as spodumeme, and the variety of mica called lepidolite. It is obtained from these in combination with oxygen as the protoxide, lilhia. From this the metal may be procured with some diffi- culty by means of galvanism. It is a white metal, like sodium. The protoxide, lithia, is a powerful alkali, like potash or soda, but is less soluble The name is from the Greek, lithos, a stone, in allusion to the source from which it is obtained. The salts of lithia, heated before the blowpipe, give a red tinge to the flame. QUESTIONS. 382. How are the soluble salts of potash and soda dis- tinguished from other salts? Describe the mode of distinguishing a soluble salt of potash from one of soda by means of tartaric acid. By means of solution of chloride of platinum. 383. What is said of lithium? From what is the name derived ? AMMONIUM. 319 Ammonium, (Not IsolaUe.') 384. History, Etc. This name is given to a supposed com- pound of nitrogen and hydrogen, NH 4 , which has never yet been obtained in a separate state, but is believed by many to enter into the composition of most of the ammoniacal compounds, and to possess in some respects the characters of a metal. Its symbol is written NH 4 , or Am. \ When strong aqua ammonias (225), in contact with a little mercury, which is connected with the negative electrode of the galvanic battery, is subjected to the action of a strong electrical current, ozygen is liberated at the positive electrode and the mer- cury increases very much in volume, and becomes less fluid, having the consistency of butter or soft lard, but still retains perfectly its metallic lustre. This has very much the character of an amalgam ; and we may suppose that under the influence of the current, ammonium, NH 4 (equal to NH 3 -f H) has been formed from the ammonia and the hydrogen of the water, and at once united with the mercury, the oxygen escaping at the other electrode. The same compound may also be obtained simply by com- bining a little potassium or sodium with 50 or 100 times its weight of mercury, and pouring on it a strong solution of sal ammoniac, NH 3 ,HC1. In this case the reaction seems to be KHg + NH 3 ,HCl = KCl+NH 4 ,Hg. This compound, called ammoniacal amalgam, when removed from the solution in which it was formed, rapidly undergoes spontaneous decomposition, yielding ammonia and hydrogen in the proportion of 2 volumes of the former and 1 volume of the latter. After a little time the mercury alone is found entirely unchanged. QUESTIONS. 384. What is the compound to which the name ammo- nium is given ? Has it been obtained in a separate state ? What is the mode of preparing ammoniacal amalgam by the xise of the galvanic bat- tery? Explain the. reactions by which we may suppose the new sub- stance to be produced. Describe the mode of producing it by the use of sal ammoniac in solution. ,What are the reactions that appear to take place ? What is the effect when the amalgam is removed from the solu- tion ? What are obtained when it decomposes ? 320 BINARY COMPOUNDS OF AMMONIUM. If this amalgam is subjected to a temperature of 32, it crys- talizes in cubes, and its decomposition is retarded. Although this compound, NH 4 , which has received the- name of ammonium, has not been obtained in a separate state, its existence in combination with other bodies would seem to be established ; and also its peculiar metallic character. It is capable of replacing potassium and sodium in combination, and is there- fore isomorphous with them. Ammonia, NH 3 , has heretofore (224) been described. It has been called volatile alkali, because of its reactions with other substances, and especially with the acids, being the same as those of the other alkalies, the protoxides of potassium, sodium, and lithium. We 'introduce the subject again for the purpose of describing some of its more important compounds, which we shall do according to this ammonium theory, as it is called; because it affords us, in the present state of our knowledge, the most simple and lucid view of this important class of bodies that can be presented. But, at the same time, it should always be kept in mind that the existence of ammonium, NH 4 , even in com- bination with other substances, is not to be considered as fully determined. Binary Compounds of Ammonium. 385. Protoxide of Ammonium, NH 4 0, or AmO. As is the case with ammonium, the existence of this compound is hypo- thetical. But all the ammonia salts of oxygen acids, contain an atom of water in their composition, which appears to be essential to their existence. This atom of water, combined with the am- monia, NH 3 , forms the compound in question, protoxide of ammo- nium, NH 4 0, which unites with the acid to form the salt. Thus, the composition of nitrate of ammonia, as formerly supposed, is NH 3 ,N0 5 ,HO, which evidently is the same as NH 4 0,N0 5 , except as to the mode of the arrangement of the particles. QUESTIONS. How is this amalgam affected by a cold of 32 ? What is said of the relation of ammonium to potassium and sodium ? Why has ammonia been called volatile alkali ? 885. What is said of protoxide f ammonium ? SALTS OP AMMONIA. 321 As ammonium is isomorphous with potassium and sodium, so this compound is isomorphous with potash and soda, which it is capable of replacing in many of their compounds. 386, Chloride of Ammonium, NH 4 C1. This is the compound often called sal-ammoniac, and hydrochlorate of ammonia. If it be considered as a proper hydrochlorate of ammonia, its formula of course will be NH 3 ,HC1. It may be obtained by neutralizing carbonate of ammonia by hydrochloric acid ; but for use in the arts it is procured from the liquor obtained in the distillation of bones, in preparing animal charcoal, and also from that which condenses in the manufacture of coal-gas. The latter affords it in large quantities. Sal-ammoniac is a white solid, very tough, and difficult to pulverize, and has a density of about 145. It has a pungent, saline taste, and is very soluble in water; and sublimes without fusion at a temperature below redness. Triturated with recently- slaked lime, it yields ammonia, which is easily recognised by its pungent odor. It is used for various purposes in the arts and in medicine. Salts of Ammonia. 387. Carbonates of Ammonia, There are several carbonates of ammonia. The one best known is the sal-volatile of the shops, which is a sesquicarbonate. It is a semi-transparent solid, which is very soluble in water, and has the pungent odor of ammonia. Its composition, on the " ammonium theory," is 2NH 4 0,3C0 2 ; but considered without reference to this theoryj its formula is usually written 2NH 3 ,3C0 2 4-2HO. By long exposure to the air it is converted into a bicarbonate, NH 4 O,2C0 2 -f HO. Besides these, there is also a neutral carbonate of ammonia. Sulphate of Ammonia, NH 4 0,S0 3 . Sulphate of ammonia is a soluble salt, isomorphous with sulphate of potassa. It is some- QUESTIONS. Is ammonium isomorphous with potassium and sodium ? 386. What is sal-ammoniac ? How is it obtained ? Describe its pro- perties. 387. What carbonates of ammonia are mentioned? Describe sulphate of ammonia. 322 SILICATES OF POTASH AND SODA GLASS. <4 times found in the lava of volcanos, and may be formed artificially by saturating aqua ammonise or solution of carbonate of ammonia with sulphuric acid. It is sometimes used as a manure. Nitrate of Ammonia, NH 3 ,N0 5 + HO, or, as it is now con- sidered, nitrate of oxide of ammonium, NH 4 0,N0 5 , is prepared by neutralizing nitric acid with ammonia, or its carbonate. It IB a white salt, very soluble in water, and destitute of any arnmo- niacal odor. It is used in preparing nitrous oxide (215). 388. Phosphate of Soda and Ammonia, (NaO,NH 4 0,HO)P0 5 . This is the compound called microcosmic salt, and much used as a flux in blow- pipe operations. Its crystals contain 8 eq. of water of crystalization, which is given up at a very moderate heat ; and, at a high temperature, both the basic water and ammonia are expelled, and the very fusible metaphosphate of soda only remains. It is prepared by dissolving in 2 parts of hot water 6 or 7 parts of phos- phate of soda, and then adding 1 part of sal-ammoniac. On cooling, tho salt in question crystalizes, while chloride of sodium remains in solution. 389. Hydrosulphate of Sulphide of Ammo- nium, NH 4 S, HS. This compound, it will be observed, is a sulphur salt (345), being com- posed of two sulphides, sulphides of ammo- nium and hydrogen. It is prepared by pass- ing a current of hydrosulphuric acid through aqua amrnonige, which is to be kept cool during the operation. The apparatus repre- sented in the figure will answer for the purpose. It is much used in the laboratory as a test Preparation of NHf QUESTIONS. What occasions the red color of bricks ? 418. Describe glucinum, and the mode of preparing it. 419. In what is zirconium found? 420. What other metals are mentioned as belonging to this group ? Name the metals of Group IV. How are they characterized ? 421. Are the metals of this group as well characterized as those of some other groups ? MANGANESE. 345 water, but some of them also act slightly upon liquid water. This is the case more particularly with the first named, man- ganese ; but some of the others, as iron and zinc, are oxydized by water, at ordinary temperatures, especially if atmospheric air be also present. MANGANESE. Symbol, Mn; Equivalent, 28; Density, 8 -3. 422. History. Manganese was first obtained by Grahn, from the substance then called magnesia nigra, which has since been found to be an oxide of this metal. It received its present name to distinguish it from magnesium, which has already been de- scribed. It is 'never found in nature in its metallic state, but its compounds are very generally diffused, and traces of it occur in both animal and vegetable substances. 423. Preparation. Metallic manganese, in consequence of its great affinity for oxygen, is not obtained without considerable diffi- culty. To procure it, the black oxide, in fine powder, is mixed into a paste with oil and lampblack, and exposed, in a close cru- cible, to the highest heat of a powerful furnace. The oxide should first be heated alone in a covered crucible, to reduce it to the form of protoxide, and this then mixed with the lampblack and oil, as directed above. The last heating, which should be con- tinued two hours, is best performed in a porcelain crucible, well closed by a cover, and then luted in a common Hessian crucible, as shown in the figure, which represents a section through the Preparation of centres of both crucibles. "A little powdered Manganese, borax mixed with the materials facilitates the collection of the metallic globules into a mass. The metal will be found in a button at the bottom of the crucible. QUESTIONS. 422. Give "the history of manganese. 323. How is the metal prepared ? 346 BINARY COMPOUNDS OP MANGANESE. 424. Properties. Manganese is a hard, brittle metal, of a grayish-white color, and granular texture. It is exceedingly infusible, requiring the highest heat of a wind-furnace for fusion. It soon tarnishes on exposure to the air, and absorbs oxygen with rapidity when heated to redness in open vessels. In water at ordinary temperatures it is slowly oxydized, and the action becomes more decided as the heat is raised. The metal is best preserved in pieces of glass tube, hermetically N ealed. Binary Compounds of Manganese. 425. Oxides of Manganese, There are six oxides of man- ganese, viz. : The protoxide, MnO, which is a powerful base. The sesquioxide, Mn 2 3 , which is a weak base. The red oxide, Mn 3 4 ,=MnO + Mn 2 3 , a saline oxide (344 : 4). The binoxide, Mn0 2 , called also peroxide and Hack oxide. Manganic acid, Mn0 3 , and Permanganic acid, Mn 2 7 . 426. Protoxide of Manganese, MnO. This compound, though existing frequently in combination, is obtained in a separate state with some difficulty, in consequence of its strong tendency to absorb oxygen from the air. The following is the best method of procuring it. A glass tube with a bulb, A, near the middle, is provided, and the bulb partly filled Preparation of MnO. with powdered carbonate of manganese. A larger tube, B, is filled loosely with dry chloride of c&lcium, or pieces of pumice stone impreg- nated with strong oil of vitriol, and connected with the first tube, as QUESTIONS. 424. What are the properties of manganese? 425. How many compounds of manganese and oxygen are there ? 42G. Describe the mode of preparing the protoxide by means of hydrogen gas. BINARY COMPOUNDS OP MANGANESE. 347 shown in the figure. The two-necked bottle, C, contains pieces of zinc and water. When the whole is arranged as represented, some oil of vitriol is poured into the bottle, C, and the whole interior of the apparatus is soon filled with hydrogen gas, which is deprived of its moisture by passing the tube, B, so that dry hydrogen only surrounds the manganese compound. A spirit-lamp is now placed under A, the heat of which decomposes the carbonate of manganese, leaving the protoxide as a fine powder ; and the absorption of oxygen is prevented by the hydrogen. After a proper time the tube, A, may be removed, and the extreme point closed hermetically by the lamp ; the tube on the other side of the bulb may also be drawn out and closed in the same manner, which is accom- plished the more readily if, after intro- ducing the manganese compound, the tube has been a little, reduced, as Preparation of MnO. shown in the accompanying figure. Prepared in this way, the protoxide is a powder of a delicate green color ; and thus inclosed from the air, may of course be preserved for any length of time. 427. Peroxide of Manganese, Mn0 2 . This is the common, or Uach oxide, of this metal. It is found in considerable abun- dance in the State of Vermont, and in other places in this country, and in Europe. Heated alone, it is reduced to the sesquioxide, Mn 2 3 , but when heated with sulphuric acid it is reduced to the protoxide, with which the acid combines. This last operation may be performed in glass vessels. Heated with hydrochloric acid, chloride of manganese is formed, and chlorine evolved. It is much employed in the arts, in the manufacture of glass, and bleaching-salt, and for other purposes. When crystalized, it is called by mineralogists pyrolusite. The sesquioxide very much resembles the peroxide in appearance, and is often fraudulently sold for it. 428. Manganic Acid, MnO $ . This compound has never been obtained in a separate state, but only in combination with bases. It is interesting as the first metallic acid we are called to consider in the progress of our course. It is formed, in combination with potash, by heating equal weights of peroxide of manganese and nitrate of potash to dull redness in an open crucible. The compound, manganate of potash, is of a dark-green color, and has long been known by the name of chameleon mineral. Dis- solved in cold water, it forms a beautiful green solution, which by con- tinued dilution changes to blue, purple, and, finally, to a brilliant red. QUESTIONS. 427. Is the black, or peroxide, found native ? What use is made of it ? 428. Describe the mode of preparing manganate of potash. What is it called? 348 SALTS OF MANGANESE. IRON. Hence its name. The changes are much more rapid when hot water is used. 429. Permanganic Acid, Mn 2 7 . This acid, in combination with potash, is formed when solution of the manganate of potash is made with hot water, as above described, by the absorption of oxygen from the air. It is to the formation of this compound that the red color is owing, which is finally obtained by solution of chameleon mineral. From this red solution purple crystals of permanganate of potash may be obtained; but when an attempt is made to separate either this or the preceding acid from the bases with which they are united, they are decomposed. Chloride of Manganese is formed by digesting the black oxide in hydro- chloric acid. There are two known, the protochloride, MnCl, and sesqui- chloride, Mn g Cl 8 . Salts of Manganese. There are several salts of manganese, but the only one of im- portance in the arts is the following : 430, Sulphate of Manganese, MnO,S0 3 . This salt is formed by digesting the peroxide in strong sulphuric acid by the aid of heat, and filtering when it has become cold. The crystals of the salt are of a rose-red color, and are very soluble in water. They always contain some water of crystalization, the quantity depend- ing upon the temperature of the solution in which they are formed. Carbonate of Manganese, MnO,CO r is found na-tive in the mineral called diallogite. IRON. Symbol, Fe (Ftrrum)', Equivalent, 28; Density, 7 '7 to 7-9, 431. History, Iron, the most abundant and most useful of all the metals, has been known from the remotest antiquity. The ores of the metal, as well as the metal itself, and some of its manufactures, are mentioned in the writings of Moses, and it is well known the ancient Greeks and Romans were acquainted with it. Iron has been found native in small quantities in different QUESTIONS. 429. How is permanganate of potash formed ? 430. De- scribe the sulphate of manganese. 431. Has iron been long known? Has it been found native ? IRON. 349 countries, but recently a real mine of very pure iron seems to have been discovered in the territory of Liberia, on the western coast of Africa. The occurrence of iron of meteoric origin, associated with nickel, and sometimes with cobalt and other metals, is not uncommon. One mass, at least, of this kind was actually seen to fall from the atmosphere, which was subsequently examined ; but many others have been found in such situations as to leave no doubt that they originated in the same manner. As no such compound has ever been found in proper iron-mines, it is believed that these bodies must have their origin in some region foreign to the earth. Common meteorites, which have often been seen to fall from the atmosphere, are of a different composition, containing usually no metallic iron, but various compounds of iron, manganese, sulphur, &c. There are many ores of iron, but the most important are the hydrated peroxide, called by mineralogists brown hematite / the peroxide (specular iron, or red hematite), and the black or mag- netic oxide, which is a compound of the two preceding. The last is the natural magnet, or loadstone. English iron is obtained chiefly from the clay-iron stone, which is an impure carbonate of iron, found abundantly in connection with the coal-meas'ures ; but in this country the metal is extracted almost entirely from the ores previously mentioned. 432. Preparation. The preparation of perfectly pure iron is a matter of considerable difficulty ; but the ordinary method of reducing it from its ores, is, to heat them intensely, after having been reduced to small fragments, with charcoal or coke, and lime or siliceous sand, as the nature of the particular ore may require. The oxygen of the oxide of iron is absorbed by the heated carbon and carried off as carbonic acid, while the flux for so the lime or sand is called when used for this purpose unites with the earthy part of the ore and forms a fusible compound, that remains QUESTIONS. What is said of meteoric iron ? What metals are usually found in combination with meteoric iron ? What are some of the most important ores of iron ? 432. Describe the ordinary modes of reducing the ores of iron. Why are fluxes used in the operation ? 30 350 IRON. upon the surface ; the melted iron, by its superior weight, falling to the bottom. The nature of the flux used must depend, in any particular case, upon the character of the ore that is used. Most iron ores occur in the granite rocks, and therefore the gangue (that is, the earthy matter of the ore,) is mostly silica, which of itself is very infusible (323), but forms a fusible mass when mixed with lime. Limestone, in fragments, is therefore intro- duced with the ore, which is first by the heat changed to caustic lime, by expulsion of the carbonic acid ; and the lime then unites with the silica, producing the fusible silicate of lime, which, at the Jfcgh temperature, flows freely, and allows the reduced particles of iron to unite in a mass. Occasionally, an iron ore occurs in a limestone region ; and then, the lime alone being also infusible, a flux of silica (sand) is required. When a sufficient quantity of melted iron has accumulated in the furnace, it is drawn off by an aperture at the bottom, which is opened for the purpose. After the iron has been removed, the slag, formed by the union of the flux with the earthy matter of the ore, is also drawn off. The accompanying figure represents a section of a blast-furnace, which is used for the reduction of iron ores. It is usually built of stone, thirty or forty feet high, and .lined inside with fire-brick. The charcoal, or coke, and the ore, in proper proportion, with the necessary flux, are thrown in at top ; and A A are pipes leading from a powerful bellows, worked by water or steam- power, for supplying the blast of air. This air thus forced in, will, of course, be of the same temperature as the external atmo- sphere, and constitute the cold blast; but sometimes the hot blast is used, in which case the tubes are so arranged over the top of the furnace that they are kept hot by the blaze from the burning mass, and the air, passing through them, becomes heated, and enters the fire at a temperature of 400 or 600. When once put in operation, a furnace is usually kept in full employment for many months, until repairs are needed ; the fuel, QUESTIONS. What is used for flux when the ore is dug from siliceous rocks ? Describe the blast-furnace used for reducing ores of iron. How is the air sometimes heated before being forced into the furnace ? Is a furnace, when once heated, kept long in operation ? Blast-Furnace. IRON. 351 with a proper proportion of ore and flux, being regularly supplied at the top. The iron obtained by this process is thecas* or pig-iron of com- merce, and contains a considerable quantity of carbon and other substances, by which it is rendered much more fusible than pure iron, but is at the same time harder and more brittle. It receives it name from the fact that it may be cast, or melted, and poured into moulds, so as to form articles of any desired figure For this purpose, a pattern of the desired article is formed of wood, and moulded in sand; and the melted metal is poured into the" cavity thus produced. The iron is usually melted Pouring Cast-iron, in a cupola furnace, and drawn off in vessels lined with clay (see figure), from which it is conveniently poured. To convert cast into malleable iron, it is exposed, in a melted state, to a current of air, which plays over its surface, or is forced through it. The process is usually conducted in a reverberatory fur- nace, a section of which is shown in the figure in the margin. Gr is the grate upon which the fire is kindled, and H H the hearth which contains the melted metal. As the blaze from the fuel passes to the chimney, C, it comes in contact with the melted iron, and the carbon it contains and per- Puddling Furnace, haps other impurities is gradually burnt out, and the iron becomes malleable. This process is called puddling. But it is not absolutely essential that cast-iron should be fused in order to be changed into the malleable state. When small QUESTIONS. What is the kind of iron obtained by the process de- scribed? Why is it called cast-iron? How is it fashioned into articles of any desired form ? How is cast-iron converted into malleable iron? May small articles made of cast-iron be converted into malleable irou without, being fused ? Describe the pi-ocess. 352 IRON. articles made of cast-iron are heated for a time in contact with powdered oxide of iron in close vessels, they are converted into malleable iron, and still retain their form perfectly. The carbon is gradually extracted by the oxygen of the oxide of iron used. 433. Properties. We have already, under the last head, in part described the properties of iron. It is a hard metal, of a peculiar gray color, and strong metallic lustre, which is sus- ceptible of being considerably heightened by polishing. Heated to redness, it becomes very soft and pliable, and is easily worked under the hammer, which gives it a decidedly fibrous structure. When malleable iron is strongly heated, it does not at once change to the liquid state, like most of the other metals, but becomes soft and pasty at the surface; so that two pieces in this state, upon being hammered or firmly pressed together, unite in one piece, or are welded together. Iron is, perhaps, all things considered, the most useful metal known, and it is owing in a great measure to this property, in which it is peculiar ; only a few other metals possessing it, in an inferior degree. Iron has a strong affinity for oxygen, and exposed to the air and moisture, it rusts, or oxydizes. Heated intensely in the blacksmith's forge, or in the flame of the compound blowpipe, it burns with brilliancy. The same effect is produced*by igniting a wire in a receiver of oxygen gas (192), or dropping iron-filings into the flame of a spirit-lamp. It has the property also of be- coming magnetic, under the influence of another magnet (121), or of the galvanic current (136). But pure iron loses its mag- netism when the influence of the current is removed. Some of the compounds of iron, especially steel and the black oxide, how- ever, retain their magnetism permanently. The iron of commerce is never pure, but contains in combination more or less carbon, and other substances. Perfectly pure iron can be obtained only by heating one of the oxides, QUESTIONS. 433. Describe the properties of iron. How is malleable iron affected when heated to redness? Describe the process of welding. Are there other metals capable of being welded? What is said of the affinity of iron for oxygen ? How is it affected when exposed to air arid moisture? How may iron be made to burn? How may pure iron bo procured ? IRON. 353 ar the protochloride, in an atmosphere of hydrogen. For this purpose, the same apparatus may be used as figured in paragraph 426 for forming protoxide of manganese. * The oxide or chloride being heated by a lamp, is decomposed by the current of dry hydrogen, and the iron remains as a grayish-black powder, which may take fire spontaneously if the air be admitted, but may be preserved any length of time by seal- ing the tube hermetically. By reducing the iron in a porcelain crucible, at a very high temperature, it may be obtained in a solid mass, with a metallic lustre. 434. Steel is a carbonide of iron. It is formed by heating bars of malleable iron in close vessels in contact with charcoal, by which process a small quantity of carbon is absorbed and incorporated with the iron. This process is called cementation; and, although the proportion of carbon absorbed by the iron is small, yet very important changes are produced in its properties. It becomes more fusible, and may now be melted like cast-iron, and at the same time has become harder, and is capable of being tempered, that is, of being made hard or soft, at pleasure. This is done by first heating the article to redness, and then cooling it suddenly by plunging it into cold water, or oil, by which it is made very hard and brittle, and subsequently heating it mode- rately, and allowing it to cool slowly. By the last heating, a partial annealing (336) is effected, and, if the operation has been well conducted, a proper degree of hardness is produced. Bars of steel, from the cementation process, always present a blistered surface, occasioned by the liberation of gaseous mat- ter probably carbonic oxide within their substance ; but when the metal has been melted and cast in moulds, it has a per- fectly uniform texture, and is called cast-steel. The melting of blistered steel, to form cast-steel, requires a very high temperature, and is performed in a furnace, a vertical section of which is represented by the first figure on next page. A is a small rectangular chamber, containing the crucible and fuel, and connects with the chim- ney, C, by a horizontal flue, B. The top of this chamber is covered with a lid, EF, which may be removed, at pleasure, to allow the introduction of the fuel and the crucibles, and the current of air is regulated by a iamper, B,. The crucibles are made of 'the most refractory clays, and of the form represented in the second figure. When the steel is perfectly QUESTIONS. 434. What is steel ? How is it formed ? In what does it differ from iron in its properties? How afre bars of blistered steel con- verted into cast-steel ? How are articles made of steel tempered ? What is meant bv this ? 80* 354 IRON. fused, the crucible is withdrawn, and the melted metal poured into iron ingot- iioulds prepared for the purpose. Melting Furnace. Crucible. Binary Compounds of Iron. 435. Oxides of Iron. There are four oxides of iron, as follows, viz : The protoxide, FeO, which is a powerful base. The sesquioxide, Fe 2 3 , which is a feeble base, isoraorphous with alumina, A1 2 3 . It is often called the peroxide. The oxide, Fe 3 4 , called also black or magnetic oxide, which is considered a compound of the proto and sesquwxides ; thus, FeO -f Fe 2 3 = Fe 3 4 . It belongs to the class of " saline oxides" (344 : 4). Ferric acid, Fe0 3 . The red, or sesquioxide of iron, is obtained by heating green vitriol (sulphate of the protoxide of iron) to redness in the open air, and is used as a polishing-powder, under the name of rouge QUESTIONS. 435. Describe the oxides of iron, qui oxide obtained ? How is the red or ses- IRON. 355 or colcothar. Earth or clay highly impregnated with it forms the red ochre used by painters. The black oxide constitutes the scale that always forms upon the surface of iron when heated to redness ^in the open air. Large accumulations of it are often seen by the side of the smith's anvil. This oxide, found native, con- stitutes the native magnet, or loadstone, as stated above. It is found crystalized in beautiful octahedrons, and in masses, and is one of the best ores of the metal. . Ferric acid, Fe0 3 , in combination with potash, as ferrate of potash, is formed by heating a mixture of iron-filings and nitrate of potash in an iron crucible ; and the salt may be separated from the mass by treating it with cold water. It cannot be obtained in a separate state. 436. Chlorides of Iron. There are two chlorides of iron, the proto- chloride, FeCl, and the sesquichloride, Fe 2 Cl 3 ; the first may be obtained by dis'solving iron in hydrochloric acid, and the second by treating the sesquioxide in the same manner. They possess no particular interest. 437. Sulphides of Iron. The protosulphide, FeS, of iron is readily formed by heating a mixture of iron-filings and sulphur, or by pressing a bar of iron heated to whiteness into a mass of sulphur. The sulphur and iron combine with great energy, and the liquid sulphide collects in a mass at the bottom, forming, on cooling, a hard, brittle solid. It is used in preparing hydrosul- phuric acid (263). Bisulphide of iron, FeS 2 , is the iron pyrites of mineralogists. It is of a beautiful yellow color, resembling gold, for which it has often been mistaken. It is usually crystalized in cubes. It is used in the manufacture of green vitriol and sulphuric acid ; and sometimes for extracting its sulphur. Though the sulphides of iron are very abundant in nature, they cannot be used for the extraction of the metal, because of the great expense it requires, and the iron obtained is of an inferior quality. 438. Carbonides of Iron. Both cast-iron and steel, as -we have seen, are considered as carbonides of iron, but the ingredients do QUESTIONS. What is the red ochre of painters ? What is the natural magnot, or loadstone f 436. Describe the chlorides of iron. 437. Describe the sulphides of iron. How may the protosulphide be formed ? FOP what is the bisulphide sometimes mistaken? 438. What is said of the carbonides of iron ? 356 SALTS OF IRON. not seem to be united exactly in definite proportions. Cast-iron usually contains from 2 to 5 per cent, of carbon, while steel seldom contains as much as 2 per cent. Graphite, called also plumbago, and black lead, has been considered as a carbgnide of iron, but probably it is only a particular form of carbon, usually containing a portion of iron as an accidental impurity. It is found abundantly in nature, and is used in the manufacture of pencils and crucibles, and as a polishing-powder for stoves and other articles made of iron. Protiodide of iron, Fel, is formed by digesting iron-filings or wire in water containing iodine, and evaporating the solution obtained. It is used in medicine. Salts of Iron. 439. Carbonate of Iron, FeO,C0 2 , occurs native and is called spathic iron, or steel ore, by mineralogists. An impure variety is called clay-iron stone. It may also be obtained by adding solu-tion of carbonate of soda to solution of green vitriol. Car- bonate of iron, though insoluble in pure water, is dissolved by water charged with carbonic acid, and is thus contained in the water of chalybeate springs. 440. Sulphate of iron, FeO,S0 3 . This salt is the green vitriol or copperas of commerce, so extensively used in the arts. In crys- tals it contains 7 eq. of water, and its formula of course is FeO,S0 3 4-7HO. The crystals belong to the monoclinic system. It is a sulphate of the protoxide, and is prepared on a large scale at Strafford, Vermont, and other places, from iron pyrites, which is first roasted slightly, and then exposed in heaps to the atmo- sphere, from which oxygen is absorbed, converting the sulphur into sulphuric acid, and the iron into oxide of iron; the two together then uniting to form the salt in question. For use in the laboratory, it is readily formed by the action of dilute oil of vitriol upon metallic iron. It often forms upon specimens of QUESTIONS. What is graphite? 439. Is carbonate of iron found na- tive? What is it called by mineralogists? 440. What is the green vitriol or copperas of commerce ? How is it manufactured in Vermont ? What use is made of it ? CHROMIUM. 857 : ron ores contained in cabinets, by the action of the atmosphere, md is seen as a yellowish-white powder. It is used in coloring black, and in the manufacture of writing- ink, and for other purposes. When this salt is heated it first parts with its water, and at a full red heat, with its sulphuric acid, a portion of which is de- composed into sulphurous acid and oxygen, but the rest passea off unchanged. By the oxygen of the decomposed acid, the iron is peroxydized, forming the colcothar of commence, before mentioned. 441. Nitrate of Iron, FeO,N0 5 . Nitric acid acts readily upon iron, and at the same time with the nitrate of iron there is formed also nitrate of ammonia, the ammonia being produced by the union of a portion of the nitrogen of the acid with the hydrogen of the water. The nitric acid should be considerably diluted. 442. Tests of Iron. The usual test for iron is solution of yel- low prussiate of potash, which forms with it a beautiful blue. For an experiment, let a small quantity of common hydrochloric acid be largely diluted with water, and then pour into it a few drops of solution of this prussiate, which will instantly give a fine sky- blue color if iron be present in the acid, as is almost certain to be the case. The iron is derived from the utensils made use of in the manufacture of the acid. With tincture of nutgalls, the soluble salts of iron form at first a dark-blue precipitate, which finally becomes black. CHROMIUM. Symbol, Cr; Equivalent, 26 -7; Density, 6. 443. iKistory, Etc. Chromium was discovered in 1797. It is found in considerable abundance in Massachusetts, Penn- sylvania, and other States, in the mineral called chrome iron, and also in combination with oxide of lead. Its name comes from the Greek chroma, color, in allusion to the splendid color QUESTIONS. 441. How is nitrate of iron formed? 442. What tests of iron are mentioned ? 443. What is said of chromium ? From what is the name derived ? 358 SALTS OP CHROMIC ACID. of many of its compounds. It is prepared by heating its oxides mixed with charcoal, but not without' difficulty. The metal has a white color, and distinct metallic lustre. It is very brittle, and with -difficulty fusible. Metallic chromium is not used in the arts, but several of its compounds are important. Binary Compounds of Chromium. 444. Oxides of Chromium, Oxygen forms several compounds with chromium, which, in composition and many of their pro- perties, are analogous to the oxides of iron and manganese ; so that these three metals form a kind of natural family, in the same manner as potassium, sodium, and lithium. Only two of these oxides, the sesquioxide, Cr 2 3 , and the teroxide, or chromic acid, Cr0 3 , are of sufficient importance to claim attention here. The former of these, Cr 2 3 , in combination with protoxide of iron, form- ing the compound, FeO,Cr 2 3 , constitutes the native chromic iron, which is the most abundant ore of the metal. It may be prepared by various modes, but the following is perhaps the best, as it leaves the oxide in a proper state for use in the arts. Heat in a crucible an intimate mixture of 4 parts of bichromate of potash and 1 part of starch, and wash the mass thoroughly with hot water, to separate the carbonate of potash that has been formed. The residue, after being dried, is again heated, and the pure sesquioxide remains. Sesquioxide of chromium is not decomposed by heat, and when fused with fluxes, it imparts to them a green color. It is used in staining glass and porcelain. It replaces alumina (415) in the chromic alums. Chromic acid Cr0 3 , is prepared by decomposing a saturated solution of bichromate of potash with 1 times its volume of oil of vitriol ; bisul- phate of potash is form'ed, and the chromic acid separates in brilliant red crystals, which are very soluble in water, and deliquescent in the air. It is a powerful oxydizing agent, and strong alcohol thrown upon the dry crystals is very soon inflamed. With bases it forms important salts. The chlorides and sulphides of chromium are not important. Salts of Chromic Acid. 445. The Chromates of Potash are formed by heating a mix- ture of native 'chrome iron in powder with nitre, digesting the QUESTIONS. 444. What is said of the oxides of chromium ? How may the sesquioxide be formed? How is chromic acid prepared? What is said of the action of alcohol upon it? 445. How is bichromate of potash formed ? ZINC. , 359 mass obtained in hot water, and saturating the solution with dilute sulphuric acid. After a little time the clear red liquid is poured off and evaporated, when crystals of bichromate of potash, KO, 2Cr0 3 , are separated, from the excess of sulphuric acid present, and the sulphates of iron and alumina. The neutral chromate of potash, KO,Cr0 3 , is now easily pro- cured by neutralizing a solution of the bichromate with carbonate of potash, and crystalizing. The bichromate, which is of a deep red color, is much used in dyeing, and in calico-printing, and for many purposes in the chemical laboratory. 446. Chromate of Lead, PbO,Cr0 3 . This is the beautiful chrome yellow, used as a paint. It is formed by mixing solutions of one of the chromates of potash and acetate or nitrate of lead. The beauty of the color will depend somewhat on the strength of the solutions used, and other circumstances. Chrome green is formed by mixing the chromate of lead with Prussian blue, in a particular stage of the process of manufacture. ZINC. Symbol, Zn; Equivalent, 32-5; Density, 7. 447. History. This metal has been known several centuries, but was not, for many years, much used. Its chief ores are calamine, which is a native carbonate, and blende, which is a sulphide; but several others are known. These ores are found in considerable abundance in New Jersey, and other parts of this country. 448, Preparation. The ores of zinc are reduced by first roasting them in the open air, and then distilling them with charcoal in close crucibles, from which a tube descends directly QUESTIONS. How is the neutral chromate of potash formed ? 446. De- scribe the mode of preparing chromate of lead. By w^fttxetime is it familiarly known ? What use is made of it ? How is chrome green pre- pared? 447. Has zinc been long known? What ores of it are men- tioned ? 448. Describe the mode of reducing the metal from its ores. 360 ZINO through the bottom. The metal is volatilized by the heat, and descends through the tube, from which it is received into a vessel of water. The necessity of excluding the air perfectly, arises from the fact that vapor of zinc, on coming in contact with the oxygen of the air, is at once oxydized; and the object of having the tube which conveys away the volatilized metal pass directly downward, is, to preserve its temperature so high that it shall not be- come clogged by the condensed metal. The figure in the margin represents the section of a crucible used for this purpose, with its charge of ore and charcoal, and tube made of fire-clay passing downward through the bottom. The cover is carefully luted on, and it is supported a little above the grate of the furnace by a fire-brick. The zinc, as it is separated from the ore, taking the gaseous state, passes downward through the tube into a basin of water placed below to receive it. The part of the tube below the bottom of the crucible, not being surrounded by the fire, remains comparatively cold ; and the metal, before it reaches the water, is condensed to the liquid state, and falls in drops into the water. Commercial zinc usually contains iron, lead, and other impurities, from most of which it may be separated by distillation in this manner. 449. Properties. Zinc has a -bluish-white color and a strong metallic lustre. In masses, it always has a highly crystaline structure, and in commerce it is called spelter. When cold it is quite brittle; but heated to about 300, it becomes malleable, and may be rolled into thin sheets. Heated to 773, it melts; at a little higher temperature, in the open air, it takes fire and burns with a brilliant white flame, producing the protoxide, which assumes an exceedingly delicate gossamer appearance, and has been called nihil album, pJiilosophers' wool, and by other names. Zinc is much used in the arts, in the preparation of brass, in the construction of galvanic batteries, and, rolled in thin sheets, as a substitute for sheet-iron and tin-plate. Recently it has been Crucible for reducing Zinc is it necessary to exclude the air? Describe the form of crucible used in reducing these ores. 449. Describe the pro- perties of zinc. What is its melting point? What is produced when it is highly heated in the open air ? What use is made of zinc ? SALT 8 OF ZINC. 361 considerably used as a coating for sheet-iron, in the same manner as tin, to protect it from oxydation. The iron thus prepared is known in the arts as galvanized iron. Binary Compounds of Zinc. 450. Protoxide of Zinc, ZnO. This is the only oxide of zinc known. It is of a yellowish-white color, and may be prepared, as above described, by heating zinc in the open air, or by precipi- tating it from solution of white vitriol (sulphate of zinc) by car- bonate of ammonia. It is much used in painting as a substitute for white lead ; and is manufactured on a large scale directly from the ores of zinc, in' France, and in New Jersey. 451. Chloride of Zinc, ZnCl. Chloride of zinc is formed by dissolving commercial zinc in hydrochloric acid, or by burning zinc in chlorine gas. By evaporation it may be obtained as a white solid, but is very deliquescent in the air. Mixed with sal-ammoniac, it serves an excellent purpose in tinning articles of copper, brass, and other metals. Sulphide of Zinc, ZnS. This compound of zinc is found native, and constitutes, as has been stated, one of its ores. It may be prepared arti- ficially by heating the metal with sulphur. * Salts of Zinc. There are several salts of zinc, but the most important is the following : 452. Sulphate of Zinc, ZnO,S0 3 . Sulphate of zinc is a white salt, which, in commerce, is called white vitriol. It is very soluble hi water ; and is sometimes used in medicine as a power- ful emetic. The ordinary salt contains 7 atoms of water of crystalization, and its formula is ZnO,S0 3 + 7HO; but by using the proper means, it may be crystalized with 5,. 2, or even 1 atom of water. QUESTIONS. 450. What is the only, oxide of zinc that is known ? What use is made of it? 451. How is chloride of zinc formed? To what use is it applied ? 452. What is sulphate of zinc called in commerce ? 31 362 CADMIUM. TIN. Oxide of zinc is precipitated from its soluble salts by the caustic alka- lies, but the precipitate is again dissolved by an excess of the alkali. Carbonate of zinc is found native, and called calamine. CADMIUM. Symbol, Cd; Equivalent, 56; Density, 8-6. 453. History, Etc, Cadmium is a very volatile metal, usually found associated with zinc. In appearance it can scarcely be distin- guished by the eye from tin, but is rather harder. It melts at 442, the melting point of tin, and sublimes at a temperature but little above the boiling point of mercury. Its properties indicate that it would be a useful metal in the arts, but it has hitherto been found only in small quantities. Protoxide of Cadmium, CdO, is the only compound of these two elements that is known. The protosulphide, CdS, is found native, as thegrenockite of mineralogists. TIN. Symbol, Sn ^Stannum); Equivalent, 58; Density, 7 '3. 454. History. Tin has been known from the most remote antiquity, and was in common use in the time of Moses. It is supposed the ancients obtained it chiefly from Cornwall, England, the mines of which still yield a large part of the tin of commerce. It is found also in India, Germany, Chili, and Mexico ; but has not yet been discovered in the United States, except a few small crystals of the oxide in Chesterfield, Massachusetts, and at Mid- dletown, Connecticut, and a small vein of the same ore in the town of Jackson, New Hampshire. The chief ores are the oxide and sulphide. 455. Preparation and Properties. Most of the tin of com- merce is obtained from the oxide, which is reduced by the action QUESTIONS. 453. What is said of cadmium? What is its melting point? 454. Has tin been long known? Where was it obtained in ancient times ? What countries now produce tiij ? Is it found in the United States ? What are the chief ores of tin ? 455. Mention some of its more important properties. BINARY COMPOUNDS OP TIN. 363 of charcoal at a high temperature. It is a brilliant white metal, . like silver, but is less hard than the latter It is very malleable, and is rolled into very thin leaves, called tin-foil. It is inelastic, and when a rod of it is bent, a peculiar crackling noise, called the cry of tin, is produced, occasioned by its crystaline structure. It melts at 442, and at a red heat is rapidly oxydized; at a whi^ heat it burns with flame. Tin is not readily acted on by the atmosphere or by moisture, bu dissolved slowly by hydrochloric acid, forming chloride of tin, and b. hot sulphuric acid, forming sulphate of the protoxide ; by dilute nitric acid it is converted into the binoxide, which is insoluble in the acids. Uses. Tin is used for many purposes, in the arts, both alone and combined with 'other metals, as in Britannia metal, which is an alloy of tin and antimony, with a small proportion of copper. It is also used extensively to coat sheets of copper and iron, to prevent the oxydizing influence of the air and moisture, and other agents. Thin sheets of iron, coated over with tin, constitute the well-known and highly useful tin-plate. Binary Compounds of Tin. 456. Oxides of Tin. There are two well-defined oxides of tin, the protoxide, SnO, and the peroxide, SnO a ; but the latter alone possesses sufficient importance to require a description. Peroxide of Tin is formed by exposing the metal to the action of nitric acid a little diluted. It may also be precipitated from a solution of the perchloride of tin (soon to be described) by an alkali. As obtained by the mode last mentioned, it is soluble in acids, but not as procured by the other mode. It is of a yellowish-gray color, and from the circumstance that it is capable of combining with bases in the manner of an acid, it has been called stannic acid. It is much used as a polishing-powder, under the name of putty of tin. Melted with ingredients for forming glass, it produces a white enamel. 457. Chlorides of Tin. Protochloride of Tin, SnCl, is formed by dis- solving the metal in boiling hydrochloric acid. By evaporating the solution it may be obtained in crystals, which contain 2 eq. of water. It is used as a mordant in dyeing, and as a powerful deoxydizing agent in the laboratory. The perchloride, SnCl 2 , is formed by distilling a mix- ture of 1 part of tin-filings and 3 parts of corrosive sublimate, or by cau- QUESTIONS. To what use is tin applied ? What is the tin-plate of com- merce? 456. What oxides of tin are known? What is the substance called putty of tin? To what use is it applied? 457. What chlorides f tin are there ? 364 COBALT. BINARf COMPOUNDS OF COBALT. tiously dissolving the metal in nitre-hydrochloric acid. It is much used as a mordant in dyeing, and as a disinfecting agent. There are two sulphides of tin; the persulphide, SnS 2 , sometimes called aurum musivum, or mosaic gold, has a yellow color, and metallic lustre, and is used as a paint, and also instead of the zinc amalgam (90) for exciting electrical machines. There are no important salts of tin. COBALT. Symbol, Co; Equivalent, 29 -5; Density, 8-5. 458. History, Etc. Cobalt is almost always found associated with nickel, the metal next to be described ; as found in mines both are usually in combination with arsenic. The pure metal is obtained with some difficulty. The best mode is to heat oxa- late of cobalt in a small crucible, on which a cover is closely luted. It is of a reddish-white color, and is hard and brittle, and difficult to fuse. It is capable of becoming magnetic. Cobalt is comparatively a rare metal. In combination with arsenic, it is found at Chatham, in Connecticut, in the minerals called smaltine and chloanthite. Binary and Other Compounds of CoLalt. 459. Oxides of Cobalt. There are two oxides of cobalt, the protoxide, CoO, and the sesguioxide, Co 2 3 , the former of which, mixed with some impurities, is sold in commerce as a gray powder, under the name of zaffre. Fused with silica and potash, it forms smalt, which is used for coloring glass, porcelain, &c., blue. The sesqui or peroxide is unimportant. 460. Chloride of Cobalt, CoCl, is formed by dissolving zaffre in hydro- chloric acid. The solution has a pink color, and yields by evaporation small crystals of the same tint. Writing made with a diluted solution of it is nearly invisible, but becomes of a beautiful but pale blue color when the paper is warmed by the fire, and again disappears as the paper cools. It has been called Hellofs Sympathetic Ink. The addition of a salt of nickel gives the writing a green color. The salts of cobalt possess no especial interest. The subcarbonate is a fine powder of a very delicate pink tint. QUESTIONS. What sulphides of tin are there ? 458. With what other metal is cobalt usually found associated ? Where is this metal found ? 469. What oxides of cobalt are there ? 460. How is chloride of cobalt formed ? Describe the mode of using Hellot's Sympathetic Ink NICKEL. ANTIMONY. 365 4 NICKEL. Symbol, Ni; Equivalent, 29-6 } Density, 8-8. 461. History, Etc. Nickel and cobalt, as. before intimated; are in nature almost inseparable companions. Arsenical nickel and cobalt are found at Chatham, in Connecticut, and also in Missouri, and in various places in Europe ; but mines of these metals are not common. Nickel is generally, if not always, com- bined with meteoric iron (431), of the mass of which it sometimes constitutes as much as ten per cent. Pure nickel has a grayish-white color, and strong metallic lustre. It is quite hard, but malleable, and is nearly as difficult to melt as iron. Like iron and cobalt, it is capable of becoming magnetic. It is not readily acted upon by the air or by moisture. It is much used in the arts to form the alloy called German silver, which is composed of copper 10 parts, zinc 6, and nickel 4. None of the compounds of nickel possess sufficient interest to require description here. GROUP V. ANTIMONY BISMUTH .LEAD JOPPE-R VANADIUM MOLYBDENUM TUNGSTEN TITANIUM URANIUM ' COLUMBIUM PELOPIUM Metals which are incapable of decomposing water, and whose oxides are not reduced by the mere action of heat. All of them, except lead and copper, are brittle ; and all, except antimony, bismuth, lead, and copper, are fusible only at very high temperatures. ANTIMONY. Symbol, Sb (Stibium}', Equivalent, 129'; Density, 67. 462. History. Antimony is remarkable as having been the first metal discovered after the seven metals (332) known to the QUESTIONS. 461. What is said of the metal nickel ? In what is it almost always found? Describe the metal. For what is it used? . How are the metals of Group V. characterized ? Name the metals of this group. 462. For what is antimony remarkable ? 31* 366 BINARY COMPOUNDS OF ANTIMONY. ancients. It has been found in the metallic state, but is prepared chiefly from the sulphide, which is not of unfrequent occurrence. 463. Preparation. The metal, called also reyulus of antimony, is obtained by heating the sulphide with iron-filings, or carbonate of potash. When iron-filings are used, the sulphur is simply transferred from the antimony to the iron, and, of course, sul- phide of iron is formed; but the metal thus obtained always contains a portion of iron, and is otherwise impure. By the other process, the sulphur is converted into sulphuric acid, which combines with the potash, forming sulphate of potash ; and the metallic antimony, being thus set free, falls to the bottom of the crucible. 464. Properties. Antimony is a very brittle metal, of a white color, and brilliant lustre. It always has a highly crystaline structure, and melts at a temperature a little below redness ; and may be slowly distilled in a current of hydrogen gas. A small fragment, heated on a piece of charcoal, before the blowpipe, takes fire ; and when thrown upon the floor breaks into numerous globules, which continue to burn as they are scattered, leaving a train to mark their path, and filling the air with fumes of the oxide. 465. Alloys of Antimony. Antimony, being very brittle, is not adapted for use alone in the arts, but with other metals it forms several very useful alloys. One of these, called Britannia metal, is composed, of tin 88 or 90 parts, and antimony 12 to 10 parts. Sometimes a small proportion of copper is added, not exceeding 3 or 4 per cent, of the whole. Its alloy with lead will be described hereafter. Binary Compounds of Antimony. 466. Oxides of Antimony. Antimony forms with oxygen two com- pounds which are well-defined, viz., oxide of antimony, SbO s , and and- monic acid, Sb0 6 ; but these are capable of combining with each other so as to form one or two other intermediate compounds. QUESTIONS. 463. How is antimony obtained from the native sulphide ? Describe the two processes. 464. Describe the metal. How is it affected When intensely heated in the air? 465. What alloys of antimony are used in the arts ? 466. What oxides of antimony are mentioned ? BISMUTH. 367 467. Chlorides of Antimony. There are two chlorides of antimony, SljCl 3 , and SbC' 5 , corresponding in composition, it will be seen, with the oxides. The terchloride, Sb01 3 , is sometimes called butter of antimony. It is soluble in a small quantity of water, but if the solution be diluted, a white powder is precipitated, called powder of algoroth. It is an oxy- chloride, SbCl 3 ,2Sb0 3 -f- HO. 488. Sulphides of Antimony. Two sulphides of antimony are known, corresponding in composition with the oxides and chlorides, and having the formulae SbS 3 , and SbS 6 . The first of these is the native sulphide ; when this is roasted in the air, oxygen is absorbed, and oxysulphid of antimony, SbS 3 -j- Sb0 3 , is formed, often called glass of antimony, or liver of antimony. When the native sulphide is boiled in a solution of potassa or soda, a liquid is obtained, from which, on cooling, an orange-red matter is de- posited, called Kermes mineral. On subsequently neutralizing the cold solution with an acid, the golden sulphide of the pharmacopoeia is ob- tained. These compounds . now possess little interest, but formerly were much used in medicine. The salts of antimony are unimportant, except tartar emetic, used in medicine, which will be described hereafter. BISMUTH. Symbol, Bi; Equivalent, 213 ; Density, 9-8. 469. History, Etc. Metallic bismuth is found in small quan- tities in Monroe, Connecticut, and other places, but is chiefly obtained from the native sulphide. In mass, it much resembles antimony in its crystaline structure, but has less lustre, and is of a reddish color. It is brittle when cold, but may be ham- mered when moderately heated. It melts at about 477, and sublimes at a high temperature. By melting a considerable quantity in a large crucible, placing it in a situation to cool very slowly, and pouring off all that remains liquid, as soon as it begins, to solidify at the surface, crystals of considerable size may be obtained. The metal is unchanged in the atmosphere, but tarnishes slightly by moisture. Heated in the open air it burns with a bluish flame. It is too brittle for use by itself in the arts, but with some other meta 9 QUESTIONS. 467. What is said of the chlorides of antimony ? 468. What sulphides of antimony are known ? 469. Is bismuth found native ? De- scribe the metal. May it be obtained in crystals ? What is said of its use in the arts ? 368 LEAD. it forms important alloys. It may be substituted, in whole or in part, for antimony in Britannia metal (4G5). In some of their chemical properties, antimony and bismuth are analo- gous to phosphorus and arsenic, and also to nitrogen. Binary and other Compounds of Bismuth. There are several oxides, chlorides, &c. ; but they possess no special iiterest. 470. Nitrate of Bismuth, BiO,N0 5 . This salt is formed by dissolving the metal in nitric acid. It is soluble in water ; but if the solution is largely diluted, the salt is decomposed, and subnitrate of bismuth precipi- tated. This last salt is used in medicine, and also as a cosmetic. LEAD. Symbol, Pb (Plumbum); Equivalent, 103-7; Density, 1144. 471. History, Lead is one of the seven metals known to the ancients. Its most important and most abundant ore, from which all the lead of commerce is extracted, is the sulphide, the galena of mineralogists ; but it is found in many other forms, as carbonate, sulphate, phosphate, &c. It is very abundant in different parts of this country. 472. Preparation. The metal is reduced from the native sul- phide by first roasting it in the open air, and subsequently heating it with lime in a charcoal fire. The ore usually contains a little silver, which remains in combination with the lead. The metal is also easily reduced by heating the native sulphide, in fine powder, with iron nails, in a close crucible. The sulphur of the ore, in this case, passes directly to the iron, forming sul- phide of iron. 473. Properties. Lead is a bluish-gray metal, and when recently cut has a strong metallic lustre ; but the surface soon tarnishes on exposure to the air. It is soft and malleable, but QUESTIONS. 470. Describe the nitrate of bismuth. 471. What is the most common ore of lead ? What other ores are mentioned ? 472. How is the metal reduced from the native sulphide ? What is the fiiecond modo mentioned ? 473. Describe the properties of lead. BINARY COMPOUNDS OF LEAD. 369 not very tenacious. Heated to about 635 it melts, and at very high temperatures is slightly volatilized. Exposed to the air and moisture, it is gradually corroded ; and a crust, the white car- bonate, is formed upon its surface. The peculiar properties of lead fit it for use in the arts for many purposes; but one of its most important uses is in con- structing pipes for conveying water. But when the water is to be used for drinking, care should always be taken to have the tubes kept constantly filled with water, as the introduction of air tends to form the highly poisonous carbonate ; and even then the water should not be used until it has been proved by experiment that the particular water to be discharged by the tube is not capable of acting upon the lead. Lead is gradually acted .on by boiling sulphuric acid ; but its only proper solvent among mineral acids is the nitric, which forms with it a soluble salt. 474. Alloys of Lead. Lead forms with other metals many useful alloys. Two parts of tin and one of lead, fused together, form soft solder, which is much used in cementing together the different pieces of articles made of tin-plate, Britannia metal, &c. A coarser kind, which requires a higher temperature to melt it, is composed of lead 3 parts and tin 1 part. Pewter is an alloy of lead and antimony, and sometimes a little copper. ' Type- metal is an alloy of 3 parts of lead to 1 of antimony. Tin, lead, and bismuth, form a very fusible alloy ; when made of 8 parts of bismuth, 5 of lead, and 3 of tin, it will melt in boiling water. Binary Compounds of Lead. 475. 'Protoxide of Lead, PbO. Protoxide of lead is formed by heating lead, in the open air, a little above its melting point; oxygen is gradually absorbed, and a yellow powder formed, which was formerly used as a paint, and called massicot. As usually manufactured, it is in the form of reddish-yellow scales, occa- QUESTIONS. What is said of the use of lead for water-pipes ? What is the only mineral acid that dissolves lead ? 474. What alloys of lead are mentioned? What is pewter? Type-metal? What alloy of lead melts in boiling water ? 475. How is protoxide of lead formed ? 370 SALTSOF LEAD. sioned by its having been partially fused. It is much used in painting as a dryer, and is called litharge. It fuses readily at high temperatures, and enters into combination with several of the earths and alkalies, producing a transparent glass, which renders it an excellent substance for glazing some kinds of earthenware. With powerful bases it is capable of combining as an acid. 476. Peroxide of Lead, Pb0 2 . This oxide is obtained by digesting red lead (the compound next to be described) in nitric acid, which dissolves out the protoxide, leaving the peroxide quite pure, in the form of powder. It is also called plumbic acid. 477. Red Oxide of Lead, Pb 3 O 4 . This compound is the red lead, or minium, of commerce, much used in the arts as a paint, and as one of the ingredients in the manufacture of flint glass. It is formed by heating metallic lead to a temperature of 500 or 600, in the open air, so as to oxydize it without fusing the oxide, and continuing the heat for some time. Heated to redness, it gives up a portion of its oxygen and is reduced to the protoxide. Minium is a compound of the proto and peroxides (2PbO,Pb0 2 ), and is therefore a plumbate of the protoxide of lead. 478. Sulphide of Lead, PbS. This compound has already been men- tioned as constituting the only important ore of lead, called galena. It is also formed by passing a current of sulphuretted hydrogen through a solution of any salt of lead. As it occurs native, its color very much resembles that of metallic lead, and its structure is always crystaliue. Salts of Lead. 479. Carbonate of Lead, PbO,C0 2 . This is the white lead of commerce, so extensively used in painting. It is formed by several different modes, and is also found as a natural production. Nearly all the white lead of commerce, at the present time, is adulterated by mixing sulphate of baryta (399) with it in fine powder. By treating the mixture with nitric acid, the carbonate QUESTIONS. What use is made of the protoxide of lead ? What is said of its fusibility? 476. Describe the mode of preparing the peroxide. 477. What is the red lead or minium of commerce? What use is made of it? 478. Describe sulphide of lead. 479. What is the white lesul used by painters ? With what is it usually adulterated ? How may the fraud be detected ? COPPER. 371 of lead will be dissolved, and the baryta left as a white powder. Taken into the system, white lead acts as a violent poison, pro- ducing the disease called painters' cholic. 480. Sulphate of Lead, PbO,S0 3 . Sulphate of lead is found native, and called anglesite by mineralogists. It is also formed when solution of any sulphate, as sulphate of soda, is mixed with solution of any salt of lead. It is sometimes used in painting as a substitute for white lead. Nitrate of Lead, PbO,N0 5 . Nitrate of lead is easily formed by dis- solving metallic lead, or its protoxide, or carbonate, in nitric acid. Zinc, iron, and tin precipitate lead from all its soluble salts in its metallic state. Make a solution of 1 part of nitrate or acetate of lead in 24 parts of distilled water, acidulated with acetic acid, and suspend in it, near the top, a piece of clean zinc ; the precipitation of the lead will immediately commence, and in the course of 24 or 48 hours, the metal will appear in the form of large thin leaves, called sometimes arbor Saturni. 481. Test of Lead. Hydrosulphuric acid precipitates lead, as a dark- colored sulphide from all its soluble salts, and even blackens those that are insoluble, as the carbonate, when suspended as a fine powder in water. COPPER. Symbol, Cu (^Cuprum)} Equivalent, 31-7; Density, 8-9. 482. History. Copper has been known from the earliest ages, and is often found in the earth in its metallic state. Masses of immense size of nearly pure metal have been found in the region of Lake Superior. One, 40 feet long, was estimated to weigh 200 tons. It is also found as a carbonate, sulphide, and oxide, as well as in other combinations. The ores of copper are very generally diffused, some of them being found in almost every country. 483. Preparation. Metallic copper is obtained from the oxides and the native carbonates, simply by heating these ores with char- coal; but the sulphide, especially when mixed with iron, is QUESTIONS. -480. What is said of the sulphate of lead ? Describe the mode of forming the arbor Saturni. 481. What test of lead when in solution is mentioned? 482. Has copper been long known? What is eaid of masses that have been found native ? What ores of copper are mentioned ? 483. How may the metal be reduced from its oxf des and carbonates ? 372 BINARY COMPOUNDS OP COPPER. reduced with more difficulty, and the process is too complicated fco be given here in detail. 484. Properties. Copper is distinguished by its peculiar red color. It is very ductile and malleable, but less tenacious than iron. To fuse it a bright red heat is required, but its melting point is much below that of cast-iron. It forms crystals belong- ing to the monometric system. It is less liable to be corroded by air and moisture than iron, but is gradually acted on by the joint agency of these elements, and becomes coated with a green crust, which is carbonate of copper. Heated to redness in the air, it becomes oxydized, andjiitric acid readily dissolves it. It is used extensively in the arts, both alone and in combination with other metals. 485. Alloys of Copper. Copper forms with other metals many very useful alloys. Three parts of copper with one of zinc con- stitutes brass ; and by a variation of the proportions, the alloys called tombac, Dutch gold, and pinchbeck, are produced. Bronze is an alloy of copper and about 10 per cent, of its weight of tin ; and bell-metal, an alloy of 4 parts of copper with 1 of tin; while speculum metal, used for the mirrors of reflecting telescopes, con- tains about 2 parts of this metal to 1 of tin. Equal parts of copper and zinc form hard solder, which is used in soldering articles of brass. Binary Compounds of Copper. 486. Oxides of Copper. Red oxide of copper, Cu 2 0, is a sub- oxide ; it is found native. The black or protoxide, CuO, is also found native, and is produced when copper is heated to redness in the open air. It is also easily procured by heating to redness the sulphate or nitrate of copper. There are two other oxides. Chlorides of Copper. Of these there are two, the subchloride, Cu 2 Cl, and the protochloride, CuCl, but they possess no special interest. Sulphides of Copper.- There are two sulphides of copper, corresponding in composition to the chlorides, viz., the subsulphide, Cu 2 S, and the proto- sulphide, CuS. Copper pyrites,, vitreous copper, and variegated copper are native sulphides of copper, or copper and iron. QUESTIONS. 484. How is copper readily distinguished from the other metals ? Describe its properties. 485. What alloys of copper are used in the arts ? 486. What oxides of copper are there ? What chlorides ? What sulphides ? SALTS OP COPPEE. 373 Salts of Copper. 487. Sulphate of Copper, CuO,S0 3 , or, in crystals, CuO,S0 3 -f 5HO. This is the blue vitriol of commerce; and is formed by dissolving the protoxide in sulphuric acid. It is very soluble in water, and is extensively used in the arts. Its color is a fme blue. 488. Nitrate of Copper, CuO,N0 6 , or, in crystals, CuOjNOg -f 3HO, is easily formed by dissolving metallic copper in dilute nitric acid. It does not crystalize readily; and is deliquescent in the air, and exceedingly corrosive. * 489. Carbonates of Copper. There are several carbonates of copper, as azurite and green malachite, which are found native, and are made use of as ores of copper. They also contain water. Green verditer, or mineral green, is a hydrated subcarbonate, obtained by precipitating a solution of blue vitriol with carbonate of potash or soda. Silicates of Copper, more or less hydrated, are found native in the mineraf species called dioplase and chrysocolla. 490. Arsenite of Copper, or ScKeele's ffreen, is prepared by first dissolving arsenious acid and pearlash together in warm water, and then pouring into it gradually warm solution of ;ulphate of copper. It is of a beau- tiful green color, and is much used in painting. In commerce, it is called Paris green. Test of Copper. Ammonia produces a deep blue color in diluted solutions of any of the salts of copper, by which they may always be distinguished. 491. Vanadium, V ; Eq., 68-6. This is a metal of rare occurrence, being found only in some iron ores in Sweden, some lead ores in Scot- land and Mexico, and recently in some copper ores from Lake Superior, Molybdenum, Mo; Eq., 46. Molybdenum is found as a sulphide IP. the mineral species called molybdenite, and also in other combinations. It is a white metal, and has a density of 8 '6." Tungsten, W, (Wolfram); Eft., 95. This metal is found in several mineral species, especially the "species called wolfram, which is a tung- ' state of iron and manganese. It forms several oxides, chlorides, sul- phides, &c. Titanium, Ti; Eq., 25. Titanium is found in several mineral species, as rutilc, anatase, and brookite. It is of a red color, and resembles cop- QUESTIONS. 487. What is the commercial name for sulphate of cop- per ? 488. How is nitrate of copper formed ? 489. What is said of the carbonates of copper ? 490. What use is made of arsenite of copper ? What test of copper is mentioned? 491. What other metals are men- tioned as belonging to this K group ? 32 374 MERCURY. per. Its density is about 5-3. The native oxide is used m coloring mineral teeth, so as to imitate the color of natural teeth. Uranium, U; Eq., 60. Uranium occurs in several species as pitch- blende, uranite, &c. Many binary compounds of it are known, as well as some of its salts. Columbium, Cb, is the name given to a metal found in the mineral species called columbite, which is obtained at Middletown and Haddam, in the State of Connecticut. Tantalum, Ta, is a metal very similar to the preceding, which is ob- tained from the European mineral, tantalite. Little is really known of these two metals*last mentioned. The existence of the two metals named pelopium and norium (Table, p. 145), is doubtful. MERCURY SILVER GOLD PLATINUM OSMIUM IRIDIUM PALLADIUM RHODIUM GROUP VI. Noble metals, ivhose oxides are reduced by a red heat. No one of them, except osmium, is capable of decomposing water under any circumstances. The oxides of iridium and ruthenium, and some of those of osmium, are not perfectly reduced by heat, without the presence of carbon, or some deoxydizing agent. " RUTHENIUM J MERCURY. Symbol, Hg (Hydrargyrum); Equivalent, 100; Density, 13-6. 492. History and Preparation. Mercury, or quicksilver, is on^ of the seven metals of the ancients. It is sometimes found in its metallic state ; but most of the mercury of commerce is reduced from the native sulphide, called cinnabar. It is not very generally diffused, -there being but few mines that afford it in any considerable quantity. Most of the mercury used in this country comes from Spain ', but it is obtained also in Germany, Siberia, in Southern Asia, and in California. The metal is extracted from the native sulphide either by roasting it alone, so as to oxydize the sulphur and sublime the mercury'; or by heating it with lime. QUESTIONS. What use is made of the native oxide of titanium 1 How are the metals of Group VI. characterized ? Name the metals of this group. 492. Was mercury known to the ancients ? By what other name is it known ? From what ore is it obtained ? What is the mode of ex- tracting the metal from the native sulphide ? *** MERCURY. 375 Besides the native compound above mentioned, there are other ores of the metal, but they are found only in small quantities. 493. Properties. Mercury is distinguished from all other metals by being liquid at -ordinary temperatures. It is white as silver, and has a brilliant lustre. Cooled to 40, it freezes or becomes solid, and is then very malleable, and nearly the color of lead j at 662, it boils and forms a colorless vapor, the density of which (air being 1) is 6-976. At lower temperatures, even as low as 70, it gives off vapor, as is shown by the whitening of pieces of gold-leaf suspended above it in a close glass bottle, and by its action upon the iodized silver plates in the Daguerreotype process. The best method to obtain solid mercury is by means of solidi- fied carbonic acid (58). A portion of the solid acid is made in the form of a ball, with a cavity in the uppe*r side to receive the mercury, and the whole enveloped in cotton to protect it from the atmosphere. In a few minutes the mercury will be solid, and may be preserved in this condition for several hours with a very small quantity of -the solid acid. The metal is also readily frozen by a mixture of the solid acid and ether. . By slow cooling, mercury forms crystals belonging to the monometric system. 494. Mercury is usually imported into this country in strong iron bottles, and generally is very pure, and serves for every purpose without purification. In this state it is scarcely oxydized by the atmosphere, but as it is capable of dissolving other* metals, as tin, lead, silver, and gold, by use in the laboratory it often becomes contaminated with them, and thus is more liable to become oxydized, as will be shown by a pellicle of oxide floating upon its surface. In this state, a portion will adhere to the fingers, or other substance, when dipped in it; and it' does not roll in perfect globules over the surface of other bodies, like pure mercury. , To purify mercury, several processes are resorted to ; one method is to pour it into a bottle with some sulphuric, acid, or dilute nitric acid, which oxydizes and dissolves the foreign metals. It should stand in the bottle several days, and be frequently shaken to expose all the metal to the action of the acid. At the proper time, the mercury is to be removed and washed with water. QUESTIONS. 493. Describe the properties of mercury. Give its freez- ing and boiling points. Does it evaporate at temperatures below its boiling point ? How may it be solidified ? 494. What other metals will mercury dissolve ? How may it be known when other metals are held in Bolution in it? Describe the method of purifying mercury. 376 MERCURY. Another method is to distil the mercury, by which it is separated perfectly from silver, gold, and tin, but not from arsenic, zinc, or cad- mium, which are also volatile. To distil mercury, a cast-iron vessel is used of the form represented in the figure. When using it, the cover should be well luted on, and the tube kept cold by a constant stream of cold water. To obtain mercury of sufficient .^^^^^^^^^ purity for use in thermometers and Distilling Mercury. % barometers, and especially the latter, it will generally be found necessary to subject it to both of these modes of purification in succession, the distillation being first in order. 495, The only acids that a'ct on mercury are the sulphuric and nitric acids. The farmer has no action whatever in the cold; but on the application of heat, the mercury is oxydized at the expense of the acid, pure sulphurous acid gas is disengaged, and a sulphate of mercury is generated. Nitric acid acts energetically upon mercury, both with and without the aid of heat, oxydizing and dissolving it with evolution of binoxide of nitrogen. 496, Uses, Mercury is made use of for many important pur- poses, in medicine, in the laboratory, and in the arts. In the construction of thermometers and barometers it is absolutely essential, and for the mercurial bath, to enable the chemist to collect and transfer gases that are absorbed by water. In union with various other substances it constitutes the bases of many important medicines. Several of these preparations will be described in their proper places. 497, Amalgams. This term is exclusively applied to the alloys of mercury with the other metals. Quicksilver unites with potassium and sodium when agitated in a glass tube with that metal, forming a solid amalgam. When he amalgam is put into water, the alkaline metal is gradually QUESTIONS. What will be necessary, in order to obtain mercury of sufficient purity for thermometers and barometers? 495. What acids only act upon mercury ? Explain the action of sulphuric acid. Of nitric acid. 496. To what uses is mercury applied? 497. To what is the name amalgam given ? BINARY COMPOUNDS OP MEROtFRY. 377 wxydized, hydrogen gas is disengaged, and the mercury resumes its liquid form. A solid amalgam of tin constitutes the silvering of looking- glasses ; and an amalgam made of 1 part of lead, 1 of tin, 2 of bismuth, and 4 of mercury, is used for silvering* the inside of hollow glass globes. This amalgam is solid at common tem- peratures; but it is fused by a slight degree of heat. The amalgam of zinc and tin (90) is used for promoting the action of the electrical machine. . Binary Compounds of Mercury. 498. There are two oxides of mercury, the gray oxide, which is considered a suboxide, Hg 2 0, and the protoxide, HgO, which is of a red color. The suboxide, Hg 2 0, is readily prepared by mixing calomel briskly in a mortar with pure potassa in excess, so as -to effect its decomposition as rapidly as possible, and then washing the precipitate formed in cold water, and drying sponta- neously in a dark place. This oxide is a black powder, and is insoluble in water, but unites with the acids as a weak base. The protoxide, HgO, is the red precipitate used in medicine. It is formed either by heating mercury nearly to its boiling point in a vessel to which the air has access, or by cautiously heating the nitrate so as to expel the nitric acid. The latter mode is the one usually adopted. It is usually seen in very small, shining, crystaline scales, which have a brick-red color. Heated to red- ness, it is decomposed, yielding mercury in the gaseous state, and oxygen. Red oxide of mercury is slightly soluble in water, and gives it an alkaline reaction. 499. Subchloride of Mercury, Hg 2 Cl; eq., (200 +35-4=) 235-4. This compound, the well-known calomel used in medi- cine, is easily prepared by pouring a solution of nitrate of the suboxide of mercury into a dilute solution of common salt, when QUESTIONS. What is it that forms the silvering of mirrors ? 498. What oxides of mercury are there ? How is the suboxide prepared ? How is the protoxide prepared ? What is it called ? How is it affected when heated? Is it soluble in water? 499. What is calomel? Describe the mode of preparing it. To what use is it applied ? 32* 378 BINARY COMPOUNDS OF MERCURY. the calomel is precipitated as a -white powder, which is insoluble in water and the acids when cold. It is sometimes found native, and is called horn-quicksilver, or native calomel. Its density is about 7. Calomel is sublimed without change by a moderate heat, and may be obtained in small crystals. It is usually seen as a white powder, with a slight yellowish tinge j and may always be knowr by instantly turning black as ink, when touched with a drop of aqua ammonite, or solution of any caustic alkali. This compound of mercury has long been extensively used in meelicine, and the estimation in which it has been held may, perhaps, be inferred from the names by which it has been known at different times, and in different countries. The following are some of them : Mercurius dulcis, draco miligalus, sublimatum dulce, aquila alba, aquila mitigata, manna metal-' lorum, panchymogogurn minerale, panchymogogum quercetanu's ! Calomel vapor has a density of nearly 8-2, and is composed of 1 vol. of mercury vapor, \ of a vol. of chlorine condensed to 1 vol. Thus, 1 vol. of mercury vapor weighs 6-976 " chlorine * " 1.220 1 vol. subchloride vapor weighs 8-196 500. Chloride of Mercury, HgCl; eq., (100 + 354=) 135 4. Chloride of mercury the corrosive sublimate of the pharma- copoeia is obtained either by acting on mercury by nitrohydro- chloric acid, or by sublimation from a mixture of sulphate of the protoxide of mercury, and common salt. The latter is the mode usually adopted in practice. Both the sulphate and the salt should be perfectly dry and well mixed ; the reactions will then be as follows : HgO,S0 3 + NaCl = NaO,S0 3 + HgCl. The sublimation may be effected in a retort of hard glass over a charcoal fire; and the operation should be conducted in such a situation that all the fumes escaping may be immediately con- veyed away by a strong draft of air. QUESTIONS. May 'calomel be sublimed? How many volumes of its constituents does one volume of it contain ? 500. How is chloride of mercury prepared ? By what name is it known in'pharmacy ? Describe the reactions wheel sulphate of mercury and common salt arc used in its preparation. BINARYCOMPOUNDS OP MERCURY. 879 As corrosive sublimate is usually seen, it is colorless, semi- transparent, and has a crystaline structure. It has an acrid, burning taste, and leaves a nauseous metallic flavor on the tongue. It has a density of 6-5, fuses at 509, and boils at 563. It is soluble in 16 times its weight of water, and in alcohol and ether. When its solution in water is agitated, with ether, the latter abstracts the* bichloride, and rises with it to the surface of the former ; and it may thus be separated from many other substances when contained with them in solution. Its aqueous solution is gradually decomposed by light, calomel being deposited. Applied externally, it is highly corrosive to the flesh; and taken internally is a most deadly poison. Albumen precipitates it as an inert compound, and is therefore indicated as a proper remedy in cases of poisoning with it. 501. The kyanizing (from the name of the inventor, Mr. Kyan,) of tim- ber consists in soaking it for a time in a solution of this substance, which protects it from the attacks of worins and insects ; and also, by combining with the albumen contained in it, preserves it from decay. The method given above for the preparation of calomel, though very easy, is not the one usually adopted in practice; a better result is obtained by mixing 100 parts (1 eq.) of mercury and 135-4 parts (1 eq.) of corrosive sublimate, and subliming with a moderate Ixeat, the whole being converted into calomel. Thus, Hg-f HgCl = Hg 2 Cl. 502. Iodides of Mercury. There are two iodides of mercury, corre- sponding in composition with the oxides and chlorides. The protiodide is precipitated as a beautiful red powder by mixing together solutions of iodide of potassium and chloride, of mercury. The powder, after washing and drying, may be sublimed by a moderate heat, but it then becomes yellow. After cooling, the color gradually changes to red; and the change is instantaneous if it is rubbed in a mortar. Its vapor has the highest density of any known gaseous substance, being 15-69. It appears to be composed of equal volumes of mercury vapor and iodine vapor, condensed to oe volume. 1 vol. iodine vapor weighs 8-716 1 " mercury " " 6-976 1 vol. vapor of HgLweighs 15-692 QUESTIONS. Describe chloride of mercury. Is it poisonous ? How is a solution of it affected by albumen ? 501. In what does the kyanizing of timber consist? Describe the mode of preparing calomel (or sub- chloride) by using the chloride and metallic mercury. 502. What iodides of mercury are there ? Describe the protiodide, and the mode of pre- paring it. What is said of the density of its vapor ? Of what is a volume of the vapor composed ? 380 SALTS OP MERCURY. 503. Sulphides of Mercury. There are two sulphides of mercury, which are exactly analogous in composition to the preceding compounds. The protosulphide, HgS, as we have seen, constitutes the chief ore of mercury, being found native, as cinnabar. It may also be prepared by art in several ways, and then forms the brilliant red pigment called vermillion. In vapor the density of this substance is about 5-4 ; and 1 volume of it ontains of a volume of mercury vapor, and J of a volume of sulphur vapor, as shown below : |- vol. mercury vapor weighs (6-976 x =) 4-651 vol. sulphur ^^ 0-739 1 vol. vapor of HgS weighs 5-390 As -f- - = - -j- a" = ' ^ * s ev ident that the union of these two sub- stances is accompanied by an expansion ; it is the only instance of the kind yet known. The other binary compounds of mercury possess no special interest. Salts of Mercury. 504. Nitrates of Mercury. Nitric acid acts violently upon mercury, and forms with its oxides several salts, differing from each other accord- ing as the temperature may be more or less elevated, or the acid more or le.=s diluted. Cold, dilute nitric acid acts slowly upon mercury, and forms With it a salt of the suboxide, which crystalizes with two atoms of water, and has for its formula Hg 2 0,N0 5 -f2HO ; but if the acid is hot, and of the usual strength, a salt of the protoxide is formed, which, when crys- talized, has the formula, 2HgO,N0 5 -f 2HO. Still other nitrates of this metal may be formed, but these are the most important. 505. Sulphates of Mercury. Sulphuric acid acts but slightly upon mercury when cold; but if healed, a sulphate of either the .suboxide or protoxide is formed, according to the temperature. If 5 parts of sul- phuric acid are boiled upon 4 parts of mercury, sulphate of the protoxide, HgO,S0 3 , is formed the compound used (500) in the manufacture of cor- rosive sublimate. Boiling water decomposes this sulphate, forming a yellow basic salt, 3HgO,S0 3 , called turpetk mineral. 506. Chlorosalts of Mercury. Protochloride of mercury combine- readily with other metallic chlorides, forming numerous crystalizable sajts, which by some have been called Ilydrar -go- chlorides. Compounds QUESTIONS. 503. What is said of the sulphides of mercury ? What is vermillion 9 Of what is one volume of vapor of HgS composed? What is said of the union of these two substances ? 504. What is said of the nitrates of mercury ? 505. What is said of the action of sulphuric acid upon mercury? 506. Does chloride of mercury combine with other metallic chlorides ? What are the compounds called ? SILVER. 381 of this character, -with the chlorides of potassium, sodium, lithium, am- monium, barium, &c., are made simply by mixing their solutions. The double chloride of mercury and ammonium was formerly used in medical practice, under the name of salt of alembroth. ' . SILVER. j Symbol, Ag (Argentum) ', Equivalent, 108; Density, 10'5. 507, History. This metal was known to the ancients. It frequently occurs native in silver mines, both massive and in octahedral or cubic crystals. It is also found in combination with gold, tellurium, antimony, copper, arsenic, and sulphur. In the state of sulphide, it so frequently accompanies galena, the chief ore of lead, that the lead of commerce is rarely quite free from traces of silver. Most of the silver mines, which afford the metal at the present day, are in South America and Mexico ; but in smaller quantities it is obtained in several countries of Europe, and other parts of the world. NearJy all the silver obtained from the mines at the present time is found native, or is extracted from the sulphide ; but there are many other mineral species which contain the metal. 508. Preparation. When metallic silver is contained in small particles, disseminated through the ore, it is extracted by tritu- rating the ore in fine powder with mercury, which dissolves the silver, and separates it at once from the mass, as an amalgam. The amalgam is then subjected to pressure in leather bags, by which a portion of the mercury is separated, and tjie remainder is expelled by heat. This is called the process Qfjftmalgamation. Other ores of silver require to be treated differently, but the numerous processes adopted cannot be here described. Silver is purified from small quantities of other metals present, except gold, by the process of cupellation, which has been prac tised from a very remote age. The process depends upon the QUESTIONS. What is salt of alembroth? 507. Has silver been long known? With what other metals is it found associated? From what ores is most of the silver of commerce extracted? 508. Describe the mode of extracting silver from its ores by the amalgamating process. 382 SILVER. fact that the metals (except gold) which are usually in combina- tion with silver, as copper, lead, tin, &c., are more oxidable than silver, and therefore when the alloy is kept for a time at a high temperature in the open air, these metals are oxydized, and the silver left perfectly pure. In large refineries, the oxide, as it is formed, is blown off by a bellows, so as to expose constantly a fresh surface to the air) but in small opera- tions, as in the testing of coin or plate, the cupel proper is used, which is made of bone- earth, of the form of a small cup, as represented Cupel< in the figure. This has the peculiar property of absorbing the mixed oxides as they are formed, and thus the necessity of using the bellows is avoided. For small operations, cupels are made about an inch in diameter, and half an inch deep. A vertical Section of cupel. section is shown in the annexed figure. 509. We will suppose the object is to test some coin or plate, which contains with the silver some copper, and perhaps a little tin or lead. A small piece of the alloy is accurately weighed, and placed in the cupel with 10 or 20 times its weight of pure lead, and subjected to a strong heat, in such a manner that the air shall have constant access to it. When it becomes suffi- ciently heated, oxydation of the lead and other metals com- mences, and the mixed oxides being absorbed as they are formed, after a little time the silver is left perfectly pure. The cupel with the silver is then removed, and when cold the button of silver is detached and again carefully weighed. The heating is usually conducted in a muffle, placed in a proper furnace, so as to exclude dust and smoke, but allow the access of air. The muffle (see figure) Muffle * s * n f a t a small oven, made of fire-clay, and is placed in the furnace so as to be entirely surrounded by the burning fuel, as shown in the figure on next page, which repre- sents a vertical section of the furnace through its centre, with the muffle in its place. M is the muffle, with several cupels in it; A, B and C openings, which may be closed at pleasure by means of fire-brick doors, A, B, C, prepared for the purpose. To insure perfect success in the. QUESTIONS. 509. Describe the process of cupellation. Of what is the cupel formed ? What purpose does it serve ? Describe the muffle. SILVER. 383 operation, attention is required to various particulars, which cannot be here given in detail. Alloys of gold, subjected to the same process, are purified from all other metals except silver and platinum. 510 Andther mode of testing alloys of silver, called the wet method, is to dissolve the silver alloy in nitric acid, and precipitate the silver by a standard solution of common salt, previously pre- pared with accuracy. This solution is made of such a strength, that 1000 parts of it, by measure, will precipitate exactly 1000 parts by weight of pure silver ; and the proportion of silver in the alloy will of course be determined by the number of parts of the solution required to pre- cipitate it. This is the mode practised at the United States mints, to determine the fineness of coin. This method cannot be .used when the alloy contains a metal, as mercury, whose chloride is insoluble. Section of Furnace and Muffle. 511. Properties. Silver is a soft, white metal, and is very malleable and ductile. It has a brilliant lustre, and is susceptible of receiving a very fine polish. It is not acted upon by the atmosphere or by moisture, but is readily blackened by sulphur. Articles of -silver often become tarnished, merely by the sulphurous gases which are diffused from the fires in houses in which mineral coal is used for fuel. Its melting point is about 1873, and if kept some time in fusion it absorbs oxygen in large quantity, which is given off again when the metal cools. Silver is attacked by sulphuric acid only by the aid of heat, but is freely dissolved by nitric acid, even when cold. Silver is used in every country for many important purposes for coin, and for manufacture into various articles of utility or ornament ; but to render it more stiff and hard it is always alloyed with a portion of copper. QUESTIONS. 510. Describe the wet method of testing alloys of silver. 611. Describe the properties of silver. What acids act upon it? For what purposes is silver used ? 884 BINARY COMPOUNDS OF SILVER. The standard of purity for silver coin varies in different countries; but the coin of the United States contains 900 parts of pure silver and 100 parts of capper ; that is, one-tenth part of the -weight of the coin is copper, except the three-cent piece, of which fths are silver and th copper. At the present time, the largest silver coin issued from the United States Mint is the half-dollar, which is required to weigh 192 grains ; the weight of the smaller coins being in the same proportion, except that of the three-cent piece, which is 12f grains. The quantity of pure silver in the half-dollar is, according to the above, 172-8 grs. = 192 19-2. This gives as the value of pure silver $1,38.8 per ounce. The value of coin is always estimated in proportion to the amount of pure metal it contains, no attention being paid to the alloy. It is remarkable that the addition of copper scarcely produces any change in the brilliant white color of silver, provided it does not exceed about one- eighth of the latter metal. Silver combines with other metals, forming alloys, which, however, possess no particular interest. Binary Compounds of Silver. 512. Oxides of Silver. Silver forms with oxygen three compounds, a suboxide, Ag 2 0, protoxide, AgO, and binoxide, Ag0 2 ; but only the protoxide is important. This is thrown down as a dark-colored powder, when solu- tion of caustic potash is poured into a solution of nitrate of silver. Heated to redness it gives up all its oxygen, and pure silver is obtained. It forms the base of all the oxysalts of silver ; is slightly soluble in water, but very soluble in aqua ammonise. By digesting this oxide for a time in concentrated aqua ammonise, a black compound is formed, which is highly explosive, sometimes called fulminating silver. Its composition has not been satisfactorily determined. The most probable opinion is, that it is a nitride of silver, NAg 3 , formed by the reaction : 3 AgO + NH 3 = NAg 3 4. 3HO. 513. Chloride of Silver, AgCl; eq., (108 -f 35-4=) 143-4. This com- pound is occasionally found as a natural production, and called horn silver, and is easily formed artificially, by pouring solution of common salt into a solution of nitrate of silver. Formed by this mode, it is a beautiful white powder, which, however, soon becomes purple in dif- fused light, or black if exposed to the direct light of the sun, or if warmed before a fire. It is insoluble in water, but soluble in ammonia and hyposulphurous acid. QUESTIONS. What proportion of the silver coin of this country is sil- ver? Wiat is the alloy? What is the largest silver coin now issued from the "United States. Mint? What does this give as the value per ounce of pure silver ? In estimating the value of coin, is any allowance made for the value of the alloy used? 512. What oxides of silver are there? Which of these constitutes the base of the salts of silver? 613. Describe the. chloride of silver. How is it prepared artificially? SALTS OF SILVER. 385 Nascent hydrogen reduces it to the metallic state by absorbing the chlorine to form hydrochloric acid. To effect the reduction, the chloride is covered with water acidulated with sulphuric acid, and pieces of zinc introduced, and the whole occasionally stirred. The metallic silver is obtained in fine grains. Iodide of Silver, Agl, is found as a natural production, and may also be formed by precipitation from solution of nitrate of silver by iodide of potassium. Sulphide of Silver, AgS. This compound is found in nature, alone, and in combination with other metallic sulphides, particularly sulphide of lead, in the ore called argentiferous galena. Sulphide of silver may also be formed artificially by several processes. Salts of Silver. 614. Nitrate of Silver, AgO,N0 5 . This is the only salt of silver of any practical importance, and is well known' by the name of lunar caustic. It is usually sold in small sticks, which are wrapped in paper, but may also be obtained in beautiful white, tubular crystals. The sticks usually contain a portion of nitre, which has been melted with it when cast in the moulds. Nitrate of silver is formed by dissolving silver in nitric acid, diluted with twice its weight of distilled water. It is soluble in one-half its weight of boiling water, and its own weight of cold water. It is the basis of indelible ink, as it is called; but writing done with it, and stains made by it, may be removed by solution of cyanide of potassium. Nitrate of silver is very caustic to the flesh, and is used in medicine as a cautery. From its solu- tion, metallic copper precipitates the silver as a fine powder; by mercury, the silver is thrown down in an arborescent form, which has been called the arbor Diance. Sttphate of Silver, AgO,S0 3 , may be formed by boiling sul- phuric acid upon metallic silver. It is a colorless salt, slightly soluble in boiling water. QUESTIONS. Describe the mode of reducing the chloride by means of zinc and oil of vitriol. What other binary compounds of silver are mentioned? 514. "What is lunar caustic? Describe its properties. What use is made of it ? 33 GOLD. GOLD. Symbol, Au (Aurum); Equivalent, 198; Density, 19-26. 515. History. Gold appears to have been known to the earliest races of men, and to have been esteemed by them as much as by the moderns. With the exception of the rare mineral telluride of gold, it has hitherto been found only in the metallic state, either pure, or in combination with other metals. It is sometimes found in quartzose rocks, but more frequently in alluvial depositions, especially among sand in the beds of rivers, having been washed by water out of disintegrated rocks in which it originally existed. Though usually found in irregular rounded lumps and grains, it is sometimes obtained in crystals of the monometric system as Crystals of Gold. represented by the accompanying figures, taken from the American Journal of Science. Gold is obtained at the present day in large quantities in California, Australia, and some parts of the Ural Mountains, and less abundantly in Hungary, and other countries of Europe. In small quantities, it occurs in Georgia, North Carolina, and Virginia. 516. Preparation. As gold exists in its ores in the metallic state, it is generally separated from them by the process of amal- QUESTIONS. 515. Give the history of gold. In what situations is it found? Is it occasionally found in crystals? 516. Describe the mode f separating silver from gold, called quartation. GOLD. 887 Carnation, similar to that already described for obtaining silver, by which means it is separated from all other metals except silver. To remove this, so much silver must be added to it that the gold shall constitute but a fourth of the whole, and the mass boiled in nitric acid, which then readily acts upon it, dissolving out all the silver, and leaving the gold in a state of purity. This process has been called quartatton, from the circumstance that the pro- portion of gold, in order that the nitric acid shall dissolve out all the silver, must not exceed a quarter of the whole mass. Other metals, except silver, may also be separated from it by cupel- lation (508). To prepare absolutely pure gold, a piece of coin may be dis- solved in aqua regia, and precipitated with soluti.on of sulphate of protoxide of iron. The reactions are as follows : AuCl 3 + 6FeO,S0 3 = Au'+ Fe 2 Cl 3 + 2(Fe 2 3? 3S0 3 ). The gold thus obtained is in a minutely divided state, and is of a purplish brown color. It is to be collected on a filter, and washed with very dilute hydrochloric acid, and fused with a little borax and saltpetre. 517. Properties. Gold is readily distinguished from all other metals by its brilliant yellow color, and by its great malleability and ductility. It is capable of being beaten out into leaves so thin that light may be transmitted through them, which then appears of a greenish yellow color. It is not acted upon by air or moisture, though exposed to their influence for ages ; nor is it oxydized by being kept in a state of fusion for any length of time. When intensely heated by the galvanic current, or by means of the compound blowpipe, it burns with a greenish blue flame, and is dissipated in the form of a purple powder, which is supposed to be an oxide. Selenic acid, aided by heat, dissolves it, and a mixture of selenic and hydrochloric acids, without heat ; but its proper solvent is aqua regia, which is a mixture of 1 part of nitric and 2 parts of hydrochloric acid. It fuses at about 2016. QUESTIONS. Why does the process for separating silver from gold here described receive the name quartaiion ? How may absolutely pure gold be prepared? 517. How is gold distinguished from the other metals? Describe some of its properties. What is the only proper solvent of gold ? 388 BINARY COMPOUNDS OF GOLD. 518. Gold and silver, from the estimation in which they have been held, have been long known as the "precious metals;" and it is usual to esti- mate their purity in carats. A carat is to be understood as J ? th part of the mass ; and a piece of gold or silver is 14, 18, or 20 carats fine, when so many 24ths of the whole are fine metal, the rest being alloy, But in the Mint of the United States, their fineness is estimated in thou- sandths: thus, gold or silver !s said to be "of the fineness 654, 789, 921, or 994 thousandths, when so many thousandths of the whole mass con sist of pure metal, the rest being alloy. The alloy of silver is always copper, but the alloy of gold may be either copper or silver, or a mixture of the two. Pure gold is so soft that some alloy is always needed to give it the proper stiffness, and to prevent too rapid wearing. In the gold coins of this country, one-tenth part is alloy, which is a mixtxire of silver and copper. The gold eagle of the United States weighs 258 grains, of which 25-8 grains are alloy. The value of standard gold is therefore estimated at $18.604 per ounce, and that of pure gold at $20.671 per ounce. Native gold is almost always alloyed with silver, but the proportion of this metal is very variable. Gilding consists in coating over the surfaces of bodies with a thin film of gold. Articles made of metal were formerly gilded .by applying to their surface, properly cleaned and smeared with nitrate of mercury, amalgam of gold, and then expelling the mercury by heat ; but this mode has been entirely superseded by the electrotype process, heretofore (116) described. In both cases the surface of gold requires to be burnished. . Articles made of non-metallic substances are gilded by a- coating of gold leaf. Binary Compounds of Gold. 519. Oxides of Gold. There are two, and perhaps three, oxides of gold ; but the teroxide, Au0 3 , alone possesses any special importance. It is of a yellow color when first formed, but becomes black when all the water is expelled. It is used in coloring glass and porcelain purple. In some cases it seems to act the part of a feeble acid, and has been called ' auric acid. 520. Chlorides of Gold. There are two chlorides of gold ; the terchloride, the one usually seen, is formed when gold is dissolved in aqua regia. By evaporating the solution carefully, the chloride may be obtained as a solid, which is very soluble in water, alcohol, and ether. Solution of chloride of gold is very easily decomposed by green vitriol, and by organic QUESTIONS. 518. Why have gold and silver been called the precious metals? How has the fineness of these metals, or rather alloys of them, usually been estimated ? What is meant when an article of gold or silver is said to be 18 carats fine? How is the fineness of these metals esti- mated at the United States Mint ? What is the alloy used for the gold coins of this country ? What is the weight of the United States eagle ? What does this give as the value per ounce of standard gold ? Of pure gold? How is gilding performed ? 519. What oxides of 'gold are there? 620. What chlorides ? PLATINUM. 389 substances, Protochloride of tin forms with it a beautiful purple powder, called purple of Cassius. Aqua ammonia precipitates, from solutions of terchloride of gold, a fulminating compound called fulminating gold, of uncertain composition. Salts of Gold. 521. The oxides of gold do not unite as bases with the acids, but the teroxide, as an acid, combines with bases, forming some unimportant salts, which are called aurates. Chlorosalts of Gold. Terchloride of gold combines with many other metallic chlorides, like the chloride of mercury, forming a series of chloro- salts, sometimes called auro-chlorides. PLATINUM. Symbol, Pt; Equivalent, 99; Density, 21 '5. 522. History, Platinum was first recognised as a distinct metal in 1741, but was not described until 1749. It has hitherto been obtained chiefly from Brazil, Peru, and some other parts of South America, and from the Ural Mountains. It occurs only in the me- tallic state, associated with other metals, as gold, silver, lead, palladium, osmium, iridium, and rhodium. 523. Preparation. To prepare pure platinum, the native grains, or com- mercial platinum, are dissolved in boiling aqua regia, and, after standing for a time, the clear solution is poured off, and the platinum precipitated by solution of sal- ammoniac, as a double chloride of plati- num and ammonium. By heating this precipitate, both the chlorine and am- monia are expelled, and the metallic QUESTIONS. How is purple of Cassius formed? 521. What is said of the chlorosalts of gold ? 522. Give the history of platinum. What is the state in which it occurs ? 523. Describe the mode of preparing pure platinum. 390 PLATINUM. platinum remains as platinum sponge, which, when treated with hot water, appears as a dark gray mud. This is now pressed in a hollow cylinder, by which means the particles of metal are made to adhere, so that the disc thus obtained may be carefully heated, and hammered on an anvil. The metallic grains now become firmly welded together, and the mass may be worked in any desired form. 524. Properties, Platinum is a white metal, much resembling silver, but of a darker color, and of inferior lustre. When pure, it is very malleable and ductile. It is the most dense substance known to man (except, perhaps, iridium), but is quite soft; and pieces of it, when heated, may be welded like iron, though not so easily. No single acid attacks it, but it is soluble in heated aqua regia. By heated nitre, or potassa, or soda, it is oxydized. It cannot be melted by the most intense heat of the hottest fur- nace ; but may be fused by the compound blowpipe. When a large surface of the metal is exposed to a mixture of oxygen and hydrogen, it has the singular property of causing them to com- bine, either silently or by an explosion. It acts in this way more readily when used in the spongy form (200, 523), as precipitated from its solution by sal-ammoniac. Platinum black, in which the metal is in a still more finely divided state, acts energetically in the same manner, causing the rapid union of various gases besides oxygen and hydrogen, when submitted to its influence. This form of platinum is prepared by electrolizing a dilute solution of chloride of the metal, or by boiling a solution of the chloride mixed with carbonate of soda and sugar. If a coil of platinum wire, recently ignited, be sus- pended in a deep glass, containing a little ether at the bottom, it will instantly become incandescent, and glow Wire of Plati- >vith a red heat ' uutil the etlier is entirel y dissipated. nam over Ether. The same effect may be produced by placing a coil of QUESTIONS. How are the particles of finely divided metal made to unite so as to form a solid mass ? 524. Describe the properties of plati- num. By what alone is it dissolved ? How is it affected by heated nitre or potash ? How is a mixture of oxygen and hydrogen affected when exposed to a large surface of this metal ? What is said of platinum black in this connection? Describe the experiment with a coil of platinum wire and ether. BINARY COMPOUNDS OF PLATINUM. 391 small platinum wire over the wick of a spirit-lamp, and after lighting it, suddenly extinguishing the flame. The wire will continue at a red heat until all the alcohol is consumed. Such a lamp (called a flamelcss 'lamp) is represented in the accompanying figure. 525. Uses. Platinum is of great importance in the laboratory, and is much used in the arts, especially for retorts for condensing (261) sul- phuric acid. Its present value in the market is about half that of gold. It was formerly issued AS coin by the Russian government, but the practice has been discontinued. Binary Compounds of Platinum. 526. Oxides of Platinum. Platinum forms with oxygen two compounds, the protoxide, PtO, and the peroxide, Pt0 2 , both of which are feeble bases, and unite with some of the acids to form salts. Chlorides of Platinum. Two chlorides of platinum are known, analo- gous in coinposition^o the oxides. The bichloride, PtCl 2 , is the most important of all the impounds, of this metal, and is obtained by treating the metal with boiling aqua regia, and carefully evaporating, to expel the excess of acid. It is much used in the laboratory. Sulphide of Platinum, PtS, may be formed by heating platinum-filings in vapor of sulphur. 527. Salts of Platinum. The salts of platinum, at least the oxysalts, are not important. Oxalate of the protoxide, and sulphate and nitrate of the binoxide, are known. Chlorosalts of Platinum. The bichloride of platinum combines with other metallic chlorides, forming a series of chlorosalts, called also platino-chlorides. 528. Osmium, Os; Eq., 99-5. This rare metal is in combination with platinum arid iridium ; with the former in the so called native platinum grains, and with the latter in the mineral species called iridosmine. It is of a grayish oolor, and metallic lustre ; is slightly malleable, and has a density of about 10. It combines readily with oxygen when heated, and is attacked by nitric acid, which converts it into osmic acid. Small grains of the native iridosmine are used for the tips of gold pens, because of their hardness and capability to resist the corrosive action of the ink. QUESTIONS. Describe the flameless lamp. 525. To what uses is platinum applied? 526. What oxides of platinum are known? What chlorides ? How may sulphide of platinum be formed ? 527. Are there any important salts of platinum ? 528. What is said of osmium ? What use is made of the native grains of osmium and iridium ? 392 BINARY COMPOUNDS OF PLATINUM. There are known no less than five oxides of osmium, viz., OsO, Os 2 3 , Os0 2 , Os0 3 , and Os0 4 ; of which the last two possess acid properties, and are called the osmious and osmic acids. Two chlorides only of osmium are known, a protochloride and a bichloride. 529. Iriditiin, Ir; Eq., 99. Iridium, as stated above, is found chiefly in combination with osmium* It has not been obtained in a malleable state, but only as a hard compact mass; and its density cannot therefore be well determined, but by some it is believed to exceed that of platinum. It is not attacked by nitric acid, nor even by aqua regia when pure, but at a red heat enters into combination with chlorine, with which it forma two compounds, the protochloride, IrCl, and the bichloride, IrCI 2 . 530. Palladium, Pd; Eq., 53-3. This metal, often contained in plati- num ores, is obtained chiefly from a native compound of this metal with gold, found in some parts of South America. It is nearly as white as silver, and scarcely less fusible than platinum. It is malleable and ductile, and receives a fine polish under the burnisher. Its density is 11-8. Palladium is used for the construction of the beams for delicate balances, and also for the graduated scales of astronomical instruments. 531. Bhodium, Rh ; Eq., 52-2. Rhodium, which receives its name from the rose-color of some of its compounds, is contained in small quantities in most platinum ores, and is sometimes found in cflfcibination with gold. It is of a gray color, and even more infusible than platinum. It is attacked by aqua regia only when alloyed with platinum, or some other metal. Its density is 10-6. Kuthenium, Ru, is the name given to a metal recently discovered in some platinum ores. In its general properties it resembles iridium. QUESTIONS. What oxides of osmium are known? 529. In what is iridium found? 530. Describe palladium. What use is made of it? 531. Describe rhodium. What is said of ruthenium ? PART IV. SPECIAL CHEMISTRY ORttANIO. GENERAL PROPERTIES OP ORGANIC BODIES. 532, Introduction. In the preceding part of this work, we have traced the chemical history of all the elementary substances at present known, and that of many of their most important com- pounds, as they are produced by the action of their affinities, uncontrolled except by the agencies of heat, light, and electricity; but we have now to discuss altogether another class of compounds, called organic, because produced almost exclusively by the organs of plants and animals, or derived from substances so produced. Organic Chemistry, therefore, is that branch of the general science of Chemistry which treats of the history, properties, and transformations of animal and vegetable substances. These are always compound, and differ from inorganic or mineral compounds chiefly in their origin, and in the circum- stance that most of them are of a more complex composition. 533. Organic and Organized Bodies. There is, however, a certain class of organic bodies, called organized bodies, whoso essential physical properties are altogether peculiar. These are always insoluble, and incapable of crystalization, and exhibit an organized structure, often visible to the naked eye, and always apparent under the microscope. To this class belong all the proper tissues of the animal and vegetable systems, constituting the organs by which all their various functions are performed. Sugar, gum, alcohol, and urea are organic substances, the twc QUESTIONS. 532. What has been treated of in the preceding parts of this work? What are now to be treated of? Define Organic Chem- istry. How do organic bodies diifer from inorganic ? 533. What are organized bodies? What is said of sugar, gum, c ? (393) 394 GENERAL PROPERTIES former being found ready formed in plants and sometimes in animals, and the two latter, being derived usually from sub- stances so produced, but they are not organized. On the other hand, the cellular tissue of wood, the pith of an elder tree, and the skin of an animal, are organized; and their pecu- liar structure is apparent to the eye, at least when aided by the microscope. The figure in the margin, from Regnault's Chem- istry, represents a cross section of the pith of the elder, as seen under the microscope. This ex- hibits a peculiar regularity of structure, which, however, is not common ; the structure of two different organized bodies seldom presents any striking similarity. Of the next two figures, the first repre- sents a microscopic .view of a longi- Pith of Elder. Stalk of Asparagus. Cross Section of Same. tudinal section of a stalk of asparagus, and the second a cross section of the same. 534, Vitality. In the production of organic bodies, the simple affinities of the particles of which they are composed are over- QUESTIONS. What is said of the various tissues of the system ? How may the organized structure always be seen? What is represented by the figure in the margin? What by the next two figures? 534. By what are the affinities of matter controlled in the production of organic eompounds ? OF ORGANIC BODIES. 395 ruled or controlled by another power or force, called the vitat power, vitality, or the principle of life. Its influence is abso- lutely essential for the production of most organic compounds, which, it is believed, can never be formed by the simple opera- tion of the ordinary affinities of the elements of these compounds. And it follows, as a necessary consequence, -that after death, that is, when this principle has ceased its influence, and the simple affinities of the elements of an organic compound are left uncon- trolled, they will show a disposition to break up, and re-arrange themselves in a new order. In this way the old compound is destroyed, and perhaps several new ones formed; or the simple elements may be entirely set free. This is what is termed the spontaneous decay, or putrefaction of a substance. Often this process is affected by the presence of the atmosphere, and is always much influenced by the temperature, and other circum- stances. Although many organic compounds are found, as such, in the bodies of plants and animals, by far the greater number are produced by the actions of the various reagents, as the acids, alkalies, and salts, either cold or aided by heat, upon these compounds. Thus, sugar and starch occur abundantly in plants, but from them, by the action of reagents, a long list of other compounds are produced, which are never found in the plants themselves. Alcohol, the almost innumerable ethers, and many acids, are of this kind. . Some compounds, as acetic and oxalic acid, are found ready formed in organic bodies, and may also be produced by the action of reagents upon other organic substances. But it is not to be understood that all organic substances are equally liable to decay; some of them, as sugar, wood, and gum, of vegetable origin, and gelatine, of animal origin, if kept dry, may be preserved apparently for any length of time. The chief elements of organic bodies are carbon, hydrogen, oxygen, and nitrogen, which are combined in different modes, and in different proportions ; but besides these some organic substances also contain sul- phur, phosphorus, chlorine, calcium, potassium, sodium, magnesium, iron, silicon, &c. Some few organic compounds have been formed artificially, that is, without the aid of the vital principle ; but not any organized body. QUESTIONS. Is the influence of this principle of vitality essential to the production of organic compounds ? Why, after death, do most organic siibstances spontaneously decay ? Are most organic compounds found ready formed in the bodies of plants and animals ? What is said of alcohol and the ethers ? May some organic bodies be preserved for a long period ? What are the chief elements of organic bodies ? 896 GENERAL PROPERTIES 535. Molecular Structure of Compounds, It is well known that two compounds, exactly the same in composition (172), often differ very considerably in their properties. This difference is believed to be occasioned by differences in the mode of arrange- ment of the particles in the cpmpounds, or, in other words, in their molecular structure. In general, while we understand well the elements of many compounds, we really know little of the mode in which these elements are grouped together in any particular case. We know, for instance, that the equivalent of sulphuric acid, S0 3 , contains 1 atom of sulphur and 3 atoms of oxygen, but we cannot say whether these are grouped as S + 30, SO + 20, or S0 2 -f 0, for these three modes are all alike possible. Here it would seem that there can be only three modes of combination, but in more complex compounds the number of possible modes may be greatly increased. This supposed difference in the mode of combination or grouping of the atoms of a compound, may be represented to the eye by means of a dia- gram. Thus, let us suppose that we have a compound of two simple Modes of Grouping. substances, and that in the atom of the compound there are 8 atoms of each of the elements ; representing the particles of one kind of mat- ter by the dark squares, and the other by the light ones, the four figures show as many independent modes of grouping. Now, as every inde- pendent mode of grouping of the particles may produce a new substance, it is plain that we may thus have four substances, all having the same ultimate composition, yet possessing properties altogether different. 536, Compound Radicals Nomenclature. Compound radi- cals are chemical compounds which are capable of performing the functions of simple substances; they combine with elementary bodies and with other compounds in the same manner as simple QUESTIONS. 535. May substances having the same composition differ in their properties ? How is this difference believed to be occasioned ? What is said of sulphuric acid in this connection ? How is the supposed difference in the mode of grouping among the atoms of a compound illus- trated by the figure ? 536. What are compound radicals ? OFORGANIC BODIES. 397 substances, and may often be substituted for these in the com- pounds of which they form a part. One of the best known of these compound radicals is cyanogen, C 2 N (316), which, as is shown by the formula, is a bicarbonide of nitrogen. This group of atoms, it is well determined, is capable of combining with the metals and other substances in the same manner as oxygen, chlorine, sulphur, &c., producing compounds similar to the oxides, chlorides, &c., which are called cyanides. United with oxygen it forms cyanic acid, with hydrogen it forms hydrocyanic acid, &c. So through a long series of other com- pounds, this group of atoms is found everywhere performing the functions of a simple substance. Other compound radicals which have been determined, are m/thyle, C 2 H 3 ; ethyle, C 4 H 5 ; bufyryle, C 6 H 7 ; valyle, C 8 H 9 ; amyle, C 10 H n , &o. Still other compounds of the same character, but having a more com- plex composition, are benzyle, C ]4 H 5 2 ; cacodyle, C 4 H 6 As; stanmethyle, C 4 H 5 Sn ; zincmethyle, C 2 H 3 Zn ; stibmethyle, (C 2 H 3 ) 3 Sb, &c. 537. That these groups of atoms, and many others, do enter, as such, into composition with the simple substances, and with each other, and are capable of being transferred by single or double decomposition from one compound to another, are facts too well established to be contro- verted. All those mentioned above, except perhaps benzyle, have also been obtained in a separate state ; and many that have not been thus obtained may, with grjat probability, be assumed as having a real existence. Considering the existence of these groups denominated compound radicals as fully established, it will be seen at once that it furnishes a ready mode of classifying organic compounds, and also for forming for them a systematic nomenclature. Thus, if we take ethyle, C 4 H 5 , as the basis or starting point of a series, we have for its binary compounds the oxide, chloride, iodide, sulphide, &c. ; and for salts of its oxide, the hyponitrite, nitrate, acetate, &c., as follows, viz. : Binary Compounds. 1. Ethyle C 4 H 6 . - 2. Oxide of ethyle, C 4 H 6 0, common sulphuric ether. 3. Chloride " C 4 H 5 C1, hydrochloric " 4. Iodide " C 4 H 6 I, hydriodic " 5. Sulphide " C 4 H 6 S, hydrosulphuric Salts of Oxide of Ethyle. 1 Nitrite of oxide of ethyle, C 4 H 5 0,N0 4 , hyponitrous ether, 2. Nitrate " " C 6 H 5 0,N0 5 , nitric " 3. Acetate " " C 4 H 6 0,C 4 H 3 3 , acetic QUESTIONS. What compound radicals are mentioned? 537. Have many of these groups have been obtained in a separate state ? 34 898 GENERAL PROPERTIES The foregoing are given as examples only; this series might be extended much further, and many other series might be introduced, as the methyle series, which would include the compounds of methyle, C 2 H S , analogous to the above, the acetyle series, the cacodyle series, &c. A nomenclature of organic compounds constructed on this principle has been adopted by able and judicious chemists ; but as there is no proof that such a nomenclature truly represents the real molecular structure of these compounds, we do not make use of it in this work. 538. A slight examination only is needed to show that most organic eompounds may be arranged in series in a variety of ways, each new mode requiring or supposing a new molecular arrangement. 1'hus in the compounds represented in the table- above, if we commence with ole- fiant gas, or ethylene, C 4 H 4 , instead of ethyle, C 4 H 5 , then we may con- sider the latter, C 4 H 5 = C 4 H 4 ,H, as the hydride of ethylene, and ether, C 4 H 5 = C 4 H 4 ,HO, as hydrate of ethylene, hydrochloric ether, C 4 H 6 C1=: C 4 H 4 , HC1, as hydrochlorate of ethylene, &c. <* 539. The real mode in which the particles of organic compounds are arranged (535), at least in most cases, has not yet been satisfactorily determined ; and it is therefore impossible, in the present state of our knowledge, to fix upon a proper systematic nomenclature. The same may also be said of the formulae used to represent these compounds. A distinction is often made between empirical and rational formula), the former representing the composition as determined by ordinary analysis, without any attempt to indicate the arrangement of the particles ; the latter, on the other hand, representing not only the composition of the compound, but also its molecular structure. Thus, the composition of acetic acid, as determined by analysis, is C 4 H 4 4 ; but when this acid combines with a base it always parts with one equivalent of water (or its elements), so that its salts, the acetates, have the general formula, RO,C 4 H 3 3 . This would seem to indicate that the formula for the acid should be written C 4 H 3 3 ,HO. But certain considerations have led us to the belief that in anhydrous acetic acid, C 4 H 3 3 , 1 equivalent of the oxygen is held in a different state from the rest, and therefore its fornmla should be C 4 H 3 2 ,0. Adopting these views, then, while it is admitted that the empirical formula, C 4 H 4 4 , represents correctly the elements of acetic acid, its rational formula will be, C 4 H 3 2 .0 -\- HO. In other words, it is a compound having for its primary radical, acetyle, C 4 H 3 , and for its secondary radical, C 4 H 3 2 . (Dr. Gibbs' Report, p. 43.) 540. In the following pages, a systematic nomenclature, according to any particular theory, is not attempted; the names of compounds adopted are those in general use, with a few unimportant modifications. ; QUESTIONS. Why is not the nomenclature of the compound radical theory made use of in this work? 538. May most of the organic com- pounds be arranged in series in a variety of ways ? Give the illustration in the text. 539. Has the real molecular structure of organic compounds been determined ? What are empirical, and what rational formulee ? Give the illustration by reference to acetic acid. 540. What is said of the nomenclature used in the remaining part of this work ? OF ORGANIC BODIES. 899 In many cases, compounds are named from some one of the natural pro- ductions in which they are found, as malic add from malum, an apple ; citric acid, from citron, a lemon ; valerianic acid, found in the root of the plant called valeriana, offidnalis ; cinchonia, obtained from the bark of the cinrhonia condaminea, &c. The formulae, in general, are to be considered only as empirical ; frequently, two formulae are given for the same com- pound, with the sign = between them. In such cases, the first is always the empirical formula, while the second indicates something further, as it regards the supposed constitution of the compound, or the mode of its reactions with other substances. The formula for cane sugar, for in- stance, is written C l2 H n O n C l2 H 9 O g -\- 2110, by which it is indicated that 2 equivalents of water (or the elements of water) sustain a relation to the compound different from that of the other atoms of these elements. Laws of Combination and Transformation. 541, We have seen (536), that in organic compounds -certain groups of atoms, called compound radicals, frequently are found to perform the functions of simple substances. Many of these groups are already known, and many more will probably be here- after discovered. . If all the groups capable of acting in this man- ner, with their properties and relations, were known, it is very probable that the transformations of organic bodies would not differ essentially from those of inorganic matter, except as they are affected by this circumstance. In other words, all cases of chemical action would be reduced to instances of direct union, or of single or double elective affinity. When potassium is burned in oxygen gas, direct union takes place between the two elements, and potassa (oxide of po'tassium) is formed K -f- =KO. But when potassium is thrown into water, we have a case of single elective affinity, as shown *by the equation representing the reaction ; thus, K -j- HO = KO -f- H. We may say in this case, either that the oxygen is transferred from the hydrogen to the potassium, or that the potassium has replaced the hydrogen of the water. When solutions of nitrate of baryta and sulphate of soda are mixed together, we have an instance of what is called double elective affinity ; and by a double transfer of elements we have formed the two new compounds, sul- phate of baryta and nitrate of soda. Thus, BaO,N0 5 -f NaO,S0 3 = BaO,S0 3 -f NaO,N0 5 . QUESTIONS.- How are compounds often named? Are the formulae given to be considered as empirical or rational? 541. What is said of the transformations of organic compounds as compared with thoso of inorganic matter? What illustrations are given from inorganic chemistry ? 400 GENERAL PROPERTIES 542. So in organic chemistry, most if not all reactions mil be similar to one or another of the above cases. When olefiant gas, C 4 H 4 (308), which is properly an organic product, and chlorine, Cl, are brought together, they combine to form an oil-like liquid, C 4 H 4 C1 2 . But often when two compounds have in this way combined, the new and more com- plex compound that is formed may, by a slight change of circumstances, or even spontaneously, break up into compounds of less complex consti- . tution. We have a case of this kind in sulpho-vinic acid, which is formed by the union of alcohol, C 4 H 6 2 , with sulphuric acid. Thus, C 4 H 6 2 +2(S0 3 ,HO) =C 4 H 6 O a ,2(S0 3 HO) = C 4 H 6 0,HO, 2(S0 3 HO). This last substance, called monohydrated sulpho-vinic acid, when heated, breaks up, not into alcohol and monohydrated sulphuric acid, but into ether, C 4 H 5 0, and 2S0 3 ,3HO. But most of the transformations in organic bodies may be considered as instances of double decomposition, or double elective affinity. The action of chlorine upon acetic acid is properly of this kind, as is shown by the following equation. Thus, C 4 H 4 4 -f 6C1 = C 4 HC1 3 4 + 3HC1. , Acetic Acid. - Cbloracetic Acid. It is, indeed, true that chlorine, one of the substances used, is not a com pound, but we are to consider that the action is the same as if each of the three atoms of hydrogen were successively replaced, giving for tha first step in the process the reaction, C 4 H 4 4 -f- 2C1 = C 4 H 3 C10 4 -f HC1. One atom of the chlorine is transferred to the acetic acid, which at the same time gives up 1 atom of its hydrogen to combine with the second atom of chlorine, to form hydrochloric acid. This reaction three times repeated results as given above, in the replacement of 3 atoms of hydrogen by as many atoms of chlorine. 543, Substitution or Metalepsy. We have seen above that by the action of chlorine upon acetic acid, C 4 H 4 4 , the latter loses 3 atoms of hydrogen, and takes in their place 3 atoms of chlorine ; in other words, 3 atoms of chlorine are substituted in the acid for an equal number of atoms of hydrogen. The new compound, C 4 HC1 3 4 , is called chloracetic acid, and in most of its properties closely resembles acetic acid, from which it has been formed. Transformations of this kind are of very frequent occurrence; QUESTIONS. 542. What is the effect when olefiant gas and chlorine are brought together? When two siibstances combine so as to form a more complex compound, will they sometimes break up in such a manner as to form compounds different from those which at first united ? Give the illustration by reference to alcohol and sulphuric acid. What is said of acetic acid and chlorine in this connection ? 543. What is the change produced in acetic acid by the action of chlorine ? OF ORGANIC BODIES. 401 and the exchange or substitution may take place between atoms or groups of atoms (compound radicals) which are similar to each other in their chemical relations. Hydrogen seems to be more frequently replaced than any other element; and there may be substituted for it chlorine, iodine, bromine, or a metal, or even a compound radical, -as methyle, ethyle, &c. Instances of the latter kind are seen in ethylamine, diethylamine, &c., in which one or more atoms of hydrogen in ammonia are replaced by ethyle. Thus, ammonia ==NHHH, ethylamine = NHHC 4 H 6 , dietnylamine = NH(C 4 H 5 ) (C 4 II 6 ) = NH(C 4 H 6 ) 2 , &c. As hydrogen, chlorine, iodine, &c., form a natural family, one of which may replace another in the compounds they form ; so nitrogen, phos- phorus, arsenic, antimony, and bismuth form another family, the indi- viduals of which ^sustain a similar relation to each other. Arsenide of hydrogen, AsH 3 (292), corresponds to ammonia in which the nitrogen is replaced by arsenic ; and the compound, Sb(C 4 H 6 ) s , may be regarded as ammonia in which the nitrogen is replaced by antimony, and the hydrogen by ethyle. Still another natural family is formed by oxygen, sulphur,, selenium, and tellurium. Alcohol, C 4 II 6 2 , by a substitution of sulphur for its oxygen, forms mercaptan, or sulphur alcohol, C 4 H 6 S 2 . 544. Conjugated or Coupled Compounds. Many of the com- pounds produced by transformations in accordance with the above principles," are frequently called conjugated or coupled compounds. They may be radicals only, or acids, or bases. As the name implies, they are supposed to be formed by the union of other compounds ; and usually the characteristic properties of one or the other of the coupling compounds will be more or less pre- served in the new or coupled compound. Thus, ethylamine, NHHC 4 H 5 , is a coupled or conjugated ammonia; it is a sub- stance formed on the type of ammonia, and possessing nearly the same properties, ethyle, C 4 H 5 , being the couplet. So the com- pounds, (C 4 H 6 ) 3 Sb, C 4 H 5 ,Zn, C 2 H 3 Bi, &c., are called conjugate metals: 545. Homologous Bodies. Homologous bodies are bodies which may be arranged in series, all the members of which are similar in their general properties and chemical relations, QUESTIONS. Between what may substitutions take place ? What other elements or compound radicals may be substituted for hydrogen ? What elements constitute a natural family with nitrogen, capable of replacing each other? 544. What are conjugated or coupled compounds? What examples are given ? 545. What are homologous bodies ? 34* 402 GENERAL PROPERTIES and are composed of the same elements, but differ from each other in^ composition by the addition or subtraction of the ele- ments, C 2 H 2 , or some multiple of this expression. Of this kind are the alcohols, all of which, though they differ greatly in some of their properties, still have many points of resemblance. The composition of all that are known will be seen by the following table : Names. Formulae. 1. Methylic alcohol (wood spirit) .................. C 2 H 4 O i 2. Common, or wine alcohol ......................... C 4 H 6 2 . 3. Propylic alcohol ..................................... C 6 H 8 2 . 4. Butyric .................................. C 8 H 10 2 . 5. Amylic " (fusel oil) ........................ C 10 H, 2 2 . 6. Caprylic " ................................... C, 6 IT 18 2 . 7. Ethal (ethalic alcohol) ............................ C 32 TT 34 2 8. Cerotine (cerotic alcohol) ......................... C^II^O^ 9. Melissine (melissic alcohol) ....................... C 60 H 62 2 . Each of these compounds, denominated alcohols, it will be seen, con- tains 2 atoms of oxygen; the first, or methylic alcohol, contains C 2 H 4 ; the second, C 4 TT 6 = C 2 H 4 -f C 2 H 2 ; the third, C 6 H 8 , and so on for the others, by the addition in each case of C 2 H 2 , or some multiple of this expression. In the crises requiring a multiple of C 2 H 2 , it would seem that one or more intermediate compounds are wanting. These may here- after be supplied ; as, for instance, between amylic and caprylic alcohol the compound, C, 4 H 16 2 , is not yet known, but when a compound having this constitution shall be discovered, it is safe to predict that it will have the general properties of this class of bodies. We have, therefore, as a general expressive for the alcohols, the formula, C 8B H 2 ( B + ,)0 2 . Besides the above series of alcohols, many other series are known, among which are the following, taken from Gibbs' Keport : Hydrogens. Acetenes. Formic Acids. Oleic Acids. H C 2 II 2 C 2 H 2 4 C 6 H 4 4 C 2 H 3 C 4 H 4 C 4 H 4 4 C 8 H 6 4 C 4 H 6 C 6 H 6 C 6 H 6 4 C JO H 8 4 C 6 H 7 C 8 H 8 C 8 H 8 4 C 12 H 10 4 4 C 2n H 2 ( n _ 1 )0 4 546. The compound, C 2 H 2 , which in all these series sustains so im- portant a relation, has been called the homologizing body. But it is QUESTIONS. In what do homologous bodies of the same series differ from each other in composition ? What series of substances of thia kind is mentioned? What is said of the composition of the alcohols? Give the general formula for the alcohols. 546. What is the compound, C t H 8 , here called? OP O R a A N 1 BODIES. 403 probable, that in other series other compounds, or perhaps a certain number of atoms of an element, may serve as the homologizing body. Thus, the ethyle and phenyle compounds differ from each other by Cg, which may be considered as the homologizing body connecting the cor responding compounds of the two classes, so as to form two terms of a homologous series. 547. Homologous bodies of the same series are in general similarly affected by the action of a reagent ; and the resulting compounds will be homologous. This is implied in the definition of those bodies given above. The alcohols, C^H^n-j-^O^ f r instance, by the action of oxydizing reagents yield corresponding homologous acids, C 2 ;iH 2n 4 ; and intermediate between the alcohol and acid, in several cases, another compound is known, called an aldehyde (from alcohol dehydrogenatus), and having the composition, C^H^Og. Other compounds of this series, we may confidently anticipate, will hereafter be discovered. The following table contains the formulae of the alcohols, their cor- responding aldehydes (when known), and acids: Alcohols. Aldehydes. Acids. 1. Methylic... C 2 H 4 2 C 2 H 2 4 . 2. Wine C 4 H 6 2 C 4 H 4 2 C 4 H 4 4 . 3. Propylic.... C 6 H 8 2 C 6 H 6 2 C 6 H 6 4 . 4. Butyric C 8 H 10 2 C 8 H 8 2 C 8 H 8 4 . 5. Amylic C 10 H 12 2 C 10 H 10 2 6. Caprylic . 7. Ethalic 8. Cerotic 9. Melissic.. Besides the acids in the above list, several others are known of the same series, some of which will hereafter be mentioned ; but the cor- responding alcohols and aldehydes have not been discovered. 548. In every homologous series as yet known, containing oxygen, the number of atoms of this element is constant ; and the same appears to be true of nitrogen, as will hereafter be shown. In the alcohol series, C 2 ,,H 2 ( n -f-j)0 2 , it is evident the smallest value we can give to n is 1, and the formula then becomes C 2 II 4 2 , which represents methylic alcohol, but what the extreme upper limit may be we are ignorant. If in the general formula for the alcohols we make n = o, the formula becomes H 2 2 = 2HO, which represents 2 atoms j)f water. Water is therefore said to be the type of the series. In like QUESTIONS. May there be other homologizing bodies ? 547. What is said of the effect of reagents upon homologous bodies of the same series? Into what are the alcohols converted by oxydizing reagents ? What inter- mediate product is obtained in some cases ? What are contained in the table in this paragraph ? 548. What is said of the oxygen and nitrogen in the homologous series now known ? Why is water said to be the type of the series of alcohols ? 404 GENERAL PROPERTIES OF ORGANIC BODIES. manner the general formula for the oleic acids, C 2 H 2 ( W j)0 4 , when = 1, becomes C 2 4 = 2C0 2 ; the type of the series is therefore car- bonic acid, C0 2 . 549. Although all the compounds of any homologous series are essen- tially similar in their leading properties, yet we may often observe a gradual transition as we pass from one to another of the same series. The carbo-liydrogens (Hydrogens and Acetencs, p. 402 ,) having the smallest number of atoms are gaseous at ordinary temperatures, but as we ascend in the series, that is, as the number of atoms in the com- pound is increased, they become less and less volatile, until the higher members of the series, at the ordinary temperature, are liquid, or even solid. Methylic alcohol, the first in the alcohol series, boils at 152, and the others have each a higher boiling point in proportion as the number of atoms is increased. The last three are solid at ordinary temperatures. In general, in any series, the boiling point becomes higher as the whole number of atoms in the compound is greater. 550. Analysis of Organic Substances. The analysis of a compound has for its object to determine its composition ; and in organic chemistry may be either proximate or ultimate. By the proximate analysis of a substance we separate and determine its proximate principles, or, in other words, the several organic compounds which may be contained in it, as sugar, gum, albumen, &c. ; but by its ultimate analysis we determine its ultimate elements, as carbon, hydrogen, nitrogen, &c. The methods of separating the proximate principles will be described as we progress, but for general modes of analyses the intelligent student will consult works treating specially of Analytical Chemistry.. 551. Proximate principles are the proper organic compounds, which cannot be separated into other kinds without evidently changing their nature ; they are usually characterized by one or more of the following properties, viz. : 1. Capability of combining in definite proportions with other elementary substances, or well determined compounds. 2. Capability of crystalizing, when obtained in the solid state, or having a definite melting point. 3. Having a definite boiling point, and being capable of distillation, or sublimation, without decomposition, or a change of properties. Thee compounds are seldom found uncombined in organized bodies, and their separation, or the proximate analysis of the substances con- taining them, becomes an important object to the chemist, and is often attended with no little difficulty. QUESTIONS. 549. Do we observe a gradual transition in the properties of the members of a homologous series as we pass from one to another ? Give an instance to illustrate. 550. Define what is meant by the proxi- mate and what by the ultimate analyses of an organic compound. What is a proximate principle? 551. What are the characteristics by one or more of which an organic compound will usually be distinguished ? STARCH. 405 STARCH, SUGAR, GUM, LIGNINE. 552. These four organic bodies constitute a natural family, possessing this remarkable peculiarity, that each member is composed of 'twelve atoms of carbon, united with a certain num- ber of atoms of water, or rather with the elements of water, oxygen and hydrogen. In general, they are nutritious sub- stances, and do not possess any very active chemical affinities. STARCH, OR TECULA, C 12 H 10 10 . 553. Sources. Starch, or fecula, is obtained from a variety of vegetable substances, as the different grains ; and from many roots, as the potato ; and also sometimes from the stems of plants. It is contained in the cavities of the vegetable tissues, in the form of small, white grains, which always have a rounded outline, but vary considerably in size and form, as obtained from different sub- stances. Each grain is inclosed in a delicate envelope that is not readily acted upon by cold water, but is ruptured by the expansion of the inclosed substance, when the water is heated nearly to the boiling point. To show the appearance of the starch globules, in their cells in the vegetable tissue, cut a very thin slice of a potato, and examine it carefully by means of the Sec t ion of potato, compound microscope; their appearance will be much as repre- sented in the above figure. If the slice before examination is moistened with a very dilute alcoholic solution of iodine, the starch globules will be colored blue, while the other parts remain uncolored. The next figure shows the arrange- ment of the starch globules in a grain sta rch Globules in a Grain of n y . QUESTIONS. 552.. Of what are starch, sugar, gam, &c., composed? 553. From what is starch obtained ? How is each grain inclosed ? How may the grains of starch be shown in the potato ? 406 STARCH. of rye. A, the outer seed-coat, which constitutes the bran after grinding; B, the gluten (to be described hereafter); and C, the grains of starch. The grains of starch from .different sources vary greatly in size, and present different outlines. Of the following figures, A repre- sents starch grains of the potato, B those of wheat, and G those of peas. ABC Starch Grams of the Potato. Ditto of Wheat. 554. Preparation and Properties. Starch is easily obtained from potatoes by mashing the tubers, and then inclosing the pulp in a piece of cloth, and washing it freely with cold water, at the same time pressing the mass between the hands. From wheat or rye flour it is easily procured by placing the flour upon a piece of muslin, and working it with the hand while a small stream of water is poured upon it. The starch is washed through with the water, while the gluten remains as a tenacious mass upon the muslin. After a few hours the starch will all subside. Separating Starch from Wheat Flour. QUESTIONS. What is said of the appearance of starch globules from different sources ? 554. How may starch bo obtained from the potato t How from wheat or rye flour ? STARCH. 407 Starch is an insipid white solid, quite insoluble in cold, but slightly soluble in boiling water. In the latter case, the granules are broken, and the broken envelopes floating in the solution give it the consistence of a jelly. In this state it is used for stiffening linen. Though quite insipid to the taste, it forms a large part of many articles of food, as the different grains, rice, the potato, and qjther esculent roots. It also performs important functions in nearly all vegetables during their growth. The substances known as arrow-root, tapioca, and sago are different varieties of starch. Iodine forms with starch a beautiful blue compound, which is quite insoluble in water ; it therefore serves as an excellent test for it. 555. When starch is kept for some time at a temperature between 300 and 400, it undergoes a peculiar chage, and becomes soluble in cold water, and is called British gum, or leiocome. A substance very similar to the above, but called dextrine, is produced by gently heating starch in water acidulated with sulphuric acid, or con- taining infusion of malt. It has the same composition as starch, but is very soluble in cold water, and is not colored by iodine. If the mixture is boiled for some time, grape-sugar is formed, of which more will be said hereafter. Diastase is a substance produced in small quantity in the process of malting grain, and is found in the potato soon after germination coni- menc*es, in the parts near the young germs. It is noted for its specific action upon starch, converting it first into dextrine, in the same manner as diluted sulphuric acid, and afterwards into grape-sugar. Diastase is known to contain nitrogen, but its composition, further than this, has not been well determined. 556. The operation of malting consists in exposing grain (usually bar- ley) to the proper degree of heat and moisture, with the free accession of atmospheric air, to produce incipient germination, and then suddenly checking it by elevating the temperature. This is done by first soaking the grain in water until it is fully swelled, and then placing it in heaps upon a floor until it begins to germinate, when the further progress of the vegetable process is arrested by quickly drying it at a moderately-elevated temperature. During the incipient germination, a portion of diastase is produced, by which, in the subsequent processes to which the grain is subjected, much of the starch of the grain is converted into dextrine and grape-sugar ;. and the grain (now called malt) becomes fitted for the us"e to which it is applied. It is chiefly used in the manufacture of beer. QUESTIONS. What is said of the properties of starch ? What varieties of it are mentioned ? 555. What test of starch is mentioned ? How is starch affected by a heat of 300 or 400 ? What is dextrine ? What diastase 9 656. What is malt ? What use is made of malt? 408 SUGARS. SUGARS. 557, There are several varieties of sugar, but the most important are cane and grape-sugar, names suggested by the sources from which they are respectively obtained. All the varieties of sugar possess a sweet taste, are soluble in water, and are susceptible of undergoing a peculiar change, called the vinous fermentation, by which alcohol is produced. 558. Cane-Sugar, C 12 H n O n . Most of the sugar of commerce is obtained from the sugar-cane (arundo saccharifcra), repre- sented in the figure ; scale, one inch to four feet. But it is procured also in this country in large quantities from the sap of the sugar-maple (acer saccharinuiri). Many plants contain it in their juices, as the common beet and other roots, and the stalks of Indian corn. Their juices, after being expressed from the plant, are evaporated until a dense syrup is obtained, from which a large portion of the sugar crystalizes on cooling; and the remaining liquid portion is then drained oflf, and constitutes treacle, or molasses. Pure sugar is a white, inodorous sub- stance, of a very agreeable, sweet taste, which it imparts to its solutions. By slow evaporation, in a very warm room, it is obtained in large rhomboidal crys- tals, which are sold as rock-candy. It is very soluble in water, but is dissolved Sugar-cane. on ]y j n gma u quantity in alcohol. Its density is 1-6. It melts at about 356, and on cooling forms a transparent, vitreous mass, called Parley-sugar ', which, however, QUESTIONS. 557. How are the sugars characterized ? 558. From what is cane-sugar obtained ? Give some of the properties of sugar ? Wha* is barley-sugar ? SUGARS. 409 after a time, becomes white and opaque, and is then found to be a mass of small crystals. Its composition remains without change. By heating cane-sugar to 420 or 425, a change of composition is effected ; it then gives up 2 atoms of water, and a brown substance is formed, called caramel, which has the composition, Ci 2 H g 9 . 559. Grape-sugar-Glucose, C B H M M = C 12 H 12 12 + 2H(X This substance, which much resembles the preceding, has -for its composition, when crystulized, C,2H, 4 Q 14 ; but by a boiling heat, two equivalents of water are expelled. It is more generally diffused in nature than cane-sugar, being found in the grape and most other sweet fruits. It constitutes also the solid part of honey. It may be obtained from grapes by expressing the juice, and neu- tralizing the free acid with chalk, and then clarifying and crys- talizing in the same manner as with cane-sugar. Grape-sugar is less soluble in water, and forms a less tenacious syrup, and is less sweet than cane-sugar. One ounce of water will dissolve three ounces of cane-sugar, but only about two-thirds of an ounce of grape-sugar ; and it is estimated that one ounce of the former has an equal sweetening capacity with two and a half ounces of the latter. Grape-sugar does not crystalize as readily as cane-sugar, and is soluble in oil of vitriol, while cane- sugar is blackened by it. A dilute solution of sulphate of copper, containing a little potassa, or tartrate of potassa, is at once rendered colorless by grape-sugar, at the ordinary temperature, but this effect is produced by cane-sugar only by boiling. This serves as an unfailing test to distinguish the two varieties of sugar. The color of the copper solution is destroyed by the precipita- tion of suboxide of copper, Cn 2 0. 560, Grape-sugar may be prepared from several substances which have a similar composition, as starch, gum, and woody- fibre or lignine, and is occasionally found in the animal system, as in the disease called diabetes. It then makes its appearance in the urine. It is sometimes called starch, sugar, diabetic sugar, and glucose. The latter name is more properly applied to the QUESTIONS. What is caramel? 559. Describe grape-sugar. What is said of its solubility in water and its sweetness, as compared with cane- Bugar? How may the two kinds be distinguished from each other? 660. Describe the mode of preparing grape-sugar, or glucose, from itarch. 35 410 SUGARS. sugar prepared from starch, &c. 3 but the identity of this substanoo with the sugar of grapes is generally admitted. To prepare grape-sugar from starch, 1 part of sulphuric acid is mixed with, 200 parts of water, and heat applied 'until the mixture begins to boil ; 50 parts of starch are then added, and the boiling continued until the liquid becomes perfectly clear. Powdered chalk is then introduced, a li ttle at a time, in order to neutralize the acid ; and by a few hours standing the sulphate of lime formed will be precipitated, leaving the liquid clear, which is now solution of glucose. By evaporation of the , water it may be obtained in crystals. Wood, the composition of which, as we shall hereafter see, is nearly the same as that of starch, also yields grape-sugar, or glucose, by boiling with sulphuric acid. The process is essentially the same as the above, except that a large proportional quantity of the acid is used. In both of these processes the acid remains unchanged, but by its pre- sence, in some unexplained mode, it. occasions the starch and the cellulose of the wood to unite with an additional quantity of water or the elements of water thus converting it into sugar. Thus, Starch (or cellulose), C 12 H 10 0, + 4HO = C 12 H 14 14 . From clean linen, or cotton rags, more than their own weight of sugar may be formed. Grape-sugar, prepared in this way, is used o adulterate cane-sugar, and in the manufacture of beer and alcohol. Sugar of sour fruits, as currants, cherries, plums, &c., possesses the composition, C, 2 H 12 0, 2 , and readily ferments, producing alcohol, but is uncrystalizable. 561. Milk Sugar, Lactine, CaJI^O^ = C^H^O^ -f 5HO. This sweet principle is obtained by evaporating the whey of milk, purifying with animal charcoal, and crystalizing. It is less soluble in water than either of the other varieties of sugar, and less sweet to the taste. Under cer- tain circumstances, it is capable of undergoing the alcoholic fermentation, like the other varieties of sugar ; and in some countries, it is well known that an intoxicating drink is made from camels' milk. But when in solution it is allowed to stand in the open air, at ordinary temperatures, lactic fermentation takes place, and lactic acid, C 6 H 6 6 = C 6 H 5 5 ,HO, is formed. This change takes place in the ordinary souring of milk. By the action of dilute acids at 212, lactine is converted into grape-sugar. 562. ilannite, C 6 H 7 6 , though not analogous to sugar in composition, is similar to it in some of its properties. It is found in many plants, it chiefly in a substance, called manna, obtained from certain speciea jf the ash. QUESTIONS. Describe the mode of preparing grape-sugar from wood. Does the acid remain unchanged in the operation ? What is said of the sugar of sour fruits? 561. What is milk-sugar, or lactine? May it undergo the alcoholic fermentation ? 5*62. Describe mannite. GUMS. WOODY FIBAE. GUMS, C I2 H 10 O 10 . 563. We designate by the name of gum a variety of vegetable substances, which are very soluble in water, but insoluble in alcohol, and uncrystalizable. Their composition is the same as that of starch, but they differ from this substance in several of their properties. The gums generally exude from the bark of trees, as the cherry and peach trees, and are found on the outside in trans- parent masses, which are more or less globular in form. A gum is a colorless, transparent, insipid, inodorous solid, and when perfectly dry is very brittle, and has a vitreous fracture. When put into water, it first so'ftens and swells up considerably, and then dissolves, forming a mucilage which is often used as a substitute for paste, for which it answers well. Its solubility is increased both by acids and alkalies. Gum Arabic, gum Sene- gal, and gum tragacanth are the most common varieties of this substance. Solutions of gum Arabic, and probably also those of the other gums, yield sugar by boiling with sulphuric acid; boiled with nitric acid, mucic acid is formed. 564. Pectine is a substance closely resembling gum, which is found in many fruits and in certain roots ; it is the substance contained in cur- rants, cherries, apples, &c., which they yield on being boiled, and espe- cially when boiled with sugar. It is a kind of vegetable mucus, and found in small quantity in many vegetables. By the action of an alkali, or almost any base, it is converted into an acid, called pectic acid. WOODY FIBRE, LIGNINE, CELLULOSE. 565. Wood from a growing tree is of a very, complex compo- sition. By examination with the microscope, it is found to possess a highly organized structure (533), consisting of vascular tissue, having its cells filled with a variety of substances, as starch, solution of sugar and mineral salts, albuminous com- QUESTIONS. 563. Describe the gums. From what are -they obtained? What are some of the varieties of gum? How are the gums affected by sulphuric acid ? By nitric acid ? 564. Describe pectine. 565. What is said of the composition of growing trees ? ' 412 W O O-D Y FIBRE. Section of Stem. pounds, oils, and resins, depending upon the natural family and species to which the tree belongs. The first figure in the margin repre- sents a transverse section of the stem of a tree. A is the outer bark, which is usually rough, and has lost its vitality, and serves only as a covering to the parts 'within. B is the inner fibrous bark, in which the sap-vessels are found, serving the purpose of the veins of animals. Inside of this is the wood, consisting of the part C, which is usually whiter than the rest, and is therefore called the alburnum, or sap-wood; and the heart-wood, D, which is more solid and durable than the sap-wood, and of a darker color. Both the alburnum and the heart-wood are composed of concentric layers, an addition of a layer being made to the alburnum each year, im- mediately beneath the bark. The next figure represents a transverse section, B magnified, of a piece of pine, showing the two kinds of wood A, the albur- num; B, the heart-wood. The inner rings of the alburnum are gradually converted into firm heart-wood, and seem then no longer to partake of the vitality of the tree. In annual plants, the woody part corresponds to the alburnum of trees. 566. Cellulose, C 12 H 10 0, . The vascular tissue of which we have spoken is composed chiefly of cellulose, the composition of which, it will be observed, is the same as that of starch, though it differs essen- tially from this substance in some of its properties. Cellulose constitutes the basis of wood, and is obtained by digesting saw-dust, paper, or linen or cotton rags, successively in alcohol, ether, diluted acid, diluted alkaline solutions, and water, so as to remove every- thing which is soluble in these menstrua. It is found in very different states ; as indigestible and hard, in wood, and in the shells of nuts ; as tender and easily digestible, in the esculent QUESTIONS. What is represented by the first figure on this page ? What by the second? 566. In what is cellulose found? What is said of its composition ? Section of Pine. WOODY FIBRE. 413 roots, and in the pulp of fruits, as the apple, pear, &c. ; as light and porous, in the pith of the elder, and in cork ; and as soft and flexible, in the fibres of cotton, flax and hemp. 587, Lignine, Woody Fibre. The vascular tissue of plants, when first formed, is composed of nearly pure cellulose., but after- wards the cells become lined with a hard incrusting substance, which, in trees and shrubs, for years increases in thickness and, solidity. This is called lignine, or sometimes woody fibre, though the latter term is more properly applied to wood as found in the tree, and composed of both cellulose and lignine. Lignine is found more abundant in the heart-wood than in the alburnum. The composition of lignine is believed to be essentially the same as that of cellulose, but it has not been fully determined. We have seen above (560), that wood treated by sulphuric acid is con- verted into grape-sugar, but it is only the cellulose that is capable of this change ; lignine is not affected by sulphuric acid, or only charred. The mutual relations of starch, sugar, and woody fibre, are singular and important. Their composition, we have seen, is nearly the same ; and they are convertible into each other by easy processes ; indeed, we are able to recognise this conversion as really taking place, in certain cases, in the natural process of vegetation, as shown in the malting of grain. The same change takes place in the ripening of many fruits, as the apple and pear, which are acid until they approach maturity, when they become more or less sweet. The sap of the maple and other trees contain sugar, which subsequently becomes changed into woody fibre, and thus contributes to the enlargement of the tree. Changes produced upon Woody Fibre by Acids. 568, Wood, plunged into strong sulphuric acid, especially if a little warm, is instantly charred, as if held near a hot fire. This is occasioned, it is believed, by the strong affinity of the acid for water, the elements of which, oxygen and hydrogen, are abstracted by it from the wood, leaving the black carbon. If the sulphuric acid be diluted, or if added in small quantities, so as entirely to avoid any rise of temperature, the effect is to form sugar, as we have already seen. QUESTIONS. 567. In what is lignine or woody fibre found ? What is said of the mutual relations of starch, sugar, and woody fibre? Are they capable of conversion one into another? 568. What is the effect ot strong sulphuric acid upon wood ? What if the acid is diluted ? 35* 414 WOODY FIBRE. 569. Gun Cotton Pyroxyline. This substance, which is noted for its explosive property, is formed by the action of very strong nitric acid, or better, by a mixture of the most concen- trated nitric and sulphuric acids, upon cotton, flax, paper, or fine saw-dust. To prepare it, make a mixture of equal parts (by volume) of the strongest nitric and sulphuric acids, and then press into it as nvjch cotton as can be moistened with it; and, after standing five or ten minutes, press out as much of the acid as possible, and wash thoroughly with a large supply of pure water, and dry carefully without artificial heat. It will be found that two ounces of each of the mixed acids will be sufficient for 75 or 100 grains of cotton. When thus prepared, the cotton appears much as before the process, but has a harsh feeling, and the fibres are less tenacious than in the original cotton. It also gains considerably in weight during the process, so that from 100 grains of cotton as much as 175 grains of gun-cotton will often be obtained. It takes fire very readily, often at a temperature even below 212, especially if the heat is suddenly applied ; and burns with an immense volume of flame. Placed on a plate of metal, and very gradually heated, it may sometimes be completely decomposed, without igniting, leaving behind a residue of carbon. When properly prepared, it explodes with great violence, and is entirely consumed. Its power to propel balls is much greater than that of the best gunpowder, which is still further increased by soaking it in a solution of chlorate of potash before drying. The composition of pyroxyline is is uncertain; but it is known that, by the action of the acids, oxygen and hydrogen (in the form of water) are separated from the cotton, and, at the same time, nitric acid com- bines with it. The most probable opinion is that 2 equivalents of cellulose combine with 5 equivalents of nitric acid, giving up at the time 3 equiva- lents of water. Thus, C 2 + 5N0 5 = C 24 H 17 17 ,6N0 6 4. 3HO. Gun-cotton, though insoluble in water or alcohol, is usually found quite soluble in sulphuric ether containing a little alcohol. But this is not always the case ; and it is believed there are at least two different com- pounds formed in the process, one of them being soluble in alcoholic ether, and the other insoluble. The insoluble variety appears also to explode with more violence than the other. The gelatinous ethereal solution of gun-cotton is used in surgery, as a substitute for sticking-plaster, or court-plaster, under the names of col- lodion and liquid cuticle. JTyloidine is an explosive compound similar to pyroxyline, produced by the action of strong nitric acid upon starch. QUESTIONS. 569. Describe the process of preparing gun-cotton. Give its properties. What is the most probable opinion concerning the com- position of pyroxyline, or gun-cotton ? In what is it soluble ? What is xyloidine ? WOODY FIBRE 415 Changes of Woody Fibre, by Air and Moisture. 570. When lignine is kept perfectly dry, or constantly im- mersed in water, it may be preserved for any length of time; but exposed to air and moisture, it undergoes a slow decay, called eremacausis (from erema, slow, and kausis, combustion), by tho absorption of oxygen, and the evolution of water, or its elements, and carbonic acid. The chemical changes which in this case occur, are very nearly the sLrae as in combustion, except that they take place more slowly. In both cases, the constituents of the wood, with the addition of oxygen from the air, are converted into carbonic acid and water; in both cases, also, the hydrogen is oxydized more rapidly than the carbon, as is shown by the black color during combustion, and the dark brown during the slow decay of vegetable matter. The flame which appears during the combustion of wood and other vegetable substances, is occasioned by the burning of the gaseous hydro-carbons, evolved as the first effects of the application of heat. 571. Humus, Geine. Every fertile soil contains more or less organic matter in a state of decay, to which its fertility is, in a great measure, owing, and which has received various names, as humus, geine, ulmine, vegetable mould, humic, geic, and ulmic acids, &c. This decaying matter, which we will call vegetable mould, is ever changing, as the carbon and hydrogen are oxydized and separated ; and from this and the carbonic acid, water, and ammonia, formed from them in the soil, the plants derive their chief nourishment, by means of their roots, which are extended in every direction. 572. Peat. Peat consists of partially decayed vegetable matter, which is found in beds, in moist places, in every country, and is usually mixed with more or less matter of mineral origin. It is formed from vegetable matter when slowly decaying under water, and of course free from the influence of the oxygen of the air. Water is decomposed, yielding its oxygen to one portion of carbon, to produce carbonic acid, while another portion of carbon unites with the hydrogen, forming light carburetted hydrogen (307), which often issues from the soil in large quantities, as the fire-damp of coal mines ; but most of the carbon remains behind as peat. Recently formed peat is also usually found interlaced witli tha QUESTIONS. 570. May wood^ be preserved if kept perfectly dry? What is the eifect when exposed to air and moisture? What is said of the chemical changes which take place in eremacausis? 571. What is contained in every fertile soil ? 572. Describe the formation of peat. 116 WOODY FI-BRE. fibrous roots of growing plants, and retains, more or less distinctly, the forms of many of the plants of which it has been composed ; but old peat is more homogeneous, and may be cut into the form of bricks, like moist clay. In many countries it is used extensively for fuel, being first thoroughly dried. 573. Coal. A sufficient description of the different kinds of mineral coal has already (298) been given. Immense deposits of this mineral nre found in many countries, which have no doubt been formed from vegetable matter, at a comparatively early period in the world's history. They are usually not very distant beneath the surface ; and are con- tained between rocky strata of great extent. . Occasionally these strata are covered with many feet of rock and earth ; everything indicating that vast changes ha've taken place in the earth's surface since their formation. That all the varieties of mineral coal have been produced from the matter of plants, which in former periods grew up and flourished pre- cisely as plants now do, is universally believed by men of science. The evidence is found in the position of the coal, which always occurs in the form of beds interstratified above and below .with solid rock formed at the same time with itself ; -in the vegetable impressions which abound in the rocky strata of every coal formation; and in the organized structure often exhibited by the coal itself. We may suppose that, by the decay of the vegetable matter, peat was first produced, which was subsequently converted into proper .coal, in a manner not fully understood. Mines of coal are limited to the temperate zone, none of it being found in very warm or very cold climates. 574. Petroleum. Petroleum, or rock-oil, is an odoriferous, oily liquid, which, in many countries, exudes from the rocks and ground, being formed, in all probability, from vegetable matter at the same time with peat and coal. It is often found upon the surface of lakes and springs, as at Seneca Lake in New York, where it is called Seneca oil. By distil- lation, petroleum yields a yellowish liquid, lighter than water, called naphtha, or oil of naphtha ; which is probably a mixture of several com- pounds that have not yet been separated. It is the liquid used to pre- serve the alkaline metals. Asphaltum, or mineral pitch, is a substance closely allied to petroleum. When cold it is solid, but becomes soft as it is heated, and melts at about 212. Dissolved in oil of turpentine, it forms a varnish which is used for certain purposes. 575. Distillation of Coal and Wood. Illuminating Gas. Coal and wood are subjected to distillation by heating them to redness in large cast-iron retorts, prepared for the purpose. Usually the retorts are kept at a red heat, and are capable of being opened at one end, so that the charge may be changed when necessary. QUESTIONS. What use is made of peat? 573. How have the deposits of mineral coal been formed? What evidence of this is there ? 574. De- Bcribe petroleum. How is naphtha obtained from it ? What is asphaltum, or mineral pitch ? 575. How are coal and wood distilled ? WOODY FIBRE. 417 Coal subjected to this process gives off large quantities of gaseous car- buretted hydrogens (309), with carbonic acid and sulphuretted hydrogen, And a resinous substance not unlike tar, called coal-tar. This last substance is a mixture of several compounds, as naphthalene, phenol, salts of ammonia, &c. A gas, not unlike that prepared by the distillation of coal, is often found to issue, ready formed, from the earth, and may be collected and used like that formed by art. The village of Fredonia, in the State of New York, is lighted by natural gas, in this way ; and in some salt-works in Virginia, it is said, no other fuel is used for boiling the brine. 576. Wood by distillation yields illuminating gas with water, acetic acid, creosote, pyroxylic spirit (methylic alcohol], tar, &c. The acetic acid, as first obtained, is mixed with creosote and other substances, and is called pyroligneous acid. Creosote, C^HjgC^, which passes over, with other products, in the dis- tillation of wood, is a colorless, transparent liquid, of an oily consistence, and retains its fluidity at 1 7. It has a specific gravity of 1 -04 ; boils at 397, and is a non-conductor of electricity. It has a burning taste, and its odor is like that of wood-smoke, or rather of smoked meat. It is highly antiseptic to meat : the antiseptic virtue of tar, smoke, and crude .pyroligueous acid, seems owing to the presence of creosote. Its name (from kreas, flesh, and sozein, to save} was suggested by this property. Creosote requires about 80 parts of water for solution, but is soluble in every proportion in alcohol and ether. It has neither an acid nor alka- line reaction with test-paper, but combines both with acids and alkalies. It is used both internally and externally in medical practice. Naphthaline, C 20 H 8 , is a solid substance, obtained by distillation from coal-tar. It is a white, crystaline solid, which melts at 175, and boils at about 422. It has a specific gravity of 1-05, and is insoluble in water, but dissolves in alcohol and ether. By the action of chlorine and bromine, and also by the action of acids, as the sulphuric and nitric, upon this substance, various interesting com- pounds are formed. Paraffine is sometimes found in petroleum, but is generally procured by the distillation of wood-tar. It is a white, waxlike solid, of specific gravity 0-87, which melts at about 110. It may be distilled without alteration. It received its name (parum affinis) from the circumstance that it manifests little affinity for other substances. Eupione; C 6 H 6 , is a fragrant, colorless liquid, obtained by the distil- lation of wood. Its specific gravity is 0-655, and its boiling point about 340. Phenol is obtained from coal-tar by distillation. Its composition is CjjHgOg, in which, as well as in many of its chemical relations, it re- QUESTIONS. What are formed when coal is distilled ? 676. What com- pounds are mentioned as being obtained by the distillation of wood t Describe creosote. What is the* derivation of the name, creosote ? Do- scribe naphthaline. Paraffine. Eupione. What is said of phenol ? 418 WINE ALCOHOL. sembles the alcohols (547), and has therefore been called phenylic ikohol By the action of reagents, many compounds are formed from it, analo- gous to those obtained from the alcohols. ALCOHOLS AND SUBSTANCES DERIVED FROM THEM. 577. The name alcohol has long been applied to a well known liquid, obtained by fermentation and distillation from solution of sugar, and starch, or substances containing one or the other of these compounds. But in the progress of the science, several other compounds, analogous to common alcohol, both in compo- sition and properties, have been discovered, to which the name is also given. The general formula, C 8M H a(n+1) O g (545), may represent their composition. The three most important of the alcohols are, common, or wine alcohol, methylic alcohol, and amylic alcohol, which, with their derivatives, will be here described ; the others will be attended to in their proper places. WINE ALCOHOL, C 4 H 6 2 . 578. Common, or wine alcohol, is always produced by the fer- mentation of sugar or starch, or compounds containing one or the other of these substances. *- 579. Fermentation. By the fermentation of a substance, we mean a change or modification which takes place in its constitu- tion under the influence of another substance, called a ferment, which acts simply by its presence. Several different fermentations have received separate names, as the vinous or alcoholic fermentation, by which alcohol is pro- duced from starch or sugar , the viscous fermentation, by which sugar is converted into a viscous, or mucilaginous substance; the acetic fermentation, by which diluted alcohol and other substances are changed to acetic acid, &o. The most important ferment used for inducing the vinous fermentation is yeast, or leaven; but blood, albumen, caseine, and the juices of many QUESTIONS. 577. Give the general formula for the alcohols. Name tho three most important alcohols. 678. How is common, or wine alcohol, always produced? 579. What is meant by fermentation? What dif- ferent fermentations are mentioned ? What ferment is generally used te produce the vinous fermentation ? WINE ALCOHOL. 419 Yeast Plant. fruits, as currants, apples, grapes, &c., are capable, after being exposed for a time to the air, of producing the same effect. Yeast is a substance which collects as a froth upon the surface of beer, and other liquids, in the process of fermentation. It always contains a portion of nitrogen, which seems essential to it, but the mode of its action has not been determined. Active yeast is believed by many to contain a kind of microscopic vegetable, which is developed spontaneously in the organs of plants, and in many nitrogenized substances when left to putrefy. It can be observed only by use of the microscope. See figure in the margin. To induce the vinous fermentation, a quantity of sugar is dissolved, or an equal quantity of starch diffused, in 4 or 6 times its weight of water, a small quantity of yeast stirred in, and the mixture placed in a situation where it may retain a uniform temperature of 70 to 85. After a time the solution will be found in brisk efferves- cence, occasioned by the escape of gaseous matter, which may easily be collected over mer- cury (see figure), and on ex- amination proves to be pure carbonic acid. When the action has ceased the liquid again be- comes clear, and is found to contain, not sugar, but alcohol, which may be separated by dis- tillation, and by other modes. Alcoholic Fermentation. ^ In this way it is found that alcohol and carbonic acid alone are pro- duced by the vinous fermentation, in the proportion of 2 equivalents of the former to 4 equivalents of the latter. It would not seem difficult, therefore, to understand the nature of the change that takes place when, fruit-sugar (560) is used, for this sugar contains precisely the elements of these compounds in this proportion. Thus, C 12 H 12 0, ; 2(C 4 H 6 2 )-f 4C0 2 . But when starcn, C 12 H 10 10 , cane-sugar, C 12 R U 1V or grape-sugar, C W H 14 14 , is fermented, the case is a little different, and the first effect of the ferment is to convert them into fruit-sugar, by an obvious change. 580. Preparation and Properties, Alcohol obtained by dis- tillation always contains a portion of water, even after several QUESTIONS. What is yeast? What is represented by the figure? What are the products of the vinous fermentation ? How many equiva- lents of alcohol and carbonic acid are produced from an atom of fruit- sugar ? 580. May pure alcohol be obtained by distillation ? 420 . WINE ALCOHOL. successive, distillations. When most highly rectified in this mode, it contains about 90 per cent, of pure alcohol, the rest being water. The alcohol, or spirits of wine, of commerce is seldom as pure as this. To obtain absolute alcohol, or alcohol in a state of purity, common alcohol is carefully distilled, by the heat of a water-bath, from pearlash or chloride of calcium, pre- viously dried and mixed with it. The water combines with the salt and remain.s behind, while the' pure alcohol distils over. Alcohol sufficiently pure for almost any pur- pose, may be obtained, without distillation, by means of well-dried pearlash. For this purpose, take common alcohol, or even proof-spirit, or Whiskey, and pour into it half its weight or more of pearlash, which has previously been thoroughly dried by heat. The whole is then to be shaken together a few minutes, and allowed to stand several hours ; there will then appear in the vessel two liquids entirely separate, one above the other, as shown in the figure. The upper portion is to be carefully drawn off and subjected to a second operation of the same kind, by means of a fresh portion of dried pearlash ; and this Solution of Pearlash in operation is to be continued as long as the intro- duction of the pearlash produces any effect. Pearlash is soluble in water, but quite insoluble in alcohol; when, therefore, a portion of it, perfectly dry, is introduced into alcohol con- taining water, the latter dissolves it, and the dense solution settles to the bottom, while the alcohol remains above. After several repeated opera- tions, all the water, or nearly all, is thus separated. 581. Pure alcohol is a colorless liquid, of a pungent taste and odor; and at 60 has a density of 0-795. It boils at 172; and its vapor is highly inflammable, and burns with a pale yellowish flame, without smoke. It has never been frozen by any cold yet produced ; but at a temperature of 146, becomes thick and tenacious, like melted wax. It is -a powerful solvent for many substances totally insoluble in water, especially many of the resins. Hydrate of potassa (and also of the other alkalies) dis- solves readily in alcohol, forming a solution often used in the laboratory. When potassium (or sodium) is immersed in absolute alcohol, QUESTIONS. How may pure or absolute alcohol be procured? De- scribe the mode by the use of pearlash. 581. Describe the properties of alcoho 1 . WINE ALCOHOL. * 421 hydrogen is given off, and a crystaline compound formed having the same composition as alcohol, except that 1 atom of hydrogen is replaced by 1 atom of potassium. Thus. C 4 H 6 2 + K = C 4 H 5 K0 2 . By contact with water, this compound is converted into alcohol and hydrate of potassa. Vapor of alcohol has a density, as determined by experiment, of 1-613; but, as calculated from the densities of its constituents, it is 1-596, Thus, - , 4 vols. carbon vapor weigh (-836 x 4) 3-344 12 hydrogen " (-069 Xl2) -828 2' " oxygen " (1-106 x 2) 2-212 4 vols. alcohol vapor weigh 6-384 One vol. alcohol, vapor therefore weighs 1-596. Alcohol exists in every kind of spirituous liquors, and may be separated from them by distillation. The diiferent kinds of brandy, rum, gin, and whiskey, usually contain from 45 to 55 per cent, of pure alcohol ; the stronger wines from 18 to 25 per cent. ; and the weaker, not more than 12 or 15 per cent. In cider, ale, and porter, the quantity varies from 4 to 10 per cent. Alcohol is extensively used in the arts and in medicine, chiefly in consequence of its powerful solvent qualities. Taken internally, it operates, as is well known, as a powerful stimulant ; and various alarming diseases, often terminating in extreme moral degra- dation and death, attend its habitual use. Used in lamps instead of oil, great heat is produced, and the combustion is unattended with smoke, for which reason it is much em- ployed in the laboratory. A cover, a, fitting accurately upon b, prevents evaporation when not in use. Spirit-lamp. 582. Bread-making. The ordinary mode of raising bread by means of yeast, also furnishes an instance of the vinous fermentation. The yeast contained in the flour-paste, or dough, causes the fermentation to commence, as already explained, and both alcohol and carbonic acid are formed in the dough ; arid the latter being retained in the tenacious mass causes it to swell up, or rise. This effect is further increased by the expansion of the gas by the heat in the process of baking, giving the QUESTIONS. What is the effect when potassium is immersed in alco- hol ? In what is alcohol always contained I 682. What is said of bread- making ? 36 - 422 WINE ALCOHOL. bread its light, porous character. The small quantity of alcohol formed is dissipated by the heat of the oven. Bread is also raised, as is well known, by the use of bicarbonate of soda, or potash, and an acid, as the hydrochloric or tartaric acid, or the acid tartrate of potash (cream of tartar). The rising is in this case produced by carbonic acid liberated in the dough from the alkaline carbonate ; and the same light, spongy character given to the bread. Products of the Oxydation of Wine Alcohol. 583, Aldehyde, C 4 H 4 2 . Aldehyde (from alcohol dehydro- genatus), as will be seen by an inspection of its formula, is dehydrogenated alcohol, alcohol from which two atoms of hydrogen have been separated. The separation of the hydrogen is effected by distilling alcohol with highly oxydized substances, which readily give up a portion of their oxygen to form water with the eliminated hydrogen. The best method for preparing it, is to mix in a retort equal parts of powdered bichromate of potash and strong alcohol, and then add, in successive portions, 1J parts of sulphuric acid. Energetic action commences at once, much carbonic acid is given off, and aldehyde, mixed with a small quantity of acetic acid and other substances, distils over into the receiver, which is kept surrounded with ice. To the liquid thus obtained, some ether is added, and it is then saturated with ammonia, which forms with aldehyde a crystaline compound, aldehyde ammonia, NH3,C 4 H 4 2 . This solid, distilled at a gentle heat with dilute sulphuric acid, and then re-distilled from chloride of calcium, previously fused, affords the pure aldehyde. Aldehyde is a colorless liquid, of a peculiar suffocating odor; at 60 its density is 0-790, and it boils at the low temperature of 70 or 71. It is soluble in water, alcohol and ether; and burns with a pale flame. It dissolves sulphur, phosphorus, and iodine ; and is especially remarkable for its affinity for oxygen, in consequence of which it is capable of reducing many of the metallic salts. Its action upon nitrate of silver is remarkable. If a solution of this salt is poured into a clean glass vessel, with QUESTIONS. What occasions the rising which gives to bread its spongy character? 583. What is aldehyde? Describe the mode of preparing it. What are some of its properties ? WINE ALCOHOL. 423 a little ammonia, the addition of some water, mixed- with alde- hyde, causes an immediate precipitation of the silver upon the surface of the glass, which retains its perfect metallic lustre, like the coating of a looking-glass. Aldehyde is instantly decomposed by contact with an alkali ; and if kept only a short time, it changes spontaneously into one or two other compounds isomeric with itself, depending upon the temperature ; these are, daldehyde and metaldehyde, the former of which is liquid and the latter solid. By combining with oxygen, aldehyde forms aldehydic or acetous acid, C 4 H 4 3 . 581 Acetic Acid, C 4 H 4 4 ==C 4 H 3 3J HO. Acetic acid is well known as the acid contained in vinegar (from the French vin, wine, and aigre, sour), which is, in fact, a very dilute acetic acid, containing also much saccharine and mucilaginous matter. Acetic acid is one of the most important of the organic acids, and is found, in combination with bases, in many plants. This acid is formed artificially by a variety of processes, but the usual method of preparing it is to subject liquids containing alcohol, as the weaker wines, cider, &c., to the action of some ferment, while exposed to the atmosphere. The process has sometimes been called the acetic fermentation ; and the chemical changes which take place in it consist in the separation from the alcohol of 2 atoms of hydrogen by the oxygen of the air, forming aldehyde and water, and the subsequent absorption of 2 additional atoms of oxygen by the aldehyde. Thus, C 4 H 6 2 + 20 = C 4 H 4 2 + 2 HO, and C 4 H 4 2 + 20 = C 4 H 4 4 . The access of. atmospheric air is absolutely es- sential to the formation of vinegar by the ordinary process, as is well known ; and its production is much facilitated by a method invented in Germany. A cask, as shown in the figure, is filled with wood shavings, and closed at top by a pan, b, the bottom of which is perforated with many small holes, through which small threads are passed to conduct the liquid downward. The shavings, being first well soaked in vinegar, are placed lightly in the cask; and below them are several small holes, cc, about half an inch in diameter, to admit the free Prep, of Vinegar. QUESTIONS. Can aldehyde be kept without change? 584. What is vinegar? How is it formed artificially ? Describe the German process. 424 WINE ALCOHOL. accession of air. If now proof-spirit, diluted with four times its weight of water, and having mixed with it a very little honey or yeast, is poured into the pan above, it gradually trickles down upon the shavings, where, a large surface being exposed to the atmosphere, rapid absorption of oxygen takes place, the temperature is raised, and acetic acid is formed. As the liquid passes down, it is collected in the vessel a ; and when passed through three or four times, which requires but about 36 hours, it is converted into vinegar. Acetic acid .cannot be separated from water by mere distillation ; but the pure acid is obtained by distilling some acetate, as acetate of soda or lime, &c., with a proper quantity of sulphuric acid, and collecting the product in a cold receiver. Wood-vinegar, or pyroligneous acid, is obtained by distilling wood in close vessels. It is a very impure acetic acid, having a disagreeable, smoky odor, and containing empyreumatic oils, and other substances derived from the wood. It is much used in calico-printing ; and often the cloths, not having been properly cleansed, possess its disgusting odor. 585. Pure acetic acid, at 63, is a colorless liquid, of a pungent, refreshing odor, and excessively sour to the taste. Applied to the skin for a time, it produces blisters. It boils at 248 ; and cooled below 63, it may be obtained in crystals. At 63, the density of the liquid is 1-06. It mixes readily with water, ether, or alcohol. 586. Acetal, C 12 H M 3 . This compound is a clear, colorless liquid, which boils at about 167, and has a density of 0-844. It is formed by the slow action of moistened platinum black upon a mixture of vapor of alcohol and oxygen, in a large bell-glass. The bell- glass is to be open at top, and elevated a little from the bottom of the basin in which it is placed, as represented in the figure, so as to allow a gradual circulation of the air through it. A watch-glass, A, is placed in the centre of the basin, contain- ing a little platinum black; and a small Prep, of Acetal. , funnel, with a long neck, B, contains strong alcohol, which drops very slowly" into the watch-glass. By the QUESTIONS. What is pyroligneous acid ? 585. Describe the properties of pure acetic acid. 686. How is acetal formed ? WINE ALCOHOL. 425 catalytic action of the platinum, the alcohol is decomposed, and acetal, aldehyde, and acetic acid, are formed, and, condensing together upon the sides of the bell-glass, are collected in the basin. This liquid is now to be neutralized with powdered chalk, and carefully distilled from chloride of calcium. Salts of Acetic Acid, and Other Allied Compounds. 587. Acetic acid combines with most bases, forming salts called acetates. In combination, its composition is C 4 H 3 3 ; from which it appears that in the process of combining, one atom of water or the elements of water is given up. Or, we may consider (with some chemists) the metal of the base as simply replacing 1 equivalent of the hydrogen of the acid (353). Thus, when acetic acid combines with soda, the acetate of soda formed has for its composition, NaO, C 4 H 3 3 ; and we may indi- cate the supposed relationship of the sodium as replacing 1 equiva- lent of the hydrogen of the acid by writing its formula thus, C 4 II 3 (Na)0 4 . Acetic acid is monobasic ; that is, the salts it forms contain a single equivalent of the acid with one equivalent of base. These salts are also said to be monobasic (170, 349). We shall describe only a few of the more important acetates. 588, Acetate of Lead, PbO,C 4 H 3 3 + 3HO. This is the sugar of lead of commerce. It is formed by dissolving oxide of lead (litharge) in acetic acid. It is very soluble in pure water, and has a sweet, astringent taste. Taken internally, it is poi- sonous; but is used in various preparations in medicine. The 3 HO is water of crystalization. If we consider the metal as replacing an equivalent of the hydrogen of the acid, its formula may be written, C 4 H 3 (Pb)0 4 . Besides the above neutral acetate of lead, there are several other acetates of the same base, which are formed by the combination of this compound with additional equivalents of oxide of lead, as 2PbO,3C 4 H 3 O s , and 3PbO,C 4 H 8 3 . The latter of these, sometimes called tribasic acetate of lead, is used in medicine, and in the proximate'analysis of organic QUESTIONS. 587. What are the salts of acetic acid called? What is said .of acetic acid as it combines with bases ? Is this acid monobasic ? What is meant by this ? 588. Describe acetate of lead. What is it called in commerce? 36* 426 WINE ALCOHOL. compounds. It is formed by digesting 7 parts of litharge iit <. parts of the neutral acetate in 30 parts of water, and evaporating tiie Solution until crystals are formed on cooling. The solution is called in pharmacy Goulard's extract of lead. 589. Acetate of Copper, CuO,C 4 H 3 3 . Acetate of copper is obtained by dissolving verdigris in hot acetic acid. On cooling, it is obtained in fine green crystals, yMch contain one atom of water, and is sometimes called distilled verdigris. This salt i capable of uniting with additiona' equivalents of oxide of copper, forming sub-acetates ; and the erdigris of commerce, used as a paint, appears to be a mixtirjj of these. It is prepared in large quantities, in the south of, France, by covering copper with the refuse of grapes, after tLe juice has been extracted for making wine ; the saccharinp matter contained in the husks furnishes acetic acid by fermentation, and in four or six weeks the plates acquire a coating of the acetate. A purer and better article is prepared by covering copper plates with cloths soaked in pyro- ligneous acid 590. Acef /.a of Ah?m?na, Ab 2 3 ,3(C 4 H 3 3 ). This salt is prepared by decomposing solution of sugar of lead by alum. It is used in dyeing, and calico -printing. 591. Acetate of Iron. By treating iron-filings with dilute acetic acid, a mixture of the acetates of the proto and sesquioxides of iron is obtained, which is considerably used in the arts. 592. Acetate of Ammonia, NH 3 ,C 4 H 3 3 ,HO = C 4 H 3 (NH 4 )0 4 , is readily formed by neutralizing acetic acid with ammonia, or its carbonate. It has been used in medicine under the name of spirit of Mindererus. 593. ChloraceticAcid, C 4 H0 4 Cl 3 =:C 4 Cl 3 03,HO,orC 4 H(C] 3 )0 4 . This acid is formed from acetic acid, by the abstraction of 3 atoms of its hydrogen, and the substitution of 3 atoms of chlorine. It is prepared by placing some crystals of acetic acid under a large bell- glass filled with chlorine, and exposing it to the direct rays of the sun. Other compounds are formed at the same time, which are to be separated from it, and then it is obtained in colorless rhomboidal crystals. QUESTIONS. 589. How is acetate of copper formed? What is the verdigris of commerce ? How is verdigris prepared ? 590. What acetates are mentioned ? 593. How is chloracetic acid formed ? WINE ALCOHOL. 427 Neglecting the secondary compounds formed, the reactions will be represented as follows, viz. : C 4 H 3 3 ,HO + 6C1 = C 4 C1 3 3 ,HO 4 3HC1. The crystals, when heated, melt at 113, and the liquid boils at about 392. It closely resembles acetic acid in its properties, neutralizes the same quantity of bases, and forms salts similar to the acetates. 594. Acetone, C 6 H 6 2 . Acetone, or pyroacetic spirit, is a limpid liquid, obtained by passing vapor of acetic acid through a red-hot tube, or by distilling a mixture of dry sugar of lead and powdered quicklime, and condensing the product in a cool receiver. Much uncondensable, gaseous matter passes over at the same time, which is allowed to escape. It has a density of 0*792, and boils at 132. In some of its properties, acetone appears to be closely allied to the alcohols, but in its composition it is isomeric with the aldehyde of propylic alcohol (547). In the preparation of acetone, another allied compound often makes its appearance, called metacetone, or propione, C 6 H 6 0. (We should prefer to call it propylone.} A corresponding acid is known, called the metace- tonic, propionic, or propylic acid, C 6 H 6 4 . Action of Chlorine upon Alcohol. 595. When a current of dry chlorine is passed through anhydrous alcohol, the first effect is to produce aldehyde and hydrochloric acid. Thus, C 4 H 6 2 + 2C1 = C 4 H 4 2 + 2HC1. Two equivalents of chlorine, therefore, have separated 2 eq. of the hydrogen of the alcohol, forming 2 eq. of hydrochloric acid, the residue of the alcohol constituting aldehyde. But if the action of the chlorine is continued, a new compound is formed, called chloral, C 4 HC1 3 2 . It may be regarded as aldehyde in which 3 eq. of hydrogen have been replaced by 3 eq of chlorine. The reactions are as follows : C 4 H 4 2 4. 601= C 4 HC1 3 2 4- 3HC1. Or, regarding it from the beginning of the process, ^ C 4 II 6 2 4 8C1 = C 4 HC1 3 2 4 5HC1. QUESTIONS. 594. Describe the mode of preparing acetone. 695. What is the first effect when dry chlorine is passed through pure alcohol? What is formed when the process is continued ? How may chloral be regarded? 428 METHYLIC ALCOHOL. Chloral is an oily liquid, of specific gravity 1-5, which boils at 201, and has a strong affinity for water, being soluble in water, alcohol, or ether. METHYLIO ALCOHOL, OR WOOD -SPIRIT, C 2 H 4 2 . 596, Preparation and Properties, When wood is subjected to distillation in a close vessel, besides the uncondensable gases which pass over, there is obtained an aqueous liquid, composed of pyroligneous acid (584), and other compounds ; among which, is a volatile, inflammable liquid, long known as wood-spirit, or pyroxylic spirit (from pur, fire, and xulon, wood). But from its resemblance to alcohol, in composition (547) and many of its properties, it is more properly designated as methylic alcohol, (from methuj wine, and xulon, wood). To separate it from the other compounds, the crude liquid is first neutralized with lime, and carefully distilled, only the part that passes over first being preserved, as this will contain nearly the whole of the wood-spirit. To obtain it pure, it must be several times re-distilled from chloride of calcium and lime. Metbylic alcohol is a colorless liquid, with an odor and taste somewhat resembling those of common alcohol. It has a density of 0-798, and boils at 152, and burns freely in a lamp. It mixes readily with water, alcohol, and ether, and, like com- mon alcohol, dissolves freely most resinous substances. Some use has been made of it in the treatment of diseases, under the name of wood naphtha. The formula of this compound, C 2 H 4 2 , represents 4 vols. of its vapor, the density of which, by calculation, is 1-109, as follows: 2 vols. carbon vapor weigh (-836 x 2) 1-672 8 vols. hydrogen, (-069 x B) -552 2 vols. oxygen, (1-106 x 2) 2-212 Giving for 4 vols. vapor of methylic alcohol, 4-436 The weight of 1 vol., or density, therefore, is 1-109 Products of the Oxyclation of Methylic Alcohol. 597. Formic Acid, C 2 H 2 4 = C 2 H0 3 ,HO. This acid was first obtained, by distillation, from the bodies of red ants (^formica QUESTIONS. 596. From what is methylic alcohol, or wood-spirit, ob- tained ? Describe methylic alcohol. 597. From what was formic acid first obtained ? METHYLIC ALCOHOL. 429 rufa) ; and hence its name. Its relation to methyhc alcohol is the same as that of acetic acid to common alcohol. It may be obtained by exposing the vapor of wood-spirit, mixed with air, to the action of platinum black, under a receiver, water and formic acid being produced at the same time. It appears that two atoms of oxygen combine with 2 atoms of the hydrogen of the spirit, forming 2 atoms of water; and then 2 atoms more of oxygen unite with the residue to form the acid. Thus, C 2 H 4 2 + 20 = C 2 H 2 2 + 2HO, and C 2 H 2 2 + 20 = C 2 H 2 4 . Formic acid may also be produced by distilling a mixture of sugar, bichromate of potash, and oil of vitriol, and by other means. Formic acid is .a clear liquid, of specific gravity 1-24, has a strong acid taste and pungent odor, and quickly blisters the skin. It boils at 212, producing an inflam- mable vapor, and solidifies at about 32. It is contained in small quan- tities in many plants, as the nettle, and produces the pain occasioned by handling them. The figure repre- sents the "sting" of the nettle, greatly magnified, with the sacks at the base containing the acid. When this acid combines with bases, like acetic acid, it gives up the elements of an atom of water; and is therefore by many considered as a hydrate, and its formula written C 2 H0 3 + HO. Or, as in the case of acetic acid (587), we may consider the metal of the base as replacing 1 equivalent of the hydrogen of the acid. Thus, the forrniate of lead, PbO,C 2 H0 3 , on this supposition, will have for its formula, C 2 H(Pb)0 4 . It is monobasic, like, acetic acid. QUESTIONS. What is said of the relation of formic acid to methylic alcohol? May it be procured from sugar ? Describe the process. De- scribe its properties. Is it found in plants ? What is said of the nettle ? Sting of Nettle. 430 AMTLIC ALCOHOL. 598. The formiaies, in their general properties, resemble the cor- responding acetates. The alkaline formiates are used in the analyses of some minerals. 599. Methylal, C 6 H 8 4 . This substance is procured by distilling a mixture, in proper proportion, of methylic alcohol, dilute oil of vitriol, and peroxide of manganese, and purifying the product. It is a colorless liquid, of an agreeable aromatic odor, and burns with a yellow flame. It has a density of 0-85, and boils at 108. AMYLIC ALCOHOL, , 012 02. 600. Amylic alcohol is a peculiar oily substance, which is col- lected in the process of distilling spiri* from potatoes. It is supposed to be formed from the starch (amylum) of the potato, and hence its name. It is also called potato oil, and fusel oil. It is found in some kinds of brandy, and in other spirituous liquors, being probably formed during the fermenting process, in circumstances not well understood. In distilling spirit from potatoes, it is particularly abundant towards the close of the process ; it is then mixed with water, to which it gives a milky appearance, but after standing for a time it rises to the surface. Amylic alcohol is a clear, colorless liquid, insoluble in water, but very soluble in alcohol and ether. Its density is 0-82, and it boils at 270. Its taste and smell are burning and pungent. If its vapor, mixed with air, is breathed for a little time, asthmatic pains and coughing are likely to ensue, and even vomiting. It dissolves phosphorus, sulphur, and iodine, without change ; and, unlike wine alcohol, is congealed by a temperature of 4. The formula of amylic alcohol, C 10 H, 2 2 , answers to 4 vols. of the sub- Btance in the gaseous state. The calculated density of its vapor is 3-057. Thus, 10 vols. carbon vapor weigh (-836 x 10) 8-360 24 hydrogen " (-069 X 24) 1-656 2 " oxygen " (1-106 x 2) 2-212 Thus, 4 vols. amylic alcohol vapor weigh 12-228 The weight of 1 vol., or the density, is therefore 3-057 _ _ ___ _ _ __ QUESTIONS. 598. What do the formiates resemble in their general properties ? 599. Describe methylal. 600. From what is amylic alcohol obtained ? Describe its properties. When its vapor, mixed with air, is breathed, what is the effect ? AMYLIC ALCOHOL. 431 Product of the Oxydation of Amylic Alcohol. 601, Valerianic Acid, C 10 H J0 4 = C 10 H 9 3 ,HO. This acid sustains the same relation to amylic alcohol as acetic acid sustains to wine alcohol, or formic acid to methylic alcohol. It is con- tained in the valerian root (yaleriana officinalis'), which is extensively used in medicine, and is obtained by distilling the root with water. It is also formed artificially by dropping warm potato oil upon platinum black in contact with atmospheric air, or by distilling a mixture of amylic alcohol, sulphuric acid, and bichromate of potash. In the process of its formation from amylic alcohol, the same chemical changes are required as in the formation of acetic acid from wine alcohol ; the alcohol loses 2 eq. of hydrogen, which combine with oxygen, forming water, and then 2 eq. additional of oxygen are absorbed. Thus, C 10 H I2 2 + 20 = C 10 H 1( A + 2HO, and C 10 H 10 2 + 20 = C 10 H 12 4 . Pure valerianic acid is a colorless, oily liquid, of specific gravity 0*937. Its taste is pungent and acid, and its odor like that of valerian. Its boiling point is 347. It is little soluble in water, but dissolves freely in alcohol and ether. It combines with bases, forming salts in many respects similar to the acetates and formates. When it enters into combination, it gives up the elements of 1 equivalent of water, precisely like the acetic and formic acids, and is therefore monobasic. Some of the valerianates, especially valerianate of zinc, are used in medical practice, as a substitute for the preparation of the valerian root. 602. Amylic aldehyde, C ]0 H, 2 , analogous to the aldehyde of wine alcohol, is formed by distilling valerianate of baryta. QUESTIONS. 601. From what is valerianic acid obtained? How may it be formed artificially ? What is said of the chemical changes which take place in its formation ? Describe its properties. What salt of this acid is used in medical practice ? 602. How is amylic alcohol obtained? 432 SULPHUR ALCOHOLS. The three alcohols above described are the most important of this homologous series (547), but six others are known, which will be here- after described. These all have the formula, C 2? iH 2 (n+ j)0 2 , as we have before (545) seen. Some other compounds, similar in their properties to the above, but not strictly homologous with them, have been denominated alcohols, as phenylic alcohol, C^HgO^ and acrylic alcohol, C 6 H 6 2 . SULPHUR. ALCOHOLS, OR MERCAPTANS. 603. These compounds are formed on the same type as the alcohols, but differ from them by containing sulphur instead of oxygen. They are called mercaptans (mercurium captans), be- cause of their great affinity for mercury, with which they eagerly combine, on coming in contact with its oxide. Wine-alcohol Mercaptan, C 4 H 6 S 2 C 4 H 6 S,HS. This com- pound is formed by saturating a solution of caustic potash, of density 1-3, with sulphuretted hydrogen, and distilling it with an equal measure of sulphovinate of lime (a substance to be here- after described,) of the same density. It is a colorless liquid, which has a specific gravity of about 0-84, and boils at 97. Its odor resembles that of onions. Mercaptan vapor has a density of 2-152, as may be thus calculated: 4 vols. carbon vapor weigh (-836 X 4) 3-344 12 vols. hydrogen " '" (-069 Xl2) '-828 vol. sulphur " " (6-654 X I) 4-436. 4 vols. mercaptan vapor 8-608 The density therefore is, or the weight of 1 vol., 2-152 By the action of this compound upon metallic oxides, 1 equiva- lent of its hydrogen unites with the oxygen of the oxide, forming water, and the metal takes the 'place of the hydrogen in the ori- ginal compound. Thus, by the action of mercaptan on oxide of lead, PbO, we have C 4 H 6 S 2 + PbO=C 4 H 5 S,PbS + HO=C 4 H 5 PbS 2 + HO. These metallic compounds, of which several more are known, are called mercaptides. QUESTIONS. Are there other alcohols besides the three described above? 603. What are the mercaptans, or sulphur alcohols? Describe wine alcohol mercaptan. What are the compounds of this substance with the metals called ? ETHERS. 433 as are The compound, C 4 H 4 S 2 , called mercaplan aldehyde, is known, also methylic mercaptan, C 2 H 4 S 2 , and amylic mercaptan, C 10 H, 2 S 2 . Selenium may be made to replace the sulphur in the commoa alcohol uiercaptans, forming seleno-mercaplans. ETHERS. COUPLED, OR VINIC ACIDS. 604. The substance usually designated by the simple term, ether, is a compound obtained by the reciprocal action of alcohol and acids, as, the sulphuric, phosphoric, or arsenic, or the chlorides of zinc, tin, &c. It is often called sulphuric etherj from the circumstance that sulphuric acid is generally used in its preparation. The name ether, given to it, indicates its volatility. -But the term is now extended to a very numerous class of similar compounds, most of which are liquid at ordinary tempera- tures, and are very volatile, but differ from each other as to the temperature at which ebullition takes place. Some few of them are solid. There are several families of ethers derived from the several alcohols; and in naming them, except in the case of those be- longing to the common alcohol group, the family or group is usually indicated. Thus we have hydrochloric ether, methylic hydrochloric ether, and amylic hydrochloric ether ; the first of which belongs to the wine alcohol group, but the others to the groups severally indicated. And in each alcohol series, there are also two distinct classes of ethers, which we may call simple ethers, and compound ethers. The former, or simple ethers, have the general formula, C 2n H 2n + 1 A (the Greek letter A being used to indicate one equivalent of any one of the elements, oxygen, chlorine, bromine,- iodine, fluorine, sulphur, -selenium, tellurium, or a compound radical, cyanogen, bisulphide of carbon, &c.,) while the compound ethers always contain an acid in combination with a simple ether, C 2n H 2n+ ,A. Thus, common sulphuric ether is a simple ether, C 4 H 5 0; but QUESTIONS. 604. How is the compound usually called ether obtained ? Why is it often called sulphuric ether ? How is the name ether now used ? Do the different alcohols afford ethers ? What two classes of ethers are there in each alcohol aeries ? In what do the individuals of the two classes differ ? 37 484 ETHERS. nitric ether is a compound ether having the formula, C 4 H 6 NOa =* C 4 H 6 0,N0 5 . There are some simple ethers which contain more than one equivalent of A ; and in both the simple and compound ethers, one or more equivalents of the hydrogen may be replaced by chlorine (and possibly other elements), as in the chlorocarbonio ether, C 4 H 3 C1 2 0,C0 2 . Ethers of Wine Alcohol. I. SIMPLE ETHERS. 605. Ether (Sulphuric Ether), C 4 H 5 0. This ether may be formed by several modes ; but the best is to distil a mixture of equal parts of alcohol and strong sulphuric acid in a glass retort, the process being discontinued as soon as the mixture begins to become colored. For distilling it, an alembic or other distilling apparatus (48) may be used. The product should be washed with water, to separate a little alcohol and sulphurous acid that usually pass over with the ether. This is done by filling a bottle about half full with the impure ether, and then pouring in a quarter or one-half as much water, and shaking them well together. After standing a few minutes, the liquids separate, and the water may be drawn off by perforating the cork and inverting the bottle, taking care to notice when the water has all escaped. Pure sulphuric ether is a colorless liquid, of a hot, pungent- taste, and fragrant odor. At the temperature of 60, its density is 0-72, and it boils at 96 or 98 in the atmosphere, and at about 40 below zero in a vacuum. In the open air, it evaporates with great rapidity, producing intense cold, so that water may easily be frozen by it It is very combustible, and burns with a yellow flame. Exposed to the light, in vessels partly filled with air, it gradually absorbs oxygen, with the formation of acetic acid. The solvent powers of ether are not as extensive as those of alcohol, but it dissolves the essential oils, resins, and many of the fatty principles. 606, When the vapor of ether is inhaled, it first produces a species of intoxication, similar to that occasioned by exhilarating QUESTIONS. 605. Describe the mode of preparing ether. What are its properties ? 606. What is the effect when vapor of ether is inhaled f ETHERS. 435 gas ; and afterwards a kind of stupor follows, during which the person is nearly insensible to pain ; the effect being much the same as that produced by chloroform. When used for this pur- pose, it has been called letheon. 607. Sulphovinic Acid. Theory of the Formation of Ether. By comparing the formula of alcohol, C 4 H 6 2 = C 4 H 5 0,HO, with that of ether, C 4 H 5 0, it is evident that the former may be con- sidered as a hydrate of the latter j and the effect of the acid upon the alcohol in producing ether is simply to abstract from it one equivalent of water, or its elements. But although this is the final result, other intermediate chemical changes take place. When equal parts of sulphuric acid and alcohol are mixed, and slightly heated, sulphovinic acid, C 4 H 5 0,2S0 3 HO, is first formed, and may be obtained in a free state, as a syrupy liquid. This acid is capable of combining with bases and forming salts, which are called sulphovinates, as sulphovinate of baryta, BaO,C 4 H 3 0,2SO 3| , and sulphovinate of lime, CaO,C 4 H 5 0,2S0 3 . These, and sulpho- vinates of other bases, are easily obtained in crystals. Sulphovinic acid, though very stable at ordinary temperatures, is decomposed when heated to about 310, and ether is separated in the gaseous state, and may be condensed, the sulphuric acid and water remaining behind. Thus we have, neglecting the water of the oil of vitriol, C 4 H 6 2 ,2S0 3 = C 4 H 6 + 2S0 3 ,HO. 608. By using alcohol nearly pure, and regulating the temperature constantly at about 300, both the ether and the water formed from the alcohol may be made to distil over together, leaving unchanged the acid, which has produced the whole effect. Let A (see figure on next page) be a flask, with rather a wide mouth, 'containing a mixture of five parts of alcohol and eight parts of sulphuric acid, so as to fill it about half full. In the cork insert a bent tube, B, through which the alcohol required in the process is to pass, and an- other, C, to connect with the condenser of the distilling apparatus (96) ; QUESTIONS. 607. Why may alcohol be considered a hydrate of ether? What is the effect , produced upon alcohol by sulphuric acid ? What is first produced when equal parts of alcohol and sulphuric acid are mixed ? What is the composition of this acid ? Is it capable of forming salts with bases ? What is the effect when sulphovinic acid is heated ? 608. De- Bcribe the mode of forming ether by a continuous stream of alcohol. 436 ETHERS. o Preparation of Ether. and between them place a thermome- ter, T, the bulb of which must extend to the mixture with- in, to determine the temperature. So also the alcohol tube, B, should extend a little below the surface of the liquid, as repre- sented in the figure. 'When the mixture has become suffi- ciently heated, a continuous stream of alcohol is made to enter, just so as to keep the liquid in the flask at its ori- ginal level. The sup- ply of alcohol is regu- lated by the stopcock in the vessel D, which must be supported a little above the flask by a shelf or stand. The ether and water that pass over are, of course, collected together; but, as they do not mix, the ether is easily separated. The mixture, during the operation, should be kept continually boiling, and the heat very carefully regulated. The ether, after being separated from the water, should be redistilled from a weak solution of caustic potash, to separate it from any acid which may have passed over with it. 609. Many other acids, as the phosphoric, arsenic, carbonic, oxalic, tartaric, &c., produce with alcohol vinic acids called also coupled acids which are entirely similar to the sulphovinic. Such acids are properly to be considered as bibasic (or tribasic). To indicate the basic character of the water in sulphovinic acid, we may write its formulae, HO,C 4 H 6 0,2S0 3 ; now this water may be replaced by another equivalent of ether, C 4 H 5 0, and we then have the compound, 2(C 4 H 5 0,S0 3 ), which is per- fectly neutral, and is called a compound ether. QUESTIONS. 609. What other acids are mentioned as capable of form- ing vinic or coupled acids with alcohol ? To what class of acids do they ETHERS. 487 Some acids, as the sulphuric, oxalic, and carbonic, form both vinic acids and compound ethers, while others, as the phosphoric, form only vinic -acids; and others still, as the nitric and acetic, form only compound ethers. Acids of this latter kind are strictly monobasic. Besides the acids, several of the chlorides (604), as the chlorides of zinc and tin, and the fluoride of boron, effect the transformation of alcohol into ether, with the elimination always of an atom of water. By distillation with an alkaline solution, the compound ethers and vinic acids are decomposed, and alcohol reproduced. In this case the acid of the compound ether, or vinic acid, combines with the alkali ; and the ether, C 4 H 5 0, as it is set free, unites with an atom of water, thus reproducing alcohol, C 4 H 6 2 . 610. Hydrochloric Ether, C 4 H 6 C1. This ether is formed by saturating common alcohol with hydrochloric acid gas, and then distilling with a very moderate heat. As the vapor distils over, it should be made to pass through warm water, to free it from impurities, and is then to be condensed in a receiver surrounded by ice. It may also be formed by distilling a mixture of equal parts of alcohol and the hydrochloric acid of commerce, and by other means. The reaction producing it is shown by the following equation : C 4 H 6 2 + HC1 = C 4 H 5 C1 + 2HO. This ether is a colorless liquid, which has a density of 0-874, and boils at the low temperature of 52. In the warm weather of summer, it can be preserved only in tubes hermetically sealed. By its formula it will be seen that its composition ?s the same QUESTIONS. What acids are mentioned as forming both vinic acids and compound ethers ? What as forming only compound ethers? What is their character? What other compounds are mentioned as being capable of transforming alcohol into ether? How are the compound ethers and vinic acids affected when distilled with a solution of alkali ? 610. How is hydrochloric ether formed? What are the reactions by which it is produced when alcohol and hydrochloric acid are used ? What are some of the properties of this ether ? 37* 438 ETHERS. as that of sulphuric ether, except that the oxygen of the latter substance is replaced by chlorine. By passing a current of chlorine through a portion, of this ether, in direct sunlight, 1 equivalent after another of the * hydrogen is replaced by chlorine, until at length it all disappears, and we have only the com- pound C 4 C1 6 . We have therefore the following series of compounds, viz. : Boiling Point. Density. Hydrochloric ether C 4 H 5 C1 52 0-874 Bichlorinated do C 4 H 4 C1 2 147 1-174 Trichlorinated do C 4 H 3 C1 3 167 1-372 Quadrichlorinated ether C 4 H 2 C1 4 215 1-539 Quinquechlorinated do .. C 4 HC1 6 295 1-640 Sesquichloride of carbon C 4 H 6 = C 2 H 3 356 Oil. Hydrdbromie Ether, C 4 H 5 Br. This ether is prepared from a mix- ture of alcohol, phosphorus, and bromine. It is a colorless liquid, having a density of 1-47, and boiling at 106. Hydriodic Ether, C 4 H 5 I. Preparation similar to the preceding. It is a limpid liquid, of density 1-97, and boils at 158. Hydrosulphuric Ether, C 4 H 5 S. This ether is very volatile, colorless, and of a penetrating, nauseous odor. Its density is 0-825, and its boiling point 163. Hydrocyanic Ether, C 4 H 5 Cy. A poisonous, volatile liquid, of density 787, and having its boiling point at 180. II. COMPOUND ETHERS. 612. Sulphuric Ether (proper), C 4 H 5 0,S0 3 . This is the only compound properly called sulphuric ether, on the principles adopted in naming the other compound ethers. It is obtained by the action of anhydrous sulphuric acid upon ordinary, ether. It is a neutral, oily liquid, having a density of 1-12, and a sharp, burning taste. Heated to 285 or 300, it is decomposed, so that its boiling point cannot be ascertained. 613. Hyponitrous Ether, C 4 H 5 N0 4 = Q g H 5 0,N0 3 . This ether may be formed by the direct action of nitric acid upon alcohol ; but a better mode is to pass a current of nitrous acid vapor (obtained by the action of nitric acid upon starch) through dilute QUESTIONS. What is the effect when a current of chlorine is passed through hydrochloric ether? 611. What other simple ethers are men- tioned ? 612. What is the composition of sulphuric ether proper ? How is it obtained ? 613. Describe hyponitrous ether. ETHERS. 4^ alcohol. Heat is generated by the process, and the vapor is condensed in a cold receiver. As the action of the acid upon the alcohol is often very tumultuous, the process should be con- ducted with caution. Hyponitrous ether is a liquid of a pale yellow color, and fragrant odor; its density is about O94, and it boils at 70. In a pure state it cannot be kept long ; but mixed with alcohol it is more permanent, and is extensively used in medicine, under the name of sweet spirits of nitre. Nitric Ether, 4 H 5 N0 6 = C 4 H 5 0,N0 5 . Nitric ether is formed by distilling equal parts of nitric acid and alcohol with a few grains of urea. It is a colorless liquid, of a sweet taste, and is heavier than water. It boils at about 185, and its vapor explodes by heat. * 614. Carbonic Ether, C 4 H 5 0,C0 2 . This ether is obtained by distilling oxalic ether (soon to be described) with potassium or sodium. It is a colorless liquid, very volatile, and having an aromatic odor and acrid taste. Its density is - 975, and it boils at 259. With chlorine it yields several chlorinated carbonic ethers, by the replacement of 1 or more equivalents of the hydrogen of the simple ether, C 4 H 6 0, by an equal number of equivalents of chlorine. 615, Silicic Ethers. Silicic ethers, of which there are two (or perhaps three), are formed by the action of chloride of silicon upon absolute alcohol. They are volatile liquids, having a pene- trating odor and a pungent taste. By water, or by long standing in bottles, from which the air is not perfectly excluded, they are gradually decomposed; and the hydrated silica is left^in hard, vitreous masses, resembling quartz. Acetic Ether, C 8 H 8 4 = C 4 H 5 0,C 4 H 3 3 . Acetic ether may be prepared by several modes, but the best is to distil a mixture of 3 parts of acetate of potash, 3 of absolute alcohol, and 2 of sulphuric acid. Acetic ether is a volatile liquid, of a fragrant odor, like that of strong vinegar. It boils at 165, and has a density of about 0-89. QUESTIONS. What is said of nitric ether? 614. Of what is carbonic ether composed? 615. What is said of the silicic ethers? What of acetic ether? 440 ETHERS. 616. Oxalic Ether, C 6 H 6 O 4 = C 4 H 5 0,C 2 3 .This ether is pre- pared by distilling a mixture of 4 parts of binoxalate of potash, 5 parts of sulphuric acid, and 4 of strong alcohol, and thoroughly washing the product with water. It is a volatile liquid, which has an aromatic odor, and is a little heavier than water. Oxalic ether is decomposed by contact with an alcoholic solution of potash, forming alcohol and oxalic acid. Ammonia acts upon it, producing two compounds, called oxamide, C 2 2 NH 3 , and oxamic acid, C 4 5 NH 2 ,HO. By the action of chlorine upon it, several chlorinated compounds are formed. 617. Formic Ether, C 6 H 6 4 = C 4 H 5 0,C 2 H0 3 . This ether is formed by distilling a mixture of dry formiate of soda, sulphuric acid, and strong alcohol. It is also produced in considerable quantity during the process for preparing fulminating mercury, to be hereafter described. Formic ether is a colorless liquid, which boils at about 130, and has a specific gravity of 0-915. It has a very penetrating, agreeable odor, and is soluble in about ten times its weight of water. Many other compound ethers of the wine alcohol series, cannot be here described* 'Recent writers enumerate nearly a hundred, formed by the organic acids alone. In their composition they evidently possess the character of salts, being formed by the union of ether, C 4 H 5 0, acting as a base, with the several acids ; but in their properties they differ essentially from proper saline compounds. This appears in the fact that the acid cannot be detected by the ordinary tests; thus, oxalic ether is a compound of vinic ether, C 4 H 6 0, and oxalic acid, C 2 3 ; but lime, which separates oxalic acid from its saline compounds, forming oxalate of lime, will not separate Jhis acid from oxalic ether. The same remark applies to the coupled, or vinic acids. Ethers of Methylic Alcohol. I. SIMPLE ETHEKS. 618. Methylic Ether Wood Ether, C 2 H 3 0. This ether is formed from methylic alcohol, in the same manner as sulphuric QUESTIONS. G16. Plow is oxalic ether prepared ? 617. Formic ether? How are the compound ethers formed ? Are they really salts ? Do they differ in any respect from proper saline compounds? Illustrate with reference to oxalic ether. 618. How is methylic ether formed ? E T H E E S . 441 ether is prepared from common alcohol, by distilling methylic alcohol with an equal volume of sulphuric acid. It is a color- less gas, of a pungent odor and taste, and is rapidly absorbed by cold water, but given off again unchanged by boiling. It is con- densed to the liquid form by a temperature of 3; and is chiefly interesting as taking the place, in this series, which the ether first described (605), sometimes called sulphuric ether, occupies in the common alcohol series. The theory of its formation corresponds in every respect with that already explained (607) in describing ordinary or sulphuric ether.. When methylic alcohol and sulphuric acid are mixed, at a moderately elevated temperature, sulplw-metliylic acid is formed, having the composition, C 2 H 4 2 ,2S0 3 = C 2 H 3 Q,2S0 3 ,HO, which, by further elevation of temperature, is decomposed; the methylic ether being separated, and the sulphuric acid and water alone remaining. 619. Hydrochloric Methylic Ether, C 2 H 3 C1. This compound is formed by distilling a mixture of common salt, wood-spirit, and oil of vitriol. It is a colorless gas, of a peculiar odor, and cor- responds to the ether of similar name in the common alcohol series ; the oxygen of the preceding compound being replaced by chlorine. It is not reduced to a liquid state by a temperature of zero. By the action of chlorine upon this ether, in the direct rays of the sun, the several equivalents of hydrogen may be successively replaced by chlorine, as heretofore shown in another case (610), and important com- pounds formed, the formulae of which, with their densities and boiling points, are given in the following table : Boil. Point. Density. Hydrochloric methylic ether, C 2 H 3 C1 ...... 0-0 1.74 Bicblorinated " " C 3 H 2 C1 2 87 ...... 1-34 Trichlorinated " " C 2 HC1 3 142 1-49 Sesquichloride of carbon, C a II 4 172 1-60 620. Chloroform, C 2 HC1 3 , is the trichlorinated compound of this series. It is produced by the direct action of chlorine QUESTIONS. What is said of the relation methylic ether sustains to methylic alcohol ? What is sulpho-methylic acid ? 619. Describe hydro* chloric methylic ether. What is the eifect when a current of chlorine is made to pass through this ether ? 620. What is chloroform ? 442 ETHERS. upon hydrochloric methylic ether, but the best method of pre- paring it is "to distil a mixture of hypochlorite of lime (common bleaching salt) and wine alcohol, or wood-spirit. Chloroform is a dense, oily liquid, of an agreeable ethereal odor, and sweetish taste. It is not dissolved by water, but mixes readily with alcohol. Its density is 149, and it boils at about 142. By breathing its vapor mixed with atmospheric air, a kind of intoxica- tion is produced, much like that occasioned by exhilarating gas, or the vapor of sulphuric ether. If the vapor is breathed some time, total insensibility to pain is produced, and loss of consciousness, during which difficult surgical operations may often be performed, without even the knowledge of the patient. It readily dissolves caoutchouc and gutta percha, and solid carbonic acid. By alcoholic solution of potash, chloroform is changed into formiate of potash and chloride of potassium. It was this cir- cumstance that suggested the name chloroform. lodoform, C 2 HI 3 , bromoform, C 2 HBr 3 , and sulphoform, C 2 HS 3 , are analo- gous compounds of iodine, bromine, and sulphur. 621. Hydriodic Methylic Ether, C 2 H 3 I, is a colorless liquid, obtained by distilling a mixture of iodine, methylic alcohol, and phosphorus. It is remarkable for its great density, which is 2-24. Hydrobromic Methylic Ether, C 2 H 3 Br, is prepared in a manner similar to the above, only substituting bromine instead of iodine. It is liquid at temperatures below 55. Hydrosulphuric Methylic Ether, C 2 H 3 S, is a liquid, of a density 0-845, which boils at 106. Still other simple methylic ethers are known, but they cannot be here described. II. COMPOUND METHYLIC ETHERS. 622. Sulphuric Methylic Ether, C 2 H 3 0,S0 3 . This ether 13 formed by distilling 1 part of methylic alcohol with 8 or 10 parts of sulphuric acid. It is a liquid, having a density of 1-32, and boils at 370. Nitric Methylic Ether, C 2 H 3 N0 6 = C 2 H 3 0,N0 5 .~ This ether corresponds to the ether of similar name in the common alcohol QUESTIONS. How is chloroform prepared? What use is made of it? 621. What other methylic ethers are mentioned? 622. How is sul- phuric methylic ether formed ? Describe nitric methylic ether ? ETHERS. 448 series. It is formed by distilling a mixture of wood-spirit, nitrate of potash, and sulphuric acid. It is a dense, colorless liquid, which boils at about 150. Its vapor, when heated to 248, is decomposed with a violent explosion. Oxalic Methylic Ether, C 4 H 3 4 = C 2 H 3 OC 2 3 . Oxalic me- thylic ether is prepared by distilling a mixture, in proper pro- portions, of sulphuric acid, binoxalate of potassa, and methylic jalcohol. At ordinary temperatures, it is a white crystaline solid, which melts at 124, and boils at 322. Acetic Methylic Ether, C 6 H 6 4 = C 2 H 3 0,C 4 H 3 3 . This ether is formed by distilling an acetate with methylic alcohol, and sul- phuric acid. It is always formed in the distillation of wood. It is a colorless liquid, of an agreeable ethereal odor, and has a specific gravity of 0-919. It boils at a temperature of 137. The close resemblance between the methylic ethers and those of the common alcohol group will be seen at once. There are many more of this group, which cannot be here described, late writers enumerating more than seventy. Ethers of Amylic Alcohol. 623. Amylic alcohol, treated with sulphuric acid, produces sulphoamylic acid, similar to the sulphovinic and sulphomethylic acids, which is easily obtained in combination with bases, but with difficulty in a free state. Treated with an excess of concentrated sulphuric acid, and heated to boiling, a carburetted hydrogen, C 10 H, , is obtained, called amylene, which is a volatile, colorless liquid, boiling at 102. At the same time two other compounds, isomeric with it, are usually obtained, called paramylene, $%$.<& and metamy- lene, C^H^, 624. Amylic Ether, C, H U 0. This ether is prepared from the hydrochloric amylic ether, to be next described, by the action of a 'strong solution of potassa. It is a liquid of an agreeable odor, the boiling point of which is about 234. QUESTIONS. What is said of the resemblance between the methylio ' ethers and those of the common alcohol series ? 623. What is said of the sulphoamylic acid ? What is amylene ? What two substances isomeric with it are mentioned ? 624. What is amylic ether ? 444 , VOLATILE OILS. This ether, it will be seen, corresponds precisely to common ether in the wine alcohol group of ethers, and to methylic ether in the methylic alcohol group. Hydrochloric Amylic Ether, C,oH n Cl. To obtain this ether, equal parts of amylic alcohol and perchloride of phosphorus are distilled in a glass retort, and the vapor condensed in the ordinary mode. It is a colorless liquid, with an aromatic odor, and boils at about 215. If may also be obtained b;y the action, long continued, of hydro- chloric acid upon alcohol. 625. Ilydriodic amylic ether, C 10 H,,I, and hydrosulphuric amylic ether, C 10 H n S, are known. The latter has the smell of onions. Acetic Amylic Ether, C 14 H 14 4 ==C, H,,0,C 4 H 3 p 3 . To prepare acetic amylic ether, equal parts of amylic alcohol and oil of vitriol are distilled with 2 parts of acetate of potash, and the resulting liquid purified. It is a limpid liquid, a little lighter than water, with an agreeable aromatic odor. Its boiling point is 257. By some its composition is said to be 3(C 10 H U 0),C 4 H 3 3 . The odor of this ether closely resembles that of the ripe banana fruit, and it is used to give the banana flavor to sugar-candy. The preparation is sometimes called banana drops. The peculiar flavor of many ripe fruits may in this mode be very closely imitated by the use of ethers. Oxalic Amylic Ether, C, 2 H n 3 =C 10 H u O,C 2 3 . This compound is pro- cured by distilling a mixture of amylic alcohol and oxalic acid. It is liquid at ordinary temperatures, and boils at 500. Its odor is exceed- ingly offensive. VOLATILE, OR ESSENTIAL OILS. 626. These oils constitute a very numerous class of compounds, and, as the name indicates, are distinguished by being volatile at ordinary or slightly elevated temperatures. Most of them are liquid at a temperature of 50, or above ; but a few are solid, as common camphor. They are also usually distinguished by their powerful odor, which is often very agreeable. Most of them are obtained from QUESTIONS.- What relation does amylic ether sustain to this series of ethers? What other ethers of .this series are mentioned? 625. What is said of the odor of acetic amylic ether ? 626. What is said of the volatile oils ? Are any of them solid at ordinary temperatures ? What ia said of their odor ? From what are they obtained ? VOLATILE OILS. 445 the leaves and stalks of plants, but some are found in the flowers, fruit, bark, wood, or in the pericarp. In general, these oils are obtained by distilling the part of the plant containing them, with water; both the oil and the water pass over in vapor, and are condensed in the usual mode ; and are afterwards separated by the oil rising to the surface. In a few cases only is the oil heavier than water, when, as a matter of course, it sinks to the bottom. To separate such as are lighter than water, a vessel of the form represented in the margin answers well. It is simply a vessel of proper size, with a small spout which starts nearly from the bottom, and rises nearly as high as the mouth. It is first filled with water to the line A, and then the mixed liquids are poured into it in a small stream, the oil remaining at the surface, while the water escapes at C. This, it is evident, may be continued until the vessel is. nearly filled with the pure oil ; or until, if more were added, the oil itself would begin to escape by the spout C. Separating Volatile Oils. Water is necessary in the distilling process, to prevent the decom- position of a portion of the oil by the heat ; and in most cases the distillation can be effected in this mode, even though the boiling point of the oil be considerably above that of water. In some cases, a higher temperature than 212 is required, when some soluble salt is added to the water, as common salt; a saturated solution of this compound boiling at about 230. Some few of the essential oils are obtained from the plant by pressure, or by the action of a solvent, as alcohol or ether. 627. These oils being volatile, if a small portion is dropped on a piece of white paper, the stain produced soon disappears, espe- cially if -the paper be warmed. In this way they may be dis- tinguished from other oils, which produce upon paper a permanent stain. Most of the essential oils consist of at least two principles ; one of which is less fusible than the other, and may be separated by cold. Thus, exposing oil of peppermint to severe cold, a solid QUESTIONS. Why is water necessary in distilling these oils ? 627. How may the volatile oils be distinguished? What is said of the composition of most of them ? 88 446 VOLATILE OILS. not unlike camphor is crystalized out, and may be separated from the portion that remains liquid. These solids, sometimes called stearoptens, are different in the different oils; some being much more easily solidified than others. Their composition is also various ; some being isomeric with, the oil which yields them, and others, hydrates or oxides of the oil. Most of them exist, as such, in the plant or part of the plant from which they are obtained, but some are formed in the process of distillation from materials contained in the substance distilled. 628. If we have regard to the elements of which these oils are com- posed, we may divide them into three classes, viz. : 1. Oils composed entirely of carbon and hydrogen. 2. Oils which, in addition to the above elements, also contain oxygen ; and 3. Oils of which sulphur is an ingredient ; these also usually contain nitrogen. Carbo-liydrogen Volatile Oils. 629. Oil of Turpentine Camphene, C 20 H 16 . This oil is pro- cured by distilling common turpentine with water. Turpentine is obtained from several species of the pine, in the wood of which it is contained in large quantities. At the proper seasons of the year, incisions are made with an axe in the trunks of the trees, from which it gradually exudes, and is collected and preserved. This viscous substance is a solution of resin (common rosin") in oil of turpentine, and the latter is separated in the process of distillation. Common spirits of turpentine is an impure camphene, con- taining a portion of resin in solution. Exposed to the air, oil of turpentine evaporates rapidly, but at the same time oxygen is absorbed, and a portion of the oil is con- verted into resin, which remains in solution. It can therefore be preserved pure only in vessels from which the air is perfectly excluded. When pure, it is a limpid liquid, of specific gravity 0-87, which boils at 315. QUESTIONS. Do the essential oils exist ready formed in. the plant? 628. Into what three classes may they be divided? 629. How is oil of turpentine procured ? From what is it obtained ? What are the ordinary spirits of turpentine ? VOLATILE OILS. 447 Oil of turpentine is not soluble in water, but dissolves readily in alcohol and ether, and in other essential oils. Mixed with three or four times its volume of strong alcohol, it constitutes the ordinary burning fluid. When left for some time in contact with water, a portion of the two unite, forming a solid hydrate of camphene, which has the formula, C 20 1I 16 ,6HO. Other hydrates may also be prepared, containing, seve- rally, 4, 2, and 1 equivalents of water. Many substances, as caoutchouc, insoluble in alcohol and ether, dis- solve readily in this oil, which renders it an important substance in the arts. It is also largely used in mixing paints, in the manufacture of varnishes, and in the practice of medicine. 630. Hydro chlorate of camphene, or artificial camphor, C 20 H ]6 ,HC1, is prepared by passing a current of dry hydrochloric acid gas through pure oil of turpentine. It makes its appearance as a white crystaline solid, which melts at about 302, and may be sublimed, without change, at about 338. In many of its ^properties it closely resembles common camphor. The portion which remains liquid has the same composition as the crystals, but it cannot be solidified, so far as is known, by any tem- perature. Hydriodic and hydrobromic acids form with oil of turpentine com- pounds similar to those formed by the hydrochloric. Sulphuric and nitric acids act readily upon oil of turpentine, forming several interesting compounds. 631. Oil of Lemons, C IO H 8 . This oil is obtained by pressure from the yellow part of the peel of the fruit, and is isomeric with the preceding, having the same ultimate composition, but its equiva- lent being only one-half that of oil of turpentine. By distillation it yields two oils, which differ in their boiling points. Oil of lemons has a specific gravity of 0-847, and it boils at 338. By the action of hydrochloric acid, it forms two camphors, similar to those formed from oil of turpentine, one being solid and the other liquid. Orange peel yields an oil isomeric with the above, but having a dif- ferent specific gravity, and a different boiling point. Oil of elemi, oil of juniper, oil of pepper, &c., have a similar composition to the above, and they are all isomeric. QUESTIONS. What is the effect when oil of turpentine is left in contact with water? What use is made of this oil? 630. What is artificial cam- phor? How is it formed? 631. Describe the oil of lemons. What is baid of oil of elemi, oil of juniper, c. ? 448 VOLATILE OILS. Oxygenated Volatile Oils. 632. Oil of Bitter Almonds. Benzoic Series of Compounds, Bitter almond oil, C, 4 H 6 2 , is obtained from the kernels of bitter almonds by distillation with water after the fixed oil con- tained in the seed has been expressed. It does not pre-exist in the seed, but is formed from the amygdaline of the seed, in a manner soon to be explained. Its density is a little above that of water, and it boils at 356. It is quite colorless, and has a pungent taste and fragrant odor, and is poisonous. After the fixed oil has been expressed, the pulp is allowed to stand for some hours, and a kind of fermentation takes place in the amygdalkie by virtue of the presence of another proximate principle contained in the almond, called synaptase, or emulsine. During this fermentation there are produced, besides the oil, hydrocyanic acid and glucose. 633. Amygdaline, C 40 H 27 N0 22 , may be obtained in a free state. It is a crystaline, colorless powder, very soluble in water and alcohol. Synaptase also may be isolated ; it is a yellowish-white solid. 634. Chlorinated Oil of Bitter Almonds Chloride of Benzyle, C 14 TT 6 C10 2 . This substance is obtained by passing a current of dry chlorine through oil of bitter almonds, and expelling the excess of chlorine by heat. It is a colorless liquid, heavier than water, and has a peculiar, disagreeable odor. It is formed from the oil by the substitution of an atom of chlorine for one of hydrogon. Iodine and bromine form similar compounds. When this chlorinated oil is treated with gaseous ammonia, there are formed benzamide, C 14 H 6 2 ,NH 2 , and hydrochlorate of ammonia. Thus, C 14 H 5 C10 2 + 2NH 3 = C 14 H 6 2 ,NK J + NH 3 ,HC1 Benzamide is a white crystaline solid, and may be entirely purified from the sal-ammoniac by washing it with water. By remaining long in contact with water, benzamide is converted into hydrobenzamide, C^HjgNg.GHO; and this, by solution in alcohol and boiling, is recon- verted into bitter almond oil and ammonia. Benzoic Acid. When exposed to the atmosphere, oil of bitter lilrnonds rapidly absorbs oxygen, and is converted into lenzoic acid, C 14 H 6 4 = C U H 6 3 ,HO. This acid is also formed when QUESTIONS. G32. Describe bitter almond oil. From what proximate principle contained in the kernel is the oil formed? G33. Describe amygdaline. 634. Describe the chlorinated oil. Describe benzoic acid. VOLATILE OILS. 449 the oil is 'boiled with a solution of potassa. It is a beautiful, crystaline solid, which melts at 248, and boils at about 463. It may, however, be sublimed at a temperature considerably below its boiling point. Benzoic acid is found in considerable quantity in the resinous substance usually called gum benzoin, a product of the laurus benzoin. From this compound it may be procured by direct sublimation, in the following manner. Place a small quantity of the resin, coarsely powdered, upon a plate of metal on a stand, and put over it a glass receiver, having suspended in it a small twig of mint, or other substance, as shown in the figure, and apply the heat of a lamp beneath it. In a short time the leaves will be covered with delicate crystals of the acid. * Benzoic acid with bases forms numerous salts called ben- zoates, but none of them are of sufficient importance to require description here. 635. Benzoic Ether, C 4 H 5 0,C I4 H 5 03, is formed by distilling a mixture of 1 part of benzoic acid, 2 parts of alcohol, and 6 parts of hydrochloric acid. It is a colorless liquid, heavier than water, and boiling at' 410. By substituting methylic instead of wine alcohol in the mixture, benzoic-methylic ether is formed, which boils at 226. 636. Benzoine, C 28 H 12 4 , is formed when crude oil of bitter almonds is shaken with an alcoholic solution of potassa, and is separated by crys- talization. The crystals melt at 248. It is isomeric with the oil. It may be sublimed without change ; but by passing its vapor through a red-hot tube the oil is reproduced. By heating benzoine with nitric acid, it loses 2 equivalents of its hydrogen, and a new compound is formed, called benzile. By the ad- dition of oxygen, benzilic acid is formed. 637. Benzone, C n H 10 8 , is a compound formed when benzoate of lime is distilled. It is a solid, little soluble in water, but very soluble in alco- hol and ether. 638. Benzene, C, 2 H 6 , at ordinary temperatures, is a liquid of specific gravity 0-85, which boils at 187. It ia formed by distilling a mixture of 3 parts of dry recently-slaked lime and 1 part of benzoic acid. It ia QUESTIONS. Describe the mode of subliming a small quantity of benzoio acid. 635. Describe benzoic ether. 636. Describe benzoine. 637. Ben- zone. 638. Benzene. 98* 450 VOLATILE OILS. of a sweet taste and agreeable odor, and crystalizes when cooled to 32. It has also been called benzol and phene ; and is produced by the decom- position of many organic substances by heat. 639. Oil of Spiraea TJlmaria, Salicine Series of Compounds. Flowers of the plant called meadow-sweet (spiraea ulmaria), when distilled with water, yield an acid essential oil, C U H 6 4 , which, like the oil of bitter almonds, is of special interest because of its intimate relations with numerous other compounds. It doea not pre-exist in the flowers, but is formed in the process of dis- tillation. It is a liquid more dense than water, and boils at 385. In composition it is isomeric with benzoic acid, and is sometimes called salicylous acid. 640. Salicjne, C 2 6'H 18 1 4, is a substance obtained from the bark of certain species of willow (salix), and from many other plants, by digesting them with water, and then precipitating the gummy matter also contained in the solution by boiling with oxide of lead. After precipitating the lead by means of sulphuric acid, and sulphide of barium, salicine is obtained by evaporation in small, white, acicular crystals. Its taste is bitter, and it is very soluble in hot water and alcohol, but not in ether. Cold sul- phuric acid dissolves it, forming a deep red solution. A mixture of equal parts of salicine and bichromate of potash, digested for some time with 6 or 8 times their combined weight of dilute sulphuric acid, and afterwards distilled, yields salicylous acid, or oil of spiraea ulmaria, described above. Treated with dilute sulphuric or hydrochloric acids, or with nitric acid, various other compounds are produced, which cannot be here described. 641. Salicylic Acid, C, 4 H60 6 = C 14 H 5 5 ,HO. This acid is formed when salicylous acid is heated with an excess of caustic potash. The alkali is then separated by a mineral acid, and the salicylic acid is obtained in colorless crystals, which are soluble in boiling water and in alcohol and ether. "When salicylic acid is distilled with an excess of lime, carbonic acid and a new compound called phenol or phenylic alcohol, C 12 H 6 2 , are formed. Thus, = C 12 H 6 2 -f2C0 2 . QUESTIONS. 639^ Describe the mode of procuring oil of spiraea ulmaria. 640. Describe salicine. How is salicylous acid, or the oil last mentioned, obtained from salicine ? 641 . Describe salicylic acid. What is phenol or phenylic alcohol ? VOLATILE OILS. 451 Phenol is sometimes classed with the acids, and called carbolic acid. It resembles the alcohols in many of its properties. 642. By distilling a mixture of 2 parts of absolute alcohol, 1 part of sulphuric, and 1 \ parts of salicylic acid, salicylic ether, C 4 H 6 0,C 14 H 6 6> is obtained. It is a dense liquid, boiling at 437, and possesses acid properties, readily combining with bases and forming proper salts. By substituting methylic alcohol in the above mixture, and using 2 parts of salicylic acid, we obtain salicylic methylic ether, C 2 H 3 0,Ci 4 H 5 5 , which is of special interest as being identical with the chief constituent of oil of winter- green (gaultheria procumbens), a substance well known, as obtained by distilling with water the leaves and berries of this plant. The oil is an aromatic liquid, heavier than water, having its boiling point at 435. 643. Oil of Cinnamon. Cinnamic Series of Compounds. Oil of cinnamon is prepared by distilling with. water the cin- namon of commerce, which is the prepared bark of two or more species of trees, found in Ceylon and other Eastern countries. It possesses the peculiar taste and odor of the bark. Its compo- sition when pure seems to be C, 8 H 8 2 , but when exposed to the air it absorbs oxygen, and perhaps undergoes other changes not understood, so that different chemists have arrived at different results as regards its true composition. 644. Cinnamic Acid, C 18 H 7 3 ,HO, is always found in the oil after it has been kept for a time exposed to the air, and is also contained with benzoic acid in the balsams of Tolu and Peru. It is a crystaline solid, which melts at 264, and boils at about 570. Cinnamic acid forms ethers with common and methylic alco- hols, analogous to those formed by salicylic acid. When vapor of cinnamic acid is made to pass through a glass tube heated to dull redness, it is decomposed, and a carbo-hydrogen, C 16 H 8 , is formed, called cinnamene. It is a colorless liquid, of an agreeable, pene- trating odor. This compound may also be obtained from the resinous substance called styrax, and has in consequence sometimes received the name styrole. By treament with different reagents, still other compounds belonging to this series may be obtained. 645. Oil of Aniseed. Anisic Series of Compounds. Aniseed (the seeds of the anisem sativum'), when distilled with water, QUESTIONS. 642. Describe salicylic ether. What is said of the oil of winter-green? 643. How is oil of cinnamon procured? 644. 'De- scribe cinnamic acid. 645. Describe aniseed oil. 452 VOLATILE OILS. yields an essential oil from which crystals are deposited at a low temperature, having the composition, C 2 oH 12 2 . Treated with reagents, it forms a series of compounds known as the anisic series. Among them are anisic acid, C, 6 H 7 5 ,HO, which, with wine and methylic alcohols, yields ethers, and anisene, C, 4 H S . These sustain the same relation to each other, and to the oil, as cinnamon sustains to cinnamic acid and the oil of cinnamon. 646. Oil of Cumin, obtained by distilling with water the seeds of the cuminum cyminum, treated in a similar manner with reagents, forms a series of compounds, analogous to the above. Another series; called the eugenic series, is formed from the oil of cloves or oil of pimento. 647. Oil of Peppermint, C 20 H 20 2 , is contained in the leaves and stem of the plant, from which it is separated by distillation with water. This oil is used in large quantities by confectioners ; and in some of the western states, the plant is extensively cul- tivated, to be distilled for the oil. Dissolved in alcohol, it forms the well-known essence of peppermint. This is the general method of preparing what are called essences. Oil of peppermint is liquid at ordinary temperatures; but, when cooled gradually, it deposites a white crystaline stearopten (627), resembling camphor, which has the same composition as the oil. There are very many other oxygenated volatile oils, but as they possess no properties giving them peculiar interest, they cannot be here described. Sulphuretted Volatile Oils. 648. OH of Black Mustard, C 8 E 5 NS 2 . This oil does not exist, as such, in the seed, but is formed from substances contained in them, after the fixed oil has been expressed, as in the case of bitter almond oil. The active substances in the mustard-seed, producing the oil when the bruised seed is digested -with water, are called myrosine and myronic acid, both of which have been isolated ; but their composition has not been determined. Oil of mustard is a colorless liquid, boiling at 293, and forming a most pungent, irritating vapor. Treated with reagents, it forms several other compounds. QUESTIONS. 646. From what is oil of cumin obtained? 647. De- scribe oil of peppermint. 648. What is the composition of oil of black mustard ? VOLATILE OILS. 453 649. Oil of Garlic, C 6 H 5 S. This oil is procured by distilling garlic with water,' and redistilling the product first obtained in a salt-water bath, and then rectifying it with potassium. It is a colorless liquid, lighter thiiii water, and of an offensive odor. It has been called sulphide of alyl, being composed of sulphur and the carbo-hydrogen, C 6 H 6 , called alyl. Camphors. 650. The camphors are allied both to the essential oils and to the resins. There is a large number of them, if we include the stearoptens (627), deposited at low temperatures from the vola tile oils; but only common or Japan camphor, and Borneo camphor, with a few of the compounds formed from them, will be here described 651. Common, or Japan Camphor, C 20 H 16 2 . This substance, which is always seen as a white crystaline solid, is obtained by distilling with water the roots and wood of the laurus cam- phor a, a tree found in the island of Japan, and other parts of the East (see figure). It is a little lighteAhan water, and is readily soluble in alcohol, and ether, and every variety of ardent spirits. Water dissolves about one-thousandth of its weight, which is sufficient to communicate to it something of its peculiar, pungent, but agreeable odor. At 347 the solid melts, and at 410 it boils. In the open air, at ordi- Lauras Camphora. nary temperatures, it. gradually evaporates. When some lumps of it are contained in a close glass vessel, of somewhat larger capacity than is merely sufficient to receive it, the vapor that forma is gradually condensed in small crystals upon the side^ of the QUESTIONS. 649. What is the composition of oil of garlic ? 650. To what are the camphors allied? 651. From what is common camphor procured ? Describe its properties. 454 VOLATILE OILS. glass ; and if the vessel stand in a place so that the light can fall <5nly on one side, the chief deposition will be on the side exposed to the light. When subjected to the action of chlorine, a part of the hydrogen of the camphor is replaced by chlorine, forming chlorinated cam- phor, C 20 H 10 C] 6 2 . By the action of heated nitric acid upon camphor, camphoric acid, C 20 H 16 8 = C 20 H, 4 6 ,2HO, is formed, which is bibasic, and forms with alcohol a coupled acid (609) and a compound ether. By the action of a mixture of potassa and lime, at an elevated temperature, upon vapor of camphor, another acid is formed, called the camphoh'c acid, the composition of which is C2oH, 7 3 ,HO. ' Distilling this acid with phosphoric acid, we obtain the carbo- hydrogen, C, 8 H 16 , called campholene, which is liquid, and boils at 275. Borneo Camphor, C 2 oH 18 2 . This compound comes chiefly from the island of Borneo, and hence its name. In some of its properties it closely resembles the preceding, but its odor and taste are different. It melts at 383, and boils at 419. In composition it differs from Japan camphor only by containing two more equivalents of hydrogen* By heating it with nitric acid, these two equivalents are separated from it, and common camphor formed. Coumarine. 652 By this name a crystaline, odoriferous substance is known, which is extracted from the Tonka bean, but is also contained in several plants, as the sweet vernal grass (anthoxanthum odoratum). It is procured by digesting the bruised beans in strong alcohol, which dissolves the odori- ferous principle. Coumarine is the basis of the perfume called vanilla. By the action of reagents it forms cdumaric add, C 18 H 7 6 ,HO. QUESTIONS, What effect is produced when common camphor is sub- jected to the action of chlorine? How is camphoric acid formed? What is said of Borneo camphor? 652. From what is coumarino obtained ? In what perfume is it used ? FIXED OILS AND TATS. 455 FIXED OILS AND FATS. 653, The fixed oils are so called because, unlike tlie essential or volatile oils, they are incapable of being volatilized without change ; consequently, when spread upon paper they produce a permanent stain. The fats are essentially the same as the oils, except that they are usually solid at ordinary temperatures, while the oils are generally liquid. But the distinction is unimportant. Fatty substances a phrase which may include both the fixed oils and fats are found both in the animal and vegetable king- doms ; and their ultimate elements are always carbon, hydrogen, and oxygen. The fatty substance of a plant is usually found in the seeds or pericarp, occasionally upon the surface of the leaves or bark. When contained in the seed or pericarp, it exists in peculiar cells, which require to be broken before it can be separated ; and usually heat is applied to render it more liquid, when the separation is effected by severe pressure. Animal fats are separated from the tissues containing it either by pressure or by the protracted action of heat. Most oils absorb oxygen from the atmosphere, by which their con- sistency is changed ; but by some the absorption is much more rapid than by . others. Such as absorb oxygen rapidly as linseed oil are called siccative, or drying oils, and are used in painting. When mixed with the coloring substance, or pigment, and spread upon the surface of wood, or other material, by means of a brush, oxygen is absorbed and a resinous coating formed, by which the coloring substance is firmly retained. By heating a drying oil nearly to the point at which decom- position begins to take place, the tendency to absorb oxygen is increased. This effect is still greater if, before heating, some highly oxydized body, as oxide of lead or manganese, is mixed with the oil. Unctuous oils are such as do not absorb oxygen from the air, or do it but slowly. ' Rancidity in oils is usually occasioned by the absorption of oxygen. Some oils, while they absorb oxygen also give off carbonic acid or hydrogen. 654. Proximate Principles of the Fats. All the fats and fixed oils are composed of several proximate principles, which QUESTIONS. 653. Why are the fixed oils so called ? Are they found both in animal and vegetable bodies ? In what part of the plant are they usually found ? What are siccative, or drying oils ? What are unctuous oils ? 654. What are the chief proximate principles of the fats ? 456 FIXED OTLS AND TATS. are usually combined in definite proportions. The most common of these are glycerine, stearine, margarine, and oleine, of which nearly all the animal fats and oils are almost wholly composed. In several fatty substances, as butter, we find, in addition, small quantities of other proximate principles, as butyrine, caprine, and caproine. In some instances still other principles are found, which will be described in their proper places. The proportion of stearine, margarine, and oleine in the dif- ferent fats is exceedingly variable, and occasionally one or another of them may be wanting ; in the more solid fats stearine and mar- garine are more abundant, while oleine is the chief constituent of the oils and more fusible fats. All of them contain glycerine except spermaceti, in which, instead of this principle, another peculiar compound is found, called eihal, a substance in com- position allied to the alcohols. The fats and fixed oils generally are capable of combining with the caustic alkalies to form soaps, and are therefore said to be saponifiable. The process consists in digesting the fatty substance with a solution of a fixed alkali, as potassa, or soda, when the stearine, margarine, oleine, &c., disappear, and corresponding acids, called stearic, margaric, oleic, &c., acids, are formed, which unite with the alkali, glycerine being at the same time get free. These acids probably do not exist as such in the fats, or even in the proximate principles from which they are derived, but are formed during the process of saponification, as will appear more clearly hereafter. The presence of water is necessary to the process, a small portion, of it, as we shall see, being required to produce the compounds formed. Glycerine. 655. Glycerine, C 6 H 8 6 = C 6 H 7 5 HO, was discovered by Scheele, and called the " sweet principle of fat." It is best obtained by boiling, for some time, a mixture of equal parts of olive oil and oxide of lead diffused in water, filtering the liquid which remains, and then passing through it a current of sul- phuretted hydrogen, to separate all the lead. Lastly, it is heated for a few moments to the boiling point, and all the water care- fully evaporated in a vacuum. QUESTIONS. In what fats do stearine and margarine usually abound ? In what is oleine the chief constituent ? What is said of spermaceti ? What is meant by the saponification of a fat ? What are formed in the process of saponification 2 655. How is glycerine obtained ? *IXED OILS AND FATS. 457 As thus prepared, glycerine is an oily liquid, very soluble in water and alcohol, but insoluble in ether ; quite inodorous, but having a sweet taste. Its specific gravity is about 1-27. Its name is derived from the Greek, ylukus, sweet, in allusion to its taste. With sulphuric and phosphoric acid it forms coupled acids (607) similar to those formed by these acids with the alcohols, which are called respectively the sulphoyly eerie and the phospliogly eerie acids. Glycerine is not volatile, but is decomposed when heated, yielding a peculiar, acrid volatile principle, called acroleine, C 6 H 4 2 . ' It is this sub- stance which constitutes the acrid, irritating fumes always perceived when any fatty substance is decomposed by heat, in such circumstances that the product of the decomposition cannot be immediately consumed, as in the manufacture of gas from oil. Stearine and Stearic Acid. 656. Stearine, C,4 2 H 140 0, 6 . Stearine (Greek, stear, tallow) forms the chief constituent of tallow, and is a white crystaline solid, much resembling spermaceti. It exists in nearly all fats, and in many of the oils, both animal and vegetable; and is found in greater proportion as the point of congelation of the fat or oil is more elevated. The best method to obtain it is to heat moderately some mutton suet with 8 or 10 times its volume of camphene, in which it will be dissolved ; and, on cooling, the stearine will be deposited in white pearly crystals. These are entirely insoluble in water, and melt at 140. Stearine, by saponification with potash, forms stearate of potash, and hydrated glycerine is set free ; and the stearate, by subse- quent decomposition by a mineral acid, yields stearic acid, CwHeA = CegHajOg^HO, which is obtained as a white, crys- taline solid. Stearic acid is the substance of which " stearine" and " ada- mantine" candles are formed; and therefore constitutes an im- portant article of commerce. It melts at 167, and solidifies at about 158. QUESTIONS. Describe the properties of glycerine. What is acroleine? 656. What is the derivation of the word stearine ? From what is this substance obtained? How is stearic acid formed ? Describe it. What use is made of it ? 39 458 FIXED OILS AND FATS. 657. Stearic acid for the manufacture of candles is prepared by two different processes. One method is to digest the natural fat, as tallow, with lime-water, aided by heat, by which an insoluble lime-soap is formed : and this is then decomposed by dilute sulphuric acid, the lime of course all being separated, as a sulphate. The fatty acids now rising to the top are washed to separate the glycerine, and compressed to remove the oleic and most of the margaric acids ; and the cakeu of nearly pure stearic acid are ready for use. By the other mode dilute sulphuric acid is used, by which nearly the eame effect is produced, this acid combining with the glycerine to form sulphoglyceric acid (655), which is washed away with the water. The fatty acids now obtained are distilled, at a high temperature, in an appa- ratus in which' a partial vacuum is kept up, and through which a current of steam is continually passing. By pressure most of the oleic acid is now separated, and the mixed stearic and margaric acids .obtained. The composition of stearine corresponds to 2 equivalents of anhydrous stearic acid, and 1 equivalent of hydrated glycerine. Thus, Ci42H 140 i6 = 2(0^^0.) + C 6 H 7 6 ,HO. 658. Stearic ether is formed by treating wine alcohol with stearic acid, and passing through the solution a current of hydrochloric acid ; and by a similar process with methylic alcohol stearic methylic ether is formed, Both are solid at temperatures below abojut 85 or 90. Margarine and Margaric Acid. 659. Margarine and margaric acid have the same composition, respectively, as stearine and stearic acid, of which they are isomeric modifications. The melting point of margarine is 118, and that of margaric acid 140. 660. Margarone, CegHegC^, is a white pearly substance, formed by dis- tilling a mixture of 4 parts of margaric acid and 1 part of lime. The following equation illustrates the chemical changes produced in the acid to form the margarone^ CsgHggOg -f 2CaO = C^H^-}- 2CaO,CO, -f- 2HO. Oleine and Oleic Acid. 661. Oleine is the chief ingredient of most of the fixed oils, and is found also in many of the fats. It is difficult to obtain it pure, and therefore its formula cannot be given with certainty. QUESTIONS.- 657. What two methods are given for preparing stearic acid for the manufacture of candles? 658. Describe stearic ether. 659. What is said of the relation of margarine and margaric acid to stearine and stearic acid respectively ? 660. What is margarone ? 661. What is said of oleine ? FIXED OILS AND FATS. 459 It is best prepared from olive oil. Oleine is a yellowish liquid, of an oily consistency, which requires a temperature of about zero for congelation. Okie acid, C 36 H3 3 03,HO, is an oily liquid, having a density of about 0-808, and solidifies at about 32. It is formed by eaponification of oleine, and subsequent decomposition of the soap l>y hydrochloric acid. By distillation in close vessels oleic acid forms sebacic acid, C ]0 H 8 3 ,HO ; ffhich, distilled with alcohol and hydrochloric acid, forms sebacic elher. Action of Nitric Acid upon the Fatty Acids. 662. Nitric acid acts energetically upon the fatty acids, pro- ducing a variety of other acids, some, of which are volatile, and others fixed at moderate temperatures. The former arc the formic, acetic, propylic or acetonic, butyric, valerianic, caproic, ceenanthylic, caprylic, pelargonic, and capric acids ; all of which are homologous, and have the general formula, C 2n H 2n O 4 = CA.AjHO. At the same time the following non-volatile acids are formed, and may be separated by the proper means, viz., the succinic, adipic, pimelic, suberic, and sebacic. These also are homologous, and have the general formula, C 2n H 2(n _ n 8 = C 2n H 2(n _2)0 6 ,2HO. Most of these acids, it will be observed, are also obtained from other sources. The pelargonic is obtained from the rose-geranium (pelargonium roseum), the succinic, from amber (Latin, SMC- cinum), and the suberic, from cork, which is the prepared bark of the quercus suber. Other Proximate Principles of the Fats, as Butyrine, Pal- matine, &c. 663. Butter contains several proximate principles, besides those above described, as butyrine, caprine, and caproine, but it is difficult to separate them. By digesting butter with an alkali, decomposing the compound formed by tartaric acid, and distilling, butyric acid, C 8 H 8 4 = QUESTIONS. Describe oleic acid. 662. What is said of the action of nitric acid upon the fatty. acids? 663. What is said of butter? How is butyric acid obtained ? 460 FIXED OILS AND PATS. C 8 H 7 8 ,HO, is obtained, mixed with other substances, from which it is easily separated. Butyric acid may also be formed from sugar, by mixing with a solution of it a little curds of milk and powdered chalk, and allow- ing it to stand for a time in a place where it shall be kept at a temperature of about 90. A peculiar fermentation takes place, called the butyric fermentation, and the butyric acid, as it forms, combines with the lime, and forms butyrate of lime, which is decomposed by hydrochloric acid, and the butyric acid separated by careful distillation. Butyric acid is liquid at ordinary temperatures, and boils at about 327. Its density is about 0-963, and it is soluble in both water and alcohol. With alcohol and sulphuric acid butyric acid forms butyric ether, C 4 H50,C 8 ri 7 03. This substance, dissolved in 5 or 6 times its volume of alcohol, forms pine-apple oil, which is used by con- fectioners for its pine-apple flavor. Butyrone, C 7 H 7 0, and the compound, C 8 H 8 2 , sometimes called butyral, are formed by distilling butyrate of lime. Butyral is the proper alde- hyde (547) of butyric acid, and may be called butyric aldehyde. Caproic. caprylic, and capric acids, are also obtained from the decom- position of butter. Each of them forms a vinic and a methylic ether. 664. Castor oil (obtained from the plant called ricinus communis) by saponification forms ricinoleic acid, 33113606= C 38 H 35 5 ,HO; and this acid, distilled with solution of potassa, yields the com- pound, 0| 6 H, 8 2 , which is evidently homologous with the alcohols, and has beeo placed in our list (547) as caprylic alcohol. Palmaline, and palmitic acid, C 94 'H^0 9 =C B4 'H 92 & 2'HO J are obtained from palni oil, which is imported largely into this country from the coast of Africa, and used in the manufacture of soap. 665. Spermaceti called also cetine, when pure is a beautiful white substance, found mixed with oil in cavities of the heads of certain species of whales. The oil is separated from it by pres- sure ; and the hard, white, crystaline substance thus obtained QUESTIONS. How may butyric acid be formed from sugar? Describe its properties. How is butyric ether formed ? "What is butyrone ? What is said of butyric aldehyde ? 664. How is caprylic alcohol procured ? 666. What is ethal ? From what is it obtained ? FIXED OILS AND PATS. 461 melts at about 120, and maybe sublimed unchanged, .in close vessels, at about 680. Spermaceti contains no glycerine; but in its place a peculiar principle called etlial, CaaH^Oa, is found, which may be separated as a colorless, crystaline solid. Etlial, in many of its properties, as has been stated, closely resembles the alcohols; and various bodies are derived from it gimilar to those derived from the alcohols. Thus, when treated with sulphuric acid, it forms a coupled acid, called the sulpkethalic acid, which corresponds to the sulphovinic acid ; and, distilled with perchloride of phosphorus, it yields a liquid ether, C^^Gl, corresponding exactly with the hydrochloric ether, C 4 H 6 C1, pre- viously described. This substance yields an acid, called the ethalic, C a ^J. 32 4 = C 32 TI 3 ,0 3 , HO, corresponding to acetic acid in the common alcohol series. 666. Wax. Many substances, mostly of vegetable origin, are known as wax, of which bees' -wax is the proper type. This, as is well known, is obtained from honey-comb, by heating it with water; the wax melts and swims upon the surface, while the impurities it contains are dissolved in the water, or settle to the bottom. It appears to be a compound of two principles, cerine and myricine, which may be separated by boiling alcohol. Com- mon bees'- wax is of a yellow color, but is whitened by exposing it in thin layers to the action of the atmosphere and of light. Bayberry tallow, or myrtle wax, is a fat obtained from the fruit of the common bayberry (myvica cerifera). It is obtained from the berries by steeping them in hot water, and is found in other vegetables. Its composition is essentially the same as com- mon tallow, but it contains other principles in small quantity, among which is myricine. It melts at 117, but is very hard when cold, and may be formed into candles. 667. Myricine, C 92 H 92 4 , subjected to the action of a boiling alkaline solution, is converted into palmitic acid, C 3 2H 32 04, and QUESTIONS. What is said of the properties of ethal? 666. From what is bees'-wax obtained ? What two principles are mentioned as contained in it ? From what is myrtle wax procured ? What use is made of it ? 66Z What is inelissic ftlcohol? 39* 462 FIXED OILS AND TATS. a compound called melissine, C 6 oH 62 02, which, being analogous in composition to the alcohols, may be called melissic alcohol. Treated with potassa or lime, melissic alcohol forms melissic acid, CeaHeA = C,H 59 3 ,HO (547). Cerotine, CwHsAj and cerotic acid, C M H 54 4 := C^Hs-jOgjHO, are other compounds obtained from wax. The former substanc* in composition . ranks with the alcohols, and may be called ccrotir alcohol. Soaps and Plasters. 668. Soaps. Frequent allusion has already been made to the action of the alkalies upon the fats and oils; when these are boiled together, union takes place between them, and a well-known and very important substance is formed, called soap. The acids contained in the fat or oil, as the margaric, stearic, oleic, &c., described above, combine with the alkalies, forming proper salts, which exist in the soap together with other substances. The soaps formed by potassa, soda, and ammonia only are soluble in water. Potash soaps are generally soft, while those made with soda are hard ; but their consistency depends also upon the nature of the fat used. All soaps contain a large pro- portion of water in their composition. Potash or soda for soap-making should be in the caustic state, in order to act readily upon fatty substances. Soft soaps are made entirely of potash and tallow or oil, and often other animal matters. For the coarser kinds, very impure fats are used, without even separating them from the animal tissues in which they are contained. The common yellow hard soaps contain a portion of common rosin. Toilet soaps are often perfumed with the essential oils. 669. The mode in which soaps of all kinds operate to produce their cleans- ing effects is easily understood. All soaps are always more or less alkaline, as the alkalies contained in them are not entirely neutralized by the oily acids with which they are combined; they are therefore ever ready to combine with more fatty or oily matter with which they may come in contact, as that constantly given off in the insensible perspiration from QUESTIONS. What is cerotic alcohol ? 668. How are soaps formed ? What soaps are soluble in water ? What are insoluble ? What are soft* and what hard soaps ? 669. Explain the action of soaps. RESINOUS SUBSTANCES. 463 the skin. Caustic alkali always has a soapy feeling to the fingers, from the circumstance that it attacks the cuticle, and forms with it a soapy compound, at the same time absorbing a portion of water from the atmosphere. * 670. Plasters. The lead-plaster, or diachylon, used in surgery, is a kind of metallic soap, which is made by boiling olive oil and oxide of lead together, with a little water. The oleic and margaric acids contained in the oil unite with the oxide of lead, in the same manner as they combine with the alkalies (oxides of potassium and sodium) in the formation of soaps. There are two kinds of diachylon, the yellow and the brown the former of which is made with litharge, and the latter with red lead ; but their properties are essentially the same. Both are quite hard at ordinary temperatures, but melt with a moderate heat. RESINOUS SUBSTANCES. 671. llesins are solid substances contained in many plants and trees, usually in a state of solution in some essential oil. When exposed to the air the oil evaporates, and the solid resin is obtained. By friction they usually become negatively electrical. They are all insoluble in water, but most of them are soluble in alcohol, ether, and the essential oils. Most of them act as weak acids, and are capable of combining with the alkalies and other metallic oxides. Common resin, or rosin (French, colophane), is obtained from different species of pine, in which it exists combined with oil of turpentine. The substance called turpentine is obtained from the trunk of the tree by incisions made in it while growing; and this, by distillation, yields the oil of turpentine, the resin remaining behind in the boiler. There are, in commerce, several different kinds of turpentine, as Venice turpentine, Strasbourg turpentine, Canada balsam, &c. When the tree is felled, and the turpentine extracted by heat, it is partially decomposed, and acquires a dark color, and an offensive burnt odor, and is called tar. By heating tar, so as to expel all the oil of tur- pentine contained in it, the common pitch of commerce is obtained. From the different turpentines, by the action of- reagents, many im- portant substances may be formed, as the pimar'ic, silvic, and pinic acids. 672. Lac, or gum lac, as it is often called, is procured from a species of tree called Jicus, by punctures made in the bark by QUESTIONS. 670. How is lead-plaster or diachylon formed ? 671. What are resins? What is common resin or rosin? How is tat obtained? 672. From what is lac procured ? 464 RESINOUS SUBSTANCES. insects. It is soluble in alcohol and heated oil of turpentine, but is quite insoluble in water. Its composition seems to be quite complex, there being contained in the common lac of commerce a mixture of as many as five different resins. Lac is much used in the preparation of varnish and the manufacture of sealing-wax. Copal is the resin of the rhus copallinum and eleocarpus copaliferuSj trees found only in warm climates. It is of a light yellow color, and very hard, and without odor or taste. Its specific gravity is about 1-11. It is believed to be a mixture of several different resins, which, by proper processes, may be caparated from each other. This resin is quite insoluble in common alcohol or ether, but is softened, though not dissolved, by some of the essential oils. Its complete solution is effected by carefully fusing it, and then treating it with boiling alcohol or oil of turpentine. Copal varnish is made by fusing the resin in a deep copper vessel, to prevent it from igniting, and then pouring in liot linseed oil, and oil of turpentine, to give the proper consistency. Mastic and sandarac are other resins used in the preparation of varnishes. 673. Amber (electron of the ancient Greeks, and succinum of the Romans,) is always found as a fossil, but it appears to be the resin of some ancient tree that has become extinct. It is found on the shores of the Baltic sea, on the Yorkshire coast of England, and in some of the United States, as in New Jersey. It is found in masses seldom weighing more than a few ounces, and in small grains. Its color is usually some shade of yellow, often inclining to red. It has a specific gravity of 1-07 to 1-09, and is insoluble in water, and is acted on but slightly by alcohol, ether, or the oils. It is capable of being worked in the lathe, and is often seen fashioned into ornaments of various forms. It is used also in the preparation of varnishes. 674. Caoutchouc. This substance, sometimes called gum elastic, or India-rubber, is prepared from the milky juice which exudes QUESTIONS. What use is made of lac? From what is copal procured? What use is made of it ? 673. Where is amber found ? Give a description of it. 674. From what is gum elastic obtained ? VEGETABLE ACIDS. 465 from certain trees, as thejicus elastica, when incisions are made in them. The white milky juice which exudes is received on masses of clay, and dried by exposure to the heat and smoke of fires kindled for the purpose. As usually seen, caoutchouc is a solid of a dark color, and specific gravity a little less than water. At 32, and lower tem- peratures, it is very hard, and has little elasticity ; but at 60 or 70, it is exceedingly flexible and elastic. It is quite insoluble in water, and alcohol, but dissolves slightly in pure ether and some of the essential oils. Chloroform dissolves it readily, as does also a solution of sulphur in oil of turpentine. By distillation it yields several peculiar products. Vulcanized India-rubber is formed by heating caoutchouc with a portion of sxilphur, which becomes incorporated with it, increases ita elasticity, and renders it less liable to be affected by changes of tem- perature. It is used for many important purposes. 675. Gutta Percha is a substance, in many of its properties, closely resembling the preceding; it is prepared in the same way from the milky juice of a tree found only in tropical climates. Like India-rubber^ it is quite insoluble in water and alcohol, but is "dissolved in small quantities by pure ether and some of the essential oils, and more largely by chloroform and sulphide of carbon. Its specific gravity is about 0-97. Gutta percha is less elastic than caoutchouc, and at ordinary temperatures is quite hard, but becomes soft at 200 to 212, and may be formed into any desired shape. It is becoming of considerable importance in the arts. VEGETABLE ACIDS NOT INCLUDED IN THE PRE- CEDING GROUPS. 676. These acids are all found ready formed in plants, a cir- cumstance in which they differ from most of those heretofore described. Sometimes they occur in a free state, but generally they are found in combination with bases. QUESTIONS. Describe the properties of gum elastic. How is vul canized India-rubber prepared ? 675. From what is gutta percha ob- tained ? Describe it. 676. What is said of the acids of this group ? 466 VEGETABLE ACIDS. 677. Oxalic Acid, C 4 H 2 8 = C 4 6 ,2HO. Oxalic acid, in com- bination with bases, is found in many plants, especially in certain species of the sorrel (oxalis), and also in certain minerals. Ifc may likewise be prepared artificially, by digesting starch, or sugar, with nitric acid, and by other processes. To prepare it artificially, add, in successive portions, 24 parts of starch to 144 of nitric acid of commerce, diluted with 10 parts of water, and heat gently till the nitrous vapors cease. When the action is over, set the whole aside to crystalize. Pure oxalic acid is a crystaline solid, in external appearance not unlike Epsom salt, for which it has sometimes been mistaken. It is very soluble in water, exceedingly sour to the taste, and poisonous. Its composition in crystals is C 4 H 2 8 + 2HO. 678. Salts of Oxalic Acid. Oxalic acid is bibasic, and, as in the case of other bibasic acids, both equivalents of its basic water may be replaced at the same time by a fixed base, or only one of them, producing the two series of salts of the forms 2(RO)C 4 6 and RO,C 4 6 ,HO; RO being used to indicate any base. 679. Oxalate of lime, 2CaO,C 4 6 , is found in many plants, in the cells of which it may often be detected in small crystals by the microscope. The crystals when thus found, or if formed by other means, always con- tain" 2. equivalents of water of crystalization. * It is very insoluble. With potash it forms three salts, called the neutral oxalate, 2KO,C 4 8 , the binozalale, KO,C 4 6 ,HO, and the quadroxalate, the latter containing twice as much acid as the next preceding. The binoxalate is often used in solution to remove stains of iron-rust, under the name of salt of sorrel. Oxalic acid forms with the alcohols, both coupled acids (609) and com- pound ethers. 680. Tartaric Acid, C 8 H 6 12 r= C 8 H 4 10 ,2HO. Tartaric acid, in combination with potash, exists in many fruits, especially in grapes and in pine-apples. When the expressed juice of the grape is fermented, as in the manufacture of wine, this salt, in an impure state, is precipitated upon the inside of the cask, as argol, or tartar. From this the pure acid is obtained, which is a white solid, very soluble in water, and of an agreeable acid taste. QUESTIONS. 677. In what is oxalic acid found? How may it be pre- pared artificially? Describe its properties. 678. What is said of the baits of oxalic acid ? 679. In what is oxalate of lime found ? 680. In What is tartaric acid found ? * VEGETABLE ACIDS. 467 Tartaric acid is bibasic, and forms two series of salts, according as one only or both equivalents of its basic water may be replaced by the base. There are only two or three important salts of this acid, among which the acid tartrate of potash, or cream of tartar, takes the first place. Its composition is KO,C 8 II 4 Oi ,HO. It is prepared entirely from the impure tartrate, or argol, forming the settlings of wine-casks by repeated crys- talizations and filterings. By saturating a solution of cream of tartar with soda, or carbonate of soda, a double tartrate of potash and soda is formed, called Rochelle salt. 681. Tartar-emetic is a double tartrate of potash and oxide of antimony, which is formed by boiling equal parts of cream of tartar and the oxide in 6 parts of water. It is much used in medicine. By the action of heat upon tartaric acid its characters are changed, and it is converted into other acids, which are generally isomeric with itself, as the metatartaric, isotartaric, and paratartaric or racemic acids. With the alcohols tartaric acid also forms coupled acids and compound ethers. 682. Citric Acid, C I2 H 8 M = C I2 H 5 U + 3HO. Citric acid is obtained chiefly from the lemon (citron), but is found in other fruits, as the orange, currant, gooseberry, strawberry, &c. When pure it forms crystals, which are very soluble in water, and have an agreeable sour taste. It is used in calico-printing, and for medicinal and domestic purposes. To prepare citric acid, lemon-juice is first saturated with lime, and then the citrate of lime, so formed, mixed with several times its weight of warm water, is decomposed by sulphuric acid. The clear liquid is then drawn off and evaporated until the crystals of citric acid are deposited as the solution cools. Citric acid is tribasic, and forms three series of salts, according as one, two, or three equivalents of its basic water may be replaced by the fixed base. By heat this acid is decomposed, forming carbonic acid and other pro- ducts, among which is aconitic acid, C 4 H0 3 ,HO, so called because first obtained from the aconitum napellus: By distillation it also yields the itaconilic and citraconic acids. Citric acid witn alcohol forms two different coupled acids, and a com- pound ether. QLESTIONS. What is said of the salts of tartaric acid ? What is cream of tartar? Rochelle salt? 681. Describe tartar-emetic. What acids iso- meric with tartaric acid are mentioned ? 682. From what is citric acid obtained ? Describe its properties. VEGETABLE ACIDS. ^ 683. Malic Acid, C 8 H 6 10 = C 8 H 4 8 ,2 HO. Malic acid is.found in many vegetables, both free and in combination with bases, espe- cially in many fruits before coining to maturity, as the apple (malum), and the plum. It is abundant in the fruit of the mountain ash (sorbus aucuparia), and in the stalk of the rhubarb or pie-plant. Pure malic acid forms crystals which are very soluble in water, and which melt at about 181. With alcohol it forms a coupled acid and an ether, in the same manner as other bibasic acids. By the influence of heat, carefully managed, it may be .converted into two other acids, which are isomeric with each other, called the maleic, and the paramaleic or fumaric acids. The latter is also found in some plants, and in Iceland moss. 684. Tannic Acid, C I6 H 8 12 = C 16 H 5 9) 3HO. Tannic acid (called also tannin), occurs in the bark and leaves of many trees, as the oak, chesnut, and hemlock^ but is especially abundant in nut-galls, which are excrescences that form upon the leaves of several species of the oak. To prepare it, nut-galls, in coarse powder, are intro- duced into a funnel, of the form A, represented in the figure, the mouth having been loosely filled with a little cotton, and pouring over them some sulphuric ether that has been previously washed. The funnel is placed in a vessel of the form B, into which the liquid gradually per- colates, and separates spontaneously into two portions ; the lower being a solution of the acid in water (a little of which was contained in the ether), with the lighter and nearly pure ether above it. The acid solution can be easily separated; and by evaporation it yields the tannio acid as a solid mass. This acid is soluble in water, and has a peculiar astringent taste. It is a feeble acid, but forms salts with bases. With salts of the peroxide of iron, it forms a deep blue or black pre- cipitate, which is the basis of writing-ink.* It forms an insoluble * To prepare an excellent black writing-ink, pour 6 pints of boiling rain-water upon 6 ounces of the best nut-galls in powder, and add 4 ounces of gum-Arabic, and let the whole stand two days in a wooden or earthen vessel. Then strain the liquid and mix with it 4 ounces of clean copperas, and let it stand one or two months, stirring it fre- quently, and pour off the part free from sediment for use. Prep, of Tannic Acid. QUESTIONS. 683. Describe malic acid. 684. In what does tannic acid or tannin occur ? Describe the mode of preparing it. ALKALOIDS. 461 And very important compound with gelatine, which is the basit of leather. Raw hides, after the hair is removed, are soaked foi a time in a decoction of bark which contains this substance, and are thus coanged into leather. 685. Gallic Acid, C 14 H 6 10 = C 14 H 3 7 ,3HO. This acid is usually associated with the preceding, and is always formed when a solution of that acid is left for some time to the action of the atmosphere, or is boiled for a time with sulphuric acid. In the latter case, the reaction is attended by the formation of grape- sugar. This acid is readily obtained in crystals, which are quite insoluble in cold, but very soluble iu hot water. By the action of heat two other acids are formed from gallic acid, called the pyrogallic and metagallic acids. ORGANIC ALKALIES, OR ALKALOIDS. 686. We have seen above, that many organic compounds are acids; so also there are others which are properly alkalies, as they readily, like potash, soda, &c., combine with acids which they neutralize, forming true salts. All the organic alkalies contain nitrogen and hydrogen, and in some sulphur is found. Some of them exist ready formed in plants, but others are produced by their destructive distillation. Nearly all of them are poisonous. 687. Morphia, or Morphine, C34H ]8 N0 6 . This substance is an essential ingredient of opium, which is the dried juice of cer- tain species of the poppy, cultivated largely in different parts of Asia. To separate the morphia, the opium is digested several days in water, and the solution precipitated by ammonia, which is added cautiously in small portions. The impure morphia thus obtained is then further purified by dissolving it in boiling alco- hol, from which it crystalizes on cooling. The morphia in opium seems to be in combination with a pecu- liar acid called meconic acid (from mecone, a poppy). QUESTIONS. What is leather ? 685. Describe gallic acid. 686. What are the organic alkalies ? What is said of their composition ? 687. From what is morphia obtained ? Describe the method of separating it. 40 470 ALKALOIDS. Pure morphia is a crystaline solid, but slightly soluble in water, and of a bitter taste. It combines readily with acids, forming salts, the most important of which are the sulphate, acetate, and hydro* chlorate. These salts are the compounds of this substance, generally used in medical practice under the name of morphine, and not the pure alkaloid, which is but slightly soluble in water, and therefore inert. ^ Narcotine and codeine are other compounds, of a similar character, procured from opium. 688. Qninia, or Quinine, CagH^N^. Quinia is obtained only from the bark of certain species of a tree called cinchona, which grows chiefly in South America. In commerce it is called Peru- vian bark, and is extensively used in medicine. To prepare quinia, the bark, in powder, is digested in waterj and from the solution obtained, the alkali is precipitated either by lime or ammonia. The quinia may then be dissolved in alcohol, and crystalized. Quinia is a crystaline solid, slightly soluble in water, and intensely bitter. It combines readily with acids, as the sulphuric and hydrochloric ; and the salts formed are extensively used in medicine, especially in certain fevers. With the sulphuric acid it forms two salts, a neutral and an acid sulphate. 689. Cinchonia, or Cinchonine, C 28 H 24 N 2 2 . Cinchonia always accompanies quinia in Peruvian bark, and is obtained from it by a similar process. It differs in composition irom quinia, in con- taining 2 atoms less of oxygen ; but in most properties, the two substances are much alike. Alone, it is but slightly soluble in water, but the salts it forms with acids dissolve more readily, and are used in medicine. Quinia and cinchonia exist together in the bark, the former being most abundant in that which is of a pale color, while the latter (cinchonia) occurs chiefly in the red bark. QUESTIONS. What are some of the properties of morphine? What other alkaloids are procured from opium ? 688. From what is quinia prepared ? Describe the mode of separating it from the bark ? 689. In what does cinchonia differ from quinia ? What is said of the color of tho bark containing these alkaloids ? ALKALOIDS OP THE ETHERS. 471 690. Strychnia, or strychnine, C 42 H2 2 N 2 4 , is a vegetable alkali obtained from nux vomica, and other plants. It is the poisonous principle of the famous Upas, of the island of Java, of which so many fables are told. It forms an extensive series of salts with the acids, and is one of the most violent poisons known. Brucia, or Irucine, is a similar alkaline substance, obtained from the same source. 691. Isaiine, Cj 6 H 6 N0 4 , is derived from indigo by heating it with dilute nitric acid. It is a crystalifle solid, of an orange-red color, soluble in hot water and in alcohol. From this substance isatinic acitt is derived, and several other compounds. Theine, and Caffeine, obtained from tea and coffee, appear to be the same substance. It is found also in the fruit of some other plants, and is contained in larger quantity in tea than in coffee. It is not certain that these articles, so extensively used among civilized nations, owe their peculiar properties to this principle. Nicotine is an alkaloid obtained chiefly from the tobacco-leaf. Piperine is extracted from black pepper ; it. is a crystaline solid, and acts as a feeble base. Picrotoxine, from the coculus Indicus, cantharadine, from cantharides, asparagim, from the roots of asparagus and other plants, and phloridzine, from the fresh bark of the apple, pear, plum, and cherry trees, are com- pounds of a similar character. ALKALOIDS OP THE ETHERS, OR CONJUGATED AMMONIAS. .692, The alkaloids of the ethers, like the ethers themselves, and the alcohols, are not found in nature, but are produced only by artificial means. They closely resemble ammonia in most of their properties, and indeed may be considered as ammonia in which one or more atoms of hydrogen has been replaced by equivalent quantities of the compound radicals, ethyle, C 4 H 5 , methyle, C 2 H 3 , acetyle, C 4 H 3 , &c. A few of these only can be described ; and in doing so we shall find it advantageous occa- sionally to represent ethyle, C 4 H 5 , by Et; methyle, C 2 H 3 , by Me; amyle, Cj H u , by Ayl; acetyle, C 4 H 8 , by Ae, &c. QUESTIONS. 690. What is said of strychnia ? From what is it pro- cured ? What other alkaloid accompanies it ? 691. From what is isatino obtained ? What is said of theine and caifeine ? What other alkaloids are mentioned ? 692. Are the alkaloids of the ethers found in nature ? What do they resemble ? From what may they be considered as formed ? 472 ALKALOIDS OF THE ETHERS. 693, Ethylamine, C 4 H 7 N = NH 2 C 4 H 5 = NH 2 Et Ethylamine is formed by various processes, as by the action of strong aqua ammoniaB upon hydrobromic ether (bromide of ethyle), and then distilling from potash or lime. The ammonia and ether are put together into a glass tube, which is sealed hermetically, and im- mersed fifteen minutes in boiling water; the reactions are as follows, viz. : C 4 H 6 Br + NH 3 = CJI 7 N,HBr = NH 3 ,C 4 F 5 ,Br. If, as intimated above, we consider ethylamine a conjugated ammonia, that is, ammonia in which 1 atom of hydrogen is replaced by ethyle, then it is evident the compound, NH 3 C 4 H 6 = NH 3 Et, is ammonium in which 1 atom of hydrogen is replaced by ethyle. It is called ethylammonium. The compound, NH 3 , C 4 H 6 ,Br, may therefore be called bromide of ethylammonium; and this when distilled with lime or an alkali yields ethylamine, precisely as sal-ammoniac, NH 4 C1, distilled with lime, yields ammonia (224). Ethylamine is a colorless, limpid liquid, having a density of about 0-696, and boiling at about 68. It has a pungent odor like ammonia, and alkaline reaction, forming salts with acids. With hydrochloric acid it forms dense white fumes, in the same manner as ammonia. 694. By the proper modes, 2, 3, and even 4 atoms of hydrogen in ammonia and ammonium may be replaced, producing the compounds, biethylamine, NH(C 4 H 5 ) 8 = NHEt a , triethylamine, N(C 4 H 6 ) 3 =NEt 3 , and tetrethylamine, N(C 4 H 6 ) 4 = NEt 4 . The latter, called also telrethylammonium, like its prototype, ammonium, can only be obtained in combination, as an iodide, bromide, or chloride. 695. Methylamine, C a H 5 N=NH a C 2 H 3 =NH 2 Me. This com- pound is prepared in the same manner as ethylamine, simply substituting in the process a methylic ether. It is a colorless gas, having a strong ammoniacal odor, and alkaline reaction. By a cold a little below zero, it is condensed to a limpid, mobile liquid. In the gaseous state, it is more soluble in water than QUESTIONS. 693. What is the composition of ethylamine ? What in ethylammonium ? Describe the properties of ethylamine. 694. What is biethylamine ? Triethylamine ? Tetrethylamine? 695. How is methyla - mine formed ? In what does it differ from ethylamine ? ALKALOIDS OP THE ETHERS. 473 any other known gas, water at 70 taking up 1000 times its own volume of the gas. 696. Bimethylamine, NH(C 2 H 3 ) 2 = NHMe 2 , trimethylamine, N(C 2 H 3 ) 3 = NMe 3 , and tetramethylamine, N(C 2 H 3 ) 4 = NMe 4 , sustain the same relations in the methylic compounds, as those of corresponding name, above de- scribed, in the ethyle series. 697. Amylamine, C 10 H I9 N=NH 8 C,oH 11 = NH 8 Ayl. Amy- lamine is prepared by a process altogether similar to those above given for preparing the corresponding compounds in the ethyle and methyle series. It is a limpid liquid, which boils at a little above 200, and has a density of 0-750. It has the odor of am- monia, and is strongly basic, forming salts with the acids. Biamylamine, &c., corresponding to ethyle and methyle compounds, above described, are known. 698. Aniline, C 12 H 7 N = NH^C^Hg, is obtained from phenol, and also by the action of nitric acid upon indigo. It is an oily liquid, having a density of 1-028, and is distinctly alkaline, forming salts with the acids. It may be considered as ammonia in which 1 equivalent of the hydrogen is replaced by the group C 12 II 5 , called phenyle. The alkaloid might therefore be named plienylamine. 699. We may even have compounds answering to ammonia iu which the three atoms of hydrogen have been replaced successively by different groups, or compound radicals, as in ethylmethi/lphe- nylamine, N,C 2 H 3 ,C 4 H 3 ,C 12 H 5 = N,MeEt,Pyl. 700. In all these compounds, it plainly appears that the groups, or compound radicals, ethyle, C 4 H 5 , methyle, C 2 Ii 3 , &c., are equivalent to H, and replace it, in ammonia, NH 3 , and ammonium, NH 4 . Now, phos- phorus, P, is equivalent in combination to N; and without experiment we might expect P to replace N in ammonia, as it does in the compound called phosphuretted hydrogen, PH 3 . So a series of compounds has been discovered, answering to ammonia, with its hydrogen replaced by the groups, ethyle, methyle, &c., and the nitrogen by phosphorus. Thus we have the compounds, P(C 2 H 3 ) 3 = PMe 3 , P(C 4 H 6 ) 8 = PEt 8 , &c. QUESTIONS. 696. What is bimethylamine ? 697. Describe amylamine. 698. Describe aniline. Why may we name it phenylamine ? 699. What is the composition of ethylmethylphenylamine ? 700. May the nitrogen in these compounds be replaced by phosphorus ? 40* 474 ALKALOIDS OF THE ETHERS. 701. The nitrogen in these compounds may even he replaced hy a metal, as 'antimony, bismuth, or tin, as in the following examples. Stibethyle, Sb,C, 2 H 15 Sb(C 4 H 5 ) 3 =SbEt 3 . Stibethyle is pre- pared by the action of hydriodic or hydrobromic ether upon anti- monide of potassium ] and afterwards distilling carefully in an atmosphere of carbonic acid. It is a transparent, colorless liquid which boils at 317, and has a density of 1'33. A drop of it exposed in the open air, first emits dense, white fumes, and then takes fire spontaneously. Stibethyle combines readily with oxygen, sulphur, chlorine, and other elements, forming both binary com- pounds and proper salts. 702. Stilme-thyle, Sb(C 2 H 3 ) 3 = SbMe 3 , is a corresponding compound, containing antimony and methyle j as is also bis- raethyle, Bi(C 4 H 5 ) 3 = BiEt 3 , of bismuth and ethyle. These latter, and many others of similar character, though formed on the type of ammonia, have less the characters of ammonia, and react with chemical agents more like simple metals. They are therefore sometimes called conjugate metals. All the preceding compounds have the same molecular type as ammonia and ammonium ; and it is worthy of notice that those having the type of ammonium, like ammonium itself, have been obtained only in com- bination. 703. There are other compounds similar in their general characters to the above, but the molecular type of ammonia does not appear in them. Of this character are such compounds as the following, viz., bisethyle, Bi,C 4 TI 6 = Bi,Et; zincethyle, Zn,C 4 H 5 =Zn,Et ; stannethyle, Sn;C 4 H 5 = Sn,Et; hydrarg ethyle, Hg 2 C 4 H 5 , &c. Each of these (and many others) combine with oxygen, sulphur, chlorine, &c., forming binary compounds ; and these again uniting with other compounds form salts. 704. Cacodyle, As,C 4 H 6 = As,Me 2 . This substance (named from the Greek, kakos, evil, and ute, principle,) serves as the basis of a long series of compounds, in which it performs the part of a quasi-metal. By distilling a mixture of equal parts of acetate of potash and arsenious acid, we obtain a liquid substance long QUESTIONS. 701. May the nitrogen be replaced by certain metals? What is the composition of Stibethyle ? Describe its properties. 702. De- scribe stibmethyle. 704. From what does cacodyle receive ita name ? ORGANIC COLORING-MATTERS. 475 known as Cadet's fuming liquid. Its composition is As,Me 2 O, which corresponds to oxide of cacodyle, but it is more frequently called akarsine. When pure it is a colorless liquid, which is highly corrosive and poisonous. According to Regnault, gaseous alcarsine has a density of 7-8 ; by cal- culation we make it 7-824. Its equivalent, as given above, represents 2 volumes, and its density is calculated as follows: 4 vols. carbon vapor weigh (-836 X 4) 3-344 12 " hydrogen " . (-069 X 12) -828 1 " arsenic vapor " 10-370 1 " oxygen " 1-106 Thus giving for 2 vols. alcarsine vapor,. 15-648 The weight of 1 vol., or its density, therefore is 7-824 705, Alcarsine, by digestion in hydrochloric acid, is converted into chloride of cacodyle, AsMe 2 ,Cl, which is decomposed by a metal, a iron or zinc, and yields cacodyle, As,C 4 H 6 , which is a colorless, transparent liquid, having a density a little above that of water, and boiling at about 338. In the open air it takes fire spontaneously ; and even when covered by a film of water it gradually absorbs oxygen from the air, being converted first into akarsine, As,Me 2 0, and then into akargen, or cacodylic acidj As,Me 2 ,0 3 . Cacodyle forms important binary compounds with oxygen, chlorine, sulphur, &c. ; and from these many interesting salts are derived, not here described. ORGANIC COLORING-MATTERS. 706. Color is a property which pertains to every substance ; but it is . proposed to treat here of certain compounds noted for their color, and the practical us.es made of them in the art of coloring. Infinite variety exists in the colors of organic substances ; but QUESTIONS. How is Cadet's fuming liquid obtained ? What is it com- posed of? What is it sometimes called ? What is the density of alcarsine rapor ? 705. What is formed when alcarsine is digested in hydrochloric acid ? How is cacodyle obtained from its chloride ? Describe cacodyle. What is said of the compounds of cacodyle ? 706. What are to be treated of under the head of organic coloring-matters ? What is said of the great variety of colors presented in nature ? 476 ORGANIC COLORING-MATTERS. the prevailing tints are red, yellow, blue, and green, or mixtures of these colors. 707. The art of dyeing consists in attaching the different color- ing-matters to the fabrics to be colored. This is accomplished in various modes, as by adding some substance that forms an inso- luble compound with the coloring-matter, or one that has the property of causing the coloring-matter to attach itself perma- nently to the fibre of the cloth. A substance used for this last purpose is called a mordant. As a general rule, substances of an animal origin, as wool and silk, are more easily colored than those composed of vegetable matter, as cotton or flax. Many coloring-matters combine readily with certain of the metallic oxides, as those of aluminum, tin, &c., forming insoluble compounds, called lakes, which are much used for painting in oils. Nearly all colors are injuriously affected by the action of light; or, in popular language, are said to fade. This, it is believed, is generally occasioned by the absorption of oxygen, which causes a decomposition of the coloring substance. 708. IndigOj C 16 H 5 N0 2 . This is a beautiful blue coloring- substance, extracted by a kind of fermenting process, from the leaves of several different American and Asiatic plants, as the isatis tinctoria, pblygonum tinctorium, gymnema tingensj &c. The leaves of the plant are digested for eight or ten days in water, during which a yellow coloring-matter appears, and is held in solution by the water. This is then drawn off, and, by stand- ing, absorbs oxygen from the air, and gradually becomes blue, and is deposited as a thick sediment. This is collected, and pressed in the form of square blocks, and constitutes the indigo o/ commerce. Indigo of commerce is far from being pure ; it is a mixture of indigo with other matters. Pure indigo sometimes called indigotine may be obtained from it by sublimation with a gentle heat, and by other means. Pure indigo is an insipid, inodorous substance, insoluble in water, but soluble in small quantity in alcohol. In strong sul- QTJESTIONS. 707. In what does the art of dyeing consist? "What is a mordant? What are lakes? What occasions the fading of colors? 708. From what is indigo obtained ? Describe the process of preparing it What is said of the action of sulphuric acid upon indigo ? ORGANIC COLORING-MATTERS. 477 pliuric acid it dissolves readily, with the formation of several new coupled acids, as the sulphidigotic, sulphindylic, &c. Alkalies act readily upon it, producing many important compounds, some of which have been described. Deoxydizing bodies, as protosulphate of iron, protochloride of tin, &c., have the effect to destroy entirely the color of the above indigo called often indigo blue and produce another compound, called indigo white. This unites readily with bases, and forms several soluble compounds which serve admirably for coloring. The solutions, though yellowish at first, gradually become blue by exposure to the air ; and articles impregnated with the solution undergo the same change. Solution of indigo in sulphuric acid is much used for coloring the Saxon Hue. 709. Litmus, archil, or turnsol, is a coloring substance resem- bling indigo, obtained from several species of lichen, as the leconora parella, and the rocella tinctoria. It is seen in small cubical masses, which are partially soluble in water, and the solution communicates a beautiful blue to substances immersed in it. This substance is much used in chemical investigations for detecting the presence of acids and bases ; the former of which change its blue color to red, and the latter again restore the blue. It is a compound of several principles, as lecanorine, orcine, rocelinine, &c. 710. Madder is a red coloring-substance, obtained from the roots of a plant called rubia tinctoria. It contains several prin- ciples, the most important of which is a red crystaline compound which has received the name alizarine, CaoHgOg. "Some of the other principles obtained from it are madder purple, or pur- purine, C 28 li] madder red, C 28 H 9 9 , and xanthine. By means of different mordants, madder is made to produce various shades of red, purple, brown, and orange. The beautiful crimson, called Turkey-red, is produced by it by means of a corn- plicated process which has not been fully explained. QUESTIONS. What is the effect of deoxydizing bodies upon indigo? 709. From what is litmus procured ? What use is made of it ? 710. From what is madder procured ? 478 AMIDES. 711. Cochineal. This is a dried insect, which was named coctus cacti by Linnaeus. It is a native of Mexico, and feeds upon a species of the cactus. As seen in commerce, it is of a dark brown, inclining to red, but when macerated in water, it yields a very beautiful red color- ing-matter, which is much used in dyeing. The beautiful red pigment called carmine is prepared from cochineal by boiling in clean water, and adding a little alum ; as the solution cools, the carmine is precipitated, and is collected and dried. 712. Brezeline is a crystaline solid, of an orange .color, obtained from Brazil-wood, which is soluble in water and alcohol. With mordants, it gives a beautiful red. The same substance is contained in the African wood called cam-wood. Hematoxyline, C 16 H 7 8 . This coloring-matter is procured from the wood of the tree called hcemotoxylon Campeachianum, and frequently, in commerce, log-wood. It is separated from the wood by digestion in water, and may be obtained in crystals. This substance, with salts of iron, gives a permanent black, and with other mordants, different shades of purple or red. 713. Quercitrine, C 16 H 8 9 ,HO, is a yellow coloring-matter, contained in the bark of the quercus tinctoria, and probably in other vegetable sub- stances used in coloring yellow. A fine yellow is also produced by the turmeric root, and by the root of the common barberry (berberis vulgaris). Chlorophyle. This name has been applied to the green coloring-matter of the leaves of plants. It is contained only in those parts of plants which are exposed to the light, and this agent may therefore be supposed to have an important influence in its formation. It is a substance of a waxy nature, and is soluble in alcohol, but not in water. The above are the most important coloring-substances obtained from vegetable bodies ; by their combination with each other, and by the use of different mordants, in different modes, all the endless variety of tints are produced. THE AMIDES AND NITRILES. 714. Amides. An amide is a nitrogenized compound answering to a salt of ammonia less one (or more) atoms of water (or its ele- ments). Thus, oxamide (731), C 2 2 ,NH 2 =C 2 3 ,HO,NH 3 2HO; that is, it answers to oxalate of ammonia less 2 atoms of water. So benzamide, C 14 H 7 N0 2 = C 14 II 5 2 ,NH 2 = C I4 H 5 3; HO,NH 3 QUESTIONS. 711. What is cochineal? 712. From what is brezelino obtained? What is hematoxyline ? 713. What is quercitrine? Do- Bcribe chlorophyle. 714. Describe an amide. AMIDES. 479 2HO; that is, it answers to benzoate of ammonia less an atom of water, or, less 2 atoms of water, if we have regard to the basic water of the salt. It is also characteristic of the amides, that they are capable of resuming the water lost so as to regenerate the ammoniacal salt ; or if a fixed alkali is used, a salt of this alkali is formed, and ammonia set free. Thus, when benzamide is treated with a boiling solution of potassa, benzoate of potassa is formed, and ammonia, being gaseous, escapes. 715. The amides are formed by several different modes, as by the simple distillation of a salt of ammonia, by the action of aqua ammonias upon the compound ethers, by the action of ammonia upon certain chlorides, &c. Oxamide, for instance, is formed by the distillation of oxalate of ammonia, but it may also be pre- pared by the action of aqua ammonias upon oxalic ether (616), alcohol being also at the same time reproduced from the ether. Thus, C 4 H 6 2 ,C 2 3 + NH 3 C 4 H 6 2 + C 2 2 ,NH 2 . Benzamide is usually prepared by the process last mentioned from the chloride of benzyle. Thus, C I4 H 5 C10 2 + 2NH 8 := C 14 H 6 2 , + NH 4 C1. It is solid, and capable of being crystalized j at a temperature of about 240 it melts, and at a still higher temperature may be sublimed. Oxamide also, mentioned above, is solid, and without odor or taste. At a high temperature it may be sublimed, but some of it will be decomposed. 716. Malamide, C 8 H 8 N 2 6 = C 8 H 4 6 ,2NH,j, is the amide of malic acid (683), and is identical in composition with asparagine, a substance found in the young shoots of asparagus, in liquorice root, and the root of marsh- mallow, and in several other plants. It may be obtained in crystals, which require about 60 times their weight of water for solution. By the action of acida, it is converted into ammonia and aspartic acid, C 8 H 7 N0 8 =a QUESTIONS. How may the ammoniacal salt be regenerated ? 715. What are some of the modes by which the amides are formed ? Describe the mode of preparing benzamide. 716. What is malamide, or asparagine? 480 NITRILES. CYANOGEN. C 8 H 8 N0 6 ,2HO. This acid is also to be considered as an amide, formed from the acid malate of ammonia by the loss of an atom of water. Thus, C 6 H 4 8 ,HO,NH 3 HO = C 8 H 6 8 ,NH 2 = C 8 H 6 N0 6 ,2HO. The above examples are given as illustrative of the mode in which bodies of this class are formed, and of their relation to the ammoniacal salts ; many are known that cannot be here mentioned. IMjpst of them are neutral in their reactions, but they may be acids as aspartic acid or bases. Those that are acid, are usually formed from acid salts of ammonia. 717, Nitriles, Many of the amides are capable of parting with still another atom of water, being then converted into compounds called nitriles. There are not many known, and they are not important. Acetonitrile, C 4 H 3 N, is formed from acetamide, C 4 H 3 2> NH 2 , by distilling the latter with anhydrous phosphoric acid, which causes it to Y ar ^ with 2 atoms of water. Thus, C 4 H 3 2 ,NH 2 2HO = C 4 H a N. Butyronitrile, C 8 H 7 N, is an oily liquid, which boils at about 245. It is prepared by distilling butyrate of ammonia, or butyramide, with anhydrous phosphoric acid, which separates an atom of water. Valero nitrile, C 10 H 9 N, is obtained in a .similar manner from valerarnide. CYANOGEN, AND ITS COMPOUNDS. Symbol, C 2 N, or Cy 5 Equivalent (12 + 14 =)26; Density, 1-82 718, History. Cyanogen has already been mentioned (315). It was discovered by Gay Lussac, in 1814, and in 1817 was recognized by Berzelius as a compound radical (536). In many of its properties it resembles chlorine, bromine, and iodine, com- bining like these with other simple substances, and forming compounds called cyanides. Like the elements above mentioned, also, it combines with oxygen, forming oxacids, and with hydrogen forming a hydracid ; QUESTIONS. Describe the mode of preparing aspartic acid. Are there acid and basic as well as neutral amides? 717. How are the nitriles formed? 718. When was cyanogen discovered ? CYANOGEN. 481 and in many other respects, it reacts precisely as a simple substance. 719. Preparation. Cyanogen may be prepared by several modes. Its elements do not combine directly, but a cyanide is first formed, and this being decomposed yields the pure cyanogen. The best method to procure a small quantity, is to heat gently in a small retort cyanide of mercury, and collect the cyanogen over mercury. At the same time a brown mass will be formed, and remain in the retort, which has received the name of para- cyanogen. It is isomeric with cyanogen. 720. Properties. Cyanogen is a colorless gas, of a density 1-82, and has a peculiar, but not disagreeable odor, resembling that of wild-cherry water. By a temperature of 4, or by a pressure of 4 atmospheres, at the ordinary summer temperature, it is converted into a liquid. The following method serves well to prepare a small quantity in the liquid form. Introduce into a strong glass tube, bent as in the figure, a little cyanide of mercury, and seal it hermetically. It is then to be held horizontally, and the heat of a lamp applied at the ex- tremity, a, containing the cyanide Preparation of Cyanogen, of silver. The other extremity, b, is to be kept cool ; and in a short time the liquid cyanogen will be seen to collect in it. In the liquid form, cyanogen is colorless and limpid, and has a density of about 0-9. By long keeping, it undergoes a change, forming para- cyanogen. Compounds of Cyanogen and Oxygen. 721. Cyanogen and oxygen -form no less than three isomerio compounds, all of which are acids. 722. Cyanic Acid, Cy 0,110. Cyanic acid is always formed when an alkaline cyanide, as cyanide of potassium, is exposed to QUESTIONS. What simple substances does cyanogen resemble in many of its properties? 719. How is cyanogen prepared? Describe para- cyanogen. 720. What are the properties of cyanogen? May it b obtained as a liquid ? May it be preserved in the liquid form T 721. How many compounds of cyanogen and oxygen are known! 722. Describe cyanic acid. 41 482 COMPOUNDS or CYANOGEN AND OXYGEN. the air at a red heat ; oxygen is absorbed, and the acid, as it is formed, combines with the alkali. But it is best prepared by heating gently cyanuric acid, a compound to be hereafter described. It is a clear transparent liquid, with a penetrating odor not unlike that of acetic acid, and is very corrosive to the flesh. Cyanates. Cyanate of potash is prepared by heating the yellow prus- siate of potash (soon to be described) with peroxide of manganese, and digesting the mass in alcohol. It is a white crystaline solid. Cyanate of ammonia, which is isomeric with urea, is formed by bringing together hydrocyanic acid gas and ammonia, and by the action .of cyanate of pot- ash upon sulphate of ammonia. It is also contained in the urine of animals, and is therefore called urea. 723, Cyanic Ether, C 4 H 5 0,CyO. Cyanic ether is formed by distilling a mixture of cyanate of potassa, and the sulphovinate (607) of the same base. It is a liquid less dense than water, and has a pungent, irritating odor. Dissolved in ammonia, it forms a crystaline compound, CgH 8 N 2 O a , which has been called ammoniacal cyanic ether. When this substance ia treated with water, carbonic acid is given off, and a new substance formed, called cyamethene, having the composition, C 10 Er, 2 N 2 2 . Treated with solution of caustic potash, cyanic ether forms 2 equiva- lents of carbonate of potash, and is transformed into a new compound, called ethylamine, C 4 H 7 N = NH 2 ,C 4 H S , which in its properties closely resembles the vegetable alkaloids (698). 724. Fulminic Acid, 2CyO,2HO. Fulminic acid has not as yet been obtained in a separate state, nor even in combination ^ith water. It is formed by pouring alcohol into a strongly acid solution of nitrate of mercury or silver, and applying a little heat, if necessary, so as to produce brisk ebullition. The acid, as it forms, combines with the oxide of the metal used, and the metallic salt, formed is at once precipitated. By digesting a solution of the metallic fulminate with another base, as potassa, the fulminate is decomposed, and the acid transferred to the new base. This acid receives its name from the tendency of its salts to explode violently by heat or friction, or other causes. Fulminic acid is bibasic, and, like other acids of this character, forms two series of salts, the neutral, which contains 2 equivalents of fixed base to each equivalent of the acid, and the acid salts which, for each equivalent of acid, contain 1 equivalent of fixed base and 1 equivalent of water. QUESTIONS. What is urea? 723. How is cyanic ether formed? 724. Has fulminic acid been obtained in a separate state ? COMPOUND OP CYANOGEN AND OXYGEN. 483 725. The Fulminates. There are several fulminates known, but those of mercury and silver are the most important. The former, fulminate of mercury, is prepared by dissolving 200 grains of mercury in an ounce of strong nitric acid by the aid of heat, and, when cold, pouring into it 4 or 6 ounces of alcohol. The mixture should be contained in a large glass or earthen vessel, and a little heat applied, if the action does not commence in a few minutes after adding the alcohol. When the action has once commenced, it goes on violently, without the further aid of heat, attended by the evolution of white, fumes, consisting of aldehyde, acetic, formic, and nitrous acids, and their corresponding vinic ethers, and the deposition of the solid fulminate in small crystals. The powder thus formed should be immediately well washed and di'ied, and may then be preserved for any length of time, if kept in the dark, but is acted upon slightly by light. Fulminate of mercury is a brown crystaline powder, without odor, but having a styptic, metallic taste. By slight- friction with any hard sub- stance, or by a blow, or by the contact of the minutest quantity of nitric or sulphuric acid, it explodes with great violence ; even when moist, it will often explode with a slight blow, and should therefore never bo touched with anything harder than wood or paper. 726. Fulminate of mercury is much used for fillhig percussion caps, for exploding fire-arms ; and for this purpose it is mixed with a little less than half its weight of nitre, and some solution of resin in alcohol, to cause it to adhere to the capsule, and to prevent the action of the air. 727. Fulminate of Silver is prepared very nearly in the same manner as the above. A dime is to be dissolved in about 2 ounces of common nitric acid, and the solution diluted with 2 ounces of distilled, water, and then 2 ounces of alcohol abided, and the whole mixed well by shaking. By application of heat, rapid ebullition will soon commence, when the heat should be removed; and the fulminate will be gradually deposited, and should be immediately washed and dried. It is a beautiful white solid, and should be handled with the utmost care, as it explodes most violently, even when 'damp, by the slightest friction, or by the mere contact of sulphuric acid. QUESTIONS. 725. Describe the mode of preparing fulminate of mer cury. Describe its properties. 726. What use is made of it ? 727. How \f fulminate of silver prepared ? What is its character? 484 COMPOUNDS OF CYANOGEN AND HYDROGEN. It is very improperly made the basis of a small toy called a torpedo, which consists of a little of the salt mixed with some gravel, and done up in paper. It explodes merely by being thrown upon a hard substance. Fulminates of copper and zinc may be prepared by digesting the ful- minates of mercury or silver with these metals. 728. Cyanuric Acid, SCyO.SHO. Cyanuric acid is a white crystaline -olid, with little taste or odor, and may be sublimed ; but a part of it is jy the operation converted into cyanic acid. It is best formed by heating irea, and digesting the mass in strong sulphuric acid, adding a few drops Df nitric acid until the solution becomes clear. To the whole then add an equal volume of water, and as it cools the acid will be deposited in smal crystals. It is a tribasic acid, as the above fonnula indicates, and, like othei tribasic acids, forms with bases three series of salts. Cyanidide is an isomeric modification of this acid. 729. Cyanuric Ether, 3C 4 H 5 0,3CyO, is prepared by distilling carefully a mixture of the cyanurate and sulphovinate of potassa. It is solid at ordinary temperatures, but melts at about 185. and boils at 529. Boiled for some time with an alcoholic solution of potash it is decom- posed, yielding alcohol, ammonia, and carbonic acid, according to the following equation : 3C 4 H 6 0,3CyO -f 12HO = 3C 4 H 6 2 + 3NH 3 Compound of Cyanogen and Hydrogen. 730. Cyanogen and hydrogen form one compound only ; which, however, is exceedingly important. Hydrocyanic Acid (Prussic Acid), C 2 N,H, or HCy. Hydro- cyanic acid is prepared by various processes, one of which is to A ^^^^^^^^^^^^5^==^ decompose cyanide of mercury by concen- trated hydrochloric acid, by the aid of heat. The mixed gases are passed through a \. tube containing first pieces of carbonate of Preparation of Hydrocyanic Acid. f. lime, to separate any free hydrochloric acid, and then fused chloride of calcium to absorb all the moisture; and the hydrocyanic acid, mixed now QUESTIONS. 728. Describe cyanuric acid. 729. Describe cyanurio 730. How is hydrocyanic acid prepared ? SULPHOCYANATES. 485 with only carbonic acid, is condensed in a bent tube, surrounded by a freezing mixture, the carbonic acid escaping into the air. Pure hydrocyanic acid is a limpid, colorless liquid, of a strong odor, similar to that of peach-blossoms. Its specific gravity is about 0-70. Its point of ebullition is 80, and at 5 it congeals. When a drop of it is placed on a piece of glass, a part of it becomes solid, because th.e cold produced by the evaporation of a portion is so great as to.freeze the remainder. It unites with water and alcohol in every proportion. Hydrocyanic acid is a powerful poison, producing, in poisonous doses, insensibility and convulsions, which are speedily followed by dea-th. A single drop of it placed on the tongue of a dog causes death in the course of a very few seconds'; and small animals, when confined in its vapor, are rapidly destroyed. The pure acid decomposes spontaneously when long kept, especially if exposed to the light; but. if largely diluted with water it may be pre- served, and is in this state used in medicine. It is contained in water distilled from the blossoms and leaves of the peach and other allied fruit trees. Sulpliocyanates or SulpJiocyan ides. 731. The sulphocyanates or sulpliocyanides constitute a class of compounds corresponding to the cyanates with the oxygen replaced by sulphur. Thus the composition of cyanate of potassa is KO,CyO, while that of the sulphocyanate is KCyS 2 = KS,CyS. 732. Sulphocyanate of Potassium, K,CyS 2 = KS,CyS. This is properly a sulphur salt. It is obtained by making a mixture of 46 parts of ferro- cyanide of potassium, 17 parts of pearlash, and 16 of sulphur, and melting them together ; and when the whole has cooled, dissolving out the sulpho- cyanate by boiling alcohol. It is solid, and crystalizes in long prisms, which are without color, and deliquesce in the open air. It is used as a delicate test of iron. 733. Sulphocyanic Acid, HCyS 2 =HS,CyS. This acid, called also hydrosulpho cyanic acid, is prepared by distilling sulphocyanate of potassa with phosphoric acid. It is a colorless liquid, .of a so.ur taste, and forms urith peroxide of iron salts of a deep red color. QUESTIONS. What are the properties of hydrocyanic acid ? Is it used in medical practice? 731. What is said of the sulphocyanates ? 732. How is sulphocyariiite of potassium formed? 733. Sulphocyanic acid? 41* 486 COMPOUNDS OF CYANOGEN AND THE METALS. 734. The following compounds are derived mostly from the sulpho- cyanates : Mellon, C 6 N 4 , is a yellow insoluble compound, obtained by distilling * Bulphocyanate of potassium in an atmosphere of chlorine. It is capable of combining with metals, forming compounds which are called mel- lonides. Melam, C 12 H U N 9 , is a grayish-white powder, procured by de- composing, by heat, the sulphocyanate of ammonia. Melamine, C 6 H 6 N 6 , results from the action of solution of potash, at a bciling heat, upor melam. It is a transparent solid, scarcely soluble in water, if cold, bu very soluble in boiling water. When dry it may be s.ublimed. At th same time with the compound just described is formed ammeline, C 6 H 5 N 5 Oj . a basic substance, capable of combining with the nitric and other acid&, to form salts. It crystalizes in fine silky needles. Ammelide, C, 2 H g N 9 6 , is formed by boiling ammeline in some acid ; it is a white compound, insoluble in water and alcohol, and possesses little interest. Compounds of Cyanocfen and the Metals. 735. Cyanogen combines readily with nearly all the metals; but a few only of the more important of the compounds thus formed can be here noticed. 736. Cyanide of Potassium, K,C 2 N, or KCy. This compound is best prepared by heating in a covered crucible 8 parts of yel- low prussiate of potash, and adding three parts of pearlash, both being first well dried. On the large scale for the manufacture of prussiate of potash above mentioned, it is prepared by heating together in an air-furnace animal charcoal and pearlash. This cyanide thus formed, acting afterwards upon iron, or oxide of iron present, produces the yellow prussiate soon to be described. Cyanide of potassium is largely used at the present time in the pro- cesses of gilding and plating by means of galvanism. 737. Cyanide of Mercury, HgCy, is prepared by pouring a hot solution of nitrate of silver into a hot concentrated solution of cyanide of potas- sium, and purifying, by recrystalization, the solid cyanide of mercury which is deposited when the mixed solution cools. It has already been mentioned as affording a ready means for procuring cyanogen. 738. Cyanide of. Silver, AgCy, is precipitated as a solid compound by mixing hydrocyanic acid with solution of any salt of silver. It is inso- QUESTIONS. 734. What other compounds are mentioned as derived from the sulphocyanates ? 735. What is said of cyanogen in rela-tion to the metals ? 736. How is cyanide of potassium formed ? What use is made of it? 737. What is said of cyanide of mercury? 738. Cyanide of silver ? DOUBLE CYANIDES. POLYCYANIDES. 487 hible in water, but is soluble in aqua ammonia, and in solution of nitrate of silver. By modes altogether similar to the above, the cyanides of gold, zinc, cobalt, nickel, lead, copper, palladium, &c., may be procured, but the compounds are not here described. Double Cyanides. Poly cyanides. 739. Nearly all the metallic cyanides are remarkable for thei, tendency to combine with each other, so as to form double cyan- ides. This is especially true of the cyanides of iron, but many others of the class show the same tendency. 740. Hydroferrocyanic Acid, FeCy,2HCy = H 2 Cy 3 Fe. This acid is best prepared by mixing a saturated solution of yellow prussiate of potash with strong hydrochloric acid, free from con- tact with the air, and then adding a small quantity of sulphuric ether. The acid is at once precipitated in small white crystals, which are to be collected and dried in a vacuum, after being washed with ether. This acid may be preserved any length of time free from contact with the air and moisture ; but in the air it is gradually decomposed, leaving a residue of Prussian blue. It acts readily upon the metals and metallic oxides, producing* ferrocyanides. 741. Ferrocyanide of Potassium. Yellow Prussiate of Potassa 2KCy,FeCy,3HO = K 2 Cy 3 Fe,3HO. This compound is prepared, on the large scale, by heating potash with animal matter, as horns, hoofs, leather, woollen rags, hair, and other animal offal, by which cyanide of potassium is formed ; which, being digested. with warm water, containing fragments of iron or smithy scales, acts upon the iron to produce the compound in question. After filtering, the yellow Prussiate, in solution, is set aside to crystalize. Instead of animal substances, as here de- scribed, common charcoal alone may be used with the carbonate of potash, and bringing in contact with it when intensely heated atmospheric nitrogen, prepared fey passing a current of air through burning coke. QUESTIONS. 739. What is said of nearly all the metallic cyanides? 740. How is hydroferi'ocyanic acid prepared? 741. Describe ferro- cyanide of potassium. 488 DOUBLE CYANIDES. P L Y C Y A N I D E 8. Ferrocyanide of potassium is a crystaline solid, of a lemon- yellow color, very soluble in water, but insoluble in alcohol and ether. It is much used in the arts as a coloring substance, and* as an important reagent in the laboratory of the chemist. Many other ferrocyanid.es, as those of sodium, barium, calcium, &&, must be passed by unnoticed, 742, Hydroferridcyanic Acid, 3HCy,Fe 8 Cy 3 = H 8 Cy 6 ,Fe 8 .-- This compound is prepared by passing a current of hydro-sul- phuric acid gas through a newly prepared solution of ferrid- cyanide of lead. It is obtained in crystals, which are soluble in water, and have an acid, astringent taste. It may be considered as a compound of 3 equivalents of hydrocyanic acid with sesquicyanide of iron, as indicated by the first of the above formulae, or as a compound of 3 equivalents of hydrogen with the assumed radical Cy 6 Fe 2 , as indicated by the second formula. 743, Ferridcyanide of Potassium. Red Prussiate of Potash, 3KCy,Fe 2 Cy3=K 3 Cy 6 Fe2- Red prussiate of potash is prepared by passing a current, of chlorine through a solution of the yellow prussiate, until it ceases to give a blue precipitate with solution of the persalts of iron, and evaporating the solution until crys- talization takes place. The action of the chlorine is to separate from 2 equivalents of the ferrocyanide one equivalent of potassium, thus forming chloride of potassium and the compound in question. Thus 2(2KCy,FeCy) + 01 = 3KCy,Fe 2 Cy 3 + KC1, the water always contained in the crystal of the ferrocyanide being omitted. The crystals beloog to the trimetric system, are of a red color, and readily burn when held in the flame of a candle. They are partially soluble in cold and very soluble in boiling water, but insoluble in alcohol. Sometimes, during the process, the solution becomes green, by the formation of the magnetic cyanide of iron (FeCy,Fe 2 Cy 3 ), which, however, disappears by boiling with a little caustic potassa. Ferridcyanide of potassium forms characteristic colors with solutions of several of the metals, producing with them precipitates in which the QUESTIONS. What use is made of ferrocyanide of potassium ? 742. How xnay hydroferridcyanic acid be procured ? Of what is it composed ? 743. De- scribe the red Prussiate of potash. What is said of the colors produced by this compound with metallic solutions ? DOUBLE CYANIDES. jfOLYCYANIDES. 89 potassium of the ferridcyanide is replaced by an equal number of equiva? lents of the new metal. Thus, with solution of the protosalts of iron it gives a blue, with those of uranium a reddish-brown, with those of nickgl and bismuth a brownish-yellow, and with those of silver and zinc an orange yellow. Similar compounds of sodium, barium, calcium, and magnesium are known. 744. Ferridcyanides of Iron, Prussian Blues. There are several different compounds known by these names. The one most common is prepared by precipitating an acid solution of sulphate of iron with solution of the yellow prussiate of potash. The compound thus formed is of a deep blue color, uncrystalizafole, and insoluble in water and alcohol. When properly dried, it has a peculiar metallic, coppery lustre, and is much used by painters ; but- the color is liable to fade, and is at once destroyed by the action of the caustic alkalies which decompose it. The production of the proper blue precipitate in this case requires the presence of the air, from which oxygen is largely absorbed. When a salt of the peroxide is made use of, this is not required. The Prussian blue of commerce is very soluble in solution of oxalic acid, and a good blue writing-ink is prepared from it. Prussian blue receives its name from the fact that it was first made at Berlin, Prussia, about the year 1710. It is sometimes called Berlin blue. The compound just described as the ordinary Prussian blue of com- merce, is probably a mixture of several different cyanides of iron. Turnbull's or Paris blue, 3FeCy,Fe 2 Cy 3 , is a definite com- pound; it is best prepared by mixing a solution of the red Prussiate of potash with ^solution of a protosalt of iron, the 3 equivalents of potassium in the Prussiate being replaced by 3 equivalents of iron. Its color is less intense but more clear than that of the ordinary Prussian blue. Its formula may be written Fe 3 Cy 6 Fe 2 . By precipitating solution of pernitrate or perchloride of iron with a solution of yellow Prussiate of potash, a definite compound is also formed sometimes called neutral Prussian blue, or sesqui- ferricyanide of iron, or hi f err id cyanide of iron. Its composition is 3FeCy,2Fe 2 Cy 3 . This probably constitutes the chief part of the common Prussian blue of commerce. QUESTIONS. 744. What is said of the Prussian blues ? How may a blue writing ink be formed from Prussian blue ? May other Prussian blues be formed ? 490 PROTEINE COMPOUNDS. . Another compound, called basic Prussian Hue, is formed by pre- cipitating a protosalt of iron with solution of ferrocyanide of potassium, and exposing the white compound thus obtained for some time to the action of the air for the absorption of oxygen. * Several other similar cyanic compounds of iron are known, called soluble. Prussian blues, but they cannot here be particularly described. 745. Cobaltocyanides. Several other metals, as cobalt, nickel, and mercury, enter into combination with cyanogen, forming com- pounds in which these metals perform essentially the same office as the iron in those of the above list. 746. Hydrocobaltocyanic Acid, 3HCy,Co 2 Cy 3 = H 3 Cy 6 Co 2 , is obtained by decomposing cobaltocyanide of lead by hydrosulphuric acid, sepa- rating the sulphide of lead by filtration, and then evaporating so as to crystalize. The crystals thus procured are colorless and fibrous, and very insoluble in water. The solution has a very sour taste, and acts readily upon the alkaline carbonates with effervescence. It will be seen that this compound corresponds to the hydroferridcyanic acid of the iron series of cyanic compounds. Like that acid, too, it is tribasic. 747. Cobalticyanide of Potassium, 3KCy,Co 2 Cy 3 = K 3 Cy 6 Co 2 , is formed by dissolving cobalt, or its carbonate, or cyanide, in solution of cyanide of potassium containing excess of hydrocyanic acid, and evaporating so as to crystalize. It will be noticed that the compound is altogether analogous in composition to the ferridcyanide of potassium, with which it is also isomorphous. The crystals are of a yellowish color, and are very soluble in water, forming a colorless solution. Very many other metallic polycyanides are known, as the platino- cyanides, aurocyanides, argenlocyanides, merduriocyanides, &c., but -it would extend our work too much to describe them.- ALBUMINOUS, OR PROTEINE COMPOUNDS. 748. These compounds, three in number, tirejibrine, albumen, and caseine. They are found both in vegetable and animal bodies, and, like sugar, starch, and woody-fibre, are capable, in certain circumstances, of being converted into each other. They are believed to be compounds of a proximate principle called QUESTIONS. 745. What other metals form cyanides similar in their properties to those of iron? 746. Describe hydrocobaltocyanic acid. 747. Describe cobaltocyanide of potassium. Are there other metallic polycyanides ? 748. What are the albuminous or proteine compounds ? PEOTEINE COMPOUNDS. 491 proteine, (jproteuo, I am first), and having the composition, C 40 H 3 ,N 5 0,2. Its real composition, however, cannot be considered as settled. To obtain proteine, albumen or caseine is to be digested suc- cessively in water, alcohol, and ether, in order to separate every- thing that is soluble in these liquids; and the mass that remains is to be soaked for a time in diluted hydrochloric acid, and then dissolved in a weak solution of caustic potash. From this-, acetic acid, cautiously added, precipitates the proteine. As thus obtained, proteine is a white, inodorous solid, which is insoluble in water or alcohol, and is capable of forming different compounds both with acids and bases. From its acid compounds it is readily precipitated by tannic acid, with which it forms an insoluble compound, by ferrocyanide of potassium, and by the alkalies. In the open air it rapidly absorbs moisture, and becomes a gelatinous mass; and by heat is decomposed, exhibiting the phenomena usually attending the combustion of nitrogenized bodies. It leaves no residue after combustion. 749, Fibrine. Gluten. Fibrine receives its name from the circumstance that it enters largely into the composition of the muscular fibre of the animal system. It is best obtained by whipping a quantity of fresh-drawn blood with a bunch of twigs, until it coagulates, and then carefully washing with water the stringy mass thus obtained. Subse- quently it is to be washed with alcohol and ether, to remove all fatty matter adhering to it, and dried. When thus obtained, fibrine is a yellowish opake mass, which is quite insoluble in water, alcohol, or ether. When long digested in water, at a very high temperature, a small proportion is dis- solved, but slight decomposition also takes place. It is not soluble in the acids, but dissolves readily in dilute solutions of tie alkalies. Fibrine, obtained in the above manner from venous and arterial blood, does not appear to be exactly the same in all its properties ; QUESTIONS. Is the compositipn of proteine known with certainty? How may it be obtained ? What are its properties ? 749. From what does fibrine derive its name ? How may it be procured ? Is it th game, whether obtained from venous or arterial blood 1^ 192 PEOTEINE COMPOUNDS. AS that from venous blood, when triturated with solution of nitrato of potash, at a high temperature, it becomes soluble, and very much resembles albumen, while that from arterial blood is not so affected. Fibrine may also be obtained from the flesh of animals, of which it seems to form the essential part. When procured from this source, it resembles that from venous blood. When the juice of various roots, as beets, turnips, carrots, &c., is allowed to stand for a time, a portion of it coagulates very much like blood, and may be separated from the uncoagulated part. It has been called vegetable fibrine, and seems to be the same as fibrine of animal origin. 750. Gluten is a substance obtained from the cereal grains It may be procured readily from wheat flour by kneading (554) it for some time in a large quantity of cold water, to wash away all the starch and other products, and then boiling for a time in alcohol. A soft, adhesive, elastic mass is thus obtained, which appears to be identical with fibrine. It is to this substance that wheat flour (which contains 20 or 25 per cent, of it) owes its adhesive, plastic nature j and it is this substance also, in a state of decomposition mixed, probably, with starch in the same state which constitutes yeast. 751, Albumen. This compound is found nearly pure in the whites of eggs, from which it derives its name. Like fibrine, it exists in two states as a liquid, in the whites of eggs, serum of the blood, humors of the eye, &c. and, as a solid, in the brain and nerves of animals, and in the seeds of plants. The latter, called vegetable albumen, is considered as altogether identical with that of animal origin. Liquid albumen may be coagulated, or solidified in various ways, as by heating to a temperature of 140, or more, or by the action of chemical reagents, as alcohol, tannic acid, corrosive sub- limate, and creosote j but when once coagulated it cannot be re- dissolved. As it forms an insoluble, and therefore inert com- pound with corrosive sublimate, it is considered a good antidote in cases of poisoning with the latter substance. QUESTIONS. What is said of the juice of certain roots, as those of beets, turnips, &c. ? 760. What is gluten? What is yeast? 751. Describe albumen. PROIEINE COMPOUNDS. 493 Vegetable albumen is found in the leaves and stalks of plants, and in the seeds, and in some cases in the roots. As obtained from plants, it is sometimes white, but is often colored. It is contained in considerable quantity in wood, and has great influence in causing its decay. It is therefore found that wood which has been saturated with a solution of corrosive sublimate is rendered more lasting when subjected to the influence of the atmosphere and moisture (501). 752. Caseine. Legumine. Caseine in many of its properties closely resembles albumen. It is most readily obtained from milk; and derives its name from caseum, curd. A very little eulphuric acid stirred in some skimmed milk causes it to coagu- late in a short time; and the curds so formed being well washed with water, and digested for a time with carbonate of baryta to separate the acid, afford the pure caseine. When dried it is but slightly soluble in water, but very soluble in solutions of the alka- lies, or alkaline carbonates. Legumine, believed to be identical with the caseine from milk, is procured from peas, beans, and other similar seeds, by bruising them in water, and straining through a fine sieve; the liquid which passes through is a solution of this substance, and contains some starch, which settles by standing. The supernatant liquid, being poured off, possesses all the characters of skimmed milk, and from it the legumine, or vegetable caseine, may be procured in the same manner as from milk. Caseine, in milk, is held in solution by free alkali present ; it is not coagulated by heat, like albumen, but coagulates readily by the action of rennet, or by acids, except the phosphoric. The three important compounds above described very closely resemble each other in many of their properties, as well as in composition ; but they are at the same time, in other properties, essentially different. Fibrine coagulates spontaneously by standing, but the other two undergo this change only by the application of certain agents. Albumen is not coagulated by acids, nor by rennet, but coagulates by heat, by contact of alcohol, and some of the metallic salts, and other compounds. Caseine does not coagulate by heat, nor by alcohol, but is readily coagulated by most of the acids, and by rennet. Probably what is considered as liqtiid caseine is only the substance held in solution by an alkali; and the coagulation of it by an acid results from the neutralization of the alkali by the acid. QUESTIONS. In what parts of plants is vegetable albumen contained ? 752. Describe caseine. Describe legumine. How is caseine coagulated ? How are fibrine and albumen coagulated? 42 494 PHENOMENA OF VEGETATION. Each of these substances appears always to contain a small quantity of sulphur ; and fibrine and albumen contain, in addition, a little phos- phorus. Decomposed by heating wifh acids or other reagents, they afford very complex results. When kept for a time they undergo spontaneous decompostion, and in certain circumstances also induce peculiar changes in other organic com- pounds, as in the production of the alcoholic and other fermentations. Being so nearly the same in composition, if not absolutely identical, it is altogether probable that, both in vegetables and animals, frequent transformations of one of these substances into another take place, by means and processes not yet understood. CHEMICAL PHENOMENA OF VEGETATION. 753. Germination is the process by which a new plant ori- ginates from seed. A seed consists essentially of two parts, the germ of the future plant, endowed with a principle of vitality, and the cotyledons, or seed-lobes, both of which are enveloped in a" common covering or cuticle. In the germ two parts, the radicle and plumula, may be distinguished, the former of which is des- tined to descend into the earth and constitute the root, the latter to rise into the air and form the stem of the plant. The office of the seed-lobes is to afford nourishment to the young plant until its organization is so far advanced that it may draw materials for its growth from extraneous sources. The conditions necessary to germination are threefold ; namely, moisture, a certain temperature, and the presence of oxygen gas. The necessity of moisture to this -process has been proved by extensive observation. It is well known that the concurrence of other conditions cannot enable seeds to germinate provided they are kept quite dry. A certain degree of warmth is not less essential than moisture. Germination cannot take place at a very low temperature; and a high temperature, as that of boiling water, destroys the vitality of the seeds. The most favorable temperature for the germination of most seeds is between 60 and 80. In the process of incipient germination a kind of saccharine fermenta- tion (556) takes place, by which nutriment is supplied for the young QUESTIONS. 753. What are the essential parts of a seed? Describe the process of germination in a seed ? What are the conditions required for healthy germination ? PHENOMENA OF VEGETATION. 495 plant during the early stages of its growth. This seems to be occasioned by the influence of the active principle diastase, which is not pre-existent in the seed, but is formed by the action of the air and moisture on the substances contained in it. When the process of germination is over, the plant is found provided with the necessary organs for procuring its nutri- ment from the atmosphere and soil ; and there remains of the seed only its ligneous husk, which sometimes perishes in the ground, but at others rises to the surface and performs for a time the functions of leaves, 754. Respiration of Plants. Assimilation of Carbon. We have already noticed (213) the beautiful provision, by which the two great classes of organized bodies mutually compensate for the change each produces in the constituents of the atmosphere, and continue that proportion of them which is conducive to the healthful existence of both. Animals, by respiration, are con- stantly giving off carbonic acid, while plants, by the action of light upon their leaves, absorb carbonic acid and exhale oxyg^p. It will be seen, therefore, that a process is ever going on in plants at least when under the influence of light not unlike the respiration of animals, in which the leaves perform the office of lungs. But the changes produced in the atmosphere being the rfverse of those occasioned by the respiration of animals, the two processes serve to support each other; and the proportional- quantity of oxygen and carbonic acid in the atmosphere is pre- served ever the same. The carbon obtained by plants by this respiratory process, and the water which is absorbed by the roots and leaves, furnish the elements of woody matter, and other substances, as sugar, starch, gum, &c., which contain oxygen and hydrogen in the proportion to form water. But the actions" that really take place are usually much more complex than this would seem to indicate. The absorption of carbonic acid, and the liberation of oxygen, take place only in the light; in the dark, an opposite process sets in oxygen is absorbed and carbonic acid is given off. But it has been well established that, on the whob, the quantity of carbonic acid absorbed is much greater that that evolved, whilst the quantity of oxygen evolved is much greater than that absorbed. Very many plants, it is believed, receive a large part of the carbon they con- tain from the atmosphere, while some few probably receive the whole. Others derive a part from the soil. Now it is not difficult to trace some of the further changes which no doubt take place in the plant. All the softer parts of most plants con- QUESTIONS. 754. What is meant by the respiration of plants ? What different effects are produced upon the atmosphere by the respiration of plants and animals ? Does the absorption of carbonic acid take place op^y in the light ? 496 PHENOMENA OP VEGETATION. tain abundance of starch ; even in the tubes and cells of ordinary wood it is found. This is so closely allied to sugar, gum, and woody-fibre, and the transformations of them from one to another so easy, that we may suppose them to be constantly taking place. The other numerous secondary products, as the vegetable acids, oils, coloring-matters, &c., which characterize plants, may be formed from starch during the inverse respiratory action just alluded to, in which carbonic acid is given off, and oxygen absorbed from the atmosphere. During the day the assimilating power of the plant is in action, and car- bonic acid is rapidly absorbed, and oxygen evolved ; but during the night, while the plant is in repose, this nutritious action ceases, and a different process commences, during which the various substances natural to the plant are elaborated, attended by the absorption of oxygen from the atmosphere, and the evolution of carbonic acid and water. This change is well illustrated by certain plants, as the cacalia ficoides, the leaves of which are bitter in the evening, but in the morning are sour, like those of sorrel. During the night oxygen has been absorbed, and an acid generated from materials that were combined the evening previous, in a different mode. Nitrogen is an essential ingredient in many of the products of plants ; it is believed to be obtained chiefly from the soil. 755, Inorganic Constituents of Plants. Besides the sub- stances which form Jhe organic matter of plants, various inor- ganic bodies, as alkaline and earthy salts, are usually found contained in them, and no doubt serve an important purpose. If a plant is made to vegetate in a soil containing in it small quantities of several salts, we find that, while it continues in health, it seems to exercise a remarkable discretionary power, absorbing some, and rejecting others. Those absorbed most freely are such as are required for its proper growth, and are not given up to the water in which the plant may be immersed ; while some are absorbed and again given off, and others still are entirely rejected, as being injurious. Most plants contain a small quantity of some salt of potassa, which exists as a car- bonate in the ashes resulting from their combustion ; but plants that grow near the sea, or springs of salt water, usually contain soda instead of potassa. Silica, lime, magnesia, &c. ? are also often contained in plants. As these inorganic substances are necessary for the proper growth of plants, and all plants do not require the same substance, it is plain that a particular plant can be expected to flourish only in soils containing the substances it, requires. QUESTIONS. Is nitrogen assimilated by plants? From what is it derived ? 755. What are the inorganic constituents of plants ? Do dif ferent plants absorb very different substances from the soil ? PHENOMENA OF VEGETATION. 497 756. Nature and Use of Manures. Every substance is called a manure which, applied to a soil, increases its productiveness. In a particular case it may be a substance which is required in the proposed crop, but of which the soil is deficient ; or it may be a substance designed merely to give the soil a proper texture, so that it may more easily be penetrated by the rootlets of the plants, or to increase its adhesiveness and enable it to retain longer the moisture that falls upon it. It is in the manner last mentioned, probably, that most mineral manures, as lime, marl, &c., usually operate. * From the preceding remarks, the great advantage of rotation of crops may readily be seen. The mineral constituents of a soil are derived from the disintegration of its subjacent rocks; and some of them being contained only in small quantities, by con- tinued succession of the same crop, may be entirely removed, and the soil become impoverished. By substituting another crop, which requires little or none of the material which has been exhausted, an abundant harvest may be obtained ; and the soil, by the gradual decomposition of its subsoil, recover its former constitution. 757. The great value of organic manures is supposed to depend almost entirely upon the nitrogen they supply to the soil. The most of the nitrogen in plants is contained in the seed, tubers, &c., those parts which are selected by man for food, or for medicinal purposes, in consequence of the active principles they contain ; and but little is found in the stem, leaves, root, &c., which are rejected as useless. The residue of a former season, therefore, may manure the land abundantly, so far as carbon is concerned, but there will be a deficiency of nitrogen, an essential ele- ment of the future desired crop. This deficiency is supplied by the decaying animal and vegetable substances used as manures ; the value of which will therefore be very nearly in proportion to the nitrogen they supply. If mere ammoniacal salts are used, or perishable animal sub- stances, their whole benefit is imparted to the crop immediately succeed- ing their application; but organic substances, which decay but slowly, yield a more permanent benefit : their nitrogen is gradually evolved, and though little benefit at first appears, the soil is at length found to be essentially improved. 758. In healthy vegetation, light serves a most important purpose; indeed, without it, no plant could come to perfection. A plant which grows in darkness, as in a cellar, however rich may be the soil in which QUESTIONS. 756. What are manures? Explain the different modes in which manures operate to produce their effects? 758. What is said of the importance of light to healthy vegetation? 42* 498 ANIMAL TISSUES. . it stands, remains soft, its color pale, and its woody fibre unformed. "When brought to the light, it perhaps increases in volume less rapidly, )>ut the healthy action of the organ at once commences ; the green color appears, and all the parts of the plant begin gradually to advance to maturity. * COMPOSITION OF THE ANIMAL TISSUES. 759. By the animal tissues we understand all the various solid found in the system, not excepting the bones and teeth. The Muscles. The muscles are the organs of motion to the animal, and they act solely by their contractions, which take place at the will of the animal. Their structure is always fibrous, and in the mammalia they are of a red color, and receive from the circulation a large supply of blood. The chief substances contained in them are fibrine, albumen, and gelatine. The two latter substances are con- tained chiefly in the membranes which en- velope the fibres. The accompanying fig- ure represents a piece of muscle, and shows its fibrous structure. When Piece of Muscle. taken from the animal and dried at a moderate temperature, it contracts greatly by the loss of water, and its weight is eventually reduced to one-fourth. 760. The Cartilages, Skin, and Membranes. The cartilages appear to have essentially the same composition as the skin and the membranes generally. They are all composed of gelatine and chondrine, both of which are entirely dissolved by long con- tinued boiling, and form with water a transparent jelly. Their exact composition has not been fully determined. Chondrine is most abundant in the cartilages. The common glue of commerce is dried gelatine, and is pre- pared by boiling cuttings of parchment, or the skins, ears, and QUESTIONS. 759. What are the muscles of animals ? What are they chiefly composed of? 760. What is said of the cartilages, &c. ? What is glue ? . ANIMAL TISSUES. 499 hoofs of animals, and evaporating the solution. Its use is well known. Isinglass, which is a very pure variety of gelatine, is prepared from the sounds of fish of the genus acipenser, especially from the sturgeon. The animal jelly of the confectioners is made from the feet of calves, the tendinous and ligamentous parts of which yield a large quantity of gelatine. . m Gelatine is insoluble in alcohol, but is dissolved readily by most of the diluted acids, which form an excellent solvent for it. Gelatine manifests little tendency to unite with metallic oxides. Cor- rosive sublimate and acetate of lead do not occasion any precipitate in a solution of gelatine, and the salts of tin and silver affect it very slightly. By boiling gelatine with dilute sulphuric acid, and precipitating the acid with chalk, a sweet crystaline compound is obtained called glycocoll (glukus, sweet, and kolla, glue), or gelatine sugar, the composition of which is C 4 H 5 N0 4 . The action of tannin or tannic acid (684) upon gelatine is peculiar and important, resulting in the' production, in certain cases, of the well known and most useful substance, leather. Leather is usually formed by subjecting the skins of animals for some time to an infusion of bark which contains a large proportion of tannic acid; and the chief chemical change which takes place is believed to consist in a union of this acid with the gelatine of the sliin. This is the common leather of which shoes are made : other varieties of this useful manufacture are prepared by different modes. Glove-leather, for instance, is prepared by impregnating the skin, after having been deprived of all its fatty matter by soaking in a weak alkali, with solution of common salt and alum, from which chloride of aluminum is formed, and unites with the gelatine of the skin. The Brain and Nerves. The substance of the brain, nerves, and spinal marrow differs from that of all other animal textures. The white and gray portions differ essentially in their nature, but are composed chiefly of water, albumen, a fatty matter, and traces of phosphates and other salts. Only about one-fifth of the whole is solid matter. The fatty matter is peculiar, and is quite unlike that of other parts of the system. The phosphorus in the brain is said to amount to 3 or 4 per cent, of all the solid matter contained in it. 761. The Bones. The bones of animals consist of earthy matter, which is chiefly phosphate and carbonate of lime, and animal matter, which is essentially the same as cartilage. These QUESTIONS. What is said of the action of tannic acid upon gelatine ? How is leather prepared? 761. What is said of the composition of tho bones? bOO THE .BLOOD. may easily be separated from each other. To separate the solid or earfctf matter, it is only necessary to digest the bone for a time in dilute hydrochloric acid, in which both the phosphate and carbonate of lime are soluble, so that they will be entirely re- moved, leaving the cartilage soft and flexible, but retaining perfectly the fbrm^of ihe bone. The cartilage may be removed by heating the bone some time in the open air, so as to burn away all the organic matter j or by digesting it in solution of an alkali, or in water at a high temperature, under pressure. In some cases of disease, as rickets, to "which children and youth are chiefly liable, there is a deficiency of earthy ^matter in the bones; and they are, in consequence, weak, and incapable of affording the necessary support to the system. Horn differs from bone in containing only a trace of earth. It consists chiefly of gelatine and a cartilaginous substance like coagulated albumen. The composition &f the nails and hoofs of animals is similar to that of horn ; and the cuticle belongs to the same class of substances. 702. The hair* seems to have essentially the same composition as horn, but the color is occasioned by an oil, which is soluble to ether, and may therefore be removed by it. It contains sulphur, and is therefore black- ened by nitrate of silver, or other metallic salt. . When horn or hair is heated, it . is first fused, and then swells up, giving off carbonate of ammonia, and carburetted hydrogen, the last of which takes fire, and burns with a brilliant flame. Shells are composed of a mixture of phosphate and carbonate of lime. The shells of the Crustacea, as lobsters, crabs, &c., usually contain 4 or 6 per ^ent. of phosphate of lime, and 50 or 60 per cent, of the carbonate, the rest being animal matter. The shells of the molusca, as the oyster and clam, are nearly pure carbonate of lime, containing only a mere trace of animal matter. THE BLOOD. PHENOMENA OF RESPIRATION AND DIGESTION. 763, The support of life in animals is attended by many chemical phenomena, which are constantly taking place in every part of the body, but especially in the blood, the lungs, the digestive system, and in the glands. The substances taken into the mouth are modified in the process of digestion, and distributed to every part QUESTIONS. How does horn differ in composition from bones ? 702. What is said of hair? 763. What is said of the chemical changes which take place in the system ? THE BLOOD. 501 by the circulation of the blood, where they come in contact with oxygen received from the air in the lungs. Among these dif- ferent principles, received in the processes of nutrition and respi- ration, important chemical changes are taking place, by which the animal heat is kept up, and the waste of all the various tissues supplied, and, indeed, all the animal functions supported. The blood of the different orders of animals is not the same, but we propose here to speak of that of the higher orders, or vertebrated animals, in which it is always of a red color. In these, the blood which i's brought from the lungs, and pro- pelled by the heart through the arteries to every part of the system, is of a bright red or scarlet color, and is called arterial blood ; but as it is returned to the heart by the veins, to be again sent to the lungs, it is of a dark red or purple, and is called venous blood. The blood is therefore of two kinds ; but, chemically, they seem to be essentially the same. The Blood. , 764, Composition of the Blood. The blood is easily dis tinguished from all the other fluids by its color. Its taste is slightly saline, its odor peculiar, and to the touch it seems some- what unctuous. Its specific gravity is variable, but usually about 1-05 ; and in man its temperature is about 98 or 100. While flowing in its vessels, or when recently drawn, it appears to the naked eye as a uniform homogeneous liquid; but if examined with a microscope of sufficient power, numerous particles of a discoid form are seen floating in a nearly colorless liquid. Most of these discs are red, and in the blood of man are about -g^^th of an inch in diameter, and one-fourth as thick; but there are also others which are without color. The figure on next page represents these discs in human blood, as seen under the micro- scope, a and b colorless discs. The figure at the right repre- sents these discs as they are sometimes seen united in rolls like pieces of coin. QUESTIONS. Is the blood the same in all animals ? What two kinds of blood are there? 764. What is said of the composition of the blood? How does it appear when viewed by the microscope ? What is the form of these corpuscles? Their size? 502 THE BLOOD Discs in Human Blood. These discs vary considerably in size in the blood of different animals, being considerably smaller in the blood of the common domestic animals than in man, but larger and of an oval form in oviparous vertebrates. They are larger in the blood of the elephant (see % ure m tne nlargin) than in that of any other mammalian species. Discs jn the Blood of , the Elephant. 765. When the blood is withdrawn from the system, these discs or globules contract into a solid mass or coagulum, which, by standing, entirely separates from the liquid serum. This is a 'thin yellowish liquid, of sp. gr. about l-03,Xhid coagulates when heated to about 140. It has a slight alkaline reaction, owing to the presence of soda, and contains a considerable quantity of albumen. In the living body the blood also contains fibrine in solution, which, however, soon separates from the coagulum after its extraction from the system. Various salts also are found, as common salt, phosphates of lime, magnesia, and ammonia, and lactates of soda and magnesia. The relative proportion of the ingredients of the blood must neces- sarily vary, independently of disease, even in the same individual, according as the nutrition is scanty or abundant. Slight variations are ^.Iso occasioned by difference of age and sex. QUESTIONS. 765. What change occurs in the blood when withdrawn from tho system? What substances are mentioned as contained in the Xood? PHENOMENA OP DIGESTION. The following table contains the results of several analyses of blood : Water 90-5 Albumen 8-0 Chlorides of sodium and potassium. -6 Lactate of soda and extractive matter -4 Soda and phosphate of soda *41 Loss , -09 100-00 The coloring-matter of the blood is confined entirely to the discs or corpuscles spoken of above, and has been called hematosine. In many of its properties it closely resembles albumen. It is composed of carbon, hydrogen, nitrogen, "oxygen, and iron, the latter of which constitutes between six and seven per cent. 766. Coagulation of the Blood. The coagulation of the blood, to which allusion has already been made (765), consists in the agglutination of the fibrine it contains, by which the red globules, and other suspended particles, are inclosed, forming the clot. The time required for the coagulation of the blood depends much upon temperature, being promoted by heat and retarded by cold. The process is also influenced by exposure to the air. If atmo- spheric air be excluded, as by filling a bottle completely with recently-drawn blood, and closing the orifice with a good stopper, coagulation is retarded. It is singular, however, that if blood be confined within the exhausted receiver of an air-pump, the coagu- lation is accelerated. *. Some substances, introduced into the blood, either retard or entirely prevent its coagulation, as saturated solution of chloride of sodium, hydrochlorate of ammonia, nitre, and a solution of potassa. The coagulation, on the contrary, is promoted by alum and the sulphates of the oxides of ?inc and copper. The blood of persons who have died a sudden, violent death, by some kinds of poison, or from mental emotion, is usually found in a fluid state. Phenomena of Digestion. 767. Digestion is the process by which the food is fitted to nourish the system, and supply the constant waste that is required for the support of the powers of life. The blood is the agent by QUESTIONS. What is the coloring-matter of the blood called ? 766. What is eaid of the coagulation of the blood ? 767. What is digestion ? 504 PHENOMENA OF DIGESTION. which the matter required for the support of the system is sup- plied to the various parts where it is needed ; but it is from the food that it is first received. 768, The Saliva. The saliva is a slightly viscid liquid, se- creted by several glands about the mouth, called the salivary glands. It serves to keep the mouth constantly moist; and the sight, or even thought of food, causes it to flow rapidly in the mouth. Besides water, and a small quantity of several salts, it contains a peculiar principle called ptydline^ which may be pre- cipitated from it by absolute alcohol. T-he use of the saliva is to mix with the food during masti- cation, and form a soft, pulpy mass, suitable to be swallowed. Probably it aids also in the process of digestion, by fitting the food to be more readily acted on by the juices of the stomach. The saliva is often much affected by disease, and occasions the bad taste in the mouth, especially on rising in the morning. In some diseases, as intermittent fever, it is often very acid. 769. The Gastric Juice. The gastric juice is an acid fluid secreted by the coats of the stomach, and contains in solution several salts, mucus, albumen, and a nitrogenized substance called pepsine. It has the property of softening down and dissolving, more or less perfectly, all the various substancss which serve for food. When the food is introduced into the stomach, it is there intimately mixed with this juice, by the agency of which it is converted into a semi-fluid matter called chyme. That this change is owing to the solvent power of the gastric juice has been fully determined ; and it seems to be well established as a further fact, that the gastric juice secreted in the stomachs of animals of any species is especially adapted for dissolving the particular kind of food upon which the species usually feed. While the food is in the stomach, it is constantly kept in motion by a peculiar movement of the muscular walls of the intestine, called its peristaltic motion. This has the effect thoroughly to mix every part, and also to propel the mass slowly forward. QUESTIONS. 768. Describe the saliva. What purpose does it serve? 769. By what is the gastric juice secreted ? What purpose does it serve' What is chyme ? PHENOMENA OF DIGESTION. 505 The chyme, as it passes from the stomach, appears as a homo- geneous, semi-fluid mass; but it has recently been found that the solvent action of the gastric juice is chiefly limited to the nitrogenized part of the fluid, as the albumen, fibrine, &c. ; the non-nitrogenized parts, as the starchy and fatty compounds, being only mechanically divided and mixed up with the mass. From the stomach, the chyme pass-as to a large intestine called the duodenum, where it is subjected to the action of two other fluids, the bile and the pancreatic juice., which we will now pro- ceed to consider. 770. The Bile. The bile is a liquid secreted by the liver, and preserved in the gall-bladder, which, when the stomach is filled, is slightly pressed and made to discharge its contents through a small duct into the duodenum. It is of a yellow, or greenish- yellow color, and has a peculiar sickening odor, and a taste at first sweet and then bitter, but exceedingly nauseous. Its consistence is variable, being sometimes limpid, but more commonly viscid and ropy. It contains a peculiar principle called cholesterine, and two organic acids called the cholic, and choleic, both of which are in combination with soda. It seems now to be very well determined that one, if not the chief, purpose served by the bile is to aid in the digestion of the fatty and oily substances taken for food. In connection with the pancreatic juice, it also aids in the separation of the chyle. Biliary calculi are concretions which occasionally form in the gall- bladder, or duct leading from it. They differ much in composition, but not unfrequently they are composed, in great part, of cholesterine. 771. The Pancreatic Juice. This is a secretion of a certain organ 'called the pancreas. It is a limpid, colorless, alkaline liquid, with a saltish taste, like that of the serum of the blood. It is slightly viscous, and coagulates by heat, and by the acids. The pancreatic juice is poured into the duodenum at the same time with the bile. Both of these liquids act energetically upon fatty and amylaceous substances, and produce important changes QUESTIONS. What fluids are poured into the blood next after it leaves the stomach? 770. By what organ is the bile secreted? Describe it. What compounds are contained in it? What purpose is served by it? 771. What is the character of the pancreatic juice? 43 506 PHENOMENA OF RESPIRATION. in them, by which they are prepared to enter into the circulating system. We have seen that the substances taken for food, after having been acted upon in the stomach by the gastric juice, and reduced to a homogeneous mass called chyme, pass into the duodenum, where the mass receives the bile and the pancreatic juice ; imme- diately a change takes place, and a milky liquid appears diffused through the mass, called chyle. This is the part of the food, which, by the digestive process, has been prepared forthe nourish- ment of the system, the rest being thrown off as refuse matter; and, as the mass passes on through the intestinal canal, it is absorbed by numerous little tubes opening into its side, called lacteals, and conveyed by them to a common reservoir, the thoracic duct. From this it is discharged into the left subclavian vein, and becomes incorporated with the blood, forming a part of its substance, and fitting it for the proper continuance of its functions. Phenomena of Respiration. 772. All organized bodies require constantly the presence of atmospheric air for the proper performance of their various func- tions, and their continued existence in the living state. All the larger land-animals are provided with lungs, in which, by the action of certain muscles, air is constantly inhaled and again expelled, and thus a continued circulation is kept up; but in some of the smaller ones, as insects, the breathing is by tubes called trachea, or is performed by the whole surface of their bodies. In fishes, certain organs called gills perform the office of lungs, and the air that is breathed is first absorbed by the water, and from this imparted to the animal. In every case the process by which the air is made to perform its office upon the living being is called respiration. The important chemical changes that attend the respiration of animals are, the constant absorption of oxygen, and the forma- tion and evolution of carbonic acid. QUESTIONS. What is the chyle? What purpose does it serve? How is it conveyed to the blood ? 772. Do all organized bodies require the constant presence of air ? What purpose is served by the lungs of ani- mals ? What important changes attend the respiration of animals ? PHENOMENA OP RESPIRATION. 507 To show the presence of carbonic acid in the air expelled from the lungs, it is only necessary to apply a small tube to- the mouth, and blow, a few seconds, into some recently-prepared lime-water ; the carbonic acid in the air from the lungs will unite with the lime, forming carbonate of lime, which gives the solution a milky appearance. It is true, there is a little carbonic acid in the air before it is taken into the lungs ; but while there the quantity is very considerably increased. This is shown satisfactorily by blowing in the same manner by a hand-bellows into another portion of lime-water, when it will be found that a much longer time will be Blowing through required to produce the milkiness alluded to (304). Lime-water. 773. The change in the blood from the venous to the arterial state, is effected in the living animal during the passage of the blood through the capillary vessels of the lungs, where it is exposed to the action of an extensive surface of atmospheric air, through the thin membranes which separate these from the air- vessels ; and the arterial blood, in traversing the capillary system of the body, imparting nourishment to it, gradually assumes the dark-colored condition in which it is returned to the heart by the veins. The same change is produced when venous blood, just taken from the system, is brought in contact with atmospheric air, and is attended with the evolution of carbonic acid gas. It takes place more speedily when air is agitated with blood ; it is still more rapid when pure oxygen is substituted for atmospheric air ; and it does not occur at all when oxygen is entirely excluded. The quantity of carbonic acid developed very exactly corresponds with that of the oxygen which disappears. The quantity of oxygen withdrawn from the atmosphere, and of car- bonic acid disengaged, is variable in different individuals, and in the same individual at different times, depending very much upon the state of the system. In a state of health, anything that accelerates the respi- ration increases the amount of oxygen absorbed, and the quantity of car- bonic acid exhaled ; but in certain cases of disease, as in inflammatory fevers, though the respiration may be very rapid, little oxygen is with- drawn from the air, and the venous blood is found to be very florid. QUESTIONS. How may the presence of carbonic acid in the air ex- haled from the lungs be shown? 773. How is the change in the blood from the venous to the arterial state effected ? What change is again produced in the blood as it circulates through the system ? 508 PHENOMENA OF RESPIRATION. 774. Animal Heat. Nutrition. It has long been known that there is a close connection between the function of respiration, and the development of heat in the animal system. Thus, in all animals whose respiratory organs are small and imperfect, and which, therefore, consume but a comparatively minute quantity of oxygen, and generate little carbonic acid, the temperature of the blood varies with that of the medium in which they live. In warm-blooded animals, on the contrary, in which the 'respiratory apparatus is larger, and the chemical changes more complicated, the temperature is almost uniform ; and those have the highest temperature whose lungs, in proportion to the size of their bodies, are largest, and which consume the greatest quantity of oxygen. The temperature of the same animal at different times is connected with the state of the respiration. When the blood circulates sluggishly, and the temperature is low, the quantity of oxygen consumed is comparatively small ; but, on the contrary, a large quantity .of that gas disappears when the circulation is brisk and the power of generating heat energetic. It has also been observed, that when an animal is placed in a very warm atmosphere, so as to require little heat to be generated within his own body, the consumption of oxygen is unusually small. We have seen already that the digestion of the food is per- formed, in part, in the stomach, by the gastric juice dissolving the nitrogenized or albuminous portion, and partly in the duode- num, where the amylaceous and fatty parts are acted on by the bile and pancreatic juice. This indicates an important division of the substances taken for food into two kinds ; and we find that the same distinction is also observed in the" purposes they serve in the system. It has been determined that the albuminous or nitrogenized parts of the food, go to support the waste of the tissues, while the non-nitrogenized parts, as starch, sugar, and the fats and oils, are consumed in preserving the temperature QUESTIONS. 774. Is there any immediate connection between the function of respiration of animals and the temperature of their systems ? What facts are mentioned as illustrating and proving the point? What two purposes are served by the food? What are the elements of respi ration and nutrition ? PHENOMENA OF RESPIRATION. of the system. The latter may therefore be called the elements of respiration, and the former elements of nutrition. 775. The combustion of carbon and hydrogen in the open air, as is well known, is always attended by the evolution of heat; and the same effect is produced in the system when these sub- stances unite with the oxygen introduced into the blood in the process of respiration. The only essential difference is, that in combustion the process is more rapid, and the heat produced pro- portionally more intense; but the absolute quantity of heat pro- duced by the consumption of a given amount of carbon or hydrogen is, in all probability, always the same. We here find the origin of the carbonic acid which is given off during respiration, and also by the insensible perspiration from the skin, while the water produced by the combustion of the hydrogen unites with the large quantity ever present in all parts of the body. We see, therefore, that the oxygen of the air is tending to consume all living beings, as really as if they were in a burning fire ; in fact,' this consumption, which is a kind of combustion, is ever going on while respiration continues. To keep up the combustion, a constant supply of fuel is needed, which is found in the respiratory food, as before stated ; and when these elements enter into combination within the ani- mal system, heat is as necessarily developed as when the same thing takes place in the open air, in ordinary combustion. 776. Use of the Fat in the Animal Economy. The fat and oils found in animals appear to be stores of respiratory food, laid up by a wise foresight of nature for time of need. Thus, it is well known that when food is abundant the fat accumulates, which is again gradually wasted away when the supply of food becomes deficient. When the supply of food is wholly withheld from an animal, the fat rapidly disappears, its carbon and hydrogen going to supply the demands of respiration ; and when this has all been consumed, the substance of the muscles is attacked, which become lean and flaccid, and lose their contractile power; and at length the brain and nerves yield to the same influence, QUESTIONS. 775. What always attends the combustion of carbon and hydrogen ? Is the same effect produced in the animal system ? 776. What purpose is served by the fat in the animal system ? What becomes of the fat when the supply of food is short ? 43* 5l6 ANIMAL SUBSTANCES. and death speedily closes the scene of suffering* In animals that lie torpid during the winter, nature has provided that in the sum- mer season a large accumulation of fat is laid up to supply the demands of respiration during the time they lie torpid in their dens; and, on the approach of the warm weather of spring, they are consequently found lean and weak. It is important to observe that the composition of the nitrogenized food consisting chiefly of the proteine compounds and gelatine, is the same a that of many of the tissues, the waste of which it supplies ; and it is the opinion of many that these compounds are never produced in the anima! system, but are appropriated directly from the food, unchanged. It is, however, known that some substances are formed in the system from the materials supplied by the food. Thus, it has been found that a lean goose, fed 'on Indian corn, will in a few days increase in weight several pounds, in consequence of the fat that will be formed in the sys- tem, which must have been contained in the corn, or formed from the substance of the corn by the organs of the animal. Now that the most of it has been formed in the latter mode is certain from the fact that all the oil or fatty matter contained in the corn will amount only to a small fraction of the fat found in the goose. So bees will form wax when fed on pure honey or pure sugar. It has been found by experiment that foi twenty parts of honey consumed they will form about one part of wax. SEVERAL ANIMAL SECRETIONS AND EXCRE- TIONS NOT BEFORE NO-TIC ED. 777. Milk. This well-known liquid is secreted by females of the class mammalia, for the support of their young. It is of a white color, and is a little heavier than water, usually having a density from 1-02 to 1-04. Its composition varies in different animals, and also in the same animal, according to the food that is taken. On an average, that of the cow contains, in an hun- dred parts, water 874 parts; butter, 4-0; milk-sugar, or lactine, and soluble salts, 5-0; caseine, albumen, and insoluble salts, 3-6. When milk is examined by a microscope, it is found to be a transparent liquid, with numerous minute globules floating in it, which consist chiefly of fatty matter, and which, if the milk stand at nest a few hours, rise to the surface as cream. If, now, the cream is separated, and violently agitated for a time, the mem- QUBSTIONS. 777. What substances are contained in cow's milk. What is cream ? ANIMAL SUBSTANCES. 511 branes enveloping these fatty corpuscles are broken, and it collects into a mass of butter, which floats in the watery liquid. Milk is not coagulated by heat, but this effect is readily pro- duced by acids and by rennet, which is prepared by soaking the inner coat of a calf's stomach in water. The coagulum so formed is called curd, and when pressed and otherwise prepared, con- stitutes cheese. 778. When milk is allowed to stand some hours, at a tempera- ture of between 60 and 70, it sours; and, on examination, a peculiar acid is found in it called lactic acid, the composition of which is C 6 H 6 6 . When highly concentrated, it is a thick, colorless liquid, of specific gravity 1-21, and has a very sour taste. It is soluble in alcohol and water, but cannot be crystalized. Lactic acid may also be formed fforn sugar by mixing with it in solution some curds from milk, and some chalk to unite with it as it is produced, and allowing the whole to stand for some time at a temperature of about 80. The chemical change that takes place appears to be very simple, as an atom of fruit-sugar contains exactly the ingredients of two atoms of lactic acid. Thus, C, 2 H, 2 0,2 = 2(C 6 H 6 6 ). It is this acid which is contained in the gastric juice. Lactic acid is also formed when the juices of beets, carrots, &c., are allowed to ferment at high temperatures. At the same time a viscid, slimy substance is formed, from which circumstance this has been termed the viscous fermentation. Milk may also be made to undergo the vinous or alcoholic fermentation. For this purpose it is exposed for some hours to a temperature of. about 100; and the alcohol, which, no doubt, is formed from the milk-sugar it contains, may subsequently be distilled from it. It has long been known that some barbarous nations are accustomed to prepare an intoxicating drink from milk, by some fermenting process. 779. Lymph. Lymph is a watery fluid, secreted by many of the membranes; it lubricates all the cavities, and moistens the QUESTIONS. 778. What acid is formed in the souring of milk? May .it be formed from sugar? May milk be made to undergo the alcoholic fermentation ? 779. What is lymph ? 512 ANIMAL SUBSTANCES. cellular tissues of the body. It much resembles the serum of the blood, and mixes readily with water. Sometimes, in diseases, this liquid, or a liquid analogous to it, is secreted in one or more organs, so abundantly as to constitute dropsy. 780, Urine. This is a yellowish liquid, secreted by the kid- neys, by which various substances, constantly accumulating in the blood, are separated from it during the healthy state of the sys- tem. This excretion is essential, as without it the substances thus thrown off would, in a short time, accumulate in such quantity as to destroy life. It has usually a specific gravity of about 1-02, and consists of water, holding in solution a small portion of urea and several different salts, as well as a little free acid, from which it acquires an acid reaction. A little mucus is also usually pre- sent, derived from the urinary passages ; and in consequence of this it putrefies if kept for a time at a summer temperature. The quantity of the urine is affected by various causes, espe- cially by the nature and quantity of the food and the liquids received into the stomach ; but on an average, a healthy person voids between thirty and forty ounces daily. The quality of this fluid is likewise influenced by the same circumstances, being some- times in a very dilute state, and at others highly concentrated. The urine of birds, insects, and reptiles, is solid, and consists chiefly of urate of ammonia. Guano, which has been so largely imported within a few years, to be used as a manure, is composed chiefly of the urine and other excrements of birds, which have been collecting for ages in the places where they are found. It is imported chiefly, if not entirely, from islands on the coast of Africa, and the west coast of South America. 781. Urea, C 2 H 4 N 2 2 = CyO,NH 3 + HO. This substance is always found in healthy urine, and may also be prepared arti- ficially. Its crystals, when pure, are transparent and colorless, of a slight pearly lustre, and have commonly the form of a four- sided prism. It leaves a sensation of coldness on the tongue, like QUESTIONS. 780. What purpose is served in the animal system by the secretion of the urine? What is guano? 781. From what is urea obtained ? ANIMAL SUBSTANCES. 513 nitre, and its -smell is faint and peculiar, but not urinous. Its specific gravity is about 1-35. Water, at 60, dissolves more than its own weight of urea, and boiling water takes up an unlimited quantity. It requires for solution about five times its weight of alcohol at 60, and rather less than its own weight at a boiling temperature. The aqueous solution of pure urea is very permanent, but if the other con- stituents of urine are present, it putrefies with rapidity, and, by a heat of 250, it is melted and resolved into carbonate of ammonia, and other products. Though urea has not any distinct alkaline properties, it unites with the nitric and oxalic acids, forming sparingly soluble com- pounds, which crystalize in scales of a pearly lustre. Urea is prepared artificially as follows. Four parts of dry Prussiate of potash are intimately mixed with 2 parts of peroxide of manganese, and heated to dull redness in an iron vessel. When the mass has become cold it is digested in cold water, and frequently stirred, until all that is soluble is taken up by the water. This is now decanted, and mixed with 3 parts of sulphate of ammonia previously dissolved in water. Sulphate of potash and cyanate of ammonia are at once formed ; and on the applica- tion of a moderate heat the latter compound is converted into urea, which is only an isomeric modification. To separate the urea, the whole solution is evaporated to dryness, and the urea taken up by strong alcohol. 782. Uric Acid, doIIjN^Oe, is found, in combination with bases, in the urine of many animals, especially that of birds of prey, and of serpents. It is a white,' tasteless, and inodorous solid, but sparingly soluble in either cold or hot water. Urate of ammonia consti- tutes a large part of the best guano. When uric acid is boiled with peroxide of lead- a substance called allantoine is formed, which has the composition, C 8 H 6 N 4 8 , carbonic acid being also evolved. It is a solid, and capable of being crystalized. Boiled with the strong acids, it forms urea and allantofc acid, C 6 H 4 N 2 6 .. Alloxan, alloxantine, alloxanic, and dialuric acids, are other closely allied substances. 783. Besides the above substances, there is found in the urine of herbivorous animals, as the cow and horse, another important QUESTIONS. Describe the artificial mode of preparing urea. 782, What is uric acid ? 783. From what is hippuric acid obtained ? 514 ANIMAL SUBSTANCES. acid, called the hippuric acid (from hippos, horse). Its com- position is C 18 H 9 N0 6 = C 18 H 8 NO & + HO. To prepare this acid, the fresh urine may be concentrated by a gentle heat, taking care not to cause it to boil, until its volume is diminished one-half; and hydrochloric acid then added until an acid reaction is produced. By standing for a time, impure hippuric acid will make its appearance in the form of long, slender crystals. These arc then to be redissolved in boiling water, mixed with some milk of lime and animal charcoal, and the resulting solution of hippurate of lime carefully filtered before cooling. To decompose this, hydrochloric acid is to be added until an acid reaction appears; and, on cooling, the pure hippuric acid will be obtained in beautiful crystals. These are only slightly insoluble in cold, but very soluble in boiling water. Some of the relations of this acid are curious and important. When boiled for some time with a strong acid, it is converted into benzole acid and glycocoll (760), 2 atoms of water being absorbed in the process. Thus, C 18 H 9 N0 6 -f 2HO = C ]4 H 6 4 -f C 4 H 5 N0 4 . By boiling with peroxide of lead, hippuric acid is converted into benza- mide (634), carbonic acid and water being formed at the same time. The action of nitrous acid upon the hippuric, results in the production of a new acid, called the benzogly collie, which has the formula, C^H^O^; water and nitrogen being eliminated. Glycocoll acted on by nitrous acid forms gtycocollic acid, C 8 H 8 Ojj. QUESTIONS. Describe the process of obtaining hippuric acid. When it is boiled with a strong acid, what compounds are formed from it ? APPENDIX. Tables of Weights and Measures, Proportion of Alcohol in Spirits of different Specific Gravities, etc. WEIGHTS. English Imperial Standard Troy Weight. 24 Grains = 1 Pennyweight. 20 Pennyweights = 1 Ounce = 480 Grains. 12 Ounces = 1 Pound = 5760 Grains. Apothecaries' Weight. 20 Grains = 1 Scruple 9. 3 Scruples =r 1 Drachm 5- 8 Drachms =. 1 Ounce g r= 480 Grains. 12 Ounces = 1 Pound =5760 Grains. The Grain, Ounce, and Pound are the same iu both the above weights. Avoidupois Weight. 1 Drachm = 27-34 Grains. 16 Drachms = 1 Ounce r= 437 -5 Grains. 16 Ounces = 1 Pound = 7000 Grains. 28 Pounds 1 Quarter. 4 Quarters = 1 Cwt. or 112 Ibs. 20 Cwt. = 1 Ton. French Decimal Weights. Gramme = 15-443 Grains. Decigramme = -1-544 Centigramme = 0-154 Milligramme = 0-015 Gramme = 15-443 Grains. Decagramme = 10 Grammes = 154-43 Hectogramme = 100 " = 1544-3 " Kilogramme = 1000 = 15443- The Kilogramme = 2-206 Ibs. Avoid., and 2-68 Ibs. Troy. Troy weight is used in all cases in weighing the precious metals, the ounce being gene- rally made the unit. Physicians, in making their prescriptions, and druggists, in com- pounding their medicines, make use of the subdivisions of the pound called Apothecaries' weight ; but drugs are always bought and sold by Avoirdupois weight. In scientific researches, as in chemical analysis, and the determination of specific gravities, either Troy weight or the French decimal system is used. When Troy weight is used, the grain is made the unit. MEASURES OF CAPACITY. Wine or Apothecaries' Measure. 60 Drops = 1 Drachm 5. 8 Drachms =: 1 Ounce g. 16 Ounces = 1 Pint. 8 Pints = 1 Gallon = 231 Cubic Inches. The cubic inch of pure water at 62 weighs 252-458 grains, or 16-283 grammes. French Decimal Measure. Litre = 61-025 Cubic Inches. Decilitre = 6-102 Centilitre = 0-610 Millilitre = 0-061 The Litre = 1-056 quart wine measure. MEASURES OF LENGTH. French Decimal System. Metre = 39-371 Inches. Decimetre = 3-937 '* Centimetre = -393 Millimetre = -039 The French Metre is one ten millionth part of the distance, upon the surface of the earth, from the equator to either pole. The Gramme (the unit of weight) is the weight of a cubic centimetre of pure water, at its greatest density. (515) 516 APPENDIX. TABLE showing the Specific Gravity of Liquids, at the Temperature of 65 Fahr.y corresponding to the Degrees of Baumfs Hydrometer. FOR LIQUIDS LIGHTER THAN WATER. Deg. Sp. Gr. 10 = 1-000 11 -990 12 -985 13 -977 14 -970 15 -963 16 -955 Deg. Sp. Gr. 17 = -949 18 -942 19 -935 20 -928 21 -922 22 -915 Deg. Sp. Gr. 23 = -909 24 -903 25 -897 28 '892 27 -886 28 -880 Deg. Sp. Gr. 29 = '874 30 -867 31 -861 32 '856 33 '852 34 -847 Deg. Sp. Gr. 35 = -842 36 -837 37 -832 38 -827 39 -822 40 -817 FOR LIQUIDS HEAVIER THAN WATER. Dug. Sp. Gr. = 1-000 3 1-020 6 1-040 9 1-064 12 1-089 Deg. Sp. Gr. 15 = 1-114 18 1-140 21 1-170 24 1-200 27 1-230 Deg. Sp. Gr. 30 = 1-261 33 1-295 36 1-333 39 1-373 42 1-414 Deg. Sp. Gr. 45 = 1-455 48 1-500 51 1-547 54 1-594 57 1-659 Deg. Sp. Gr. 60 = 1-717 63 1-779 66 1-848 69 1-920 72 2-000 TABLE showing the Quantity of Absolute Alcohol in (100 parts of) Spirits of different Specific Gravities, at 60 Fahr., the spirits being supposed to contain nothing but pure alcohol and pure water. ALCOHOL. 8P. GRAVITY. ALCOHOL. 8P. GRAVITY. ALCOHOL. SP. GRAVITY. 100 0-796 66 0-881 32 0-955 99 0.798 65 0-883 31 0-957 98 0-801 64 0-886 30 0-958 97 0-804 63 0-889 29 0-960 96 0-807 62 0-891 28 0-962 95 0-809 61 0-893 27 0-963 94 0-812 60 0-896 26 0-965 93 0-815 59 0-898 25 0-967 02 0-817 58 0-900 24 0-968 91 0-820 67 6-902 23 0-970 90 0-822 56 0'904 22 0-972 89 0-825 55 0-906 21 0-973 88 0-827 64 0-908 20 0-974 87 0-830 63 0-910 19 0-975 86 0-832 62 0-912 18 0-977 85 0-835 61 0-915 17 0-978 84 0-838 50 0-917 16 0979 83 0840 49 0-920 15 0-981 82 0-843 48 0-922 14 0-982 81 0-846 47 0-924 13 0-984 80 0-848 46 0-926 12 0-986 79 0-851 45 0-928 11 0-987 78 0-853 44 0-930 10 0-988 77 0-855 43 0-933 9 0-989 76 0-857 42 0-935 8 0-990 75 0-860 41 0-937 7 0-991 74 0-863 40 0-939 6 0-992 73 0-865 39 0-941 6 0-993 72 0-867 38 0943 4 0-994 71 0-870 37 0-945 3 0-996 70 0-872 36 0-947 2 0-998 69 0-874 35 0-949 1 0'999 68 0-875 34 '0-951 67 0-879 33 0-953 INDEX. Acetal ; 424 Acetamide 480 Ace-tone...... 427 Acetonitriles 480 Acids, coupled 422 defined 153 metallic 347 vinic 433 Acid, acetic 423 acetous 423 acetonic 459 aconitic 467 adipic 459 aldehydic 423 alloxanic 513 anisic 452 antimonic 366 arsenic 252 arsenious 251 aspartic 479 auric 388 benzoglycocollic 514 benzoic 448 benzylic 449 boracic 283 bromic 219 butyric 359 cacodylic ; 475 campholic ;... 454 camphoric 454 capric 459 caproic 459 caprylic 459 carbolic 451 carbonic 263 cerotic 462 44 Acid, chloric 211 chlorous 210 choleic , 505 cholic 605 chromic 358 cinnamic 451 citraconic 467 citric 467 cobaltocyanic 490 coumaric 454 cyanic 481 cyanuric.... 484 dialuric 513 ethalic 461 - ferric , 355 fluoboracic 283 fluosilicie 280 formic 428 fumaric 468 fulmenic 482 gallic 469 geic 415 glycocollic 514 blppuric 513 humic 415 hydriodic 217 hydrobromic 219 hydrochloric 211 hydrocyanic 484 hydroferrocyanic 487 hydroferridcyanic 488 hydrofluoric 221 hydrofluosilicic 281 hydrosulphocyanic 485 hydrosulphuric 234 hydrotelluric 241 hypochloric 210 (517) 518 INDEX. Acid, hypochlorous 210 hyponitrous 199 hypophosphoric 245 hyposulphuric 225 hypo sulphurous 225 iodic 217 iodous 217 isotinic 471 isotartario 467 itaconitic 467 lactic 511 malic 468 manganic 347 margaric 456, 458 melissic 462 meconic 469 metacetonic 427 metagallic 469 metaphosphoric 247 metatartaric 467 nmcic 411 muriatic 211 myronic 452 nitric 200 nitrous 199 oenanthylic 459 oleic.... 456, 458 oxalic * 466 oxamic 440 palmitic 460 paramaleic 468 paratartaric 467 pectic 411 pelargonic 459 perchloric 211 periodic 217 permanganic 348 phosphoric 246 phosphorous 245 phosphogly eerie 457 pimelic 459 propionic 427 PAQl Acid, propylic 427 Prussic 484 pyrogallic 469 pyroligneous 417, 424 * pyrophosphoric 247 racemic , 467 ricinoleic 460 salicilic 450 salicilous 450 sebacic 459 selenic 240 selenous 240 silicic 279 stannic 363 stearic..... .456, 457 suberic 459 succinic 459 sulpharsenic 253 sulpharsenious 253 sulphethalic , 460 sulphindigotic 477 sulphindylic 477 sulphocarbonic 276 sulphocyanic , 485 sulphogly eerie 457 sulphomethylic 441 sulphovinic 435 sulphuric 228 sulphurous 225 tannic 468 tartaric 466 telluric v 241 tellurous 241 ulmic 415 uric 513 valerianic 431 Acroleine 457 Affinity 158 Agate 279 Air, atmospheric 192 empyreal 174 fixed 263 INDEX. 519 Air inflammable 181 vital 174 Alabaster 335 Aldehyde 422 amylic 431 Albite 342 Albumen 492 Alcargen 475 Alcarsine 475 'Alcohol, acrylic 432 amylic 432 butyric 402, 403 caprylic 460 cerotic 462 melissic 462 methylic 428 phenylic 432, 450 sulphur 432 wine 418 Algaroth, powder of 367 Alizarine 437 Alkali, volatile 202 Allanite 344 Allantoine 513 Allotropism l&T Alloxan 513 Alloxantine 513 Alum 341 Alumina 340 ALUMINUM 339 Amalgams 376 Amber 464 Amides".....- 478 Ammelide 486 Ammeline 486 Ammonia 202 Ammonium 819 Amylene 443 Amygdaline 448 Amylamine 473 Anatase , 373 Anchor ice 29 Aniline 473 Anhydrite v . 335 Animal heat 511 Anisene 452 Anthracite 258, 259 ANTIMONY 365 Aquafortis 201 regia 213 Archil 477 Argol '.... 466 Arrow-root 407 ARSENIC 250 Ashes 259 Asparagine 471, 479 Asphaltum 416 Astatic needle 116 Atmosphere 192 Atomic theory 150 Atoms 14 specific heat of 151 Attraction 14 Aurum musivum 364. Azote... 191 Balloons ; - 184 Balsam, Canada 463 Peru. 451 Tolu 451 Ballistic pendulum 307 Barilla 315 BARIUM 328 Baryta, barytes 328 Batteries, galvanic 92 Bees' -wax , 461 Bell-metal 372 Benzamide 448 Benzene 449 Benzile 449 Benzoine 449 Benzone 449 BERYLLUM 344 Biliary calculi 605 Bile - &0* 520 INDEX Bisethyle PAGE 474 PAGH 4.RO BISMUTH 367 4^4. Black lead 258 471 flux 290 A p. A. 336 Caproine 45fi 4^0 Blonde 359 AK.R 4KQ Blood 501 4AQ Blowpipe ..180, 273 47ft 187 Cartilage 498 41 OKfi Bologna vial... 327 412 Bones .... 499 333 Borax 316 Cerite 344 344 4.91 462 ran y 079 Cetine 460 478 347 Brir>VEX. PAGS 337 338 111 125 113 114 126 114 132 373 479 345 410 410 497 334 43 458 458 369 464 486 486 462 486 432 432 374 427 423 400 109 443 430 472 510 410 347 373 416 370 408 373 373 Likes Lauffhinsr seas Magnetism of earth k Laws of combination . . . . terrestrial Magneto-electric machine LEAD . . extractof sugar of Leather 469, Leaven Mflrhip Loyden jar Light, decomposition of double refraction of Melissine... Mellon theories of Mercaptans , Mercaptides MERCURY, Lithia Metlrylal Milk Lunar caustic Lymph M Madder Molybdenite Magic circle INDEX, 525 Monasite 344 Mordants 476 Morphia, Morphine 469 Mortar 333 Mosaic gold 364 Muscles 498 Myricine 461 Myrosine 452 Myrtle wax 461 N Naphtha 416 Naphthalene 417 Naphthaline r. 417 Narcotine 470 Nascent state 205 Natron 319 NICKEL 365 Nicotine 470 Nitre 305 Nitriles 480 NITROGEN 194 Nomenclature 151 Nutgalls .' 468 Nutrition 508 Ohm's formula 100 Oil of aniseed 452 bitter almonds 448 cinnamon 451 cumin 452 cloves 452 elemi 447 garlic 453 juniper 447 lemons 447 mustard, black 452 pepper 447 peppermint 452 pimento 452 spiraea ulmaria 450 turpentine 446 vitriol 228 PAGB Oil of winter green 451 Oil, castor 460 fusel 430 Oleine 456 Opium 469 Orcine 477 Organic bodies 393 Orpiment 253 Orthite 344 OSMIUM , 391 Oxamide 440 OXYGEN... ,. 174 PALLADIUM 392 Palmatine 460 Pancreatic juice 505 Paracyanogen 481 Paraffine 417 Paramylene 443 Paris green 373 Pearlash 304 Peat 415 Pectine 411 PELOPIUM 374 Pendulum, ballistic , 307 Pepsine 504 Petalite 342 Petroleum 416 Pewter 369 Phenol 450, 417 PHOSPHORUS 241 Photography 70 Photometers 63 Picrotoxine 471 Pinchbeck ,... 374 Piperine , 471 Pitchblende 374 Plasters 463 Plaster of Paris 334 PLATINUM 389 Plumbago 258, 356 Polymerism 157 526 INDEX. Porcelain 342 Potassa, Potash 301 POTASSIUM 298 Potato oil 430 Propione .427 Prussian blue 489 Ptyaline 604 Pulse glass 50 Purple of Cassius 389 Purpurine 477 Pyroacetic spirit 427 Pyrochlore 344 Pyrolusite 347 Pyrometer 27 Pyroxylic spirit 417, 428 Pyroxyline 414 Q Quartz 279 Quercitrine 478 Quicklime 331 Quicksilver 374 Quinia, Quinine 470 K Bain 54 Rats-bane 251 Realgar 253 Red lead 370 precipitate 377 Prussiate of potash 488 Register thermometer 25 Repulsion 13 Resin , 463 Respiration of animals 506 plants 495 RHODIUM 392 Rocelinine >.. 477 Rochelle salt 467 Rock candy 408 Rock oil 466 Rosin 463 Rotation of crops 497 Ruby 340 Rum 421 Rupert's drops 327 RUTHENIUM 892 Rutile 373 S Safety lamp 270 Sago 407 Salseratus 305 Sal-ammoniac 321 mirabile 314 soda 315 volatile j. 321 Salt, common 312 Epsom 338 Glauber's 314 microcosmic 322 rock 312 Salicine 450 Saliva 504 Sandarac 464 Sapphire 340 Scheele's green 255, 373 Sealing-wax 464 Selenite 335 SELENIUM 239 Seneca oil 416 Shells 500 Silica 279 SILICON 278 Silurus electricus 101 SILVER 381 Smalt 364 Smaltine 364 Soap 456, 462 Soda 311 ash 315 fountains 265 SODIUM 310 Solder , 369 hard... .. 372 INDEX. 527 Solar spectrum 63 Soluble glass 280 Spathic iron 356 Specific gravity of atoms 151 Specular iron 349 Speculum metal 372 Spelter 360 Spermaceti 460 Spheroidal state of liquids...:.. 61 Spinelle 340 Spirit of hartshorn 202 Mindererus 426 turpentine 446 salt 211 wine 420 Spirit-lamp 421 Spodumeme 318, 342 Springs, sulphur 235 Stalactites 334 Stalagmites 334 Stanethyle 474 Starch, 405 Steam 43 Stearine 456 Stearoptens 446 Steel 353 Stereotype plates 335 Stibethyle 474 Stibium 365 Strichnia, Strichnine 471 *Strontia 330 STRONTIUM. 330 Styrax 451 Styrole 451 Substitution 400 Sugar, barley 408 cane 408 diabetic 409 grape 409 milk 410 of lead 425 of sour fruits,... .. 410 Sulphoform 442 SULPHUR 222 springs 235 Symbols 155 Synaptase 448 Sympathetic ink 364 T Tallow, bayberry 461 Tangential force 114 Tannin 468 Tantalite 374 TANTALUM 374 Tapioca 407 Tar 463 coal 417 Tartar 466 cream of *.. 467 emetic 467 Telegraph, electro- magnetic 133 TELLURIUM 240 TERBIUM 344 Terrestrial magnetism 114 Theine 471 Thermography 73 Thermometers ... 22 Thorina 344 Thorite 344 THORIUM 344 TIN 272 Tincal 816 TITANIUM 873 Tombac 372 Tonka bean 454 Torpedo 101, 484 Treacle 408 Trona 315 Troostite 373 TUNGSTEN 373 Turmeric root 478 Turnbull's blue 489 Turpentine, spirits of 446 528 INDEX. Turpentine, oil of 446 Turpeth, mineral. 380 Turnsol 477 Type metal 369 Ulmine 415 Upas 471 Uranite 374 URANIUM 374 Urea 482, 512 Urine... .. 512 Valeronitrile 480 VANADIUM 373 Vanilla 454 Vaporization 40 Verdigris , 426 Verditer, green 377 Vermillion.... ,,, 380 Vial, Bologna. 327 Vinegar 423 Vinous fermentation 418 Viscous " 511 Vita, air 174 Vitality 14, 394 Vitriol, blue 373 green 356 white 361 oil of 228 Volatile alkali 202 Voltaic pile 92 w Water 185 constitutional 296 of crystalization 159, 296 lime 331 Wax, bees* 461 myrtle 461 Whiskey, 421 White lead 376 Witherite 329 Wine 466 Wolfram 373 Woody fibre 413 Wood 411 Wood naphtha 428 spirit 428 vinegar 424 Xanthine 477 Xyloidine 414 Yeast .418 Yellow prussiate of potash 487 chrome 359 king's 253 YTTRIUM 344 Zaffre 364 ZINO 359 Zincethyle 474 Zircon 344 ZIRCONIUM 344 Zirconia 344 THE END. THIS BOOK IS DUE ON THE LAST DATE STAMPED BELOW AN INITIAL FINE OF 25 CENTS WILL BE ASSESSED FOR FAILURE TO RETURN THIS BOOK ON THE DATE DUE. THE PENALTY WILL INCREASE TO 5O CENTS ON THE FOURTH DAY AND TO $1.OO ON THE SEVENTH DAY OVERDUE. NO V 1 ft 1 cnr '*uv dre lyju SEP 20 S94o rTM MAR 23 1946 MA\/ s ft 1Q66 !E nuv o VJ ijsuv 1 BUib-ee * c & LD 21-100m-8,'34 ~T*'