Class Book 0& •% Elements thus marked are both physically and chemically non- metallic. •£• Elements which exhibit some of the physical properties of metals but which resemble the non-metallic elements in their chemical behavior. + Elements which are both physically and chemically metallic in their properties and behavior. Elements which are not known to enter into any chemical com- bination are printed in italics. Approximate Common Name. Latinic Name. Symbol. Relative Weight of the Atom. (Atomic Weight.) Aluminum + Aluminum Al 27 Antimony •>£• Antimonum or Stibium Sb 120 Argon Argonum A 39? Arsenic •>& Arsenum As 75 Barium + Barium Ba 137 Beryllium + Beryllium Be 9 THE CHEMICAL ELEMENTS 47 TABLE OF THE CHEMICAL ELEMENTS— Continued. Common Name. Latinic Name. Symbol.. Approximate Relative Weight of the Atom. (Atomic Weight.) Bismuth + , Boron 2g •><• Bromine •% •*• Cadmium + Csesium + Calcium + Carbon ■% •>£ Cerium + Chlorine ■& •% Chromium + Cobalt + Columbium + Copper + Erbium + Fluorine ■*■ %• Gallium + Germanium + Gold + Helium Hydrogen •}& •>£• Indium + Iodine $£■ •& Iridium + Iron + Krypton Lanthanum + Lead + Lithium + Magnesium + Manganese + Mercury + Molybdenum + Neodymium 4 Neon Nickel + Nitrogen •& •& Osmium + Oxygen •)£ •)£ Palladium + Phosphorus -)j$ •*• Platinum + Pollonium + Potassium + Praseodymium + Bismuthum Borum Bromum Cadmium Csesium Calcium Carboneum Cerium Chlorum Chromium Cobaltum Columbium Cuprum Erbium Fluorum Gallium Germanium Aurum Helium Hydrogenium Indium Iodum Iridium Ferrum Kryptum Lanthanum Plumbum Lithium Magnesium Manganum Hydrargyrum Molybdenum Neodymium Neum Niccolum Nitrogenium Osmium Oxygenium Palladium Phosphorus Platinum Pollonium Potassium or Kali Praseodymium Bi B Br Cd Cs Ca C Ce CI Cr Co Cb Cu Er F Ga Ge Au He H In I Ir Fe Kr La Pb Li Mg Mn Hg Mo Nd Ne Ni N Os O Pd P Pt Po K Pr 208 11 80 112 133 40 12 140 35.5 52 59 94 63.5 166 19 70 72 197 4 1 114 126.5 193 56 82 138 207 7 24.5 55 200 96 143 20 58.5 14 191 16 106 31 195 ? 39 140.5 48 A CORRESPONDENCE COURSE IN" PHARMACY TABLE OF THE CHEMICAL ELEMENTS— Continued. Approximate Common Name. Latinic Name. Symbol. Relative Weight op the Atom. (Atomic Weight.) Radium + Radium Ra 227 Rhodium + Rhodium Rh 103 Rubidium -f Rubidium Rb 85.5 Ruthenium + Ruthenium Ru 101.5 Samarium + Samarium Sm 150 Scandium + Scandium Sc 44 Selenium %< •>£ Selenium Se 79 Silicon j& 5& Silicium Si 28.5 Silver + Argentum Ag 108 Sodium + Sodium or Natrium ' Na 23 Strontium + Strontium Sr 88 Sulphur •% X Sulphur S 32 Tantalum + Tantalum Ta 183 Tellurium $£ Tellurium Te 127 Terbium + Terbium Tb 160 Thallium + Thallium Tl 204 Thorium + Thorium Th 233 Tin + Stannum Sri 118.5 Titanium + Titanium Ti 48 Tungsten + Wolframium W , 184 Uranium + Uranium U 240 Vanadium + Vanadium V 51.5 Xenon Xenum X 128 Ytterbium + Ytterbium Yb 173 Yttrium + Yttrium Yt 89 Zinc + Zincum Zn 65.5 Zirconium + Zirconium Zr 90.5 All the elements marked with 5K- or with X % can combine directly with hydrogen. They are chemically non-metallic elements. Elements marked + do not combine directly with hydrogen, although some of them form alloys with it. Neon, argon, krypton and xenon are gaseous elements recently discovered in the atmosphere; all efforts so far made to cause these elements to enter into chemical combination with any other elements have been unsuc- cessful. Oxygen and fluorine combine with hydrogen but not with each other. All elements can be directly united to oxygen THE CHEMICAL ELEMENTS 49 except fluorine and the four elements named in the preced- ing paragraph. 123. State of Cohesion of the Elements. All of the ele- ments enumerated in the preceding table are solids at ordinary temperatures, with the following exceptions : Mer- cury and bromine are liquids; argon, chlorine, fluorine, helium, krypton, neon, nitrogen, oxygen, xenon and hydro- gen are gases. 124. Colors of the Elements. The metals are generally opaque and white with or without a hue of grayish, bluish or reddish; but gold is yellow, barium and calcium are yellowish, copper is reddish. Bismuth displays variegated hues of purplish, while its general color is reddish-white. Of the non-metallic elements boron is black; carbon is either black, as in coal and graphite, or colorless, as in diamond; iodine is purplish-black; phosphorus is a White waxy substance or a dark red powder; selenium, red or black; silicon, brown or gray; sulphur, pale yellow, amber, dark brown, or nearly milk-white; bromine is a brown-red liquid; hydrogen, oxygen, nitrogen, argon, krypton, neon and xenon are colorless gases; chlorine is a greenish gas; and fluorine greenish-yellow. 125. Luster. All the metals possess a peculiar luster which in many cases can be greatly heightened by polishing. The only non-metallic elements that have a luster approach- ing that of metals are iodine in crystals and carbon in the form of graphite. The luster of the diamond is quite different from and far surpasses that of the metals. 126. The non-metallic elements never possess tenacity, ductility or malleability. Most of the metals exhibit one or the other of those properties. 127. Density. The specific weights of the five metals called lithium, sodium, potassium, rubidium and cassium range from 0.6 to 1.5; those of the metals called beryllium, 50 A CORRESPONDENCE COURSE IN PHARMACY magnesium, calcium, strontium and barium from 1.6 to 4; and those of the metals aluminum, scandium, yttrium, titan- ium and zirconium from 2.5 to 4. The specific weights of all other metals are higher than 5, ranging from 5.5 to 22.42. The specific weights of all physically non-metallic elements are below 5. 128. Fusibility. All metals are fusible. Of the non- metallic elements one is liquid and ten are gases. Sulphur, selenium, phosphorus and iodine are readily fusible. Carbon, boron and silicon are infusible. 129. Volatility. Of the physically metallic elements only mercury, potassium, sodium, magnesium, zinc, cadmium and arsenic may be readily distilled; and antimony and tellu- rium can be distilled with a current of hydrogen. The non-metallic elements that are not gaseous at ordinary temperatures can all be readily vaporized except carbon, boron and silicon. 130. Solubility in common solvents. All metals are absolutely insoluble in water, alcohol, ether, chloroform, glycerin, benzin, carbon disulphide, volatile oils and fixed oils. Chlorine and iodine are slightly soluble in water ; bromine more so. Iodine is soluble in alcohol, glycerin, chloroform, liquid hydrocarbons, carbon disulphide, volatile oils and fixed oils. Phosphorus is soluble in chloroform, ether, absolute alcohol, carbon disulphide and fixed oils. Sulphur dissolves in chloroform, benzine, carbon disulphide, oil of turpentine and fixed oils. 131. Metals are usually good conductors of heat and of electricity. The non-metallic elements are very feeble con- ductors. 132. Chemical behavior of metals and non-metals. The metals form various solutions and alloys with each other. Gold and several other metals dissolve in mercury at ordinary THE CHEMICAL ELEMENTS 51 temperatures. Many metals can be dissolved in each other when melted. Sometimes the combinations effected may be crystallizable bodies containing the component metals , in definite proportions corresponding to their atomic weights. But these combinations or alloys are decidedly metallic, retaining in a high degree the characteristics of the metals of which they are constituted. Hence it may be concluded that the combinations formed by the metals with each other are not true chemical compounds, but only solutions. The compounds formed by non-metallic elements with each other or with metals are strikingly different. They are countless, and they rarely resemble in any respect or degree their component elements. Thus the reddish metal copper combines with the colorless gas oxygen, forming a black powder called copper oxide; the brilliant, silver-white, liquid metal mercury combines with the colorless oxygen to form a red, or yellow, or black oxide, and with yellow sulphur to form a red or a black sulphide ; sulphur combined with its own weight of oxygen forms a colorless gas of an irritating odor, but with one and one-half times its weight of the gaseous oxygen it forms an odorless white solid; the three colorless gases nitrogen, hydrogen and oxygen form a white solid called ammonium nitrate; and the elements carbon, hydrogen, oxygen and nitrogen form innumerable compounds of a great variety of properties. Test Questions It will probably not be necessary for us to call your attention again to the form of your paper. Let it be understood that unless you are specifically directed to change your plan, you are to continue in that which has been prescribed for you. If the questions seem to call for any explanation, you will find that explanation at the beginning of the questions. 1. About how many metals are known and about how many non-metallic elements ? 52 A CORRESPONDENCE COURSE IN PHARMACY 2. What are the symbols for lead, antimony, mercury, potassium, silver, sodium and tin ? 3. What is the difference between a chemically metallic element and a chemically non-metallic element ? 4. Mention six elements which at ordinary temperatures are gases. 5. What elements are liquid at ordinary temperatures ? 6. Mention the most striking- physical properties by which metals differ from non-metallic elements. 7. Do you know of any non-metallic elements having specific weights between 6 and 10 ? 8. Can you mention some non-metallic elements which are not fusible ? 9. Mention some that are not volatile. 10. Are any of the metals soluble in each other, and if so, what are such solutions called ? 11. How many of the metals combine chemically with oxygen ? How many of them combine with hydrogen ? 12. How many of the non- metallic elements combine with oxygen and how many of them with hydrogen ? LESSON FIVE To the Student: Considerable attention has been given in this lesson and others that follow to elaborating for you the course of reasoning by which certain laws were established. It is thought that everything has been made sufficiently clear, but it is too much to expect that you will be able to follow the reasoning at first reading. We expect that you will have to go many times over the text, until not only the words become familiar to you in their meaning, but the trend of thought becomes as natural to you as it is to the writer. Do not forget your dictionary or the treatment of corresponding subjects in the school text-books. All will help you to a clearer understanding of the text. VII Definite Combining Proportions and the Atomic Hypothesis 133. Proust pointed out that all chemical compounds contain their component elements in fixed and invariable proportions. The following examples illustrate this : a, 1 gram of hydrogen unites with 16 grams of oxygen to form the compound called hydrogen dioxide, commonly known as peroxide of hydrogen. These proportions can- not be altered. And a mass of 17 grams of hydrogen dioxide always consists of 1 gram of hydrogen and 16 grams of oxygen. A 2-gram mass of hydrogen unites with a 16 -gram mass of oxygen to form the compound called water. And all water, wherever found or however produced, when de- composed yields hydrogen and oxygen in the proportion 53 54 A CORRESPONDENCE COUKSE IN" PHARMACY of 1 part of the first named to 8 parts of the other element. 1). 1 gram of hydrogen unites with 35.5 grams olthe element called chlorine to form 36.5 grams of hydrogen chloride, commonly called hydrochloric acid gas. In the following table are given in grams the combining proportions of several different elements and the product obtained from the combination. Eead from left to right, the first and third columns give the names of the elements ; the second and fourth, their combining weights; the fifth, the name of the product ; and the sixth, the weight of the product. The horizontal lines separate the compounds into related groups : Element No. OF Grams Element No. OF Grams Product Grams in Product Nitrogen Nitrogen Nitrogen Nitrogen Nitrogen Nitrogen 14 2x14 14 2x14 2x14 2x14 Hydrogen Oxygen Oxygen Oxygen Oxygen Oxygen 3 16 16 3x16 2x16 5x16 Hydrogen Nitride (Ammonia) Hyponitrous oxide Mononitrogen mon- oxide (nitrosyl) Nitrogen trioxide Nitrogen peroxide Nitrogen pentoxide 17 44 30 76 60 108 Nitrogen 14 Chlorine 3x35.5 Nitrogen trichloride 120.5 Manganese 55 Chlorine 2x35.5 Manganous chloride 126 Manganese Manganese Manganese 55 2x55 55 Oxygen Oxygen Oxygen 16 3x16 2x16 Manganous oxide Manganic oxide Manganese dioxide 71 158 87 Carbon Carbon 12 12 Oxygen Oxygen 16 2x16 Carbon monoxide (Carbonyl) Carbon dioxide 28 44 Carbon 12 Hydrogen 4x1 Methane (marsh gas) 16 Carbon 12 Sulphur 2x32 Carbon disulphide 76 Sulphur Sulphur 32 32 Oxygen Oxygen 2x16 3x16 Sulphur dioxide Sulphur trioxide 64 80 Sulphur 32 Manganese 55 Manganese sulphide 87 PKOPOKTIOtfS AND THE ATOMIC HYPOTHESIS 55 Element No OF Grams Element No. OF Grams Product Grams in Product Sulphur 32 Mercury 200 Mercuric sulphide 232 Mercury Mercury 200 2x200 Oxygen Oxygen 16 16 Mercuric oxide Mercurous oxide 216 416 Mercury Mercury 200 200 Chlorine Chlorine 35.5 2x35.5 Mercurous chloride Mercuric chloride 235.5 271 Sulphur 32 Chlorine 4x35.5 Sulphur tetrachlo- ride 174 Carbon 12 Chlorine 4x35.5 Carbon tetrachloride 154 From the foregoing facts, which have been determined by repeated experimentation, it appears that the relative com- bining masses of the several elements are simple multiples of definite values. The relative combining mass of hydrogen is 1 or a multiple of it. oxygen is 16 chlorine is 35.5 nitrogen is 14 manganese is 55 carbon is 12 sulphur is 32 mercury is 200 These comparisons might be extended to include every chemical compound known, with the same results — definite combining proportions by weight of all the different elements in all the compounds which they severally form with one another. 134. The combining proportions of hydrogen and chlorine whenever they unite to form hydrogen chloride are invariably as 1 part of hydrogen to 35.5 parts of chlorine, or 35.5 times as much chlorine as hydrogen by weight. Hydrogen and chlorine cannot be made to combine in any other pro- portions. And if a mass of 36.5 kilograms of hydrogen chloride be decomposed it will give 1 kilogram of hydrogen and 35.5 kilograms of chlorine. 56 A CORRESPONDENCE COURSE IN PHARMACY 135. Two hypotheses were formulated by John Dalton to express the definite combining proportions of the elements as exemplified in the preceding paragraphs : A. The Law of Definite Proportions. — Any given chemical compound always contains the same component elements and in the same mass proportions. B. The Law of Multiple Proportions. — Whenever any two elements unite with each other in more than one mass pro- portion, simple multiples of a fixed mass unit of either unite with a fixed mass unit or with multiples of a fixed mass unit of the other element. Any two compounds containing the same two elements but in different proportions have different properties and are differ- ent compounds. When the compound contains more than two elements the proportions are also equally simple and definite. 136. The Atomic Hypothesis. Dalton explained the definite combining proportions of the elements by adopting the ancient hypothesis that all matter is composed of indivisi- ble individual particles, and by assuming that all such parti- cles of any one element have the same mass but that the particles of one element have a different mass from that of the particles of any other element: Each element consists of indivisible atoms of fixed mass. 137. If this atomic hypothesis be accepted as true, then the fixed chemical combining proportions by weight are thereby explained and seen to be the inevitable result of the fixed atomic masses. If, on the other hand, the atomic theory be rejected, then the fixed combining weights of the elements remain unintelligible, for no other sufficient explanation thereof has yet been made. The atomic hypothesis is a lucid and reliable working theory, and the system of chemistry built upon it leads to fixed results which may be expected and realized with absolute certainty and uniformity. PROPORTIONS AKD THE ATOMIC HYPOTHESIS 5? All known facts of chemistry agree with the atomic theory. 138. Atomic Weight. The numbers expressing the rela- tive masses of the atoms of different elements are called their atomic weights. The unit of expression of atomic weights is the mass of the hydrogen atom. The specific atomic weight of hydrogen is, therefore, 1 and that of oxygen is 16, because an atom of oxygen weighs 16 times as much as an atom of hydrogen. The atomic weight of chlorine is 35.5; that of nitrogen is 14; that of manganese is 55; that of carbon is 12; that of sulphur is 32; and that of mercury is 200. The atomic weights are the smallest relative masses of ele- ments that can enter into chemical combination with other elements. A table of the elements and their atomic weights was given in Lesson Four, VI, paragraph 122. 139. Molecular Weight. As all molecules consist of atoms and as all atoms have fixed masses, it follows that the mole- cule of any given element or chemical compound must also have a fixed mass, which is the sum of the masses of the atoms contained in it. A few elemental molecules consist of single atoms, and the molecular weight of any element having monatomic molecules is of course identical with its atomic weight. The molecule of hydrogen consists of two atoms of hydro- gen. Hence, as the atomic weight of hydrogen is 1, its molecular weight is 2. A molecule of ordinary oxygen contains two atoms. Hence, as the atomic weight of oxygen is 16, its molecular weight is 32. But there is another form of oxygen called ozone, each molecule of which consists of three oxygen atoms ; the molecular weight of ozone is, therefore, 48. The molecule of water contains two atoms of hydrogen and one atom of oxygen; the molecular weight of water is accordingly 18. 58 A CORRESPONDENCE COURSE IN PHARMACY 140. Vapor Densities. The specific weights of all gases and vapors are expressed in nnits of the density of hydrogen. The specific weight of hydrogen in the gaseous state, or its vapor density, is 1. The vapor density of any other gas or vapor is the quotient obtained when the weight of any given volume of it is divided by the weight of the same volume of hydrogen. One liter of hydrogen at 0° 0. weighs 0.09 gm. ; one liter of oxygen at 0° C. weighs 1.43 gm. ; a liter of chlorine at 0° C. weighs 3.17 gm. ; and a liter of nitrogen at 0° 0. weighs 1.26 gm. Hence, as the vapor density of hydrogen is 1, that of oxygen must be 16, that of chlorine must be 35.5; that of nitrogen 14. These numbers coincide with the atomic weights ; we shall presently learn why. 141. Avogadro's Law. Equal volumes of all gases or vapors at the same temperature and under the same pressure contain the same number of individual particles of matter.* Now, as the vapor density of hydrogen is 1 and its atomic weight also 1, and as its molecule contains two atoms so that its molecular weight is 2, we see that its molecular weight is twice its vapor density. The vapor density of oxygen is 16, for one liter of it weighs 16 times as much as one liter of hydrogen at the same temperature and pressure. The molecular weight of oxygen is 32, for its molecule contains two atoms and its atomic weight is 16. Hence the molecular weight of oxygen is twice its vapor density, just as the molecular weight of hydrogen is twice the vapor density of that element. The vapor density of ozone, however, is not 16 but 24. Why ? Because each individual particle or molecule of ozone consists of ♦This hypothesis is usually expressed as follows: "Equal volumes of all gases contain the same number of molecules." But this statement is incon- sistent with the definition of the term molecule (IV, par. 68), which refers to the smallest particle of any kind of matter, as the molecule. PROPORTION'S AND THE ATOMIC HYPOTHESIS 59 three atoms of oxygen, and as equal volumes of all gases contain the same number of individual particles of matter, each individual particle of ozone must weigh 24 times as much as each individual particle of hydrogen, and as each particle or molecule of hydrogen weighs 2, since it consists of 2 atoms, the individual particle or molecule of ozone must weigh 48 and must consist of three atoms of oxygen. It is true that, in a way, a molecule of ozone is a triatomic molecule of oxygen; it contains only oxygen. But the molecule of oxygen is diatomic, and the molecular weight of oxygen is 32. Below 500° C. the vapor of iodine weighs 126.5 times as much as the same volume of hydrogen at the same temper- ature and pressure. Hence that iodine vapor must consist of diatomic particles, or particles consisting of two atoms each. But at 1700° the vapor of iodine has a density of only 63.25, or weighs only 63.25 times as much as an equal volume of hydrogen at the same temperature and pressure; this iodine vapor at 1700° 0. must accordingly consist of particles weighing only half as much as the par- ticles of iodine vapor below 500° 0. Therefore, the particles of iodine at 1700° must contain only one atom each instead of two. The question may then be asked: is the diatomic particle of iodine its molecule, or is the mon- atomic particle its molecule ? The answer must be that the molecule of iodine is its atom, and that the molecular weight of iodine is identical with its atomic weight, for the monatomic particles of iodine are the smallest particles of that element exhibiting the specific properties by which the individuality of iodine is determined. Ferric chloride is a chloride of iron composed of iron and chlorine in the proportion of 56 parts of iron to 106.5 parts of chlorine. Its vapor at temperatures below 700° weighs 162.5 times as much as the same volume of hydrogen; this 60 A CORRESPONDENCE COURSE IN PHARMACY corresponds to the formula Fe 2 Cl 6 , and the weight of each particle must be 325. But the vapor of ferric chloride at 1000° C. weighs only 81.25 times as much as hydrogen, which proves that the individual particles of the compound at that temperature must consist of FeCl 3 . The molecule of ferric chloride is, therefore, now represented as FeCl 3 and the molecular weight is given as 162.5. It was formerly represented as Fe 2 Cl 6 and its molecular weight was then, of course, put down as 325. It would be confusing to recognize two different molecules and two different molecular weights. The smaller particle is then adopted as the molecule. The double molecule Fe 2 01 6 may be represented as (FeCl 3 ) 2 . 142. Gay-Lussac's Proposition. — Gaseous elements combine in simple volume proportions, and the volumes of the products hear simple relations to the volumes of the component elements. This conclusion is self-evident from the law of Avogadro and Dalton's laws of combining proportions by weight. One liter of hydrogen and 1 liter of chlorine combine to form 2 liters of hydrogen chloride, because the molecules of hydrogen, chlorine and hydrogen chloride are all diatomic, or contain two atoms each. One liter of oxygen and 2 liters of hydrogen combine to form 2 liters of water vapor, because while the molecules of hydrogen and oxygen contain two atoms each, the molecule of water contains three atoms (=HOH), or is triatomic. Three liters of hydrogen with 1 liter of nitrogen must produce only 2 liters of ammonia, H 3 N, because while the hydrogen and nitrogen molecules are diatomic the molecule of ammonia contains four atoms, or is tetratomic. 143. Specific Heat. The relative quantity of thermal energy (heat) required to raise the temperature of a given mass of any substance one degree is called the specific heat of that substance. The specific heat of water is the unit in which the specific PROPORTIONS AND THE ATOMIC HYPOTHESIS 61 heat of any other substance is expressed. Therefore the specific heat of water is 1, and it signifies the quantity of heat energy required to raise the temperature of one weight unit of water one degree. The specific heat of mercury is 0.0319, because only yMff o as much heat energy is required to raise the temperature of mercury one degree as is necessary to raise the temperature of an equal quantity of water one degree. 144. The Law of Dulong and Petit. — All atoms have the same capacity for heat. This means that it requires exactly the same amount of heat energy to raise the temperature of any atom of any kind one degree. The specific heat of any element is inversely as its atomic Weight. The product obtained by multiplying the atomic weight of any element by its specific heat is a constant number ; it is approximately 6.4, and that number is called the atomic heat. Hence when 6.4 is divided by the specific heat of any element the quotient must be approximately the atomic weight of that element. The atomic weight of any element can, therefore, be approximately deduced from or verified by its specific heat. [6.4 -*- 0.0319=200.] 145. Neumann and Regnault proved that the specific heats of compounds are inversely proportional to their molecular weights (just as we have seen that specific heats of elements are inversely as their atomic weights). The sum of the atomic heats of the atoms of any molecule is the molecular heat of that molecule. Hence, when the molecular heat of any substance is divided by 6.4 the quotient is the number of atoms contained in the molecule, whether elemental or compound. Molecular weights can, therefore, be deduced from or verified by the specific heats of substances. 62 A CORRESPONDENCE COURSE IN PHARMACY 146. There are, furthermore, other methods by which molecular weights can be verified. These methods would be wholly out of place in elementary lessons like these, but their existence is referred to simply to indicate that the atomic theory is amply confirmed by many facts in chemical physics which have been discovered and demonstrated independently of one another and of the atomic hypothesis itself. * Test Questions In general, it is not expected that you will refer to your text in the preparation of your answers to Test Questions. We have indi- cated some things that should be committed to memory. Other things should be thoroughly understood. At the same time there may be occasions when the use of your text is almost necessary in the solution of problems. You may not remember, for instance, the numbers which are necessary. Under such circumstances you are at liberty to refer to the text of your lesson, but should never do so for principles and laws. If you know and understand a law you can apply it. The purpose of these test questions is to see whether you know and do understand. If you deceive us, even unintentionally, you suffer the consequences, for, unless you are per- fectly fair with us, we cannot give you the assistance we should like to render. It is what you know, not what you can take from a book, that we wish to determine. If your papers are not fairly prepared, you lose the best part of that for which you paid when you enrolled in the School. 1. If a given chemical compound consists of carbon and oxygen and the carbon in it weighs 6 grams, what will be the weight of the oxygen ? * The atomic hypothesis is subject to doubt and controversy, because recently observed facts would seem to prove that atoms are not indivisible. But even if it should be conclusively demonstrated that the atoms are divisible into still smaller particles (" electrons"), the facts upon which the atomic theory is based will, of course, remain unaltered, the atomic weights will be as real as ever, our conception of the atomic structure of molecules will not be materially changed, and the truth of the law of Dulong and Petit will not be shaken. New discov- eries concerning the structure of matter may modify the atomic hypothesis and render it clearer, but will not destroy it. PK0P0KTI0NS AND THE ATOMIC HYPOTHESIS 63 2. How much sulphur can be held in combination by 50 grams of mercury ? 3. How much chlorine can be held in combination by 27. 5 grams of manganese ? 4. How much chlorine can be held in combination by 7 grams of nitrogen ? 5. If a mass of 108 grams of a compound of mercury and oxygen be decomposed into its constituent elements, how much will the mercury weigh and how much will the oxygen weigh ? 6. Formulate the laws of Dalton concerning chemical combining proportions. 7. What is the atomic theory ? 8. How does it explain the law of multiple proportions ? 9. What is the molecular weight of any substance? 10. What would you call the minimum relative mass of any element capable of chemical combination with other elements ? 11. If the atomic weight of chlorine is 35.5, what is its molecular weight, assuming that its molecules are diatomic ? 12. What would be its molecular weight if the molecules are monatomic ? 13. If the vapor-density of mercury is 200, what is its atomic weight, assuming that the molecule of mercury contains half as many atoms as are contained in the molecule of hydrogen? 14. What is Avogadro's law ? 15. Is the smallest individual particle of any kind of matter capable of independent existence necessarily the molecule ? 16. If the vapor-density of any given gas is twice as great at 500° as at 1000°, what does that difference indicate ? 17. If a certain gas when heated to 2000° doubles in volume, how do you explain that expansion ? 64 A CORRESPONDENCE COURSE IN PHARMACY 18. Can any gas be increased in volume by an increase of temperature without a division of its molecules ? If so, what rate of expansion is possible ? 19. State the proposition of Gay-Lussac. 20. If you cause 3 liters of oxygen to enter into chemical combination with 6 liters of hydrogen, what will be the compound formed, and how many liters will you obtain of the compound in the" state of vapor ? Why ? 21. State the law of Dulong and Petit. 22. Define specific heat. 23. If you divide the atomic weight of an element by 6.4, what is the relation of the quotient to the specific heat of that element ? 24. How can the molecular weight of any substance be verified by its specific heat ? 25. How can the molecular weight of any substance be verified by its vapor-density ? LESSON SIX To the Student: In this lesson, particularly in the Test Questions, you will find compounds named by abbreviated formulas as a more convenient method than by the full name. From the table of elements given in Lesson Five you learned the symbols of the separate elements. The symbol alone is supposed to represent one atom; thus, H indicates one atom of hydrogen; O, one atom of oxygen. If a small Arabic numeral is placed at the right and a little below this letter, it indi- cates the number of atoms; as, H 2 means two atoms of hydrogen; 2 , two atoms of oxygen. Water is composed of two atoms of hydro- gen and one atom of oxygen, so the formula H 2 names water and indicates also its molecular composition. H 2 S0 4 means two atoms of hydrogen combined with one of sulphur and four of oxygen. The compound is sulphuric acid. Bearing these facts in mind, you will have no difficulty in understanding the formulas used in this lesson. A fuller explanation will be made to you later. VIII Chemical Polarity 147. Positive and Negative Elements. Metals and hydrogen resemble each other in their chemical behavior. They can take each other's places in many kinds of molecules without radical changes of their general character and structure. No truly metallic element forms any truly chemical com- pound by direct union with hydrogen. All truly non-metallic elements do form chemical com- pounds with hydrogen. Water is a compound of hydrogen and oxygen. Hydrogen and oxygen are essentially chemical opposites. The most decidedly typical metals, chemically considered, 65 66 A CORRESPONDENCE COURSE IN PHARMACY are the alkali metals — caesium, rubidium, potassium, sodium and lithium. These metals take the oxygen away from water. The most decidedly typical non-metallic elements are fluorine, chlorine, bromine and iodine. These take the hydrogen away from water. When water is decomposed by an electric current, the hydrogen collects at the negative pole of the battery and the oxygen at the positive pole. Hence, as opposites attract each other while likes repel each other, hydrogen is called a positive element and oxygen a negative element. When a metallic compound is decomposed in a solution, the electric current causes the metal to be collected at the negative pole and the non-metallic element (or the group of non-metallic elements with which the metal was in chemical combination) is collected at the positive pole. Hence, all true metals are called positive elements, and the non-metallic elements are negative elements as compared with hydrogen and the metals. But while the metals and hydrogen are invariably positive in relation to all other elements, and while oxygen and fluorine are invariably negative in relation to all other ele- ments, the elements boron, carbon, silicon, nitrogen, phosphorus, arsenic, antimony, sulphur, selenium, tellurium, chlorine, bromine and iodine are negative toward the metals and hydrogen, but positive toward oxygen and fluorine. 148. Chemical Polarity. By this term is meant the opposite qualities of elements entering into direct combination with each other. No two elements enter into direct combination unless they are of opposite qualities with respect to each other. Only a positive element can enter into direct combination with a negative element, and vice versa. 149. Fluorine, chlorine, bromine and iodine have a greater affinity for hydrogen than for oxygen. In fact, fluorine CHEMICAL POLARITY 67 does not enter into combination with oxygen at all, and the other three elements named have but a feeble inclination to combine with oxygen to form certain compounds called salts, in which they are directly united to oxygen, which links them indirectly to positive elements, and these salts, called chlorates, bromates, iodates, perchlorates, periodates, hypochlorites and hypobromites, are all comparatively unstable compounds. Chlorine and iodine are the only two of these four elements that form any oxides. 150. In III, par. 106, it was stated that certain compounds in solution in water undergo dissociation or are split up into two ions, the positive ion or kation and the negative ion or anion. This kind of decomposition or dissociation is called electrolysis, and the compounds capable of electrolysis are called electrolytes. The positive electrode of an electrical battery is called the anode and the negative electrode is called the katode. When an electrolyte in solution is dissociated into its two ions and a galvanic current is passed through the solution, the positive ion or kation is collected at the katode and the negative ion or anion is collected at the anode. Water cannot be decomposed by the galvanic current except after adding to it some substance to act as a con- ductor. Sulphuric acid is used for that purpose. The water can then be decomposed by the electric current, with the result that the hydrogen of the water is invariably collected at the negative pole and the oxygen at the positive pole. When the chloride of any metal or of hydrogen is dissociated, the metal or the hydrogen is the positive ion and the chlorine is the negative ion. When potassium chloride, composed of potassium and chlorine, is dissociated, the potassium constitutes the posi- tive ion and the chlorine constitutes the negative ion. 68 A CORRESPONDENCE COURSE IN PHARMACY When potassium chlorate, composed of potassium, oxygen and chlorine, is dissociated, potassium again alone constitutes the positive ion, but the oxygen and chlorine together con- stitute the compound negative ion. 151. Omitting the elements that do not form any chemical compounds (neon, argon, krypton and xenon), and omitting all invariably positive elements (hydrogen and the metals), and the two invariably negative elements (oxygen and fluorine), we find that thirteen non-metallic elements re- main which are capable of exercising either positive or negative polarity, or both concurrently. A part of the valence of an atom of carbon, or of nitrogen, or of phos- phorus, or of sulphur, may be negative and the remainder positive. Whenever any one of the thirteen elements, chlorine, bromine, iodine, sulphur, selenium, tellurium, nitrogen, phosphorus, arsenic, antimony, carbon, silicon and boron, is in direct combination, with hydrogen or with a metal it must be negative ; it is positive whenever it is in combination with oxygen or fluorine. Whenever any two of the thirteen elements named are in combination with each other, then the one named first in the list is negative toward the one named after it. This order is determined by the relative positions of the elements in the periodic system or, in other words, by their respective atomic weights and valences. Thus, chlorine is negative toward all the other twelve, so that every binary compound* of chlorine is a chloride except its compounds with fluorine or with oxygen, and as the combining value of the negative element in any of its binary compounds is invariably the same, the combining value of the chlorine in every chloride is 1. * A " binary compound " is composed of but two .elements. CHEMICAL POLAEITY 69 Bromine is negative toward any one of the eleven elements named after it, but positive toward chlorine, fluorine and oxygen. Hence, every binary compound of bromine must be a bromide except its compounds with chlorine or fluorine.* Fluorides and chlorides of bromine can never contain more than one bromine atom, because negative chlorine and fluorine always have the combining value of 1. Iodine is positive toward chlorine and bromine, but negative toward the other ten elements capable of varying polarity. Iodine has a combining value of 1 whenever it is in combination with any one of those ten, but no fluoride, chloride or bromide of iodine can contain more than one iodine atom, while it may contain one or three or five or seven atoms of F, CI or Br. Sulphur is positive toward chlorine, bromine and iodine, but negative toward the other nine; nitrogen is positive toward the halogens and the elements of the sulphur family, but is negative toward carbon ; etc. All the thirteen are negative toward hydrogen and the metals, but positive toward oxygen and fluorine. Whenever any one of these thirteen elements capable of varying polarity is directly combined with two or more other elements its polarity is still determined by the same natural law. Thus, if nitrogen is in direct combination with both hydrogen and oxygen, as in the compound represented by H 4 NOH, in which the nitrogen atom, N, holds four hydro- gen atoms and is at the same time in combination with the oxygen atom, 0, the nitrogen atom is relatively negative toward the hydrogen, which is positive, but relatively positive toward the oxygen, which is negative. In the molecule H 3 CC1 the carbon atom, C, is negative to the hydrogen but positive to the chlorine. * No binary compound of bromine with oxygen is known. 70 A CORRESPONDENCE COURSE IN PHARMACY Test Questions 1. Which is the positive element and which the negative element in a compound consisting of boron and hydrogen ? 2. Which is the positive element and which the negative element in a compound of copper and arsenic ? of sulphur and oxygen ? nitrogen and iodine ? phosphorus and sulphur ? chlorine and bromine ? sulphur and carbon ? nitrogen and hydrogen? nitrogen and oxygen? antimony and chlorine? antimony and hydrogen ? 3. Which is the positive and which the negative ion of potassium iodide? 4. What is electrolysis ? 5. What is the difference between the kation and the anion ? between the katode and the anode ? 6. Name the kation of sodium nitrate (NaN0 3 ) ; the anion of potassium nitrate (KN0 3 ). 7. What is the kation of sulphuric acid (H 2 S0 4 )? 8. What is the positive ion of any acid ? 9. Can any element in chemical combination be partly positive and partly negative ? 10. Can any element be positive in some of its com- binations and negative in other combinations ? 11. How can you identify the chemical polarity of any atom in combination ? 12. Name the chemical polarity of each of the atoms in NaOCl. 13. Which of the following molecular formulas are possible and which are evidently fictitious: IF 5 , FC1 3 , BrF, BrF 5 , ClBr 5 , C1F 5 , IBr 7 , Brl 7 ? 14. Identify the positive and negative elements in the compound represented by H 4 NC1 and in H 4 NON0 2 . LESSON SEVEN IX Binary Compounds 152. A binary compound is a molecule composed of but two elements — one positive and the other negative — united to each other in such a way that each atom of one is held in direct combination with each atom of the other. The most simple chemical compound possible is a binary compound consisting of but two atoms, one atom of each element. As examples of such compounds we may mention sodium chloride, represented by the molecular formula NaCl ; lime or calcium oxide, represented by OaO ; and hydrogen chloride, HC1. Other binary compounds contain one atom of one element and two of the other; as, for example, water, H 2 0, and calcium chloride, CaCl 2 . Other binary compounds contain one atom of one element united to three or four or five or six atoms of the other ; or two atoms of one united to two, three, five or seven atoms of the other. But no compound consisting of two elements is truly a binary compound if it contains two or more atoms of one and the same kind directly united to each other. Thus, any compound containing two or more oxygen atoms held to each other, or two or more atoms of carbon directly joined to each other, or two or more atoms of any one other element directly united together, is not a true binary compound. In 71 72 A CORRESPONDENCE COURSE IN PHARMACY the compound called hydrogen dioxide there are two hydrogen atoms and two oxygen atoms ; the two atoms of oxygen are assumed to be united to each other, and of the two hydrogen atoms one is united to each oxygen atom so that the arrange- ment of the four atoms may be represented by a chain, thus : HO OH. Hence H 2 2 is not a true binary compound, although it contains but two elements. But aluminum oxide, A1 2 3 , is a true binary compound, because its two atoms of aluminum are both held to be directly united to all the three oxygen atoms which it contains, as represented by the following structural formula : Al— 0— Al \o/ 153. The names of binary compounds are derived from their negative elements and they are given the ending " — ide." Thus a binary compound of oxygen is called an oxide ; all binary compounds of fluorine are called fluorides ; all binary compounds of chlorine are called chlorides, except the oxides of chlorine (and the fluorides if any exist) ; all the binary compounds of bromine are called bromides, except its compounds with chlorine and fluorine;* iodides are the binary compounds formed by iodine with all elements except bromine, chlorine, fluorine and oxygen. All binary com- pounds of the metals are named after their non-metallic elements, because the metals are invariably positive and any element in direct combination with a metal is consequently negative in such a compound and must be a non-metallic element. 154. The truly binary compounds, then, are of fifteen classes (and only fifteen), according to their negative ele- ments, namely: * Bromine does not form any known binary compound with oxygen. BINARY COMPOUNDS 73 Fluorides, containing fluorine. Oxides, containing oxygen. Chlorides, containing negative chlorine. - Bromides, bromine. Iodides, " ' iodine. Sulphides, ' sulphur. Selenides, " ' selenium. Tellurides, tellurium. Nitrides, " ' nitrogen. Phosphides, phosphorus Arsenides, " arsenic. Antimonides, antimony. Carbides, " carbon. Silicides, silicon. Borides, " ' boron. No other binary compounds are known. 155. True binary compounds containing fluorine, chlorine, bromine or iodine are called Halides. They never contain more than one atom of the element united to the negative halogen. Compounds such as S 2 I 2 (consisting of two atoms of sulphur and two of iodine) and Fe 2 Cl 6 (composed of two atoms of iron and six of chlorine) exist, but they are not true binary compounds. In S 2 I 2 the sulphur atoms are united directly to each other as well as to the iodine (see par. 152). The compound Fe 2 Cl 6 is a " double molecule" or a combination of FeCl 3 with FeCl 3 , and it is not understood how these two molecules of FeCl 3 are held to each other (unless the iron atoms are tetrads and directly united to each other. The position of iron in the periodic system favors this view). 156. The fluorides, chlorides, bromides and iodides of the metals are all solids at ordinary temperatures. Those of the non-metallic elements are either solids, liquids or gases. 157. Sulphides are formed by nearly all elements except oxygen, fluorine, chlorine, bromine, iodine, neon, argon, krypton, and xenon. 74 A CORRESPONDENCE COURSE IK PHARMACY The sulphides of metals are solids, and those formed by the heavy metals are all insoluble in water. The nitride of hydrogen is commonly called ammonia and is composed of three hydrogen atoms and one nitrogen atom, so that the molecule is represented by the formula H 3 N". The phosphide of hydrogen is called phosphine and is H 3 P. There is also an arsenide of hydrogen, H 3 As, called arsine, and a hydrogen antimonide, H 3 Sb, called stiline. All of these hydrogen compounds are gaseous. Saturated hydrogen carbide containing but one carbon atom is called "marsh gas," or methane, and has the molec^- ular formula H 4 C, the carbon atom holding four hydrogen atoms in combination with itself. Hydrogen silicide is H 4 Si, and hydrogen boride is H 3 B. 158. From this chapter the student will perceive that binary compounds have a comparatively simple structure. No true binary compound can have molecules containing more than nine atoms, as in Mn 2 7 . The Hydroxides, Acids, Bases and Salts 159. The Hydroxides. One atom of hydrogen and one of oxygen united to each other form an atomic group called hydroxyl. This group cannot exist alone, but it forms numerous compounds. The compounds which single ele- ments form with hydroxyl are called hydroxides. The symbol for an atom of hydrogen being H and that for the oxygen atom 0, the formula representing the radical called hydroxyl is HO or OH. The most common of all hydroxides is water, for the formula HOH is more significant of the true character of THE HYDKOXIDES, ACIDS, BASES AND SALTS 75 the compound than H 2 0. Water is the oxide of hydrogen, but it is also the hydroxide of hydrogen. It is the only compound which is at once both an oxide and a hydroxide. All true acids contain hydroxyl, and several other im- portant; classes of compounds also contain the group OH. 160. Acids. Vinegar is acid or sour because it contains acetic acid. Lemon juice is sour from citric acid. Sour milk owes its sour taste to lactic acid. Pie plant contains oxalic acid. All acid or acidulous fruits contain some organic acid or some compound formed by it. Sour grapes are tart because they contain a compound called acid tartrate of potassium, which is formed by tartaric acid and which in its purified state is called cream of tartar, the sour taste of which is familiar. Acetic acid, citric acid, lactic acid, oxalic acid and tartaric acid are all organic acids, because they are acids contained in or obtained from organic substances, or substances belong- ing to the vegetable and animal worlds. But several inorganic acids having an even more decidedly sour or acid taste are common. Among them are sulphuric acid, nitric acid, hydrochloric acid and phosphoric acid. The commercial impure strong sulphuric acid was formerly called oil of vitriol; nitric acid was known as aqua fortis, and impure strong hydrochloric acid was called muriatic acid. These names are still used by persons to whom the scientific names are not known. These strong acids are corrosive or destructive in their effects upon numerous other substances, including nearly all vegetable and animal matter. They are therefore poisonous and dangerous and must be handled with great caution. They should never be tasted except after dilution with at least ten times their weight of water, and even after that dilution they are still destructive. Many of the metals dissolve in the strong acids. Characteristic and strong acids, if water-soluble, have an 76 A CORRESPONDENCE COURSE IN" PHARMACY acid or sour taste, and even after great dilution with water they change the color of blue litmus to red. They lose these properties, partially or entirely, when brought into contact with bases, forming salts- which are not destructive in their effects upon other substances. But not all acids have an acid taste, or corrosive properties, nor do all acids turn blue litmus red. Many acids are insoluble in water and have no taste; others are but feebly acidulous, and affect litmus but slightly. But all acids, however feeble, have the power to overcome the corrosive properties of the strongest alkalies and to form salts. Any substance is an acid if its composition and structure are analogous to those of the sour acids mentioned, and if it forms a salt with any alkali. Some acids are liquids; others are solids, and still other acids are gaseous. All acids contain hydrogen. If in any hydrogen com- pound all or a part of the hydrogen can be replaced by any metal with the result that a salt is thereby produced, that hydrogen compound is an acid. 161. Four kinds of so-called acids, and only four, are each composed of only two elements, one of which is hydrogen. They are: hydrofluoric acid, composed of hydrogen and fluorine; hydrochloric acid, composed of hydrogen and chlorine; hydrobromic acid, composed of hydrogen and bromine; and hydro-iodic or hydriodic acid, composed of hydrogen and iodine. They are called hydrogen acids, or hydracids. But the structure of those compounds differs radically from that of the hydroxyl acids, which contain oxygen as well as hydrogen, and distinction must in any scientific classification be made between the hydrogen acids, which are binary compounds, being the halides of hydrogen, and the hydroxyl acids, which contain more than two elements. THE HYDROXIDES, ACIDS, BASES AND SALTS 77 The true scientific names of the so-called hydrogen acids are hydrogen fluoride, hydrogen chloride, hydrogen bromide and hydrogen iodide. 162. Hydroxyl acids are the acids formed by the chemical elements with hydroxyl, or with hydroxyl and oxygen, or with hydroxyl hydrogen and oxygen. All the true inorganic acids are hydroxyl acids. They are also frequently called "oxygen acids." Boric acid is composed exclusively of boron and hydroxyl and its molecular formula is B(OH) 3 , because it contains one boron atom united to three groups of OH. Sulphuric acid is written (HO) 2 S0 2 , because it is composed of one sulphur atom, two groups of OH and two additional oxygen atoms. Hypophosphorous acid is written HOPH 2 0, because it is composed of one phosphorus atom, one group of hydroxyl, two hydrogen atoms, and one oxygen atom. The organic acids contain the group CO, called carbonyl, as well as the hydroxyl group, or they are described as con- taining CO OH, which is called carloxyl. 163. Alkalies. "Caustic potash," "caustic soda" and "ammonia" are the principal alkalies. Potash and soda are white solids. Ammonia is the gaseous hydrogen nitride, but a water solution of it, commonly called "ammonia" or "water of ammonia," is familiar to most persons. A solution of caustic potash in water is called "potash- lye," and a solution of caustic soda is "soda-lye." Strong potash-lye and soda-lye are so corrosive and destructive that they "eat into" wood, dissolve flesh, and disintegrate bone. Strong ammonia solutions also attack organic matter in a destructive way. These alkalies have a burning, caustic, alkaline, lye-like taste; but their destructive character is such that they should not be tasted except after very great dilution with water. 78 A CORRESPONDENCE COURSE IN PHARMACY Strong alkalies, being so destructive, and, therefore, also poisonous, must be handled with great caution. Even after large dilution the solutions of alkalies change the color of red litmus to blue. 164. Opposite Properties of Acids and Alkalies. While the strong acids and the strong alkalies are alike destructive in their effects upon animal and vegetable tissues, they are chemically opposites, for, when an acid and an alkali are mixed together in certain definite proportions, the corrosive or. destructive properties of each are entirely removed or neutralized, the power of the acid to turn blue litmus red and that of the alkali to turn red litmus blue is taken away, and the sour taste of a strong acid is overcome by the alkali and the alkaline taste of the alkali is overcome by the acid, the product of the two having a taste altogether different from that of either acid or alkali. When acids and alkalies mutually neutralize or saturate each other they form a new compound called a salt. But the corrosive or destructive action and other properties of a strong acid are never diminished by the addition of another acid, nor are the characteristic properties of a strong alkali changed or diminished by the addition of another alkali or a base. 165. Experiments to Prove the Opposite Properties of Acids and Alkalies. Take a small quantity of vinegar, which is diluted acetic acid, or of any ^ther diluted acid, and dip a strip of blue litmus paper in it ; it will turn the paper red. Taste the diluted acid and note its sour taste. Dip a strip of red litmus paper in some diluted ammonia water; it will turn the paper blue. Taste the diluted ammonia and note its lye-like taste. Add ammonia water gradually to a little of the vinegar and test the mixture repeatedly with blue litmus paper. Observe that the power of the vinegar to turn the blue litmus THE HYDROXIDES, ACIDS, BASES AND SALTS 79 paper red is gradually lessened as more ammonia is added, and that finally, when enough ammonia has been used, the mixture does not change the color of the blue litmus paper at all. When this point has been reached the liquid has no longer a sour taste. If the quantity of ammonia added is just sufficient to neutralize the acetic acid, the liquid will neither turn blue litmus paper red nor red litmus paper blue, and the taste of the mixture will be neither that of vinegar nor that of ammonia, but a saline taste which is altogether different. If an excess of ammonia is added the liquid will then turn red litmus blue and its taste will be that of the ammonia. If the order of mixing be reversed, the vinegar being gradually added to the ammonia, then the power of the ammonia to turn red litmus paper blue will be gradually weakened and will be completely overcome as soon as enough vinegar has been added; and if more vinegar is added the liquid will acquire the power to turn blue litmus red and will then have an acidulous or acid taste, imparted by the excess of acetic acid. Like results will be obtained whatever may be the kind of acid used or the kind of alkali or base. As alkali carbonates also have the property of neutralizing acids, the experiment may be made with baking soda or sodium bicarbonate instead of ammonia. 166. Bases. By a base is meant, in inorganic chemistry, any hydroxide (or any oxide) having the power to neutralize acids and form salts by reaction with them. The alkalies are accordingly bases, for they are hydroxides capable of neutralizing acids and forming salts with them. The alkalies are in fact the strongest bases known. But very few bases have decidedly alkaline properties. Only the water-soluble metallic hydroxides and ammonia solutions are called alkalies. 80 A CORRESPONDENCE COURSE IN PHARMACY Most of the inorganic bases are not only insoluble in water, but on that account tasteless and apparently chemically inert in their behavior toward other substances, except the acids and some of the non-metallic elements. Insoluble metallic oxides and hydroxides do not change the color of litmus at all ; but they have the power wholly or partly to neutralize acids, and to form salts with them. The great majority of bases are solids; but some are liquid and others gaseous. The metallic bases are all solids. 187. Basic Properties and Functions. The most impor- tant characteristic property of bases is their power to form salts with the acids. "This property or function is in any metallic base due to the metal or basic element in it. All metals having oxides or hydroxides which exhibit basic properties are said to have the power to exercise the basic function. In fact, any metal which forms any salt with any acid exercises a basic function in the formation of that salt, whether any oxide or hydroxide of that metal exists or not. 168. Acidic Properties and Functions. The property of acids to form salts with the bases, or to exchange their hydrogen, or a part of it, for a metal, thereby forming salts$ is their most important characteristic. It is due to the acidic element or acidic atomic group contained in the acid. The true inorganic acids are compounds formed by an acidic element with hydrogen and oxygen. The acidic ele- ment of the most strikingly characteristic acids is a non- metallic element. In fact, all non-metallic hydroxides are acids. But several of the metals also have the power to form acids or to exercise the acidic function under certain conditions. Sulphuric acid is composed of hydrogen, oxygen and sulphur; the sulphur is the acidic element and performs the acidic function in that acid. Nitrogen is the acidic element of nitric acid, which is composed of hydrogen, oxygen and THE HYDROXIDES, ACIDS, BASES AND SALTS 81 nitrogen. Carbon is the acidic element in carbonic acid; phosphorus in phosphoric acid ; chromium in chromic acid ; chlorine in chloric acid; arsenic in arsenous acid; etc. 169. Salts are chemical compounds formed by the acids with the bases. As the inorganic bases are either oxides or hydroxides of the metals, it follows that the inorganic salts are all metallic cpmpounds or contain metals in chemical combination. The metallic salts formed by the inorganic acids, therefore, generally contain three elements — the basic element, the acidic element and oxygen. In the salt called potassium nitrate the basic element is potassium, the acidic element is nitrogen, and the third element is the oxygen; the formula is commonly written KN0 3 , because it contains one atom of each of potassium and nitrogen, but three atoms of oxygen. In sulphate of copper the basic element is copper, the acidic element sulphur, and the common formula is CuSO^. In permanganate of potas- sium the basic element is potassium, and the acidic element manganese; the common molecular formula is KMn0 4 . But a salt may contain more than one basic element, as in A1K(S0 4 ) 2 ; or hydrogen as well as metals, as in Na 2 HP0 4 ; or hydrogen united directly to the acidic element, as in NaPH 2 2 . The difference between the composition of a hydroxyl acid and a metallic salt formed by such an acid is that the acid contains hydrogen instead of the metal and the salt contains metal instead of the hydrogen or part of it. The compo- sition of sulphuric acid is expressed by the common formula H 2 S0 4 , and the composition of its potassium salt, called potassium sulphate, is expressed by the formula K 2 S0 4 . The acids may, therefore, be consistently regarded as the salts of hydrogen, with hydrogen performing the basic function. 82 A CORRESPONDENCE COURSE IN PHARMACY 170. Halides. The compounds formed by the action of "hydrogen acids" upon the bases are called halides. Their structure is radically different from that of the true salts or oxygen salts described in the preceding paragraph, formed by the true acids or hydroxyl acids, for the metallic halides contain only two elements, one of which is either fluorine, chlorine, bromine or iodine, while the other is a metal. The halides are scientifically called the fluorides, chlorides, bro- mides and iodides of the metals. As to structure, the halides formed by the metals are perfectly analogous to the fluorides, chlorides, bromides and iodides of the non-metallic elements. The structure of tri- chloride of phosphorus is represented by P01 3 and that of chloride of aluminum by A1C1 3 . 171. Scientific classification and nomenclature are neces- sary to a clear understanding of the composition and structure of matter. Many of the common names applied to chemical compounds are unfortunately unscientific, inconsistent, or misleading. Solid substances made by early chemists were commonly called salts if they resembled sodium chloride in outward form and appearance, and especially if they were soluble in water. But many substances that look like salts are not salts at all, as, for instance, boric acid, oxalic acid, ice, snow, rock candy, and numerous other common kinds of matter. On the other hand, glass, olive oil, chalk, marble, limestone, clay, soap, oil of wintergreen and butter, none of which bear any outward resemblance to our common salt or sodium chloride, are really all of them salts, for they have the chemical structure of salts, and are formed by acids with bases. Sodium chloride is not a true salt, because it does not have the structure of a salt, but is a simple binary compound, whereas all true salts contain at least three elements. THE HYDKOXIDES, ACIDS, BASES AND SALTS 83 172. The names of salts are derived from the names of the acids by which they are formed. Thus all salts formed by nitric acid are called nitrates; those formed by sulphuric acid are called sulphates; those of phosphoric acid are phosphates; acetic acid forms acetates; carbonic acid, carbonates; oxalic acid, oxalates; citric acid, citrates; tartaric acid, tartrates ; and chloric acid, chlorates. Nitrous acid forms nitrites; sulphites are the salts of sulphurous acid ; and the salts of arsenous acid are called arsenites. 173. As the salts are generally produced out of the acids and bases, so the salts can be decomposed again and the acids and bases of which they were made reproduced, or one salt may be transformed into another salt by chemical means. Nitric acid can be made from nitrates, sulphuric acid from sulphates, acetic acid from acetates, nitrous acid from nitrites, etc. 174. Some Familiar Salts. Saltpeter is potassium nitrate, or the potassium salt of nitric acid, and is composed of potassium, nitrogen and oxygen. Washing soda is sodium carbonate, or the sodium salt of carbonic acid, and is composed of sodium, carbon and oxygen. Baking soda is another sodium salt of carbonic acid. It is called "bicarbonate of sodium" or ' ' acid carbonate of sodium, ' ' because in this sodium carbonate there is but one sodium atom, while in the other there are two, so that the quantity of the group C0 3 in proportion to sodium is twice as great in the bicarbonate. The composition of sodium carbonate is commonly repre- sented by Na 2 C0 3 ; that of the bicarbonate by NaHC0 3 . Epsom salt is magnesium sulphate, or the magnesium salt of sulphuric acid, composed of magnesium, sulphur and oxygen. Green vitriol is one of the iron salts of sulphuric acid, or, in other words, a sulphate of iron. White vitriol is zinc sulphate, and blue vitriol is copper sulphate. 84 A CORRESPONDENCE COURSE IN PHARMACY True alum is a double sulphate ; it has two basic elements, namely aluminum and potassium. Limestone, chalk and marble are all different forms of calcium carbonate. 175. An elementary lesson in the chemistry of limestone will serve to show the relations of oxides, hydroxides, acids, bases and salts to one another. When calcium carbonate (limestone) is strongly heated or "calcined" in a limekiln it is decomposed into calcium oxide or "lime" and carbon dioxide, which is a colorless gas. Lime or calcium oxide is caustic and destructive to animal and vegetable tissues. It is a powerful basic oxide. When water is added to lime the two substances act upon each other chemically and calcium hydroxide is formed. This is strongly alkaline, and turns red litmus blue. When carbon dioxide is collected in water it forms carbonic acid with the water, and carbonic acid turns blue litmus paper red. Now if either the calcium oxide ("quick lime") or the calcium hydroxide ("slaked lime") be exposed to the action of the carbon dioxide ("carbonic acid gas") or to the carbonic acid solution, we will get calcium carbonate back again. This does not change the color of either blue or red litmus paper. But although calcium oxide and water may be said to unite to form calcium hydroxide, and although this calcium hydroxide when strongly heated splits up again into calcium oxide and water, there is in reality neither water nor calcium oxide in the calcium hydroxide. And although carbon dioxide and water form carbonic acid together, and although carbonic acid may be easily split up so as to form water and carbon dioxide, carbonic acid is not composed of water and carbon dioxide. To the beginner in chemistry these statements doubtless THE HYDKOXIDES, ACIDS, BASES AND SALTS 85 must appear paradoxical ; but there will be no difficulty in understanding them by the aid of symbolic formulas. Water is composed of two hydrogen atoms and one oxygen atom, the two hydrogen atoms being both of them united directly to the oxygen atom, so that the molecular formula is best represented as HOH. But there is no HOH in either carbonic acid or in calcium hydroxide. If calcium be represented by Oa, hydrogen by H, oxygen by 0, and carbon by 0, then the relative positions of the several atoms composing calcium oxide, water, calcium hydroxide, carbon dioxide and carbonic acid, respectively, may be pictured as follows : CaO HOH HOCaOH Calcium Oxide. Water. Calcium Hydroxide. 000 HOH HOOOH Carbon Dioxide. Water. Carbonic Acid. If sulphuric acid be added to calcium carbonate we get calcium sulphate water and carbon dioxide: Ca<3£>C=0 + (HO) 2 S0 2 = Ca0 2 S0 2 + Calcium Carbonate. Sulphuric Acid. Calcium Sulphate. HOH + OCO Water. Carbon Dioxide. Test Questions 1. Which of the following formulas represent binary com- pounds and which of them do not represent such compounds : Fe 2 3 , Fe(OH) 3 , H 2 S 2 , Ag 2 0? 2. What name would you give a binary compound contain- ing tellurium ? 3. What is the negative element in a phosphide ? What is the positive element in an arsenide ? 4. To what class of compounds would you refer a substance 86 A CORRESPONDENCE COURSE IN PHARMACY composed of copper and sulphur ? To what, a substance com- posed of copper and zinc ? 5. What kind of a compound is KOH ? Mn0 2 ? 6. What is HO? H 2 ? H 2 2 ? 7. What is your understanding of what constitutes an acid ? 8. What is the true scientific name of hydrobromic acid ? 9. What elements are contained in all true acids, as well as in all alkalies ? Mention six acids ; three alkalies. 10. What is the difference between a base and an alkali ? 11. What elements can exercise basic functions? Can any metals exhibit acidic properties ? 12. What is the basic element of caustic soda ? of caustic potash ? 13. What is the acidic element of boric acid ? of carbonic acid ? of chloric acid ? of iodic acid ? of antimonic acid ? of permanganic acid ? What is a salt ? 14. What is the common name of hydrogen borate ? 15. What is the difference between hydrogen chlorate and potassium chlorate ? 16. What is a halide ? a phosphite ? a phosphate ? a sulphite ? a sulphate ? an arsenite ? 17. What is baking soda, chemically considered ? What is the difference between baking soda and washing soda ? 18. What is the difference between green vitriol, blue vitriol and white vitriol ? 19. Mention three common forms of calcium carbonate. 20. What is the difference between lime and limestone ? between lime and slaked lime ? between carbon dioxide and carbonic acid ? between carbonic acid and chalk ? 21. What is the difference between water and calcium hydroxide ? LESSON EIGHT XI Atomic Valence 176. The number of atoms of any one kind which can be held in combination by any given number of atoms of any other kind is subject to natural law. Thus, for example, the number of hydrogen atoms which can be held in direct chemical combination by a single atom of any one other element in a binary compound is a constant number. One atom of either fluorine, chlorine, bromine or iodine can hold in combination with itself only one hydrogen atom; one atom of either oxygen, sulphur, selenium or tellurium can hold neither more nor less than two hydrogen atoms in combination with itself; a single atom of nitrogen, phos- phorus, arsenic, antimony or boron can hold in combination with itself neither more nor less than three hydrogen atoms ; and neither more nor less than four hydrogen atoms can be held in direct combination by a single atom of either carbon or silicon to form a binary compound. No one single individual atom of any kind can hold in direct combination with itself more than four hydrogen atoms. The individual combining value of one single atom of any given element as compared with the combining value of one single atom of any other given element is called its valence. It is also called the combining power, or combining value, or saturating capacity, or saturation value, or valency, or quantivalence of the element. 87 88 CORRESPONDENCE COURSE IN PHARMACY 177. The hydrogen valence of an element is the number of hydrogen atoms which a single atom of the element can hold in direct combination with itself, when united by all of its combining power directly or exclusively to hydrogen. Prom the preceding paragraphs it will be seen that the hydrogen valence of any given element is constant and that it may be 1, 2, 3 or 4, but can in no case exceed 4. 178. To find the oxygen valence of any element the follow- ing rule is generally applicable : Divide the number of oxygen atoms contained in one molecule of the oxide of the element by one-half the number of the other atoms in the same molecule. By the application of this rule we find from K 2 that the oxygen valence of K is 1 ; from CaO that the oxygen valence of Ca is 2; from A1 2 3 that the oxygen valence of Al is 3; from C0 2 that the oxygen valence of the C in that compound is 4; from CO that the oxygen valence of the C in CO is 2. We find that the oxygen valence of the N in N 2 is 1, that it is 2 in NO, 3 in N 2 3 , and 5 in N 2 5 . But we cannot discover the oxygen valence of the Fe in the compound expressed by the formula Fe 3 4 by the application of the rule given, because Fe 3 4 is not a true binary compound, but either a combination of two molecules — FeO and Fe 2 3 — or it may be a salt (Fe 2 4 Fe, or Fe 2 Fe0 4 ). 179. The valence of the hydrogen atom is invariably 1, because the hydrogen atom is the adopted standard of com- parison. Thus, the valence of any other atom is the number of hydrogen atoms which it equals in combining power, or the number of hydrogen atoms for which it can be exchanged, or the number of hydrogen atoms which it is capable of holding in combination. 180. The valence of the oxygen atom in combination is invariably 2. Hence any single atom of any other element which holds in direct combination with itself one single atom ATOMIC VALENCE 89 of oxygen must also have a valence of 2. (Compare this statement with par. 178.) 181. The following named elements have a constant valence : The valence of H, Li, Na, K, Eb, Cs, Ag and F is invaria- bly 1. The valence of Be, Mg, Ca, Sr, Ba, Zn, Cd and is invariably 2. The valence of Al and B is invariably 3. 182. The highest possible valence attainable by any atom is 8. But only two elements are known to attain that valence, namely Os and Eu. Whenever any atom attains a valence exceeding 6 it is in combination with oxygen. No single atom of any element can hold in direct com- bination with itself more than four oxygen atoms to form a Unary compound. No single atom of any element can hold in combination with itself more than six chlorine atoms. 183. Bonds. The term bond is very conveniently employed to express the unit of valence. Thus we say that the hydrogen atom, having a valence of 1, has 1 bond. The oxygen atom has 2 bonds, because its valence is 2. The atom of Os has 8 bonds in the compound Os0 4 . Sulphurhas6bondsinS0 3 . Carbonhas4bondsinC0 2 . 184. Atoms having an even number of bonds (2, 4, 6 or 8) are called artiads; atoms having an odd number of bonds (1, 3, 5 or 7) are called perissads. Atoms having a valence of 1 are ca 2 ' 3 4 5 6 7 8 led monads and have 1 bond diads ( a 2 bonds triads i ti 3 " tetrads t (i 4 " pentads ( cc 5 " hexads c a 6 " heptads i a 7 " octads ( u 8 " 90 A CORRESPONDENCE COURSE IN PHARMACY Monads are univalent. Diads are bivalent. Triads are trivalent. Tetrads are quadrivalent. Pentads are quinquivalent. Hexads are sexivalent. Heptads are septivalent. Octads are octivalent. 185. The manner in which atoms are held in combination with each other in the formation of molecules may be represented by picturing their bonds as connecting links between them. Using lines to represent the bonds or units of valence, we may readily see that HOI is H — — OL; that H 2 2 mustbe represented as H — — — H; that H 3 N and H H I I H 4 C must be H— N— H and H— C— H; that A1 2 3 must be /0\ Al — — Al, and that C 7 H 16 may be represented as H H H H H H H I I I I I I I H— C— C— C— C— C— C— C— H I I I I I I I H H H H H H H The student must keep in mind that the term "bond" is used only in a figurative sense to express units of valence, and that atoms are not possessed of any links, or ligaments, arms, projections, handles, or points of attachment, by which they may be tied or united or held to each other. 186. Atomic Linking. The relative positions of the atoms in a molecule and the way in which they are held to each other according to their respective valences is called the atomic linking of the molecule. It is of supreme importance as the only means at present known by which the structure ATOMIC VALENCE 91 of chemical compounds may be understood and the com- pounds themselves scientifically classified, especially in organic chemistry. 187. Variable Valence. A variable atomic combining value or valence is possible only to atoms exercising positive polarity, or, in other words, to atoms having positive bonds. 188. All atoms of exclusively negative polarity have a constant valence, or a fixed valence according to their kind. Thus, negative fluorine, chlorine, bromine and iodine are invariably monads; atoms of sulphur, selenium and tellurium are invariably diads whenever their bonds are all negative; boron, nitrogen, phosphorus, arsenic and antimony atoms invariably have three bonds whenever all their bonds are negative; carbon and silicon atoms invariably have four bonds whenever their bonds are all of negative polarity. See also paragraphs 176 and 177. 189. All bonds by which hydrogen is held in combination must be negative bonds, because hydrogen itself is invariably of positive polarity in all its compounds. 190. All bonds by which oxygen is held in combination must be positive bonds, because all the bonds of oxygen itself are invariably of negative polarity in all its compounds. 191. The valences of positive elements are found from the composition of their oxides, chlorides and salts. The valence of any negative element is the number of hydrogen atoms which one single atom of it can hold in combination. 192. It is evident that any atom having but one bond can be in combination with only one other atom, as in KC1, HBr, or Agl. Any atom having two bonds, as, for instance, the oxygen atom, can hold either one other atom having the same number of bonds, as in CaO, or two other atoms having one bond each, as in HOH and KOH. 92 A CORRESPONDENCE COURSE IN PHARMACY Any atom having three bonds can hold in combination either one other atom having three bonds, as in BN ; or one atom having two bonds and another having one bond, as the Bi in OBiCl or the N in H 2 NHgCl, or it can hold three atoms having one bond each, as in H 3 N or NI 3 . Any atom having four bonds may hold four other atoms having one bond each, as in H 4 C, C01 4 , H 3 0C1, H 2 CC1 2 , HCClg, etc. ; or it may hold one other atom having three bonds and one having but one bond, as the C in HON; or it may hold two other atoms having two bonds each, as the C in OCO, or C0 2 . Any atom having five bonds may hold one other atom with four bonds and one with but one bond; or it may hold five other atoms with, one bond each; or any number of other atoms having a total of five bonds. Other combinations possible are shown in WC1 6 , N 2 5 , Mn 2 7 , and in O — O, Ca/2^0 = and NO/ H / \ / ^ \ B.— C / 0— H HC^ COH I II and I || H-C. C— H HC. CH. C C I I H H 193. There can be no free or uncombined bond in any molecule. 194. The total number of bonds in any molecule must be an even number, and one half of the whole number must be positive bonds and the other half negative bonds, for THE ALGEBRAIC COMBINING NUMBERS OP ATOMS 93 every bond must be met by and united to another bond of opposite polarity. XII The Algebraic Combining Numbers of Atoms 195. While the valence of an atom is the number of its bonds in actual combination, there is clearly a radical difference between an atom having only positive bonds incapable of assuming negative polarity, another atom having only negative bonds incapable of assuming positive polarity, and a third atom having both positive and negative bonds, even if the total number of bonds of each atom be the same. Metals and hydrogen can be held in combination with other elements only by negative bonds. Oxygen and fluorine can be held in combination with other elements only by positive bonds. Atoms having both positive and negative bonds can hold metals or hydrogen by their negative bonds, and at the same time oxygen by their positive bonds. To indicate such differences the positive bonds may be designated by the plus sign (+) and the negative bonds by the minus sign (— ). If we then add together algebraically all the bonds of any one atom in actual combination, the sum will express truly the real combining value of that atom. The writer of this book has elsewhere called this sum the "polarity-value" of the atom. It may also be called the algebraic combining number of the atom. 196. The algebraic combining number of any atom having only positive bonds, or one having a greater number of positive than of negative bonds, is of course a plus quantity. The algebraic combining number of any atom having only negative bonds, or one having a greater number of negative than of positive bonds, must be a minus quantity. And the 94 A CORRESPONDENCE COURSE IK PHARMACY algebraic sum of any atom having an equal number of positive bonds and negative bonds must be 0. 197. By this method we will be able to see clearly that the range of true combining value possible to any one atom never exceeds 8 units. Thus the lowest algebraic combining number of the chlorine atom is — 1, for negative chlorine is always a monad ; and the highest combining number of chlorine, shown in KC10 4 , is +7, because the four oxygen atoms together have 8 negative bonds and hence the K and CI must together have 8 positive bonds, of which only 1 belongs to the potassium. The same range is seen in iodine. The lowest algebraic combining number of sulphur is —2, which is its value in all sulphides ; and its highest algebraic combining number is -f 6, as in S0 3 . The lowest algebraic combining number of nitrogen, as shown in ammonia (H 3 N) and in all ammonium compounds, is -3 ; and its highest combining value, as shown in N 2 5 and in the nitrates, is +5. The nitrogen has an algebraic combining number amount- ing to —3 in all ammonium compounds, as may be shown here by one example. The molecule of ammonium chloride is H 4 NC1; hence the nitrogen atom here has four negative bonds which hold the positive hydrogen atoms in combination and one positive bond holding the negative chlorine atom, and the sum of —4 and +1 is —3. The lowest algebraic combining value of carbon is -4, as shown in H 4 C; its highest combining value is +4, as shown in C0 2 . In all the cases referred to it will be seen that the total range, from highest to lowest, of the algebraic combining value of each element is just 8 units. That this is not mere chance but the result of natural law may be inferred from the fact that the quantity of any oxidizing agent required to increase the algebraic combining THE ALGEBRAIC COMBINING NUMBERS OF ATOMS 95 number of any atom from +1 to 4-5 is the same as the quantity required to increase it from —4 to 0, or from —1 to +3, or from —2 to +2, or from —3 to +1, or from +2 to +6, or from +3 to +7, and it is twice as great as the quantity of oxidizing agent required to raise the algebraic combining number of any atom from —4 to —2, or from —2 to 0, or from to -i-2, or from +1 to +3, etc. To increase the algebraic combining number of nitrogen from —3 to +5, as when ammonia is converted into nitric acid, requires just 8 units of oxidizing power, and to change H 2 S into H 2 S0 4 also requires just 8 units of oxidizing power, because the value of the sulphur in H 2 S is evidently —2 and that of the sulphur in H 2 S0 4 is evidently +6 (see next paragraph). 198. As one half of all the bonds of all the atoms com- posing any molecule are positive bonds and the other half negative bonds, it follows that the algebraic sum of all must in every case be 0. If, therefore, the algebraic combining number of two out of three elements in any molecule be known, the combining number of the third is easily found, for it must be in every case the difference between and the algebraic sum of the combining numbers of the other two. In H 2 S0 4 we have eight negative oxygen bonds, because each of the four oxygen atoms has two negative bonds ; the two hydrogen atoms have together two positive bonds ; the sulphur atom must, therefore, have six positive bonds, for —8 and -i-2 and +6 added together make the sum of 0. 199. The algebraic combining number of any free atom is of course 0. It cannot be known how many bonds any atom has, nor what its polarity is, except from its actual com- binations, for we have seen that many elements have a variable valence and at least thirteen elements are positive in some compounds and negative in others. Thus, a free chlorine atom is neither positive nor negative and its actual combining number is 0. If it enters into chemical com- 96 A CORRESPONDENCE COURSE IN PHARMACY bination with hydrogen, or with any metal, it then assumes negative polarity, and its algebraic combining number will be —1 ; but if it enters into direct combination with oxygen in the formation of molecules of NaOCl, the chlorine atom assumes positive polarity and its value will be +1, and if it forms KC10 3 the chlorine assumes an algebraic combining number of +5. The carbon atom in any carbon compound usually has 4 bonds. In the free or uncombined state its algebraic com- bining number is 0. When it is united to four hydrogen atoms, H 4 C, the carbon atom has a combining number of —4; if it holds three (positive) hydrogen atoms and one (negative) chlorine atom, H 3 CC1, its value is —2; if it holds two (posi- tive) hydrogen atoms and two (negative) chlorine atoms, H 2 CC1 2 , its value is 0; if it holds one hydrogen atom and three chlorine atoms, its value is —2. 200. Whenever two atoms of the same element are directly united to each other it must be assumed that they are held to each other by bonds of opposite polarities. Hence it follows that one of the hydrogen atoms in a molecule of hydrogen (composed of two atoms) must be positive and the other negative. In a molecule of oxygen containing two atoms of that element we must conclude either that each atom has one positive and one negative bond or that one has two positive bonds and the other two negative bonds, for the algebraic sum of all the bonds in any molecule must always be zero. 201. In the molecule HN 3 it is impossible to escape the /N" < . conclusion that the atomic linking must be H — N v 1 1 , which shows that the hydrogen atom with its one positive bond is united to one of the nitrogen atoms by one negative nitrogen THE ALGEBKAIC COMBINING NUMBEKS OF ATOMS 97 bond, while of the other six nitrogen bonds three are positive and the other three negative. In HO OH we assume that the algebraic sum of the bonds of both oxygen atoms together must be —2, because the hydrogen atoms together must be +2 and the total must be ; hence one of the oxygen atoms must have one positive and one negative bond and the other oxygen atom must have two negative bonds. The two bonds by which the two oxygen atoms are held to each other must therefore be one of them positive and the other negative. We must assume that the algebraic sum of the bonds by which any two atoms of the same element are held in direct combination with each other is always zero, because one half of them must be positive and the others negative, 202. To find the algebraic combining number of any atom in any molecule of simple structure is usually an easy task, unless two or more atoms of one and the same element are directly united to each other. The student can readily find the combining numbers of combined elements from the atoms known to have constant values, such as H, K, Na, Li, Ba, Sr, Ca, Mg, Al, B, Ag, Zn, and F; also from the oxygen in any molecule, unless two oxygen atoms are united directly to each other; also from the negative atoms of chlorine, bromine, iodine, sulphur and nitrogen. Since a varying algebraic combining number is possible only to elements having positive polarity, the student should find the algebraic combining numbers of any atom of such an element from the atom or atoms with which it is in direct combination; or, in other words, from any atoms in the molecule the algebraic combining values of which are con- stant and, therefore, known. 203. The algebraic combining number of the acidic element in any inorganic acid composed of that element together with hydrogen and oxygen, is found by deducting 98 A CORRESPONDENCE COURSE IN PHARMACY the algebraic sum of the oxygen and hydrogen bonds from 0. The oxygen atoms in the molecule of such an acid are the only atoms having exclusively negative bonds ; the hydrogen atoms are all positive, and either all or a majority of the bonds of the acidic element are positive. In HN0 3 the N must have five positive bonds; in H 3 P0 4 the P must have five positive bonds. But in Na 2 AsH0 3 the As has an algebraic combining number of only +3, although it has five bonds, for the structure of the molecule H is known to be N ^ /As= ; and in KPH 2 2 the P has an algebraic combining number of only +1, although it has five H I bonds, because the structure is KO — P = 0. I H 204. In the molecule commonly but erroneously written CaS 5 we know that the algebraic sum of all the bonds of the five sulphur atoms must be —2, because Ca (as shown by its position in the periodic system) can never have any other value than +2. No compound of calcium is known in which that metal has any other combining value than 2. It follows that the two positive calcium bonds must be in combination with two negative sulphur bonds and that of all the remain- ing sulphur bonds one-half must be positive and one-half negative. This leads to the structural formula in which the central sulphur atom is acidic and has six positive bonds, while all the other sulphur atoms each have THE ALGEBRAIC COMBINING NUMBERS OF ATOMS 99 two negative bonds, the molecule being perfectly analogous to CaS0 4 , which has the structure There is a molecule erroneously written K 2 S 3 which has the structure K— S— S— S— K. In this molecule the central sulphur atom is acidic and has a combining value of +2, while all the other four sulphur bonds are negative, because the structure is perfectly anal- ogous to that of KOSOK. There is a compound erroneously called ''hyposulphite of sodium," which is commonly represented as Na 2 S 2 3 . But with the aid of our conception of the algebraic combining numbers of the component atoms of molecules we can readily see that the structure must be NaS\ Q ^0 nr mO\„//8 NaO/%0 or NaO/%0 and chemists now write it Na 2 S0 3 S, to show that one sulphur atom performs the acidic function while the other performs the same function as any of the oxygen atoms in Na 2 S0 4 . 205. The algebraic sum of all the carbon bonds in any molecule composed of carbon, hydrogen and oxygen (and a vast majority of organic substances are composed of those elements) is at once found by subtracting the algebraic sum of all the bonds of the atoms of hydrogen and oxygen from 0. It is further known that all the carbon atoms in such com- pounds have each four bonds. The total number of positive LOFa 100 A CORRESPONDENCE COURSE IN PHARMACY carbon bonds and the total number of negative carbon bonds can, therefore, be readily found. It is also known that the algebraic sum of all bonds by which any of the carbon atoms are united to each other must be 0. These facts are helpful in determining the actual atomic linking. Test Questions 1. Define valence. 2. What is the valence of the boron in H 3 B ? in B 2 3 ? 3. What is the difference arithmetically between the valence of the boron in H 3 B and in B 2 3 ? 4. What is the difference between the algebraic combining number of the boron in H 3 B and the boron in B 2 3 ? 5. What are the respective valences of the elements form- ing a binary hydrogen compound ? 6. How do you find the valence of each of the two elements in any oxide ? 7. Can you name an element having a valence of 10 ? 8. What is the number of chlorine atoms in the chloride of an element having a valence of 8 ? 9. What is the number of hydrogen atoms in the hydride of an element having a valence of 6 ? 10. How many chlorine atoms are there in the chloride of a heptad ? 11. How many oxygen atoms are there in the oxide of a tetrad and how many in the oxide of a pentad ? 12. Name two octads. 13. How many bonds has a potassium atom ? 14. How many bonds has aluminum ? 15. Name the number of bonds of the zinc atom. 16. Draw a figure showing the atomic linking of As 2 3 ; C 2 H a . THE ALGEBRAIC COMBINING NUMBERS OF ATOMS 101 17. Under what circumstances can the valence of an element vary ? 18. State the number of bonds of each element in the molecule OSbCl. 19. State the number of bonds of each element in (a) KN0 3 ; (b) Na 4 P 2 7 ; (c) CaS0 4 ; (d) CaH 2 S0 5 ; (e) H 5 P0 5 ; (f) H 3 P0 4 ; (g)HP0 3 ; (h) H 3 P0 3 ; (i)HP0 2 ; (j) HPH 2 2 ; (k) H 2 PH0 3 ; (1) KMn0 4 ; (m) K 2 Mn0 4 . 20. State which of the following molecular formulas are right and which are wrong: (a) AgCl 3 ; (b) KO; (c) Mg 2 3 ; (d)H,0; (e)Na 2 S 5 . 21. What is the valence of the sulphur in S0 2 and what is the algebraic combining number of each of the two ele- ments in that molecule ? 22. What is the algebraic combining number of the sulphur in H 2 S ? 23. What is the difference between the valence of the sulphur in H 2 S0 2 and in H 2 S and what is the difference between the algebraic combining number of the S in those two molecules ? 24. What is the algebraic combining number of the N in HN0 3 and in H.lSTBr ? 25. What is the algebraic sum of the carbon bonds in C 6 H 10 O 5 ? 26. What is the algebraic combining value of the Br in a bromide ? 27. Can bromine under any circumstances have a higher algebraic combining number, and if so, when ? 28. If the valence of sulphur, with negative polarity, is 2, what is the highest possible algebraic combining number of sulphur ? 29. If zinc phosphide is Zn 3 P 2 , then what is the highest possible algebraic combining number of phos- phorus ? 102 A CORRESPONDENCE COURSE IN PHARMACY 30. What is the algebraic combining number of uncom- bined carbon ? 31. State the algebraic combining numbers of the three different elements in Na 2 S 2 3 . 32. What is the algebraic sum of the carbon bonds in HC 2 H 3 2 ? LESSON NINE XIII Chemical Notation 206. We have already made use of several chemical symbols and self-explanatory formulas. Before proceeding further we will now learn something of the principles governing the construction of symbolic formulas. In order to represent at a glance the composition and structure of molecules a system of chemical notation was invented by Berzelius, which is still in use, modified and adapted to correspond to the development of the science of chemistry since his day. 207. Each atom of any given element is represented by a specific symbol unlike the symbol of any other element. The symbol consists of one or two letters which are the initials of the latinic or other names of the elements. Two letters are used for some of the symbols in cases where the names of two or more elements begin with the same letter. The additional letter used is not always the second letter of the name, but one which will best serve to make the symbol distinctive. As the names of chlorine and chromium both begin with Ch, their symbols are made 01 and Or. The first letter of any symbol of two letters is a capital letter; the second is not. 208. The symbol of any element stands not merely for its name, but for one atom of it and for its atomic weight or combining mass. 103 104 A CORRESPONDENCE COURSE IN PHARMACY Thus S, the symbol for sulphur, means one atom of sulphur and also 32 parts of sulphur. 209. Symbolic formulas are constructed out of one. or more symbols together with one or more numerals, or of two or more symbols with or without numerals. KI is a symbolic formula because it is composed of two symbols, K and I ; Cl 2 is a formula because it is composed of a numeral as well as a symbol; 2C1 is also a formula for the same reason; 3 , H 2 0, OaCl 2 and HN0 3 are also sym- bolic formulas. Symbolic molecular formulas of compounds are so con- structed that they show not only all of the elements com- posing them but the number of atoms of each. 210. The numerals used are of two "kinds — large and small. A large numeral placed in front of a symbol multiplies it, but it also indicates that the atom represented by the symbol is a free or uncombined atom. Thus 90 means nine oxygen atoms not united to one another. A small numeral placed after a symbol also multiplies the atom, but it signifies that all the atoms are in chemical combination either with one another or with other atoms. Thus 3 means three atoms of oxygen in combination with one another, or, in other words, a molecule of ozone. The formula 30 3 means three molecules of ozone each containing three atoms of oxygen; but 90 means nine single oxygen atoms and not three molecules of ozone. A large numeral in front of any symbolic molecular formula multiplies the whole molecule, but a small numeral is never used to multiply a molecule; the latter is placed to the right of the symbol which it is intended to multiply and a little below the line, as in 3 . Thus, the formula O 6 H 10 O 5 means one molecule composed of six carbon atoms, ten hydrogen atoms and five oxygen atoms, and 2C^H 10 O 5 means two such molecules. CHEMICAL NOTATION" 105 The following examples will suffice to make these things clear : Hg stands for one atom of mercury. Hg also stands for one molecule of mercury, because each molecule of mercury contains but one atom. 2H means two free hydrogen atoms. 3H means three free hydrogen atoms. H 2 means two hydrogen atoms united to each other to form one molecule. 2H 2 means two molecules of hydrogen of two atoms each. 4H01 means four molecules of hydrogen chloride. 5H 2 means five molecules of water. 211. How to Write Molecular Formulas. The symbols representing the elements composing the molecules are to be written, and where more than one atom of the element enters into the molecule the number of atoms of each element is indi- cated by an "inferior" (lower) numeral to the right of the symbol a little below the line, as shown in Fe 2 3 , a molecule consisting of two atoms of iron and three atoms of oxygen. In writing the molecular formula of a binary compound the positive element (or ion) is always to be placed first and the negative element (or ion) last. Hence, the symbol of the metal is always written first in the molecular formula of any binary compound of a metal. In writing the molecular formula of any compound con- taining three or more elements, the ions, if known, are placed in the same order as in the molecular formulas of binary compounds. Such compounds must contain at least one ion composed of more than one element, and the elements of each ion are written in the same order as the jons themselves — the positive elements before the negative elements — when- ever practicable ; or the elements are written in the order determined by their respective valences and indicative of the actual atomic linking, so far as practicable. 106 A CORRESPONDENCE COURSE IN PHARMACY Two elements having or exercising the same polarity in any molecule may be placed beside each other for the sake of con- venience and brevity, if the formula is not intended to show the relative positions of all the atoms but only to show the ions. But whenever the whole system of atomic linking is to be shown it is evident that any two atoms placed immediately beside each other must be of opposite chemical polarity with re- spect to each other. We write KJST0 3 for convenience, because K is the positive ion and N0 3 is the negative ion ; but K is not the only positive atom, for N is also of positive polarity, so that K is not directly united to N and the actual atomic linking is therefore not shown in the formula KN0 3 . If the atomic linking of potassium nitrate is to be shown the formula should be written KOJST0 2 , for the K is directly united to one atom of oxygen and that atom of oxygen is at the same time directly united to the N, which, having five bonds, also holds the other two oxygen atoms in direct combination with itself. Molecular formulas are sometimes written in a manner inconsistent with the foregoing rules, because these rules are not explicitly stated in the text-books, although the commonly written molecular formulas in nearly all cases conform to them and no good reasons apparently exist which explain the few exceptions. H 4 NOH is a correctly written molecular formula, because the nitrogen atom is admittedly directly united to four hydrogen atoms and to the oxygen atom, and the fifth hydro- gen atom is directly united to the oxygen atom and not to the nitrogen; but the formula NH 4 HO, often seen, is incon- sistent because it separates the nitrogen from the oxygen. The actual structure of this molecule is H !>N-0-H i H CHEMICAL DOTATION 107 which may well be represented by H 4 NOH, but not by NH 4 HO. The formula NH 4 C1 is inconsistent, because the nitrogen is really directly united to the CI and the 01 is not united to hydrogen, for the nitrogen atom has five bonds and the atoms of hydrogen and chlorine have only one bond each, so that the correct formula is H 4 NC1, and four of the nitrogen bonds (holding the hydrogen atoms) are of negative chemical polarity, while the fifth bond (holding the chlorine atom) is a positive bond. 212. Large (or ordinary) figures or numerals are used to multiply single molecules. A true molecule has but one (or a continuous or undivided) system of atomic linking. Two or more molecules may be held to each other in some way not yet understood (not consistent with our conception of atomic valence), and such molecular combinations are represented by formulas which show the several combined molecules by means of their own respective molecular formulas and numerals indicating the number of molecules of each kind. The formula BaCl 2 .2H 2 or Ba01 2 +2H 2 represents a combination of one molecule of Ba01 2 with two molecules of H 2 0. This molecular combination has three separate and distinct systems of atomic linking — one for the Ba01 2 and another for each of the two molecules of water. The formula 2K 2 C0 3 +3H 2 represents a molecular com- bination of two molecules of K 2 C0 3 with three molecules of water. This combination has five separate systems of atomic linking. All molecular combinations have as many separate systems of atomic linking as the number of molecules they contain, for each molecule has its own. When any symbols or molecules are embraced in parentheses and a numeral is placed outside the parentheses, that numeral 108 A COKEESPONDENCE COUKSE IN PHAKMACY multiplies all that is enclosed within the parentheses. Thus 3(2K 2 C0 3 +3H 2 0) means three times 2K 2 C0 3 +3H 2 0; Fe (S0 4 ) 3 means Fe united to three times S0 4 ; and the expres- sion 4MgC0 3 .Mg(OH) 2 .5H 2 means a combination of 4 mole- cules of MgC0 3 with one molecule of Mg(OH) 2 and 5 of water. The formula K 4 Fe(CN) 6 represents a chemical compound known as ferrocyanide of potassium. It is recognized as a ferrous compound, which means that the iron atom in it has two bonds. The potassium atoms have one bond each. The combination consists of 4 potassium atoms, one iron atom and 4 times the group CN. The group ON, consisting of the tetrad C and the triad N, is a univalent radical. It is impos- sible to escape the conclusion that there must be six inde- pendent systems of interatomic linking in this combination, or that the only formula for it which is consistent with our conceptions of atomic valence must be 4KCN+Fe(CN) 2 . 213. Empiric formulas are formulas expressing in the simplest terms the relative numbers of the atoms of each element contained in a compound. The empiric formula for acetic acid is CH 2 0. This simply indicates that we have in the composition of acetic acid two hydrogen atoms and one oxygen for each carbon atom. It does not show the actual number of atoms of each kind con- tained in one molecule. 214. Molecular formulas show the actual number of atoms of each kind which form one molecule of the substance. The molecular formula of acetic acid is not CH 2 but C 2 H 4 2 , or HC 2 H 3 2 , or H 3 C.C0.OH, for the vapor den- sity of acetic acid proves that its molecular weight must be the sum of the weights of two carbon atoms, four hydrogen atoms, and two oyxgen atoms, which would be most simply expressed by 2 H 4 2 . The formula HC 2 H 3 2 is one which shows that one of the four hydrogen atoms can be replaced by a metal or that the two ions of acetic acid are H and C 2 H 3 2 . CHEMICAL NOTATION 109 215. The constitutional or structural formula of any com- pound is one that shows the relative positions of the atoms, or their grouping, or their interatomic linking. The struc- tural or constitutional formula for acetic acid is H 3 C.CO.OH, because the three recognized atomic groups composing its molecule are methyl (H 3 0), carbonyl (CO), and hydroxyl (OH). A graphic structural formula showing the interatomic linking of acetic acid in detail is H I II H— C— C— 0— H I H 216. To construct the molecular formula of any binary compound is an easy problem if the valence of each of the two elements is known. To do so, multiply the symbol of each element by the valence of the other: The molecular formula of bismuthous oxide must be Bi 2 3 . To arrive at it, first write down Bi for bismuth and for the oxygen. Then, as the valence of bismuthous bismuth is 3, write that numeral after the 0, and as the valence of is 2, we write that numeral after the Bi. To construct the molecular formula of any compound of two known ions is an equally simple proposition: First write the two ions and then multiply each ion (or radical) by the valence of the other. Thus, the molecular formula of tricalcium phosphate is Ca 3 (P0 4 ) 2 , because the valence of Oa is 2 and that of P0 4 is 3. The valence of P0 4 is 3, because the algebraic combining number of P in all phosphates is +5, and the valence of the oxygen atom is —2, so that P0 4 has five phosphorus bonds and eight oxygen bonds and the difference between 5 and 8 is 3, representing 3 oxygen bonds not in combination with the P. 110 A CORRESPONDENCE COURSE IN PHARMACY Tlie number of bonds of the positive ion must be the same as the number of bonds of the negative ion, or the total bonds of each must be a common multiple of the respective valences of both. Ca 3 represents 3 calcium atoms which together have 6 bonds, and (P0 4 ) 2 represents twice P0 4 , having also a total of 6 bonds. 217. The student can readily learn to write structural molecular formulas showing the combining values and inter- atomic linking, and also the common molecular formulas from the following : Each unit of combining value is represented by a line or dash, which is a solid line if the unit or "bond" is of positive polarity but dotted if the bond is a negative one. The algebraic combining values range from +8 to —4. Osmium forms a tetr oxide which may be represented as 0:::=Os=:::0 Chlorine, iodine and manganese may each exercise a value of +7 in the compounds called perchlorates, periodates and permanganates : ..o ..O K C1=::::0 "•0 K Mn— .:::0 "'0 Potassium Perchlorate. Potassium Permanganate. A combining value of +6 is exercised by S in sulphuric CHEMICAL NOTATION 111 compounds, Or in chromic acid and chromates, Mn in man- ganates, Mo in molybdates and Fe in ferrates : H S H 0. • ^ Sulphuric Acid. •O Na 0. ...O ■ Na ..■•'• ^'••'•O Sodium Chromate. A combining value of +5 is shown by N in nitric acid and other nitrates, P in phosphoric compounds, As in arsenic compounds, Sb in antimonic and Bi in bismuthic compounds; also by 01 in chloric, Br in bromic and I in iodic compounds : .0 Q> CI 6> H<" ~ 5 ;:0 \ 1 / P •'••• cK' "Qt Mercuric Nitrate. Phosphoric Chloride. .0 . Bi™0 "^Bi X"o ■"/ "0" ..,0 K_ Cl^f ^0 Bismuthic Oxide. Potassium Chlorate. A combining value of +4 is exercised by C in carbonic compounds, Si in silicic and Sn in stannic compounds ; by Pt in platinic compounds, Oe in eerie, Pb in perplumbic, S in sulphurous compounds, Fe in ferrites, Mn in manganites and in Mn0 2 , Mo in Mo0 2 and by N in N0 2 . 0:::~C=:::::0 Carbonic Oxide. o^ ;pt" Platinic Chloride. 112 A CORRESPONDENCE COURSE IN PHARMACY 0::::=Pb=::::0 Peroxide of Lead. H 0— - b ° Sulphurous Acid. An algebraic combining value of +3 is exercised by B in boric compounds, Al in all its compounds, Fe in ferric halides and salts, Ni in nickelic and Co in cobaltic compounds, Cr in Cr 2 3 and several other compounds, Mo in Mo 2 3 , Mn in Mn 2 3 , MnOl, etc., Au in auric compounds; by N" in nitrous, P in phosphorous, As in arsenous, Sb in antimonious and Bi in bismuthous compounds ; and by CI in chlorous, Br in bro- mons, and I in iodous compounds: H- B 0- . 1 -H H Al— "0- ! 6 6 i H Boric Acid . i H Aluminum Hydroxic 01 Fe CI .. • o .... 1 tii Ferric Chloride. Cr^ ~Cr "• o -" Dichromium Trioxide. H ; o N= ::::0 Nitrous Acid. ...0.... "•o"* Chlorous Oxide. CI Na— -^ — - U Sodium Phosphite. 01 1- I ■CI CI Iodine Trichloride. CHEMICAL NOTATION 113 A combining value of +2 is exercised by Mg, Ca, Sr, Ba, Zn and Cd in all their compounds; by Cu in cupric and Hg in mercuric compounds ; by Fe in ferrous, Ni in nickelous, and Co in cobaltous compounds; by Or in chromous, Mo in molybdous and Mn in manganous compounds; by Sn in stannous and Pb in plumbic compounds ; by Pt in platinous compounds; by C in carbonous compounds; by S in hypo- sulphurous compounds ; and by N in NO : Mg=::::0 01 Ca CI Magnesium Oxide. Calcium Chloride. ; o B -H H 1 Barium Hydroxide. i 6 6 i H Ferrous Sulphate. C— :::0 Na -^q Na 0- -^ Carbonous Oxide. Sodium Hyposulphite An algebraic combining value of +1 is exercised by H, Li, Na, K, and Ag in all their compounds; by Cu in cuprous, Hg in mercurous, Au in aurous compounds ; by CI in hypo- chlorous, Br in hypobromous and I in hypo-iodous com- pounds; by N in hyponitrous and P in hypophosphorous compounds : 114 A CORRESPONDENCE COURSE IN PHARMACY H H Water. Hg— -01 Mercurous Chloride. JSTa— -O CI Sodium Hypochlorite. H K Pr ::0 H Potassium Hypophosphite. An algebraic combining value of is exercised by one of the oxygen atoms in HO OH and by one of the sulphur atoms in H S S H; also by in many compounds, as in CI H— C ■H CI A combining value of -1 is shown by F in all fluorides, CI in all chlorides, Br in all bromides and I in all iodides : I Br Iodine Monobromide. <* ?. ""..* X <$■■■ "■■& Iodine Pentafluoride. .1 N^ I I Nitrogen Iodide. "X Sulphur Tetrachloride. F has a combining value of -1 in all its compounds; 01 has a value of —1 in all its compounds with all elements except F and ; Br exercises the combining value of -1 in all the compounds it forms with all elements except 01, F and ; I exercises that value in all the compounds it forms except with Br, 01, F and 0. CHEMICAL NOTATION 115 A combining value of -2 is exercised by in all the com- pounds in which it is directly unjted to any other element. In other words, it exercises that value in all cases except where two oxygen atoms are directly united to each other, in which event one of the oxygen atoms has a value of 0. Sulphur, whenever it exercises negative polarity, has a combining value of —2; it accordingly has a value of —2 whenever it is in direct combination with any element except 0, F, 01, Br and I. • The carbon atom exercises a combining value of -2 in all compounds in which it has one positive and three negative bonds, as in H 3 CC1. The combining value of -3 is exercised by B in H 3 B ; by N in all compounds in which the nitrogen atom is negative and not united to another nitrogen atom, and it, therefore, has that value in H 3 N and in all ammonium compounds, in alkaloids, and in numerous organic compounds. Negative P, negative As and negative Sb also have a combining value of —3: H N Sr— »oi ♦<■] ^Cu ^ As ••"• — Cu — '•'•• As H ""^Cu^"" Ammonium Chloride. Cupric Arsenide. H ! H 6 < ! > ":n."' *:n_....o.. n^ ^-" "^-fr 1 H Ammonium Hydroxide. Ammonium Nitrate. 116 A CORRESPONDENCE COURSE 1ST PHARMACY A combining value of —4 is exercised by the in H 4 C and by Si in H 4 Si. H H j ! H b H H— ••&•• — H H H Marsh Gas. Hydrogen Silicide. XIV Chemical Nomenclature 218. "We have already learned that classes of binary com- pounds are given generic titles ending with ide, as, for instance, oxides, sulphides, chlorides, bromides, etc; and that salts are named after their corresponding acids, such as sulphates, named after sulphuric acids; nitrates, named after nitric acids; sulphites, named after sulphurous acid; nitrites, after nitrous acid, etc. The adjectives used in the nomenclature of inorganic chemical compounds and the relation of these adjectives to the other technical terms require careful consideration, and also the prefixes which are employed wherever necessary. The substantive nouns ending in ide, ate and ite are derived from the names of the negative radicals, whereas the adjec- tives used are derived from the names of their positive radi- cals, or from positive elements. 219. In the chapter on Atomic Valence, we learned that many elements when exercising positive polarity may have two, three or four valences, and that, accordingly, they may have several oxides or sulphides or chlorides or hydroxides. These must be distinguished from one another in a system- atic way. CHEMICAL NOMENCLATURE 117 220. The Endings ic and ous. When any element exercises two different combining values, the higher value is indicated by an adjective ending in ic and the lower combining value is indicated by an adjective ending in ous. Carbon, mercury and iron will serve as examples to illustrate this rule. Carbonic carbon is positive carbon with an algebraic com- bining number of +4; carbonous carbon is positive carbon with an algebraic combining number of +2. Positive carbon has no other algebraic combining numbers. Mercury has two combining values ; its higher value is +2 and is called mercuric mercury, while its lower combining number is 1 and mercury with that combining number is called mercurous mercury. Carbonic oxide is C0 2 , carbonous oxide is CO, mercuric chloride is HgCl 2 , and mercurous chloride is HgCl. When iron exercises basic functions and when it forms binary compounds, it may have a combining value of either +2 or +3. Iron with a value of +2 is called ferrous iron ; iron with a value of +3 is called ferric iron. 221. The Prefixes hypo and per. When an element exer- cising positive polarity has three different combining values, the highest is indicated by an adjective ending in ic, the middle value is indicated by an adjective ending in ous, and the lowest value is indicated by an adjective ending with ous in addition to the prefix hypo, which means below or under. Sulphur, for instance, is sulphuric sulphur when it exercises the algebraic combining number of +6 ; it is sul- phurous when it has the combining number +4; it is hypo- sulphurous when it has the combining number of +2. When an element exercising positive polarity has four different combining values, the lowest value is indicated by the prefix hypo and the ending ous, the next higher value is indicated by the ending ous without any prefix, the third value is indicated by an adjective ending in ic without any 118 A CORRESPONDENCE COURSE IN PHARMACY prefix, and the fourth and highest value is indicated by the ending ic and the prefix per. Thus, positive chlorine forms hypochlorous compounds, chlorous compounds, chloric com- pounds and perchloric compounds. 222. But even these devices are not always sufficient. We shall accordingly learn now all the prefixes commonly employed in inorganic chemical nomenclature. They are as follows : (a) Prefixes derived from Greek numerals: Mono or mon, meaning one, single or once. Di or dis, meaning two or twice. Tri or tris, meaning three or thrice. Tetra, meaning four. Penta, meaning five. Hexa, meaning six. Hepta, meaning Seven. Octo, meaning eight. Deca, meaning ten. (b) Prefixes derived from Latin numerals: Un or uni, meaning one or single. Duo, bi, bin, or bis, meaning two or twice. Ter or tri, meaning three or thrice. Quadri or quadra, meaning four. Quinque or quinqui, meaning five. Sexa or sexi, meaning six. Septi or sept, meaning seven. Octo or octi, meaning eight. (c) Other prefixes: Hypo, meaning under, lower or below. Sub, meaning under, lower or below. Per, meaning thorough, through or to the full extent. Meta, meaning altered, different, after or beyond. Para, meaning changed, different or altered. Ortho, meaning straight, regular, common, usual or original. Pyro, meaning as produced by fire or high heat. Thio, from theion (sulphur), meaning containing sulphur. The following illustrations will suffice to render clear the mode of employment of the foregoing prefixes : A monochloride is a chloride containing but one chlorine CHEMICAL NOMENCLATURE 119 atom ; a dioxide is an oxide containing two oxygen atoms ; a tri-iodide contains three iodine atoms; a tetroxide contains four oxygen atoms; a pentafluoride contains five fluorine atoms ; a hexachloride contains six chlorine atoms ; a hep- toxide contains seven oxygen atoms. A bicarbonate contains twice as large a proportion of the carbonate radical 00 3 as a carbonate contains in proportion to the basic element, as shown by the molecular formulas KHOO3 an d K 2 00 3 , in which K is the basic element. Subsulphate of mercury contains a smaller quantity of the sulphate radical S0 4 in proportion to the mercury than the sulphate of mercury contains. Subnitrate of bismuth is a name given to OBiN0 3 , containing the N0 3 only once, while bismuth nitrate is Bi(N0 3 ) 3 . A thiocarbonate is a carbonate in which the oxygen is in part or wholly replaced by sulphur. A thiosulphate is a sulphate containing a larger proportion of sulphur than is contained in the other sulphates, some or all of the oxygen of the sulphate being replaced by sulphur atoms. Thus, sulphate of calcium is CaS0 4 , while thiosulphate of calcium is OaSS 4 , and other calcium thiosulphates are CaS0 3 S, CaS0 2 S 2 , and CaSOS 3 . 223. Meta-compounds. The prefix meta when used in connection with hydroxides and salts has a specific meaning. It signifies a compound formed by the removal of the ele- ments of water from another compound of normal structure. A normal hydroxide or a hydroxide of normal composition contains no hydrogen or oxygen, except the hydrogen and oxygen of its hydroxyl. In other words, it contains an equal number of atoms of hydrogen and oxygen, and every hydrogen atom in such a hydroxide is directly united to an oxygen atom. Thus, ferrous hydroxide is Fe(OH) 2 , because ferrous iron is a diad and can therefore hold in combination two groups of hydroxyl, OH. Normal ferric hydroxide is Fe(OH) 3 , 120 A CORRESPONDENCE COURSE IN PHARMACY because ferric iron is a triad and can accordingly hold in combination three hydroxyl groups. But OFeOH is a meta- hydroxide formed out of Fe(OH) 3 by its dissociation, result- ing in the formation of one molecule of water, H 2 0, and one molecule of the OFeOH, which is all that remains of the Fe(OH) 3 when one molecule of water has been split off from it. Normal sulphuric hydroxide or normal sulphuric acid is, of course, S(OH) 6 , because sulphuric sulphur is a hexad and can hold six hydroxyl groups. But if one molecule of water be split off from the S(OH) 6 , we would have (HO) 4 SO left, which is mono-meta-sulphuric acid, or mono-m eta-sulphuric hydroxide, the prefix mono indicating that only one molecule of water was split off. But if two molecules of water be split off from S(OH) 6 or (HO) 6 S, which is the same thing, then di-meta-sulphuric hydroxide or di-meta-sulphuric acid is formed, the formula of which is (HO) 2 S0 2 or H 2 S0 4 , which is our common sulphuric acid. A tri-meta-sulphuric acid containing but one atom of sulphur is impossible, because if three molecules of water be split off from (HO) 6 S, the remainder would be simply S0 3 , which is not a hydrox- ide nor an acid, but sulphuric oxide. The name orthophosphoric acid means the common or ordinary phosphoric acid. The prefix ortho does not indicate its composition, but the ending ic indicates that the phos- phorus in it has the combining number +5, which is the highest of the three positive algebraic combining numbers possible to phosphorus. The formula for orthophosphoric acid is H 3 P0 4 or (HO) 3 PO. A normal phosphoric hydroxide is, of course, (HO) 5 P. Accordingly, it is evident that orthophosphoric acid is a mono-meta-acid, and the name mono-meta-phosphoric acid is sufficient to indicate the structure of the compound or its true molecular formula. The glacial phosphoric acid commonly called meta-phosphoric acid has the formula HP0 3 , or HOP0 2 . It is therefore a CHEMICAL NOMENCLATURE 121 di-meta-acid or (HO) 5 P, or H 5 P0 5 with two molecules of water split off from it, leaving HP0 3 . What is commonly called pyrophosphoric acid is a phosphoric acid produced by heating orthophosphoric acid, or a pyrophosphate is obtained by heating the corresponding orthophosphate. The common phosphate of sodium is Na 2 HP0 4 . It is accord- ingly disodium monohydrogen mono-meta-phosphate. But the pyrophosphate of sodium is Na 4 P 2 7 . The name pyro- phosphate does not indicate the composition, whereas the explicit technical term sodium tri-meta-di-phosphate at once tells the whole story of its structure, for it tells us that the acidic element in the compound is phosphoric phosphorus. The term diphosphate tells us that it contains two phos- phorus atoms, and the term tri-meta informs us that it differs by three molecules of water from the normal structure of two molecules of sodium phosphate added together. Two molecules of normal phosphoric hydroxide added together would make the formula H 10 P 2 O 10 . . Three molecules of water split off from that formula would leave H 4 P 2 7 . The sodium salt corresponding to H 4 P 2 7 is Na 4 P 2 7 . Borax is a sodium penta-meta-tetra-borate, because it is the sodium salt formed out of a boric acid resulting from the splitting off of five molecules of water from four molecules of normal boric hydroxide. It is called a tetra-borate because it contains four boron atoms. A borate must, of course, be formed from boric acid, and boric boron has a valence of 3. Normal boric hydroxide is accordingly (HO) 3 B or H 3 B0 3 . Four molecules of H 3 B0 3 would be H 12 B 4 12 , and after split- ting off five molecules of water from H 12 B 4 12 , we would have H 2 B 4 7 left, which is penta-meta-tetra-boric acid, and the sodium salt of it is accordingly ]STa 2 B 4 7 . 224. From the facts stated in the foregoing paragraphs, the student will see that hypochlorous fluoride would be C1F; hypochlorous oxide must be C1 2 ; hypochlorous acid must 122 A CORRESPONDENCE COURSE IN PHARMACY be HOC1; potassium hypochlorite is KOOl; and calcium hypochlorite Ca(C10) 2 . Hypophosphorous oxide must be P 2 0. Hypophosphorous acid may be either HOP or it may be HOPH 2 0, in which the student can readily see that the algebraic combining number of the phosphorus is still +1. Phosphorous oxide must be P 2 3 ; phosphorous chloride must be PC1 3 ; and phosphorous acid may be either (HO) 3 P or HP0 2 , or it may be even (HO) 2 PHO, for in all of these formulas of acids it is clearly seen that the phosphorus atom has an algebraic combining number of +3. The student can readily see at once that H 5 P0 5 , H 3 P0 4 , HP0 3 , and H 4 P 3 7 must all be different kinds of phosphoric acid, because in every one of them the phos- phorus atom clearly has an algebraic combining value of +5. Upon examination of the formulas H 6 S0 6 , H 4 $0 5 , and H 2 S0 4 , it is seen that these formulas all represent different kinds of sulphuric acid, the first being normal sulphuric acid or sulphuric hydroxide, the second mono-meta-sulphuric acid, and the third di-meta-sulphuric acid, because in all of them the sulphur atom is seen to have a combining value of +6. The formula CaH 4 S0 6 evidently represents a calcium sulphate derived from normal sulphuric hydroxide. CaH 2 S0 5 is a sulphate derived from the mono-meta-sulphuric acid, and CaS0 4 is calcium di-meta-sulphate. FeH 2 S0 5 is ferrous mono-meta-sulphate, which is common ferrous sul- phate, or green vitriol, minus its water of crystallization. Test Questions 1. What is the meaning of Ag ? 2. Why is the symbol representing lead Pb instead of L ? 3. What is I 2 and what is the difference between 21 and I 2 ? CHEMICAL NOMENCLATURE 123 4. What is the difference between 4H and 2H 2 and H 4 ? 5. Which of the following formulas are correct and which are incorrect: (a) HgO; (b) Hg 2 0; (c) HgO a ; (d) Hg 3 ; (e)H 4 ; (f)0 4 ; (g) H 2 C1 2 ? 6. Name the two ions of each of the following : ferrous chloride, ferric chloride, sodium nitrate, potassium hy- droxide, phosphoric acid, ammonium sulphate, ammonium chloride, arsenous oxide, antimonous sulphide, potassium antimonite. 7. Write the molecular formulas of the following named compounds: (a) carbonic acid; (b) sodium carbonate; (c) calcium bromide ; (d) potassium fluoride ; (e) silver iodide , (f) nitrogen iodide; (g) barium sulphide; (h) calcium oxide; (i) sulphide of carbon ; (j) sulphide of trivalent arsenic ; (k) the sulphide of quinquivalent antimony; (1) the hydroxide of boron ; (m) three molecules of the sulphate of trivalent iron; (n) two molecules of aluminum sulphate; (o) seven molecules of magnesium hydroxide; (p) two molecules of bismuth nitrate, containing the bismuth as a triad. 8. In which of the two molecules Bi 2 (00 3 ) 3 and (OBi) 2 C0 3 is the bismuth trivalent, and what is the combining value of the bismuth in the other ? 9. Write the empiric formula of H 2 2 . 10. Write the empiric formula for H 2 2 4 . 11. Write the molecular formula for the phosphate of triad iron. 12. Write the molecular formula for barium phosphate. 13. Write the molecular formulas for : (a) hypochlorous acid; (b) chlorous acid; (c) chloric acid; (d) perchloric acid ; (e) sodium bromate; (f) potassium periodate; (g) hyposul- phurous acid; (h) sulphuric acid; (i) sulphurous acid; (j) magnesium sulphite; (k) ferrous sulphate; (1) mercuric sulphate; (m) mercurous sulphate; (n) mercuric oxide; (o) sulphurous oxide; (p) hyponitrous acid; (q) nitrous acid; 124 A CORRESPONDENCE COURSE IN PHARMACY (r) nitric acid ; (s) hypophosphite of magnesium ; (t) ferrous hypophosphite ; (u) ferric hypophosphite; (v) phosphoric oxide; (w) carbonic chloride; (x) ammonium phosphate. 14. What is the difference between sulphuric sulphur, sulphurous sulphur and hyposulphurous sulphur ? 15. What is the difference between nitric nitrogen, nitrous nitrogen and hyponitrous nitrogen ? 16. What is the difference between hypochlorous chlorine, chlorous chlorine, chloric chlorine and perchloric chlorine ? 17. What is the combining value of periodic iodine ? 18. What is the algebraic combining value of phosphoric phosphorus ? 19. What is the highest algebraic combining number possible to carbon, and what is carbon with its highest combining value called ? 20. Give the technical name of 00 and of CQ 2 ? of H 4 0. 21. What is the algebraic combining number of the acidic element in: (a) hypophosphorous acid; (b) calcium nitrate; (c) ferric sulphate; (d) ferrous sulphate; (e) sodium periodate ; (f ) potassium chlorate ; (g) potassium antimonite ; (h) sodium arsenate; (i) sodium hyposulphite; (j) sodium tetraborate; (k) pyrophosphate of iron; (1) orthophosphate of iron ; (m) metaphosphate of iron ; (n) any decaborate ? 22. How many different kinds of phosphoric acids are possible, containing only one phosphorus atom ? 23. How many different kinds of sulphuric acids are possible, containing only one sulphur atom? 24. What kind of a meta-acid is H 2 B 4 7 ? 25. Write the formula for normal nitric hydroxide. 26. Write the formula for nitric mono-meta-hydroxide. 27. Write the formula for nitric di-meta-hydroxide. 28. Write the formula for normal sulphuric hydroxide. 29. Write the formula for carbonic hydroxide of normal composition CHEMICAL NOMENCLATUBE 125 30. Write the formula for mono-meta-carbonic hydroxide, 31. What kind of a carbonate is Oa00 3 ? 32. What kind of a carbonate would you call CaH 2 C0 4 ? 33. What kind of a carbonate would you call KHC0 3 ? 34. What kind of a carbonate is K 2 C0 3 ? 35. Why are all the compounds just named called carbonates ? 36. What is the difference between a chlorate and a perchlorate, and why are both called chlorates ? 37. What is a thiosulphate and what is a hyposulphite ? 38. Give the formula for thiocarbonic acid of normal structure. 39. What would you call a compound of potassium oxygen and pentad iodine ? 40. What would you call a salt containing carbon as its acidic element? 41. What would you call a salt in which the acidic element is silicon? 42. What would you call a salt in which the acidic element is tetrad sulphur ? 43. What would you call a salt in which antimony with five bonds is the acidic element ? 44. How many bonds does the nitrogen have in a hyponitrite ? 45. How many different numbers of bonds can the nitrogen atom have in nitrates ? 46. How many different numbers of bonds can the arsenic atom have in arsenites ? 47. Write the formula for tri-meta-di-phosphoric acid. 48. Write the formula for di-meta-phosphoric acid. 49. If such a compound existed as penta-meta-tetra- phosphoric acid, what would be its formula ?' 50. How many kinds of ferric hydroxide can exist contain- ing but one iron atom ? 126 A CORRESPONDENCE COURSE IN PHARMACY 51. Write the formula for tri-meta-di-ferric hydroxide. 52. Write the formula for a salt containing hexad chromium as its acidic element. 53. What is the difference between acidic manganic manganese and permanganic manganese ? 54. Write the formula for potassium dichromate and state why it is called a dichromate. LESSON TEN XV The Relative Intensity of the Chemical Combining Energy of Different Elements 225. Different elements possess widely different degrees of intensity of chemical energy, or tendency to combine with other elements or to attack other substances chemically. Among the strikingly energetic elements are fluorine, chlorine, bromine, phosphorus, potassium and sodium. Oxygen also may be said to show considerable inclination to enter into chemical combination, at least at temperatures somewhat above the common. Among the elements of comparatively indifferent chemical energy under ordinary conditions are carbon, silicon, boron, nitrogen, gold and platinum. Neon, argon, krypton and xenon show no inclination what- ever to enter into chemical combination. The properties of the element fluorine can be studied only with the greatest difficulty, if at all, because whenever that element is liberated from one of its compounds, it instantly attacks some other substance and forms some new chemical combination by uniting with some element in that other substance. Chlorine and bromine are also strikingly energetic in their chemical action upon other substances. Fluorine, chlorine and bromine decompose water and take the hydrogen away from it, setting the oxygen free. They 127 128 A CORRESPONDENCE COURSE IN PHARMACY also attack metals vigorously by combining with them. Fluorine attacks and decomposes glass. Phosphorus ignites and burns fiercely in oxygen and in chlorine and also combines with great velocity with bromine. It decomposes potassium chlorate with great violence. Potassium and sodium and, in still greater measure, caesium and rubidium, decompose water by combining with the oxygen of the water, or with its hydroxyl, and liberating hydrogen. The alkali metals must be preserved submerged in benzoin or some other liquid hydrocarbon (hydrocarbons contain only carbon and hydrogen), to prevent their instant and violent oxidation or combination with oxygen. Carbon is so indifferent chemically that diamond, graphite, coal and charcoal remain permanently unaltered in the presence of an abundance of oxygen, except when heated strongly. Crystallized silicon, adamantine boron and nitrogen are even more indifferent than carbon. But silicon and boron immediately ignite in fluorine gas, owing to the intense chemical energy of the latter. 226. Elements differing widely from each other in their chemical quality show the greatest inclination to enter into combination with each other. Compounds formed by very energetic positive elements with very energetic negative ele- ments are stable; but compounds formed by elements exhibiting a low degree of intensity of chemical energy are comparatively unstable. The fluorides and chlorides of the alkali metals and alkaline earth metals are very stable compounds, because fluorine and chlorine are the most energetic of the decidedly negative elements and the alkaline earth metals are the most energetic of the decidedly positive elements. But most of the com- pounds formed by nitrogen show a remarkable tendency to decompose, often with explosive violence, because of the COMBINING ENEBGY OF DIFFEBENT ELEMENTS 129 indifferent ability or inclination of nitrogen to hold other elements in combination with itself. 227. Some acids are mnch more corrosive or destrnctive or energetic in their chemical action than other acids, and this difference does not depend npon their hydrogen or oxygen, since those elements belong to all true acids. But it must depend at least primarily upon the acidic element which characterizes the acid. Carbonic acid is H 2 C0 3 , or rather (HO) 2 CO. Sulphurous acid is H 2 S0 3 , or rather (HO) 2 SO. Sulphurous acid is a much more energetic acid than carbonic acid, and the difference between them is evidently due to the fact that the acidic element in one is sulphur, while in the other it is carbon. It is true that we have three kinds of hydroxyl acids in which sulphur is the acidic element, and that these three acids nevertheless differ greatly in their energetic action upon other substances. Sulphuric acid, H 2 S0 4 , is decidedly stronger than sulphurous acid, H 2 S0 3 , for sulphuric acid decomposes the salts of sulphurous acid and changes them into sulphates, while sulphurous acid does not decompose sulphates or change them into sulphites, and so sulphates are much more stable compounds than sulphites. Hypo- sulphurous acid, H 2 S0 2 , is weaker than either sulphuric or sulphurous acid. It may be said that the difference between these three acids, all containing sulphur as the acidic ele- ment, may be due not to that acidic element, since that is the same in all three, but to the differences in the proportion of oxygen, were it not for the fact that acids containing a larger proportion of oxygen are sometimes weaker acids than others that contain less oxygen. Boric acid, H 3 B0 3 , is a much more feeble acid than phosphorous acid, H 3 P0 3 , although the boric acid contains a larger proportion by weight of oxygen, the weight of the boron atom being only 11, while that of the phosphorus atom is 31. Sulphuric 130 A CORRESPONDENCE COURSE IN PHARMACY acid, H 2 S0 4 , is more destructive and energetic than chromic acid, H 2 Cr0 4 . An element performing the acidic function forms a stronger acid if it exercises a high combining value than the same element forms if it has a lower algebraic combining number. The sulphur in sulphuric acid is by no means identical in all respects with the sulphur in sulphurous acid, nor with the sulphur in hyposulphurous acid, for the chemical combining value of the sulphuric sulphur contained in sulphuric acid and all other sulphuric compounds is '+6; the chemical com- bining value of sulphurous sulphur contained in all sul- phurous compounds is 4-4, and that of hyposulphurous sulphur contained in all hyposulphurous compounds is only +2. This, then, explains the differences between sulphuric acid, sulphurous acid and hyposulphurous acid. 228. Some alkaline hydroxides are more corrosive and destructive, or more decidedly alkaline or stronger, or chemically more energetic than others. This difference can- not be due to the oxygen and hydrogen, which are common to all of them; it must be due to the basic element in them. Potassium hydroxide is decidedly more powerful as a base than lithium hydroxide. This must be due to the difference between potassium and lithium. 229. The relative intensity and power of different elements as chemical agents depend upon their polarity, valence, atomic weight, specific weight and their relative position in the natural system of classification of the elements known as the periodic system. It is also affected by physical conditions, as by solubility or want of solubility or different degrees of solubility of the compounds formed, or by their volatility or want of volatility. The apparent energy of one element is further decidedly influenced by the character and quantity of the element or elements with which it enters into combination* COMBINING ENERGY OF DIFFERENT ELEMENTS 131 230. Elements capable of performing the basic function form more powerful bases if their specific weight is low; weaker bases if their specific weight is high. In other words, the light metals are strongly basic and the heavy metals less strongly basic. The hydroxides of most of the light metals are destructive, while the hydroxides of heavy metals are not so. 231. Of the light metals, those having a low valence are more decidedly energetic in their chemical action and form stronger bases than those having a higher valence. It is equally true of the heavy metals that they are more strongly basic when of low valence than when exercising a high valence. Metals exercising a valence of more than 3 do not perform a basic function at all, but may instead perform the acidic function. 232. Light metals belonging to the same natural family or group, and therefore having the same valence, differ from one another as to the intensity of their chemical energy, according to their atomic weights, those having the higher atomic weights being more energetic and more powerfully basic than those having smaller atomic weights. 233. The hydroxides of all non-metallic elements are acids. In general, the hydroxyl acids formed by the non- metallic elements are more decidedly acid in their character the higher their algebraic combining number is, other things being equal. But non-volatile acids form more permanent salts than volatile acids, and more volatile acids form less permanent salts than less volatile acids. 234. The halogens, fluorine, chlorine, bromine and iodine, when they exercise negative polarity or form fluorides, chlorides, bromides and iodides, exhibit an intensity of chemical energy in the inverse order of their atomic weights. The student should note that this behavior of the halogens is the very opposite of the behavior of the alkali metals. 132 A CORRESPONDENCE COURSE IN PHARMACY Fluorine is the most energetic of the halogens, because it has the smallest atomic weight of all of them, while caesium is the most energetic of the alkali metals, because it has the largest atomic weight of all of those metals. But when chlorine, bromine and iodine perform the acidic function and accordingly exercise positive polarity, the stability of the salts they form is in the order of their atomic weights. Iodates are more permanent than bromates and chlorates, and the bromates are more permanent than the chlorates; the chlorides are more permanent than the bro- mides or iodides, and the bromides are more permanent than the iodides. XVI Chemical Reactions 235. Chemical changes are called chemical reactions. They are rearrangements of the atomic linking in the mol- ecules of matter. The substances which take part in chemical reactions are called the factors, and the substances formed by the reaction are called the products. The factors may be two or more, but chemical changes sometimes take place in one single substance, so that we may have but one factor. The products are most frequently two, but there may be more than two, and there may be but one product. When two factors form one product, the reaction is called a synthesis. When one factor splits up into two or more products, we call the reaction dissociation. When two factors react upon each other and both of the factors are decomposed, with the result that two new products CHEMICAL REACTIONS 133 are formed, the reaction is called a metathesis, or double decomposition. In any reaction where one element displaces another ele- ment in a compound factor, with the result that two products are formed, one of which is or contains the displaced ele- ment, we call the reaction substitution. The following examples will suffice to illustrate these several kinds of reactions : Fef2l=FeI 2 represents a synthetical reaction. CaC0 3 =CaO+C0 2 represents a dissociation. CaO+C0 2 =CaC0 3 represents a synthetical reaction. ZnO-f2HCl=ZnCl 2 +H 2 is an equation representing a metathesis. Zn+2HCl=ZnCl 2 +H 2 represents substitution. H 4 C+2C1=H 3 CC1+H01 is also a case of substitution. 236. In order to explain the course of chemical reactions we shall find it convenient to use the term radical to indicate any atom or group of atoms transferred from one molecule to another, or liberated from a molecule, or entering into combination with another atom or group of atoms. A radical differs from a molecule in that the radical has unused combining power by means of which it can enter into combinations, while a molecule has all the combining power of its atoms fully occupied, so that the molecules do not enter into chemical combination in any manner dependent upon valence. The student has also learned that molecules may be divided into two ions —the positive ion and the negative ion. These ions are radicals. . In the molecule KC10 4 , K is the positive ion and the group C10 4 is the negative ion. K is the positive radical and C10 4 is the negative radical. 237. Malaguti's Doctrine. Chemical reactions are subject to a tendency toward the pairing of the strongest radicals of opposite polarity. In other words, the strongest positive 134 A CORRESPONDENCE COURSE IN PHARMACY radical present has a tendency to unite with the strongest negative radical present, because the strongest positive radicals form the most stable and permanent compounds with the strongest negative radicals, and it is self-evident that the tendency of all matter in the universe must be in the direction of the formation of molecules of the greatest degree of stability, or in other words, molecules best able to resist change. We have already observed that some acids are stronger than other acids, and that some bases are stronger than other bases. These facts depend upon the same tendency. The light metals are more strongly basic than the heavy metals, and the metals having a low valence are more strongly basic than those having a higher valence. Of any two metals having the same valence and belonging to the same natural family in accordance with the periodic system, the metal having the highest atomic weight is a stronger positive radical than another metal having a smaller atomic weight. Acidic elements having a higher algebraic combining number form stronger acids than the same elements when they exercise a lower algebraic combining number. 238. But physical conditions affect chemical reactions very decidedly. The degree of solubility or of volatility of the products may nullify the tendency indicated by Malaguti s doctrine. Chemical reactions proceed more readily and more nearly to completion when one of the products is eliminated from the arena of chemical action as fast as formed 239. Berthollet formulated the following doctrine : When- ever the formation of a volatile product is possible at the temperature at which the reaction occurs, then the course of the reaction will be determined accordingly, and that volatile product will be formed. The same proposition may be stated in this way: Chemical reactions are facilitated and rendered more complete when one or more of their products are gases. CHEMICAL EEACTIOKS 135 Calcium carbonate can be decomposed by heat, because one of the products is the gas C0 2 . Ammonium chloride and calcium oxide heated together produce calcium chloride, water and ammonia, because the water and ammonia are volatile. Mercury sulphate and sodium chloride heated together form mercury chloride and sodium sulphate, if the temperature is high enough to vaporize the chloride of mercury. 240. Another doctrine formulated by Berthollet is to the effect that whenever by any double decomposition between com- pounds in solution an insoluble or less soluble compound can be formed, then that insoluble or less soluble compound will be formed. An equivalent statement in different words is that chemical reactions between substances in a state of solution are facilitated and proceed to completion when one of the products is insoluble or only sparingly soluble in the liquid. If you know that phosphate of iron is insoluble in water, then you know also that you cannot mix a water-solution of any phosphate with a water-solution of any iron salt without getting a precipitate of phosphate of iron. A solution of acetate or nitrate of lead or any other soluble lead compound mixed with any solution of a sulphate will give a precipitate of lead sulphate, because lead sulphate is insoluble. The well known fact that calcium oxalate is insoluble tells us that if it is desired to remove the calcium from any solution, all that is necessary is to add a solution of some oxalate, because that would cause the formation of calcium oxalate, which would be precipitated. To know that the oxides, hydroxides, sulphites, carbonates, oxalates and phosphates of the heavy metals are all insoluble in water is to know that solutions of the water-soluble salts of those metals cannot be mixed with the solutions of any of the soluble hydroxides, sulphites, carbonates, oxalates or phosphates without producing pre- cipitates. 136 A CORRESPONDENCE COURSE IN PHARMACY 241. Malaguti's doctrine would lead us to the conclusion that when a mixture is made of a solution of sulphate of potassium and acetate of lead, no precipitate would be formed, and in fact no reaction would take place, because, of the two positive radicals, potassium and lead, potassium is the stronger, and of the two negative radicals, the sulphate radical and the acetate radical, the former is the stronger, and the tendency toward the union of the stronger positive radical with the stronger negative radical would prevent any change, because the potassium and the sulphate radical are already united. But a reaction does take place and sulphate of lead is formed, despite Malaguti's doctrine, because lead sulphate is insoluble. The tendency toward the formation of insoluble compounds by double decomposition always annuls or overcomes the tendency toward the pairing of the strongest positive and negative radicals, unless both tendencies operate in the same direction. 242. From what has been said, it is evident that a good chemist must know the relative solubilities and volatilities of chemical compounds in order to be able to make a prog- nosis of chemical reactions. 243. Substances in a solid state do not readily react upon each other. Gaseous substances react with each other more freely than solids, but less favorably than liquids. Substances in a liquid condition react most readily and completely, especially when held in solution by a liquid taking no part in the reaction. Solids react with liquids more readily than with other solids or with gases. Gases react readily with substances in a liquid condition. Substances which do not react upon each other at all in a dry condition may do so immediately upon being wetted. CHEMICAL KEACTIONS 137 Solids which do not react upon each other at all at the ordinary temperature may react upon each other com- paratively freely when heated to the temperature at which they liquefy or the temperature at which one of the products formed by the reaction becomes liquid. 244. Chemical Solution. Water-soluble salts and some other water-soluble compounds are generally produced by chemical solution ; that is, by the action of one factor in liquid form upon another factor in the solid or liquid or gaseous form. The solvents used are most commonly acids or alkalies, but occasionally solutions of salts. The acids or other chemical solvents are said to be neutral- ized or saturated by metals or metallic compounds dissolved in them. Acids are among the most common materials used in the laboratory for the production of other salts. Metals or their oxides, hydroxides or carbonates are dissolved in hydrogen chloride or so-called hydrochloric acid to produce metallic chlorides; in nitric acid to produce nitrates ; in sulphuric acid to make sulphates ; in acetic acid to produce acetates, and so on. This method is practicable whenever the products are water-soluble salts together with water, or water-soluble salts together with gaseous products, or both water and gas together with the salt. 245. The Action of Heavy Metals upon the Common Acids. In common parlance, it is said that the acids attack certain metals, but it is clearly more consistent to say that the metals attack the acids, because while the metals are dissolved and turned into metallic compounds, they are not decom- posed, while it is strictly true that the metal causes the acid to decompose. Gold and the platinum metals do not attack any acid, but they dissolve in the mixture of nitric acid and hydrogen 138 A CORRESPONDENCE COURSE IN PHARMACY chloride which is called nitro-hydrochloric acid, or aqua regia. Chlorides of gold and platinum are formed with the free chlorine contained in that mixture. Aluminum decomposes hydrochloric acid, forming alu- minum chloride and setting the hydrogen free. It does not attack other acids. Antimony is only physically a metal and therefore does not perform the basic function. Hence, when it decomposes nitric acid, it is simply oxidized to form insoluble antimonious oxide. Other acids are not affected by antimony. Tin decomposes strong nitric acid, forming what is called meta-stannic acid. It also decomposes hydrochloric acid, forming stannous chloride. Sulphuric acid is not decom- posed by tin. Bismuth quickly decomposes nitric acid, forming bismuth nitrate. It also attacks hot concentrated sulphuric acid, but not hydrochloric acid. Silver decomposes dilute nitric acid, forming silver nitrate. It also decomposes hot concentrated sulphuric acid, but it does not act upon hydrochloric acid. Lead dissolves in and decomposes nitric acid, forming lead nitrate, but it scarcely affects hydrochloric and sulphuric acid. Copper vigorously attacks nitric acid and also decomposes hot strong sulphuric acid, but it is not dissolved by hydro- chloric acid or diluted sulphuric acid. Nickel decomposes hydrochloric acid, sulphuric acid and nitric acid, forming nickelous salts. Iron and zinc readily decompose the diluted acids. 246. Hydrochloric acid dissolves zinc, aluminum, iron, nickel and tin. It does not dissolve lead, copper, mercury, silver, gold, platinum, arsenic, antimony and bismuth. Diluted sulphuric acid dissolves zinc, iron and nickel, setting hydrogen free, but it does not dissolve aluminum, CHEMICAL REACTIONS 139 lead, copper, mercury, silver, gold, platinum, tin, arsenic, antimony and bismuth. Concentrated sulphuric acid dissolves copper and, if hot, it is also attacked by mercury, silver and bismuth. When mercury, silver or bismuth attacks sulphuric acid, the products formed, in addition to the sulphates, are water and S0 2 . Moderately dilute nitric acid, especially when warm, dissolves zinc, iron, nickel, lead, copper, mercury, silver, arsenic and bismuth. Arsenic is oxidized to arsenic acid and the other metals form nitrates. So much of the nitric acid used as does not enter into the formation of the nitrate yields water and the gas NO, which . oxidizes in the air to red vapors of N 2 4 or N0 2 , or both, according to the temperature. It is commonly said that "red nitrous vapors" are formed when metals are dissolved in nitric acid. Gold and very dilute nitric acid dissolves iron and zinc, forming ferrous nitrate or zinc nitrate, together with ammonium nitrate and water. This fact is particularly interesting and instructive, for it will be seen that the ammonium nitrate can only be formed by changing the algebraic combining number of a part of the nitrogen from +5, which is the combining value it possesses as the acidic element of nitric acid, to —3, which is the combining value it has in any ammonium compound. This may most clearly be shown by the following equation: 4Zn+10HONO 2 =4Zn (N"0 8 ) 2 +H 4 NON0 2 +3H 2 0. The four zinc atoms before the metal is dissolved in the nitric acid have an algebraic com- bining number of 0. But in the four molecules of zinc nitrate which the metal forms, the zinc atoms have a total algebraic combining number of +8, for zinc in combination has a valence of 2. The four zinc atoms, therefore, gained eight units of combining value. The first nitrogen atom in the molecule H 4 NON0 2 , or the nitrogen of the ammonium, 140 A CORRESPONDENCE COURSE IN PHARMACY has five bonds, four of which hold the four hydrogen atoms, while the fifth connects the H 4 N to the oxygen atom stand- ing between the two nitrogen atoms of the H 4 NON0 2 , and as the four bonds holding the hydrogen are negative bonds, while the fifth bond must be a positive bond, and as —4 added to +1 makes -3, the nitrogen atom of the H 4 N has a value of -3. Inasmuch as that nitrogen atom was furnished by the original HON0 2 , in which all the nitrogen has a value of +5, it follows that the nitrogen reduced lost eight units, for the difference between +5 and —3 is, of course, eight units. These eight units lost by the nitrogen atom are the eight units gained by the four zinc atoms. Concentrated nitric acid is not attacked by iron, but dis- solves lead, copper, mercury, silver, arsenic and bismuth. It is not affected by gold and platinum. It oxidizes tin to insoluble so-called meta-stannic acid, and antimony to insol- uble antimonious oxide. 247. The foregoing statements must not be construed to mean that metals which are not dissolved by the acids named may not be superficially affected to a considerable degree. Diluted sulphuric acid does take up copper and form copper sulphate, so that copper vessels are corroded by diluted sulphuric acid. But the diluted acid dissolves the metal so slowly and to such a limited extent that we would not think of using diluted sulphuric acid for the purpose of dissolving copper. Tin is not affected by sulphuric acid, but tinned iron or "tin plate," however heavily coated with pure tin, is com- paratively soon destroyed by not only very dilute sulphuric acid, but even by boric acid solutions and by very weak acetic acid, probably because the tin coating is not so impervious that the iron is absolutely protected. 248. Acids are readily attacked by metals if the salts formed by the reaction are soluble in the liquid. But metals CHEMICAL REACTIONS 141 cannot be dissolved in the acids if the salts formed are insoluble in the liquid. Thus, strong nitric acid does not attack iron, because the iron nitrate is not soluble in strong nitric acid, but diluted nitric acid does attack iron, because the iron nitrate is soluble in diluted nitric acid and in water. Again, lead is not soluble in moderately diluted sulphuric acid, because lead sulphate is insoluble both in diluted sul- phuric acid and in water. But the lead is acted upon by concentrated sulphuric acid, because lead sulphate is soluble in that acid when of sufficient strength. 249. Chemical reactions occurring in processes of manu- facture of chemical compounds are very generally of such character that the products formed are easily separable from each other. Were not this the case, they would be practically useless. A double decomposition resulting in the formation of one product soluble in the liquid in which the reaction takes place and another insoluble in that liquid is useful or practicable, because the insoluble substance is easily sepa- rated from the soluble. A reaction resulting in the formation of one product which is volatile and another which is not volatile is also workable, because the volatile product can be easily dissipated and separated from the non-volatile. Eeactions in which water is the only by-product are also useful, because water is volatile and can be eliminated, or, if the principal product is obtained dissolved in the water, it can be recovered from the solution by evaporation of the water and crystallization of the solid. Metallic salts are successfully made by the solution of the metal in the appropriate acid, because the by-product is either hydrogen or some other gas. Metallic salts are easily made from metallic oxides by dissolving these in acids, because the by-product is water. Salts can readily be made 142 A CORRESPONDENCE COURSE IN PHARMACY by saturating acids with carbonates of the metals, because the by-products are water and the gas C0 2 . 250. Neutralization is effected in solutions by mixing acids and alkalies, or acids and alkali carbonates, or acids and bases, etc., in the requisite proportions, adding either the acid to the metallic compound or the metallic compound to the acid. Acid salts are also neutralized by alkalies and alkali carbonates. Whenever practicable, the point of exact neutralization of an acid by a base or of a base by an acid is determined by a color reagent. The most common and useful reagent of this kind and for this purpose is litmus, which is generally employed in the form of litmus paper, which is unsized paper dipped in a solution of litmus and then dried. Litmus is a blue pigment which is very readily turned red by acids and blue by alkalies. Bine litmus paper is made from the unaltered solution of the pigment, while red litmus paper is made from a litmus solution to which just enough pure hydrochloric acid has been added barely to turn its color red. Litmus paper can also be made in such a way that it is neither red nor blue, by carefully adding just enough of the hydrochloric acid to the litmus solution used. A liquid which turns blue litmus paper red is said to have an acid reaction on test paper; one that turns red litmus paper blue is said to have an alkaline reaction upon test paper. A liquid which does not change the color of either red or blue litmus paper is said to have a neutral reaction on test paper, or to be neutral to test paper. The test is made by touching a small strip of the test paper with the liquid. 251. Salts of normal structure formed by strong acids with weak bases have an acid reaction on test paper, but those formed by weak acids with strong bases have an alkaline reaction on test paper. Only salts formed by strong CHEMICAL REACTIONS 143 acids with strong bases or weak acids with weak bases have a neutral reaction on test paper. Salts still containing some of the replaceable hydrogen of the acid are said to be acid salts, or to have an acid structure. Bicarbonate of potassium is such a salt, but bicarbonate of potassium, although of acid structure, has an alkaline reaction on test paper, because potassium is one of the most powerful basic elements, while the carbonate radical is a very feeble acid-radical. A salt containing a larger proportion of the basic element than that contained in a salt of normal structure is called a basic salt. Subsulphate of iron is such a salt, though a solution of subsulphate of iron has an acid reaction on test paper, because iron is not sufficiently strongly basic to form salts of neutral reaction with such a powerful acid as sulphuric acid. A solution of alum has an acid reaction, because aluminum is very feebly basic, although alum aiso contains potassium. 252. When acids are saturated with the metal or with metallic oxides, hydroxides or carbonates, the proportions of these materials employed are determined beforehand according to the atomic and molecular weights, even if an excess of the metal or metallic compound is to be used. When salts of normal composition are to be prepared and the reaction on test paper does not indicate the composition, the exact theoretical proportions are used. When iron or zinc is dissolved in sulphuric acid, the metal is added in excess, because the acid cannot possibly dissolve any more of the metal than the quantity required to form the sulphate. But when mercury is dissolved in nitric acid, it is necessary that the proportions of mercury and nitric acid be carefully attended to, because if the nitric acid is in large excess, mercuric nitrate is formed, while with a less propor- tion of nitric acid, mercurous nitrate of normal structure is 144 A CORRESPONDENCE COURSE IN PHARMACY formed, and with a still smaller amount of nitric acid, a basic mercurous nitrate is obtained. 253. The proportions to be employed of the factors of a chemical reaction are, of course, indicated by the molecular weights and atomic weights. In constructing a working formula, it is therefore necessary first to write down the chemical equation that represents the reaction taking place in the process, and when this equation is properly balanced, the atomic or molecular weights will show the quantities required of the factors, and also the quantities obtained of the products. But the proportions found in this way are only the theoretical proportions, and they may not be work- able, because it is generally the case that the reaction is not complete under those conditions. If it is necessary that one of the factors in a chemical reaction be completely decomposed or consumed, then the other factor or factors must be used in greater proportion than that required by theory. If a double decomposition between A and B is to be effected, A must be used in excess over the theoretical proportion, if it is necessary that B shall be completely decomposed; if A must be completely decomposed, then B must be used in excess. In other words, the course and relative completeness of chemical reactions may be materially affected by the relative masses of the factors. When a solution of sodium sulphate and a solution of barium acetate are mixed in the proportions required for even or complete metathesis, barium sulphate and sodium acetate will be formed, and the reaction proceeds to completion, because the barium sulphate is insoluble. But if barium sulphate is placed in water containing a large amount of sodium carbonate in solution, the sodium carbonate will gradually decompose . the barium sulphate so that sodium CHEMICAL REACTIONS 145 sulphate and barium carbonate are formed, and the insoluble solid matter in the liquid will become a mixture of barium carbonate and barium sulphate. If the sodium salts, which are soluble, are removed from time to time and fresh portions of sodium carbonate added, the entire amount of barium sulphate can be finally converted into bariuin carbonate. Mass reactions of this kind are numerous. 254. The most common and numerous chemical reactions are double decompositions, and, as already shown, double decompositions are most readily effected between reagents in a state of solution, under Berthollet's law with regard to the formation of insoluble or less soluble products. In other words, they are precipitations. Other common reactions between acids and bases are also double decompositions. The student should therefore learn to write chemical reactions representing double decompositions. He should bear in mind that any double decomposition between two substances is simply a mutual interchange of radicals. It is like an exchange of partners in a quadrille ; two couples meet and exchange partners. Each factor in a chemical reaction such as is called double decomposition is a couple, consisting of the positive radical and the negative radical. The positive radical of one factor gives up its negative radical to the positive radical of the other factor and takes the negative radical from that factor in exchange. For example, sil- ver nitrate meets sodium chloride. The silver and the sodium are the positive radicals, the nitrate radical (N0 3 ) and the chlorine are the negative radicals. The silver gives up its N0 3 to the sodium, taking the chlorine in exchange. This double interchange may also be likened to an exchange of horses between two riders. A red man on a white horse and a white man on a red horse meet, and the two men 14G A CORRESPONDENCE COURSE IN PHARMACY exchange horses. Both men are still there and so are the horses, hut they have changed positions. That is precisely what takes place between the several radicals concerned in a double composition. When mercuric chloride and potassium iodide, both in solution in water, are mixed with each other, the mercury leaves the chlorine and takes up the iodine instead, while the potassium, giving up the iodine to the mercury, takes up the chlorine in exchange. We started with a combina- tion of mercury and chlorine and a combination of potassium and iodine; we finish with a combination of mercury and iodine and a combination of potassium and chlorine. The equation representing the reaction is as follows: HgCl 2 +2KI=HgI 2 +2KCl. The reason why two molecules of KI are necessary is that the mercury atom has a valence of 2, whereas the atoms of chlorine, potassium and iodine each have a valence of only 1, and as we must have the same number of positive bonds as of negative bonds in any molecule, it follows that a molecule of mercuric chloride must contain two chlorine atoms to the one mercury atom, and a molecule of mercuric iodide must contain two iodine atoms to the one mercury atom. The two chlorine atoms contained in HgCl 2 require two potassium atoms to form potassium chloride, and two molecules of KI are required to furnish those two potassium atoms for the potassium chloride, as well as to furnish the two iodine atoms for the mercuric iodide. The easiest rule to follow is this: Find the valence of the positive radicals of the two factors^ and then tahe the number of atoms or molecules of each that . will give you a common multiple of the numbers expressing those valences. For example, if the valence of one of the positive radicals concerned is 1 and the valence of the other positive radical is 2, then multiply the factor containing the radical having CHEMICAL EEACTIONS 147 a valence of 1 by 2, and multiply by 1 that factor the positive radical of which has a valence of 2. If the valence of the positive radical of one factor is 2 and that of the other is 3, then multiply the 2 by 3 and the 3 by 2. In the reaction represented by the equation ]N"a 2 C0 3 +CaCl 2 = CaC0 3 +2NaCl, the student will see that the positive radicals are the Na and the Ca. The valence of ISTa is 1 and the valence of Ca is 2, but as the Na is multiplied by 2 already and since the formula of the sodium carbonate is Na 2 C0 3 , one molecule of Na 2 C0 3 is sufficient, for the two sodium atoms together form two bonds, and the single calcium atom having a valence of 2 has also two bonds. The fact which the student should keep clearly in view is that the total number of bonds of the positive radical of one of the factors must be the same as the total number of bonds of the positive radical of the other factor. In order that the exchange may be even, it takes two five-dollar bills to match five two-dollar bills. Test Questions The number of questions in this and some of the following lessons may seem too great. Theoretically, it would be better if the lessons were more uniform in length, but as the real purpose of the Course is to insure a thorough understanding on the part of the student, the number of questions bears a close relation to the importance of the subject. It is not necessary that long answers should be written nor that all answers should be expressed in complete sentences. Occasionally "yes" or "no" may serve as an answer. Still, every answer must be clear and precise. If numerical computations are necessary, it is always desirable that the entire work of the problem should be submitted. If merely the answer is given and it is wrong, the instructor has no clue as to what is really the reason for the student's mistakes and so no assist- ance can be rendered. 148 A CORRESPONDENCE COURSE IN PHARMACY 1. What is meant by the factors of chemical reactions ? 2. How many factors are necessary in a chemical reaction ? 3. How many products are formed by any chemical reaction ? 4. What is meant by dissociation ? 5. How many factors are concerned in metathesis ? 6. How many factors are necessary in a synthesis? 7. What general expression is used to signify an alteration in the atomic linking of any molecule or molecules ? 8. What is the difference between an elemental factor and a compound factor ? 9. What is the algebraic combining value of an elemental factor in a chemical reaction ? 10. When two elements enter into direct combination with each other, what is the algebraic combining number of each before the reaction and after the reaction ? 11. What is meant by substitution ? 12. What would you call a reaction in which two factors form but one product ? 13. What would you call a reaction in which one factor furnishes two or three products ? 14. What is the technical term used to designate a reaction in which two factors form two products without any change in the algebraic combining numbers of any of the ions ? 15. Write a chemical equation representing a dissociation reaction. 16. Write a chemical equation representing a synthesis. 17. Write a chemical equation representing a substitution reaction. 18. Write a chemical equation representing a double decomposition. 19. What is the difference between a radical and an ion ? 20. What is the difference between a radical and a molecule ? CHEMICAL REACTIONS 149 21. What radicals are contained in sodium nitrate ? 22. Write symbolic formulas representing the radicals con- tained in ammonium sulphate. 23. By what means is it possible to determine which of several positive radicals is the most powerful and which of several negative radicals is most powerful, in order to predict the result of a chemical reaction under Malaguti's law ? 24. Under what circumstances will the strongest positive radical unite with the weakest negative radical present in a reaction ? 25. Under what circumstances will the results of a metathesis be the direct opposite of those indicated by Malaguti's doctrine ? 26. State the laws of Berthollet governing the direction of metathetical reactions. 27. What happens if you mix a solution of the sulphate of a heavy metal with a solution of phosphate of sodium ? 28. What chemical change, if any, will take place when you mix a solution of ferric chloride with a solution of sodium hydroxide ? 29. What chemical change, if any, will take place if you mix a solution of ferric chloride with a solution of sodium chloride ? Give the reason for your answer. 30. Why will zinc oxide be obtained when zinc carbonate is strongly heated ? What else is formed at the same time ? Why does this reaction take place and what is it called ? 31. What reaction, if any, will take place when you mix a solution of sodium phosphate with a solution of sodium carbonate ? Give the reason for your answer. 32. What reaction will take place when you mix two bromides with each other ? 33. What reaction will take place when you mix several potassium salts with one another ? Give the reason for your answer. 150 A CORRESPONDENCE COURSE IN PHARMACY 34. Will any chemical change take place when you mix a solution of potassium permanganate with a solution of potassium sulphite? If so, why, and what products are possible ? 35. "Write the formula for oxalate of barium and state how it can be made by double decomposition. 36. Lead iodide being insoluble, how would you make it ? 37. What materials are necessary for the preparation of lead phosphate ? 38. If you mix a solution of zinc sulphate with a solution of sodium oxalate, what reaction will take place, if any? State the products formed and what class the reaction belongs to. LESSON ELEVEN XVII Changes of the Algebraic Combining Numbers of Atoms 255. Starting out with the assumption that the total algebraic sum of the positive and negative combining units or bonds of all atoms, free or combined, of all matter is at all times 0, we are led to the conclusion that when- ever the algebraic combining number of any atom is in- creased the algebraic combining number of some other atom or atoms must necessarily be diminished in exact proportion, and vice versa. If one atom gains one unit of combining value, that unit must be lost by some other atom. If any atom loses one unit, some other atom must gain it. If any atom gains two or more units of combining value, it must have received them from one or more other atoms. 256. Units of combining value can be transferred from one atom to another, but their total cannot be added to nor diminished. Whether this proposition be called a chemical law or a mere mathematical device, it is extremely valuable and may be employed as an infallible rule. It serves to clear up many puzzling problems in chemistry, and gives a direct answer to many questions which cannot be readily solved without it. 257. The term oxidation in its narrowest sense means 151 152 A CORRESPONDENCE COURSE IN PHARMACY combination with oxygen. But when HgCl 2 is converted into HgO by double decomposition, HgCl 2 +2KOH=2KCl+HgO+H 2 0, this change is not oxidation, although the Hg gives up its CI and enters into combination with instead. It is also frequently stated that oxidation includes any case in which any compound already containing oxygen is changed into another compound containing a greater proportion of oxygen. But this is not always true. When Na 2 S0 3 S is mixed with H 2 S0 4 the products formed are Na 2 S0 4 +S+S0 2 +H 2 0. The Na 2 S0 3 S contains a smaller percentage of oxygen than either Na 2 S0 4 or S0 2 ; but no one would say that Na 2 S0 3 S has been oxidized to Na 2 S0 4 or to S0 2 . We see instead that the Na 2 S0 3 S has been reduced to S0 2 . When Na 2 S0 3 in water solution is boiled with S the prod- uct formed is Na 2 S 2 3 . The Na 2 S0 3 contains 48 parts of oxygen in 126, while the Na 2 S 2 3 (or Na 2 S0 3 $) contains only 48 parts of oxygen in 158 parts. The proportion of oxygen, therefore, is smaller in Na 2 S0 3 S than in Na 2 S0 3 ; but the Na 2 S0 3 is oxidized to Na 2 S 2 3 , for the sulphur atom added performs the same use in the structure of the Na 2 S0 3 as one of the oxygen atoms in the analogous compound Na 2 S0 4 . The change of S0 3 to H 2 S0 4 by means of H 2 0, S0 3 +H 2 0=H 2 S0 4 , is not called oxidation, although the percentage as well as the number of atoms of oxygen is greater in H 2 S0 4 than in S0 3 . The removal of hydrogen from an organic substance is commonly called oxidation; but such a change may be effected without reference to oxygen and in cases where no oxygen is contained in any of the compounds concerned. The substitution of chlorine or any other negative element in the place of hydrogen in any organic compound is oxidation CHANGES OF ALGEBRAIC COMBINING NUMBERS OF ATOMS 153 of the atom which exchanges hydrogen for chlorine. But if another positive element or atom takes the place of the hydrogen united to any carbon atom in any organic compound, that carbon atom is not oxidized. If the group OH takes the place of a hydrogen atom in a hydrocarbon the change is oxidation, but the conversion of alcohol into ether, 2C 2 H 5 OH=(C 2 H 5 ) 2 0+H 2 0, is neither oxidation nor reduction. The conversion of FeCl 2 into FeCl 3 is generally admitted to be oxidation, or is called oxidation of the FeCl 2 to FeCl 3 , and yet no oxygen is concerned in it unless the laborious explanation (sometimes given) is accepted that the change can take place only in water ; that the chlorine decomposes the water, taking the hydrogen from it to form hydrogen chloride ; that the oxygen of the water thus decomposed by the chlorine combines with the Fe of the FeCl 2 and the chlorine of that FeCl 2 combines with other hydrogen from water, and the oxide of iron and hydrogen chloride thus formed produce FeCJ 3 and H 2 0, thus: and 2FeCl 2 +2Cl+3H 2 0=Fe 2 3 +6HCl, Fe 2 3 +6HCl=2FeCl 3 +3H 2 0. It does not seem to be necessary to discuss the question of the possible steps by which the FeCl 3 is formed. These steps are not demonstrable. But the reaction represented by the simple equation FeCl 2 +Cl=FeCl 3 is clear and intel- ligible and perfectly analogous to the reaction HgI+I=HgI 2 , which is as truly a case of oxidation as the other and which does not require the presence of any other substance. 258. Reduction is generally defined as the opposite of oxidation. The removal of oxygen from any compound is nearly always truly reduction. In the sense in which the writer of 154 A CORRESPONDENCE COURSE IN" PHARMACY this book, in common with many others, would use the term oxidation, the removal of one of the oxygen atoms from HO OH is not reduction, because the atom removed is the one having an algebraic combining number of 0, so that not one of the atoms of the HOOH undergoes any change of value. The transformation of FeCl 3 into FeCl 2 by means of zinc, 2FeCl 3 +Zn==ZnCl 2 +2FeCl 2 , is generally admitted to be a reduction, and we say that the zinc acts as a reducing agent and reduces the FeCl 3 to FeCl 2 . But no oxygen is here concerned. We also speak of reducing Hgl 2 to Hgl by triturating the Hgl 2 with mercury : HgI 2 +Hg=2HgL When CaO is placed in contact with HC1 we obtain CaCl 2 and H 2 0: CaO+2HCl=CaCl 2 +H 2 0, but no chemist would speak of this reaction as reduction, although the Ca is deprived of its oxygen. 259. The manner in which the term oxidation is now used indicates that the original restricted meaning of the term is no longer adhered to. In its broadest sense that term now means an increase of the algebraic combining number of any atom. The use of the word "oxidation" in this broad sense is objectionable on the ground that it is derived from the word oxygen and should, therefore, not be applied to signify changes with which oxygen has nothing to do, and on the further ground that many chemists still employ the term in its original sense. Nevertheless, the need of some term to denote an increase in the true combining value of an atom, or a partial or complete change of the chemical polarity of an atom from negative to positive, or any other kind of aug- mentation of its algebraic combining number, is so urgent CHANGES OF ALGEBRAIC COMBINING NUMBERS OF ATOMS 155 that the word oxidation has been employed for want of a better term, and no other single word has been suggested or used for that purpose. The whole subject of changes in the algebraic combining numbers of atoms is of so great importance that every student of chemistry must learn the fundamental facts con- cerning it before he can form any intelligent idea of some of the most common phenomena of chemical change. 260. Eeduction, in its broadest sense, means a diminution of the algebraic combining number of any atom. 261. Oxidation and reduction, understood in accordance with their broader application as stated in paragraphs 258 and 259, must of course occur together. There can be no oxidation without corresponding reduction and no reduction without corresponding oxidation. 262. An oxidizing agent is any atom having an algebraic combining number which is capable of being reduced. But the most useful and effective oxidizing agents are, of course, those atoms which most readily suffer a diminution of their algebraic combining value, and those whose algebraic combining number is so high that it may be reduced several units. Free chlorine is an effective oxidizing agent because of the great intensity of the chemical energy with which it forms chlorides with other elements or radicals. The algebraic combining number of free or uncombined chlorine is 0. When it forms chlorides its combining number falls to — 1. Hence each atom of chlorine furnishes only one unit of oxidation, for its algebraic combining number is diminished by only one unit. But it is nevertheless a powerful oxidizing agent, because it acts so readily. The combined chlorine in KC10 3 is also an effective oxidizing agent, and in this case its tendency to form, a chloride is not the only motive force which makes it a 156 A CORRESPONDENCE COURSE IN PHARMACY powerful oxidizing agent, for the chlorine of KC10 3 has a high algebraic combining number (+5) which can be reduced six units (to —1), so that, while one atom of free chlorine can furnish only one unit of oxidation, the one atom of chlorine in one molecule of KC10 3 furnishes six units of oxidation. We say that nitric acid, HN0 3 , is a powerful oxidizing agent because it is easily decomposed and reduced to the compound NO. Two molecules of HN0 3 are said to give one molecule of water, two molecules of NO and three atoms of oxygen, 2HN0 3 =H 2 0+2NO+30, and the liberated oxygen is said to effect the oxidation. But we can also and more simply explain the power of nitric acid to increase the algebraic combining number of atoms by the statement that it is the nitrogen atom of the HN0 3 which is the real oxidizing agent; that nitrogen has a value of +5 in the HN0 3 and of only +2 in NO ; each molecule of HN0 3 accordingly furnishes 3 units of oxidation. Chromic anhydride, Cr0 3 , is a powerful oxidizing substance because the Cr in it has the high combining value of +6, which can be easily reduced to +3. Potassium dichromate, K 2 Cr 2 7 , contains two chromium atoms, each of which has a value of +6 capable of reduction to +3. Potassium per- manganate, KMn0 4 , contains an atom of manganese having a value of +7 capable of reduction to +2, so that one molecule of KMn0 4 furnishes five units of oxidation. 263. Probably the strongest reasons for applying the term "oxidation" to any increase in the true combining value of any atom are these: Oxygen is the most abundant of all oxidizing agents. It is inexhaustible. Many of the most powerful oxidizing substances are oxygen compounds, and they may be said to act, at least indirectly, by giving up all or a part of their oxygen. CHANGES OP ALGEBEAIC COMBINING NUMBERS OF ATOMS 157 Owing to the fact that nearly all elements can unite with oxygen, that oxygen compounds are so numerous, and that elements attain their highest algebraic combining values only in direct combination with oxygen, it follows that an extremely large proportion of the observed cases of augmentation of atomic combining value (oxidation in the broadest sense) are coincident with oxidation in the most restricted sense of that term. Even oxidizing agents that do not contain any oxygen may be seen to have derived their oxidizing power (an algebraic combining number capable of reduction) directly or indirectly from oxygen. For example, chlorine in the free state is obtained through the action of Mn0 2 , the Mn of which owes its high combining value (+4) to the oxygen with which it is combined. When the chlorine is liberated from HC1 by reaction with Mn0 2 , Mn0 2 +4HCl=MnCl 2 +2H 2 0+2Cl, it will be seen th§t the value of the Mn falls from +4 to +2, and that two atoms of chlorine, therefore, change their value from —1 to 0. Oxidations in which oxygen is not concerned are perfectly analogous' to those in which combination with oxygen takes place or in which the proportion of oxygen in an oxygen compound is increased. 264. That there are strong reasons for using the term oxidation in its broader sense may be seen from the follow- ing examples: 1. Iodine is the oxidizing agent in the reaction, 6K0H+6I=5KI+KI0 3 +3H 2 0. All of the iodine had a combining value of 0. After the reaction five iodine atoms are seen to have each a value of —1, while the sixth iodine atom has a value of +5. KI0 3 is a powerful oxidizing agent. If this be ascribed to 158 A CORRESPONDENCE COURSE IN PHARMACY its oxygen, then the KOH which supplied all of this oxygen may well be regarded as also an oxidizing agent ; and KOH in turn received its oxygen from some other source. But no chemist would say that KOH is an oxidizing agent. All chemists agree that iodine is an oxidizing agent and also that KI0 3 is one. The explanation most frequently made why iodine acts as if it were an oxidizing agent is that it decom- poses water, combining with the hydrogen of that water, whereby its oxygen is liberated so that it — the oxygen — is the real oxidizing agent. To render this clear we should have to represent the chemical changes as follows : 5H 2 O+10I=10HI+5O. 10KOH+10HI=10KI+10H 2 O. 2KOH+2I+50=25IO s +H a O. . But KIO3 cannot be made directly out of KOH and I and 0. A more direct and satisfactory explanation is that five iodine atoms lose one unit each and form 5KI, while the sixth iodine atom gains the five units lost by the other five and forms KI0 3 . One-sixth of the iodine acts here as a reducing agent, being oxidized. 2. Chlorine is the oxidizing agent in 6Ca(OH) 3 +12Cl=50aCl 2 +Oa(C10 3 ) 2 +H 2 0. This is seen from the fact that 10 atoms of chlorine changed their algebraic combining number from to —1, thus losing together 10 units; these 10 units were taken up by the other two chlorine atoms, which each acquired a value of +5 in the Ca(C10 3 ) 2 . The Ca(OH) 2 is said to be oxidized to Ca(C10 3 ) 2 . Two atoms of CI were oxidized; ten of them were reduced. 3. Sulphur is the oxidizing agent in Na 2 S0 3 +S=Na 2 S0 3 S. CHANGES OF ALGEBKAIC COMBINING NUMBEKS OF ATOMS 159 The S in the Na 2 S0 3 evidently has a combining value of +4. The free S has a value of 0. But one of the atoms of S in the Na 2 S0 3 S has a value of -t-6, while the other has a value of -2. Hence, the S of the Na 2 S0 3 gained two units at the expense of the free sulphur. The Na 2 S0 3 is said to be oxidized to ]STa 2 S0 3 S. 4. Phosphorus is the oxidizing agent in this reaction : 3Ca(OH) 2 +8P+6H 2 0=3Ca(PH 2 2 ) 2 +2H 3 P. The student can readily see that while the P used had a value of 0, the P in the Ca(PH 2 2 ) 2 must have a value of +1, for the three calcium atoms have each a value of +2, the twelve hydrogen atoms have each a value of +1, and the twelve oxygen atoms have each a value of —2, so that the six phosphorus atoms must have a value of +1 each, for if we add +6, +12, -24 and +6 we get the sum of 0. Therefore 6 atoms of phosphorus gained together six units, the total algebraic combining number of all of them being +6. The other two phosphorus atoms lost those six units, because the P in each molecule of H 3 P must have a value of —3. Hence, 2 atoms of P acted as oxidizing agents and the other 6 atoms of P as the reducing agents. 5. Ten sulphur atoms are reduced and the two other sulphur atoms oxidized in 3Ca(OH) 2 +12S=CaS0 3 S+2CaSS 4 +3H 2 0. The first sulphur atom in CaS0 3 S has a value of +6, and that is also the value of the first sulphur atom in CaSS 4 . All the other sulphur atoms have each a value of -2. 6. In the following reaction, 3Mn0 2 +12H01+6FeS0 4 =2Fe 2 (S0 4 ) 3 -f-2FeCl 3 +3MnCl 2 +6H 2 0, we can see that the three manganese atoms were reduced from a value of +4 to one of +2 each. The six atoms of iron (Fe) changed their value from +2 to +3. That this is clearly a case of oxidation is admitted by all chemists; but it is 160 A CORRESPONDENCE COURSE IN PHARMACY difficult to explain why it is so if oxidation is combination with oxygen or an increase in the proportion of oxygen. It is true that the percentage of oxygen in Fe 2 (S0 4 ) 3 is greater than it is in FeS0 4 ; but the same is true of the percentage of sulphur. The whole truth is that the proportion of S0 4 is greater in Fe 2 (S0 4 ) 3 than in FeS0 4 . We see that the Mn exchanged its two oxygen atoms for two chlorine atoms, and that change is truly reduction. But to say that this reaction is an oxidation because the H of the HC1 takes the oxygen of the Mn0 2 to form H 2 is a very unsatisfactory explanation. The statement of fact that the three manganese atoms together lose six units and that the six iron atoms gain those six units is a more direct and satisfactory explanation. The student is requested to observe that when a strong acid acts on Mn0 2 the algebraic combining number of the manganese is forced down to +2. Compare this result with that shown in the next example. 7. In the equation, 3Mn0 2 +2KOH=K 2 Mn0 4 +Mn 2 3 +H 2 0, one manganese atom rises from a value of +4 to one of +6, while the other two manganese atoms fall from +4 to +3 each. The presentation of the strong alkali KOH to the man- ganese in the Mn0 2 forces its value up from +4 to +6 in order that K 2 Mn0 4 may be formed. Compare this result with that in the preceding example. 8. No one will deny that the H 2 S0 3 is oxidized to H 2 S0 4 and that the FeCl 3 is reduced to FeCl 2 in 2FeCl 3 +H 2 S0 3 fH 2 0=2FeCl 2 +H 2 S0 4 +2HCl. But we do not say that the water is the oxidizing agent, although it does supply the oxygen atom which changes the H 2 S0 3 to H 2 S0 4 . To say that one-third of the chlorine of the 2FeCl 3 splits off from it, leaving 2FeCl 2 , and that the CI thus set free decomposes the H 2 0, taking the hydrogen CHANGES OF ALGEBRAIC COMBINING NUMBERS OF ATOMS 161 from it to form the 2HC1, while the oxygen atom of the H 2 performs the oxidation of the H 2 S0 3 to H 2 S0 4 , is a labored explanation. The most direct and satisfactory explanation lies in the evident fact that the two iron atoms of the 2Fe01 3 lost two units and- the S of the H 2 S0 3 gained those two units of combining value. 9. In the reaction, 4Zn+10HNO 3 =4Zn(NO 3 ) 2 +H 4 NONO 2 +6H 2 O, the nitric acid certainly acts as an oxidizing agent, but only one molecule of it performs that function, for the other eight molecules form the zinc nitrate and the ammonium nitrate. The first N in the H 4 NON0 2 has a combining value of —3, while the second N in that molecule and all the nitrogen in the 4Zn(N0 3 ) 2 has a value of +5, which is also the value of all the N in the HN0 3 . The one N which fell from +5 to —3 lost 8 units. What became of them ? They went to the four zinc atoms, which have a value of in the free state but of +2 in Zn(N0 3 ) 2 . 10. In the reaction H 4 NON0 2 =2H 2 0+N' 2 we can see that the nitrate is reduced to N 2 0, but how ? The first N in the H 4 NON0 2 has a value of -3 ; the second has a value of +5. The nitrogen atoms in N 2 have each a value of +1. There- fore, one nitrogen atom gained 4 as it rose from —3 to +1, while the other lost 4 units as it fell from +5 to +1. The difference between the valence and the algebraic combining number is strikingly shown in the foregoing, for each nitrogen atom in H 4 NON0 2 has 5 bonds or a valence of 5, while one has an algebraic combining number of —3 (the sum of —4 and -f 1) and the other has five positive bonds or an algebraic combining number of +5. 11. In H 4 NONO=2H 2 0+2N, we see that the first N" in the H 4 ¥ONO has an algebraic combining number of -3 and the second of +3. As both of these atoms were liberated, one gained 3 and the other lost 3. 1G2 A CORRESPONDENCE COURSE IN PHARMACY 12. In the reaction, 2HgCl 2 +S0 2 +2H 2 0=2HgCl+2HCl+H 2 S0 4 , it is of course possible to explain that two chlorine atoms of the 2HgCl 2 decomposed one molecule of water, forming 2HC1, and that the liberated oxygen formed one molecule of H 2 S0 4 by combining with the S0 2 and the second molecule of water, but we prefer to say that the two mercury atoms lost two units of algebraic combining value which were both gained by the S of the S0 2 , thus rendering the formation of H 2 S0 4 possible. 13. In the reaction, Cu+2H 2 S0 4 =CuS0 4 +S0 2 +2H 2 0, we might explain that the copper replaced the two hydrogen atoms of one of the molecules of the H 2 S0 4 and that these two hydrogen atoms combined with one of the oxygen atoms of the other molecule of H 2 S0 4 , reducing it to H 2 S0 3 , after which this H 2 S0 3 split up into S0 2 and H 2 0. But as we know that hydrogen does not reduce H 2 S0 4 to H 2 S0 3 or decompose it in any way, we prefer to say that the copper gained two units and that the S of one of the molecules of H 2 S0 4 lost those units and therefore formed S0 2 . 265. Any atom having a low algebraic combining number capable of augmentation is a possible reducing agent. But an effective and convenient reducing agent is an atom which may be easily oxidized, and especially one which can have its algebraic combining number increased by several units. Any true metal acts as a reducing agent whenever it enters into chemical combination with any element whatsoever, because a free element has an algebraic combining number of and all metals in combination are positive. Chlorine, whenever it forms KC10 3 , or even KCIO, is a reducing agent, because that chlorine is itself oxidized, just as carbon forms either C0 2 or CO when used to reduce metallic oxides and certain other oxygen compounds. CHANGES OF ALGEBRAIC COMBINING NUMBERS OF ATOMS 163 Hydrogen sulphide is a reducing agent because the sulphur of the H 2 S has the low value of —2, which can be raised to 0, or to +2, or +4, or even to +6. Ammonia is a reducing agent because its nitrogen has a value of —3, capable of being raised to +5. S0 2 is a reducing agent because its S can have its value increased from +4 to +6. Test Questions 1. What is meant by the term algebraic combining number ? 2. What is the algebraic combining number of metallic silver ? 3. What is the algebraic combining number of chlorine ? 4. What is the algebraic combining number of silver chloride ? 5. In the reaction H+C1=HC1, what are the algebraic combining numbers of the H, the CI and the HC1 ? 6. What are the algebraic combining numbers of the Na in NaCI, the Ag in AgCl, the Na in NaN0 3 and the Ag in AgN0 3 , and what are the algebraic combining numbers of NaCl, AgCl, NaN0 3 and AgN0 3 ? 7. When H 2 2 is dissociated into H 2 and 0, is that change an oxidation or a reduction ? Give the reason for your answer. ■ 8. Can the potassium of any potassium compound act as an oxidizing agent or as a reducing agent ? 9. Can the silver of any silver compound act as an oxidiz- ing agent or a reducing agent ? If so, explain how. 10. Can sulphuric acid act as an oxidizing agent, and if so, how ? What element in the sulphuric acid is reduced ? 11. Why is permanganate of potassium so powerful an oxidizing agent ? 164 A CORRESPONDENCE COURSE IN PHARMACY 12. Why is potassium chlorate an effective oxidizing agent ? 13. Why is Mn0 2 useful as an oxidizing agent ? 14. What is formed when free sulphur acts as an oxidizing agent ? 15. What is formed when free chlorine acts as an oxidizing agent ? 16. What is formed when free phosphorus acts as a reduc- ing agent ? 17. Identify the oxidizing agent and the reducing agent in the equation: 3Mn0 2 +2KOH=K 2 Mn0 4 +Mn 2 3 +H 2 0. 18. Identify the oxidizing element and the reducing ele- ment in the following reactions : (a) 3P+5HN0 3 +2H 2 0=3H 3 P0 4 +5NO. (b) 6Sb+10HNO 3 =Sb 2 O 5 +5H 2 O+10NO. (c) 3H 2 S+8HN0 3 =3H 2 S0 4 +4H 2 0+8NO. (d) 3Hg+8HN0 8 =3Hg(NO,) a +4H a O+2NO. (e) 3Hg+4HN0 3 =3HgN0 3 +2H 2 0+NO. (f) 3Hg+3H 2 S0 4 +2HN0 3 =3HgS0 4 +4H 2 0+2NO. (g) S0 2 +2HN0 3 =H 2 S0 4 +2N0 2 . (h) HN0 3 +8H=H 3 N+3H 2 0. (i) HN0 8 +3HCl=NOCl+2H a O+2Cl. (j) 3MnO 2 +KC10 3 +6K0H=3K 2 Mn0 4 +KCl+3H 2 O. (k) 2MnO a +KC10 8 +2KOH=2KMn0 4 +KCl+H 2 0. (1) 2HgCl 2 +S0 2 +2H 2 0=2HgCl+H 2 S0 4 +2HCl. (m) C 2 H 5 0H+2C1=C 2 H 4 0+2HC1. (n) H 4 NN0 3 =2H 2 0+N 2 0. (o) H 4 NN0 2 =2H 2 0+2N. LESSON TWELVE XVIII The Periodic System >. It has been found that the elements when arranged in certain periods according to their atomic weights naturally fall into groups, the members of which exhibit striking similarities of chemical behavior. This has been expressed as follows: "The chemical properties ,of the elements are periodic functions of their atomic weights"; and this statement is called the periodic law. When the periodic system was first presented in the form in which we now state it, several of the now known elements had not yet been discovered. Nevertheless, the evidences of the' fact of the periodicity of the regularities and similari- ties of valence and functions in accordance with the atomic weights were so overwhelming as to command attention immediately, and subsequent discoveries have confirmed the belief that the natural classification of the elements in accordance with this system is based upon natural law. 267. If the seven elements beginning with lithium and ending with fluorine, arranged in accordance with their increasing atomic weights, be set down in succession, we will have : Li Be B C 1ST F 7 9 11 12 14 16 19 The elements are indicated by their symbols, and the numbers are their atomic weights. There are no known ele- 165 166 A CORRESPONDENCE COURSE IN PHARMACY ments having atomic weights between 7 and 19 except those mentioned in this period of seven. Lithium, the first mem- ber of the period, is an alkali metal and the last is a halogen. The striking result of this arrangement is that the ruling valences of these seven elements in the order in which they stand are 1, 2, 3, 4, 3, 2 and 1. The element having the next higher atomic weight above 19 was sodium, with the atomic weight of 23, which is also an alkali metal, like lithium. If we now set down another period of seven elements in the order of their atomic weights, beginning with sodium, we shall have Na Mg Al Si P S CI 23 24.2 27 28.4 31 32 35.4 No other elements with atomic weights between 19 and 36 are known. The seventh element is again a halogen, and the respective ruling valences of the elements in the order in which they are set down are again 1, 2, 3, 4, 3, 2 and 1. But the ruling valences of elements are not their only important valences. If the polarity as well as the valence be considered in connection with this second period of elements, and the maximum algebraic combining numbers be given instead of the ruling valences, the result is even more strik- ing, for the maximum algebraic combining numbers of these seven elements, beginning with Na, in the order in which they stand, are +1, +2, +3, +4, +5, +6 and +7. The element next following chlorine in the order of increas- ing atomic weight is again an alkali metal, namely, potassium. If we now set down the seven elements, beginning with potassium, in the order of their atomic weights, we get: K Ca Sc Ti V Cr Mn 39 40 44 48 51.5 52 55 In this period we find that the last element, manganese, THE PERIODIC SYSTEM 167 is not a halogen, but the maximum algebraic combining numbers of these seven elements are again, as before, +1, +2, +3, +4, +5, +6 and +7. (The student will remember that the halogens are fluorine, chlorine, bromine and iodine. ) We have seen that two periods of seven elements, beginning with alkali metals, end with the halogens fluorine and chlorine. If we now set down bromine at the right and put down in front of it the six elements standing next to bromine in the order of their decreasing atomic weights, we get the following result : Cu Zn Ga Ge As Se Br 63.5 65.3 70 72.5 75 79 80 Three elements are known having atomic weights between 55 and 63.5; namely, iron, nickel and cobalt. We have therefore a break here in the regular periodicity before noted. The maximum algebraic combining numbers of the elements from copper to bromine are +2, +2, +3, +4, +5, +6 and +5, so that in this period the first and the last elements do not appear to follow the same rule as before. Copper sometimes has the algebraic combining number +1, but no compound of bromine is known in which that element has a combining value as high as +7. If we now set down another period of six, beginning with the alkali metal rubidium, which stands next after bromine in the magnitude of its atomic weight, we have : Rb Sr Yt Zr Cb Mo 85.5 87.5 89 90.5 93.5 96 The seventh element belonging to this period is evidently not yet known, for these six elements are closely related to K, Ca, Sc, Ti, V and Or, and they have the combining values 1, 2, 3, 4, 5 and 6. The next period may be made to begin at the right with 168 A CORRESPONDENCE COURSE IN PHARMACY the halogen iodine. Going backwards from iodine to silver, we get this result : Ag Cd In Sn Sb Te I 108 112 114 119 120 125.5 126.5 In that period of seven elements, the maximum algebraic combining numbers are unmistakably +1„ +2, +3, -+4, -4-5, +6 and +7. Evidently such results as these cannot be accidental. The reasons for the irregularities and exceptions to be observed in arranging the chemical elements in accordance with this system will doubtless some day be discovered. 268. Several tables have been arranged on this plan, and of these the most useful to the beginner will be found on page 171. At the top of the table are the maximum algebraic combining numbers, and in the last four columns below the maximum combining numbers the student will find the minimum algebraic combining numbers. All of the elements in the first column are alkali metals, and no alkali metals are found in any other column. In the second column or group are the alkaline earth metals. In the last column are all of the halogens, and in the next to the last column we find oxygen and the sulphur family, which are also closely related to each other. Indeed, throughout the whole table it will be found that the members of any group or family of elements placed in a vertical column possess certain similarities and exhibit certain gradations in differences which cannot be accidental. Any element in the table will be found to possess properties intermediate between the properties of its neighbors on both sides, or above and below. Some of the elements belonging in the vacant spaces in the table from the middle down are really known, though a little uncertainty exists in regard to their atomic weights. THE PERIODIC SYSTEM 169 At least six elements are known having atomic weights between 139 and 173. Some day these vacant places in the table will probably be filled with the elements that belong there but that have not yet been discovered. 269. At the time Professor Mendeleeff constructed his first periodic table, the element scandium was unknown, also the elements gallium and germanium, but their discovery and leading properties and atomic weights were predicted by Mendeleeff, and within three years they were discovered and his predictions found to be true. He knew that scandium, with an atomic weight of about 44, must exist; calcium had a valence of 2 and titanium a valence of 4, so that an ele- ment with a valence of 3 must belong between them, and, moreover, the difference between the atomic weights 40 and 48 was too large. Gallium and germanium were believed to belong between zinc and arsenic, because zinc had a valence of 2 and arsenic a maximum algebraic combining number of +5, so that one element with a value of 3 and another with a value of 4 ought to exist having atomic weights between 65.3 and 75. Gallium and germanium fulfilled these require- ments. At the time of the construction of Mendeleeff's first table, the atomic weight 120 had been assigned to uranium, whereas antimony had that same atomic weight. Moreover, uranium could not belong in the same family with antimony and does not possess a combining value of 5, so that Mendeleeff declared that the atomic weight of uranium was probably not 120. It was subsequently shown that uranium had the atomic weight 240, which places it in the sixth group, where it properly belongs according to its combining value. • 270. Some other striking facts brought out in the periodic table are as follows : 170 A CORRESPONDENCE COURSE IN PHARMACY The range of combining values of all elements in the last four columns, so far as they have variable valences, is always eight units. The highest algebraic combining number of carbon and all the other elements in the same family is +4, and the lowest algebraic combining number, —4. In the next column, the highest value is +5 and the lowest —3. In the oxygen and sulphur group, the highest value is +6 and the lowest —2, and in the last column, the highest value is +7 and the lowest -1. It will also be found that any element standing to the right, when in chemical combination with any element to the left, has a constant combining value, and also that any element standing abo7e, when in chemical combination with any element standing below it, has a constant combining value. Thus, when chlorine is in combination with either sulphur, phosphorus or silicon, or any metal, the chlorine has a constant algebraic combining value of —1, but when chlorine is in combination with fluorine or with oxygen, it may have a combining value of +1, +3, +5 or +7. Sulphur, in combination with any element to the left, invariably has the . combining value —2. But when in combination with oxygen or with any of the elements in the last column, it may have a combining value of +2, +4 or +6. This fact may be stated in the following manner: Any atom in combination with another element has invariably the same algebraic combining number, if that combining number is a minus quantity. Thus, a single boron atom, whenever in combination with hydrogen or with any element standing to the left in the periodic table, always has a combining value of —3. A single carbon atom, in combination with any ele- ment or elements standing below it or to the left of it in the periodic table, can have no other combining value except —4. A single nitrogen atom, whenever it has a combining number represented by a minus quantity, has the algebraic combining THE PERIODIC SYSTEM 171 m H W o h- 1 Q h- 1 o H ^7 CI 35.4 25.3 CO I 126.5 25.3 Ht- 1 + CO CM ^00 iO oo ^ CO^ (M CO + + *Oco > ^^ ^ iO *Oco -Q coco fH 00 "- 1 + w O H hh pq + IO CD . ^ d cn S3 os CN T— 1 Hco^ CM + CO + 00 1> IO CO ^gs CO + + w os« CM GG 00 CO iO co CM + rH + 3^2 'S *6 CD PH00"5 DC c ^25 co°o rH + 172 A CORRESPONDENCE COURSE IN PHARMACY number —3, and sulphur always has the combining value —2 whenever it is negative. In other words, the relative polarities of any two elements in combination depend upon their relative positions in the periodic system. In the table here given, it will be seen that all the metals, together with hydrogen, are found in the first thirteen columns of the table, and that the non-metallic elements are all to be found in the upper right-hand corner of the table. 271. There are probably no elements having atomic weights between 9 and 11 and between 27 and 28.4. But lithium and beryllium certainly belong in the first two columns, and sodium, magnesium and aluminum belong in the first three columns, whereas the non-metallic elements surely belong in the last columns of the table. For this reason the first two periods of elements have been separated, as shown, in order that the natural families of elements may be pre- served. 272. Another striking fact is that in the first column of elements and in the second, the greatest energy, or inclina- tion to enter into chemical combination, is exhibited by those members having the highest atomic weights, all of these elements having positive polarity, whereas at the other end of the table, the elements having the lowest atomic weights exhibit the greatest energy if they exercise negative polarity. But when chlorine, bromine and iodine exercise positive polarity, iodine forms the most permanent com- pounds, bromine next and chlorine next. 273. While it is true that our present chemical nomen- clature was devised long before the periodic system was known, we can readily see that with a few corrections, that nomenclature is in perfect accord with the periodic system. When any positive element has but two different combining values, its higher value is expressed by the ending ic and its THE PERIODIC SYSTEM 173 lower value by the ending ous. When a positive element has three different combining values, the highest is generally expressed by the ending ic, the middle value by the ending ous, and the lowest value by the prefix hypo and the ending ous. When a positive element has four different combining values, the two middle values are indicated by the endings ous and ic, the lowest value by the prefix hypo and the end- ing ous, and the highest value by the prefix per and the end- ing ic. Thus carbonous carbon has a value of +2 and car- bonic carbon has a value of +4. Phosphoric phosphorus has a value of +5, phosphorous phosphorus a value of +3 and hypophosphorous phosphorus has a value of +1. Sulphuric sulphur has the combining value +6; the algebraic com- bining number of sulphurous sulphur is +4 and that of hyposulphurous sulphur must be +2. Perchloric chlorine has a value of +7, chloric chlorine a value of +5, chlorous chlorine a value of +3 and hypochlorous chlorine a value of+1. 274. Four elements recently discovered in the atmosphere evidently belong next after the halogens. Neon, with the atomic weight 20, belongs between fluorine and sodium; argon, with an atomic weight of probably 39, belongs between chlorine and potassium; krypton, with an atomic weight of 82, belongs between bromine and rubidium, and xenon, with an atomic weight of 128.5, belongs between iodine and caesium. Fluorine, chlorine, bromine and iodine as negative elements exhibit the most tremendous chemical energy, whereas sodium, potassium, rubidium and caesium are invariably positive elements, and as such exhibit the greatest energy shown by any elements of positive polarity. What, then, should be expected of neon, argon, krypton and xenon except a neutral behavior ? Standing between the extremely negative and the extremely positive elements, they exhibit no inclination to enter into combination at all. 17*4 A CORRESPONDENCE COURSE IN PHARMACY Test Questions 1. What is meant by the periodic system ? 2. What is the maximum algebraic combining number possible to any element in the fifth place of a period of seven elements ? 3. What is the lowest algebraic combining number possible to an element contained in the seventh place of a period of seven elements containing any elements of negative polarity ? 4. Name the sixth element in the period beginning with potassium, and the third element in the period beginning with sodium. 5. Name all the elements in the period beginning with copper. 6. How is it possible to predict approximately the prop- erties of an undiscovered element ? 7. What is the algebraic combining number of phosphorus in combination with any metal ? 8. What is the algebraic combining number of sulphur in combination with any element standing below it or above it in the table of the periodic system ? 9. What is the algebraic combining number of sulphur when in combination with oxygen or with any of the elements in the vertical column to the right of that in which the sul- phur is placed ? 10. What position in the periodic table is occupied by the two elements of invariably negative polarity ? 11. What position in the periodic table is occupied by elements combining directly with both hydrogen and oxygen ? 12. What elements form no compounds with either hydro- gen or oxygen, and what position in the periodic table do they occupy ? 13. What position in the periodic table is occupied by elements that combine with oxygen but not with hydrogen ? 14. What elements form no compounds with oxygen ? THE PERIODIC SYSTEM 175 15. What position is occupied in the periodic table by- elements that form no compounds with any of the halogens nor any compounds with any metal ? 16. What are the relative positions of the most decidedly positive and the most decidedly negative elements in the periodic table as presented in this chapter ? 17. Which is the positive element and which the nega- tive element in any compound consisting of bromine and chlorine ? 18. Which is the positive element and which the negative element in any compound consisting of sulphur and tellurium ? Why ? 19. If potassium is brought in contact with a mixture of bromine and iodine and the amount of potassium is sufficient to combine with only one of them, what compound will be formed ? 20. If bromine be added to a solution of chloride of potassium, what new binary compound will be formed, if any? 21. If bromine is added to a solution of iodide of potas- sium, what new binary compound will be formed, if any ? 22. If 39.2 grams of potassium and 23 grams of sodium be put in a vessel containing 8 grams of pure oxygen, what will be formed and why ? 23. Which is the more powerful basic element, caesium or barium ? 24. Which is the more powerful basic element, barium or calcium ? 25. Which is the more powerful negative element, chlorine or bromine ? 26. What elements form no chlorides as shown by the periodic table ? 27. What elements form no oxides as shown by the periodic table ? 176 A CORRESPONDENCE COURSE IN PHARMACY 28. Name the several elements with which positive sulphur can be in direct combination. 29. Name the several elements with which positive iodine can be in direct combination. 30. What binary compounds of bromine are not bromides ? 31. What binary compounds of sulphur are not sulphides ? 32. What binary compounds of carbon are not carbides ? 33. What would you call a compound of boron and hydrogen ? - - 34. What would you call a compound of boron and nitrogen ? 35. What would you call a compound of calcium and carbon ? 36. What would you call any binary compound formed by a metal with a non-metallic element ? 37. What would you call a substance composed of two metals ? 38. What is the probable reason why neon, argon, krypton and xenon form no chemical compounds ? LESSON THIRTEEN XIX Air and "Water — Nitrogen, Oxygen and Hydrogen 275. Air is a mixture consisting almost wholly of the two colorless, odorless and tasteless gaseous elements called nitrogen and oxygen. Each five liters of air contains about four liters of nitrogen and one of oxygen. One cubic-decimeter of pure dry air at 0° C. under 760 mm. pressure weighs 1.29303 grams. One cubic decimeter of ordinary air at 16.67° 0. weighs about 1.2125 grams. 276. Nitrogen may be obtained by burning phosphorus in air contained in a suitable closed vessel. The phosphorus takes up all the oxygen with which it enters into chemical combination, forming a white solid called phosphoric oxide, and the gas remaining in the vessel is the nitrogen, which is not combustible. Mtrogen can also be made in various other ways. It requires a pressure of 35 atmospheres at or below the temperature of -146° C. to liquefy nitrogen. One cubic-decimeter of pure nitrogen weighs about 1.26 grams. Nitrogen does not readily enter into chemical combination with other elements. It is contained chemically combined with hydrogen, carbon and oxygen, in many animal sub- stances. Among the most familiar nitrogen compounds are niter (saltpeter), from which nitrogen derives its name, and ammonia. 177 178 A CORRESPONDENCE COURSE IN PHARMACY Many nitrogen compounds are powerful explosives, as nitroglycerin, guncotton, dynamite. Nitric acid is a compound formed by nitrogen with oxygen and hydrogen, and this acid is one of the most destructive in its effects upon many other substances. The substances called alkaloids, of which quinine, strych- nine and morphine are well-known examples, all contain nitrogen. The so-called "laughing gas" employed by dentists to ren- der the patient unconscious of pain in extracting teeth is a compound of nitrogen and oxygen. Nitrogen is quite harmless when inhaled, as we know from the fact that the air we breathe contains so large a propor- tion of it, and hyponitrous oxide is also harmless if pure and properly used. But many of the most fearful poisons known, as prussic acid (hydrocyanic acid), "cacodyl cyanide," toxines, strychnine and many other alkaloids, are nitrogen compounds. 277. When nitrogen enters into chemical combination with hydrogen alone, one single atom of nitrogen holds not more and not less than three atoms of hydrogen. The compound thus formed is a colorless gas called ammonia, which is readily soluble in water. The water-solution of it is also called ammonia and is much employed. Ammonia gas is excessively pungenfc, irritating, stifling, and dangerous in its effects upon the eyes, respiratory organs, etc., and the solution or "ammonia water," unless very dilute, is also destructive. Ammonia has the power of neutralizing acids, and the compounds formed by such neutralization are called "ammonium salts." 278. When nitrogen combines chemically with oxygen alone, one nitrogen atom can hold either one or two oxygen atoms, or two nitrogen atoms together can hold one or three AIR AND WATER— NITROGEN, OXYGEN AND HYDROGEN 179 or five oxygen atoms in combination. Nitrogen, therefore, combines with oxygen in five different proportions. If we represent the nitrogen atom by its symbol N and the oxygen atom by 0, the oxides of nitrogen are pictured by the follow- ing molecular formulas : NO is a colorless gas composed of one atom of nitrogen and one of oxygen. It is nearly always produced when a metal acts chemically upon nitric acid, but as it comes in contact with the air it immediately combines with more oxygen, forming N0 2 or N 2 4 , or both, according to the temperature, and these constitute the well-known irritating "red nitrous vapors" observed when metals are dissolved in nitric acid and when that acid is decomposed by certain other substances. NO is commonly but erroneously called "nitric oxide"; its true scientific name is nitrosyl. N0 2 is a red vapor above 150° C, and is called nitrogen peroxide. It is also called nitryl. But N0 2 may be con- densed into an orange-colored liquid of the composition N 2 4 , which is called nitrogen tetroxide. N 2 is a colorless gas commonly called "nitrous oxide gas" or "laughing gas." Its true scientific name should be hyponitrous oxide. N 2 3 is a blue liquid. It is called "nitrogen trioxide," but its true scientific name should be nitrous oxide. It forms nitrous acid with water. N 2 5 is a white solid which forms nitric acid with water. It is called "nitrogen pentoxide." This is the only oxide of nitrogen that can be properly called nitric oxide. [The proper nomenclature of these nitrogen compounds will be explained later on in the chapter on chemical nomenclature.] 279. Oxygen. The vast importance of oxygen may well be appreciated from the fact that it constitutes about one- half of the whole mass of the earth. All of the well-known elements except fluorine form 180 A CORRESPONDENCE COURSE IN PHARMACY chemical compounds with oxygen, and the oxygen compounds are therefore the most numerous and abundant of all sub- stances, whether mineral, vegetable or animal. About one-fifth, by weight, of the air is oxygen. Water is composed of eight-ninths, by weight, of oxygen and one-ninth of hydrogen. The oxygen of the air is of vital importance to life. Animals inhale air and appropriate a part of its oxygen. They exhale the unused part of the oxygen together with the nitrogen and, with these, the carbon dioxide (C0 2 ) and water (H 2 0) formed in the process of oxidation, which is the important object of respiration. Oxygen is a colorless, odorless, tasteless, non-inflammable gas. It becomes liquid at —120° 0. under a pressure of 50 atmospheres. One cubic-decimeter of pure oxygen at 0° C. under 760 mm. barometric pressure weighs about 1.43 grams. Hence, 1 gram of oxygen under the conditions stated occupies a volume of about 699 cubic-centimeters. Oxygen is commonly prepared by heating certain easily decomposed compounds containing it. The substances called potassium chlorate (KOC10 2 ), mercuric oxide (HgO), man- ganese dioxide (Mn0 2 ), barium dioxide (Ba0 2 ), and lead dioxide (Pb0 2 ), may be used for this purpose. Potas- sium chlorate gives up all of its oxygen when heated, about two grams of oxygen being obtained from every five grams of the chlorate, and the residue is potassium chlo- ride (KC1). 280. Whenever one atom of oxygen enters into chemical combination with hydrogen alone the oxygen atom unites with two hydrogen atoms. We, therefore, conclude that the combining value of one oxygen atom is twice that of one hydrogen atom. No one atom of any other element can combine with more AIE AND WATER — NITROGEN, OXYGEN AND HYDROGEN 181 than four oxygen atoms unless the compound contains more than two elements. At ordinary temperatures oxygen exhibits no great inclina- tion to enter rapidly into combination with other elements except with phosphorus and with the elements called the alkali metals; but many elements are oxidized at higher temperatures and many are slowly oxidized by oxygen at the common temperature. 281. Ozone is a gas consisting of oxygen alone but differ- ing decidedly from ordinary oxygen, ozone being much more active in causing oxidation. The difference between ordinary oxygen and ozone is due to the fact that each individual particle of common oxygen (0 2 ) consists of only two atoms, while each individual particle of ozone consists of three atoms (0 3 ). 282. Oxidation signifies, in the narrowest sense of the term, the chemical combination of any element with oxygen. Fire is a violent or rapid chemical process by which the burning substances, or one or more of their component ele- ments, enter into chemical combination with the oxygen of the air. This rapid oxidation is called combustion and pro- duces heat, the intensity of which is in direct proportion to the velocity of the oxidation and dependent also upon the kind and quantity of the fuel "consumed." The elements of greatest importance as fuel are carbon and hydrogen in combination with each other and with other elements, or carbon alone. When carbon undergoes combustion it combines with oxygen to form oxides of carbon. Eespiration is attended with "slow combustion," by which certain substances contained in the venous blood entering the lungs are " oxidized" by the oxygen of the air inspired into those organs, and this process is a heat-producing chemical action. Slow oxidation may be seen not only in the results of 182 A CORRESPONDENCE COURSE IN" PHARMACY respiration but also in many other phenomena, as, for instance, in the tarnishing of iron and some other metals when exposed to moist air. 283. Oxides. Any compound consisting of only two ele- ments, one of which is oxygen, is called an oxide. But a compound of a metal with oxygen is a salt if a part of the metal performs the basic function and another part the acidic function. Silver oxide is a compound of silver and oxygen ; the metal magnesium forms magnesium oxide; zinc forms zinc oxide. But some elements have more than one oxide. Carbon has two, phosphorus has three, chlorine four, nitrogen five, and manganese seven different oxides; for the elements named, and also many other elements, can combine with oxygen in more than one proportion. Whenever any oxide consists of but two elements, each individual particle or molecule of that oxide, if it contains more than four atoms of oxygen, must contain more than two atoms of the other element ; and two atoms of one kind may hold in combination or be directly united to one, two, three, four, five or seven atoms of oxygen. [Distinction may profitably be made between oxides composed of two elements in which all of the oxygen is directly combined with all of the other element, and the so-called oxides composed of two elements in which two oxygen atoms may" be directly combined with each other. In HOH the oxygen is all combined with all of the hydrogen; but in HOOH each oxygen atom is directly combined with only one of the two hydrogen atoms.] The oxides of the metals are all solids ; but those of the non-metallic elements are some of them solids, others liquids, and others gases. Many of the oxides can be produced by combustion, or by direct combination of oxygen with other elements. AIR AND WATER— NITROGEN, OXYGEN AND HYDROGEN 183 284. Examples of Oxidation by Combustion, (a) Sulphur (S) burns with a blue flame, combining with the oxygen of the air to form that oxide of sulphur which constitutes the familiar, irritating, colorless gas produced when a sulphur match burns. No ash is formed. Each atom of the sulphur combines with two atoms of oxygen; hence the irritant sulphurous oxide is called a dioxide and it is represented by the symbolic formula S0 2 , in which S stands for one atom of sulphur and 2 for two atoms of oxygen. As one atom of sulphur weighs twice as much as one atom of oxygen, it follows that the sulphur dioxide obtained weighs twice as much as the quantity of sulphur "con- sumed." [Another oxide of sulphur exists which cannot be pro- duced by combustion. It is a white solid and it is a trioxide, the composition of which is clearly indicated by its symbolic molecular formula, S0 3 .] (b) When charcoal, which is nearly pure carbon (C), is ignited and "consumed" by fire, or undergoes combustion, the carbon is oxidized. But if the supply of air or oxygen is insufficient the carbon does not combine with the maxi- mum amount of oxygen it can hold in chemical combination, but with only one-half as much. A carbon utom weighs 12 times as much as an atom of hydrogen; but an oxygen atom weighs 16 times as much as a hydrogen atom. The carbon oxide formed by incomplete combustion of the carbon is composed of 12 parts of carbon and 16 parts of oxygen and it is in fact carbon monoxide, or CO. The oxide formed when the carbon undergoes complete combustion is composed of 12 parts of carbon and 32 parts of oxygen, and is in fact carbon dioxide, or C0 2 . Both of the oxides of carbon are colorless gases. They are the only two oxides carbon can form. 184 A CORRESPONDENCE COURSE IN PHARMACY Carbon monoxide is combustible. It burns in the air with a blue flame, taking up from the air as much more oxygen as it already contains, being thus oxidized to carbon dioxide. This oxidation is represented symbolically as follows: CO+0=C0 2 . But carbon dioxide is not combustible, because carbon can- not hold in combination with itself more than 2f times its own weight of oxygen, or, in other words, because one carbon atom cannot hold more than two oxygen atoms in direct combination if the compound contains no other element. When pure carbon is thus oxidized no ash is formed. Twelve kilograms of carbon consume for complete oxidation thirty-two kilograms of oxygen, producing forty-four kilo- grams of carbon dioxide. (c) Alcohol is composed of the three elements carbon, hydrogen and oxygen. When it is ignited and burns in a free supply of air the flame is smokeless, the combustion is complete, no ash or residue is left, and the products are carbon dioxide, C0 2 , and water, H 2 0. Each molecule of alcohol is composed of two atoms of carbon, six atoms of hydrogen and one atom of oxygen. Its molecular formula is, therefore, empirically written C 2 H 6 0. Hence, each mol- ecule of alcohol weighs 46 times as much as one hydrogen atom. Each molecule of alcohol requires 6 additional atoms of oxygen for the formation of two molecules of carbon dioxide and three molecules of water. Accordingly, the combustion of alcohol is represented by the chemical equation, C 2 H 6 0+60=2C0 2 +3H 2 0. Hence, 46 kilograms of alcohol will require 96 kilograms of oxygen for complete combustion and the products will be 88 kilograms of carbon dioxide and 54 kilograms of water vapor. AIR AND WATER — NITROGEN, OXYGEN AND HYDROGEN 185 (d) Wood is a complex mixture of organic substances com- posed mainly of carbon, hydrogen* and oxygen, but contain- ing also some compounds of potassium, calcium and other elements. When wood is used as fuel the products of the combustion are chiefly the oxides of carbon and hydrogen, which we have already mentioned. These pass off, together with some "unconsumed" carbon and other matter, as smoke, while the compounds of potassium, calcium, aluminum, silicon and other "mineral matters" contained in the wood form the ash. (e) When the soft white metal called magnesium (Mg) is ignited it burns rapidly, emitting an intense white light as it unites with the oxygen of the air to form a white solid, which is magnesium oxide, MgO. The "flash light" powder used by photographers consists of or contains powdered mag- nesium. No gas is formed in the combustion of magnesium, for the only product is the oxide, which is a fine powder, forming a cloud of white dust but no smoke. Thus the only product here is the ash. Five grams of this white ash is produced out of every three grams of the metal, because a mass of 3 grams of magnesium unites with 2 grams of oxygen. Magnesium and oxygen unite with each other in no other proportions. Hence, we see that when magnesium is "con- sumed" by combustion it yields in fact a product weighing 66 per cent more than the metal consumed. Magnesium oxide is commonly called "magnesia." (/) When the black mineral called antimonite, or "black sulphide of antimony," which is composed of the elements antimony (Sb) and sulphur (S), is strongly heated or "roasted" in the air it decomposes. As one molecule of the black sulphide of antimony is composed of 2 atoms of anti- mony and three atoms of sulphur its symbolic formula is written Sb 2 S 3 . The antimony is oxidized by the oxygen of 186 A CORRESPONDENCE COURSE IN PHARMACY the air to antimony oxide, Sb 2 3 , which fuses and forms a glass-like solid, while the sulphur forms the gas S0 2 . As the atomic weight of antimony is 120, because any given number of atoms of antimony weigh 120 times as much as the same number of atoms of hydrogen, it follows that when 336 grams of Sb 2 S 3 is completely oxidized to Sb 2 3 and S0 2 , the quantity of oxygen required must be 144 grams, and that the combustion or oxidation is represented by the equation, Sb 2 S 3 +90=Sb 2 3 +3S0 2 . From these examples the student will learn that fire or combustion does not change the amount of matter in the universe ; it simply alters the composition and form of matter by rearrangements of the atoms into other kinds of mol- ecules ; and that the weight of the product or products formed by a burning substance is greater than that of the substance burned by just the amount of oxygen taken up in combination to form the new substance or substances. 285. Water is one of the most plentiful oxygen compounds in nature. It is a most wonderful substance, composed of two of nature's most remarkable elements, hydrogen (H) and oxygen (0). In each molecule, or smallest possible individual particle of water, there are two hydrogen atoms and one atom of oxygen. Its molecular formula is, therefore, written H 2 ; but it may also, and preferably, be represented by the formula HOH. Water forms solutions of numerous kinds of matter and is indispenable to circulation and nutrition in plants and animals, rendering possible the chemical processes without which life in the world of matter must cease. It is the most, neutral or chemically indifferent substance with regard to the vast majority of other kinds of matter, serving there- fore a3 a medium in which other substances may be liquefied, whereby their molecules acquire greater freedom of motion, AIR AND WATER — NITROGEN, OXYGEN AND HYDROGEN 187 so that they can readily act upon each other. Its power to cause the dissociation of certain kinds of molecules into their component "ions" is referred to elsewhere. Molecules of water have a remarkable power and tendency to enter into some form of combination with other kinds of molecules, as "water of crystallization" and in other ways. Its uses in the economy of nature, in sanitation, and in the indus- tries of civilization could not be subserved by any other sub- stance known. Water freezes at 0° C. (32° F.). Its boiling point is 100° C. (212° F.). It attains its maximum density at 4° C. (39.2° F.). One liter of water at 4° C. in vacuo weighs 1 kilogram. One milliliter weighs 1 gram. Six pints of water (96 fluid ounces) weighs approximately 100 avoirdupois ounces. 286. Hydrogen is a colorless, odorless, tasteless, highly inflammable gas. It is the lightest of all kinds of matter, occupying nearly 14^- times as much space as is taken up by an equal weight of air, and about 11,160 times as much space as is occupied by an equal weight of water at 0° C. One cubic-decimeter of pure hydrogen at 0° 0., bar. 760 mm., weighs about 0.09 gram. Hydrogen has been obtained in liquid form at a temper- ature estimated to be below —200° 0., and under a pressure of 40 atmospheres. This element exists in nature in the free state only in extremely small quantities. In chemical combination it constitutes about 1 per cent by weight of the whole mass of the earth. Its most abundant compound is water. Hydro- gen is a constituent of nearly all of the carbon compounds of the animal and vegetable kingdoms, and of coal oil, "natural gas" and other bituminous products. 287. Hydrogen is easily prepared by the action of zinc on 188 A CORRESPONDENCE COURSE IN" PHARMACY diluted sulphuric acid. Ordinary sulphuric acid is a hydrogen sulphate composed of two hydrogen atoms, one atom of sul- phur, and four oxygen atoms. Its molecular formula, repre- senting its composition, is best written (HO) 2 S0 2 . When zinc (Zn) is added to a solution of sulphuric acid (or " diluted sulphuric acid") the zinc takes the place of the hydrogen, forming zinc sulphate, and the hydrogen is set free : Zn+(HO) 2 S0 2 =Zn0 2 S0 2 +2H. Hydrogen can also be made by passing steam (water vapor) over coal heated to a very high temperature. Carbon mon- oxide (CO) is formed at the same time, the reaction being HOH+C=CO+2H. By the action of sodium hydroxide upon sodium formiate a perfectly pure hydrogen may be made : NaOH+NaCH0 2 =Na 2 C0 3 +2H. 288. Chemically considered, hydrogen is extremely im- portant. Its properties place it between the metals and the non-metallic elements. It forms no true chemical com- pound with any true metal, but combines with all non- metallic elements. Its oxide or hydroxide, water, is neither a base nor an acid ; but if one of the hydrogen atoms of the molecule of water, HOH, be replaced by a non-metallic ele- ment an acid is the result, whereas if a metal (of low combining value or valence) is substituted for one of the hydrogen atoms a base is formed. Hydrogen is contained in all acids. Hydrogen does not at ordinary temperatures display any inclination to enter into chemical combination with other elements, but a mixture of hydrogen and chlorine, or of hydrogen and oxygen, may be exploded by an electric spark or by ignition. The most intense heat that can be produced by combustion is that produced by igniting a mixture of hydrogen and oxygen in the proportions required to form water. Practical AIR AND WATER — NITROGEN, OXYGEN AND HYDROGEN 189 use is made of this in the "oxy-hydrogen blowpipe." By means of this, hydrogen burning in oxygen is thrown against a fragment of lime which quickly rises to an intense white heat and gives off the well-known powerful "lime light." No one atom of any kind can unite directly with (or hold in combination) more than four hydrogen atoms. Carbon and silicon can unite with four hydrogen atoms ; boron, nitrogen, phosphorus, arsenic and antimony each with three ; oxygen, sulphur, selenium and tellurium with two ; and fluorine, chlorine, bromine and iodine each with only one hydrogen atom. ISTo other elements unite directly with hydrogen under any circumstances. Hydrogen forms alloys with a few of the metals, notably palladium. Ammonia (H 3 N) is the compound formed when one nitro- gen atom is combined with all the hydrogen it can hold in combination. 289. As hydrogen of all elements has the lowest atomic weight, and of all substances the lowest specific weight, and as it has a uniform atomic combining value or valence as low as that of any other element, it has been adopted as the standard of comparison and unit of expression of all such values. Thus the atomic weight of hydrogen is 1, its vapor density is 1, and its valence is 1. 290. Hydrogen and oxygen are chemical opposites. Hydrogen is one of the positive elements ; oxygen is always a negative element. Any element is oxidized whenever it combines with oxygen; it is reduced whenever it combines with hydrogen. An element is reduced whenever its oxygen compound exchanges its oxygen for hydrogen. An element is oxidized whenever its hydrogen compound exchanges its hydrogen for oxygen. Any element is positive whenever it is in direct combination with oxygen ; it is negative when- ever it is in direct combination with hydrogen. 190 A CORRESPONDENCE COURSE IK PHARMACY Test Questions 1. What is the weight of one liter of pure dry air at 25° C. under the pressure of one atmosphere? 2. Is air a chemical compound ? 3. Is water a chemical compound ? 4. Why are nitrogen compounds generally unstable ? 5. What is the proper technical name of so-called "laugh- ing gas"? 6. Name one common nitrogen compound having a decided odor. 7. What is the algebraic combining number of nitrogen in 9 H 4 NC1 and in N 2 5 8. Mention ten compounds containing oxygen. 9. Can oxygen be obtained from air ? 10. How is oxygen generally produced ? 11. What is the difference between oxygen and ozone ? 12. Name several examples of simple oxidation. 13. What is the composition of calcium oxide? 14. What is the composition of potassium oxide ? 15. What is the composition of aluminum oxide ? 16. What is the percentage of oxygen in S0 3 ? 17. What are the products of the combustion of charcoal ? 18. What are the products of the combustion of hydro- carbons ? 19. What is the composition of the ash left on the com- bustion of magnesium ? 20. How much antimonous oxide can be produced by roasting one kilogram of antimonous sulphide ? 21. What is the algebraic combining number of the oxygen in water and what is it in "hydrogen dioxide" ? 22. Is hydrogen dioxide really an oxide, or can you give a more scientific name for it? 23. What is the importance of hydrogen oxide to plants and animals? AIE AND WATEE— NITROGEN, OXYGEN AND HYDROGEN 191 24. What is meant by ionization ? 25. How is hydrogen produced ? 26. What products are formed when steam is passed over strongly heated coal ? 27. Name four great classes of compounds containing hydrogen. 28. If you remove one hydrogen atom from each of two molecules of water and put one atom of sulphur in their place, what will be the compound formed ? 29. If you put one atom of sulphur in the place of four hydrogen atoms removed from four molecules of water, what will be the resulting compound ? 30. If you put a nitrogen atom in the place of five hydrogen atoms removed from five molecules of water, what will be the resulting compound? 31. If you put a sodium atom in the place of one hydrogen atom of a molecule of water, what will you have ? 32. If you put a calcium atom in the place of two atoms of hydrogen removed from two molecules of water, what will be formed ? 33. If you put one sulphur atom in the place of six hydrogen atoms taken from six molecules of water, what will be the compound formed ? 34. If from that compound you remove two hydrogen atoms and one oxygen atom, what will remain ? 35. If you remove from it four hydrogen atoms and two oxygen atoms, what will be the technical name of the residue ? 36. If you take away three molecules of water from the compound formed by putting one sulphur atom in the place of six hydrogen atoms removed from six molecules of water, what will be left ? 37. Why are acids, bases and salts said to be built on the water type ? 192 A CORRESPONDENCE COURSE IN PHARMACY 38. In what way may the highest temperature be produced that can be obtained by chemical means ? 39. What is the composition of hydrogen telluride ? 40. Write the molecular formulas of hydrogen bromide, hydrogen nitride, hydrogen phosphide, hydrogen silicide, hydrogen carbide and hydrogen boride. 41. If the atomic weight of oxygen be set down as 100, what will be the corresponding atomic weight of hydrogen ? 42. Explain why an element is said to be reduced whenever it enters into combination with hydrogen, but oxidized whenever it enters into combination with oxygen. LESSON FOURTEEN XX Fluorine, Chlorine, Bromine and Iodine 291. The four elements called respectively fluorine, chlorine, bromine and iodine form a natural group or family of elements closely resembling one another in their chemical properties and behavior. 292. One atom of either of these elements can hold in combination but one atom of hydrogen. The only possible hydrogen compounds of fluorine, chlorine, bromine and iodine are accordingly HF, HC1, HBr and HI. These four compounds are commonly called "acids," because they resemble the real acids in their power to neutralize alkalies; but they should instead be called the hydrogen halides, for they are binary compounds of the halogens, whereas all true acids contain more than two elements. The halides of hydrogen are often called the "hydrogen acids" or "hydracids," because they contain hydrogen without any oxygen, but as all acids contain hydrogen, the term "hydro- gen acids" is ill chosen, since its employment to distinguish between these compounds and the true acids rests not upon what they contain (H) but upon what they do not contain (0). The scientific names of HF, HOI, HBr and HI are hydro- gen fluoride, hydrogen chloride, hydrogen bromide and hydrogen iodide. 293. All binary compounds of fluorine are fluorides; all 193 194 A CORRESPONDENCE COURSE IN PHARMACY * binary compounds of chlorine except its compounds with fluorine or with oxygen are chlorides ; all binary compounds of bromine are bromides, except its compounds with chlorine or fluorine (and its' compounds with oxygen, did such com- pounds exist) ; and all binary compounds of iodine are iodides, except its compounds with bromine, chlorine, fluorine or oxygen. 294. A molecule of any fluoride, chloride, bromide or iodide may contain from one to six atoms of fluorine, chlorine, bromine or iodine, but never contains more than one atom of the positive element. A compound of fluorine and chlorine cannot contain more than one chlorine atom, but may contain one or more fluorine atoms. A chloride of bromine or iodine may contain one or three or five atoms of chlorine or bromine, but it cannot contain more than one iodine atom. This is because the combining value of any negative element in any true binary compound is unchange- able; the atomic combining value of the halogen in any halide is 1, and any member of the chlorine family of ele- ments (the fluorine, chlorine, bromine and iodine are together called the " chlorine family") having a lower atomic weight is negative in its chemical relation to any other element of the same family having a higher atomic weight. The atomic weight of F is 19, that of 01 is 35.5, that of Br is 80 and that of I is 126.5. 295. Halogens. Fluorine, chlorine, bromine and iodine are called "halogens" (from hals, salt, and gennao, I generate), because their water-soluble binary compounds with the metals look like the water-soluble true salts (formed by true acids). But some metallic sulphides and many other compounds look like salts without being such. Common table salt is the chloride of sodium. But positive chlorine, bromine or iodine cannot be called a halogen. FLUORINE, CHLORINE, BROMINE AND IODINE 195 296. Halides are the binary compounds formed by the metals and by hydrogen with the halogens. Sodium chloride is therefore a halide (from hals, salt, and eidos, like). 297. Fluorine is a greenish-yellow gas. But very little is known concerning fluorine in its uncombined state, because the intensity of its chemical energy is so great that when it is set free from any one compound it cannot be prevented from entering at once into the formation of other compounds. This element occurs in nature in the form of calcium fluoride or fluorspar, CaF 2 , and as cryolite, which is a so-called "double fluoride" of aluminum and sodium. Its most interesting compound is the hydrogen fluoride, commonly called "hydrofluoric acid," which is a colorless, fuming, highly corrosive liquid, very poisonous because of its destructive chemical action. It attacks glass and is used to produce etchings on glassware. 298. Chlorine is a yellowish-green gas of suffocating, char- acteristic odor, poisonous when inhaled. At 15° C. it can be compressed into a liquid under the pressure of four atmospheres. One cubic-decimeter of chlorine at 0° 0., bar. 760 mm., weighs about 3.17 grams. One volume of water at 15° C. dissolves about 2-J- volumes of chlorine. A water-solution saturated at 10° C. contains about 0.6 per cent of CI. Such a solution is called "chlorine water. " 299. Chlorine occurs most abundantly in the form of sodium chloride, or common salt, in sea-water and salt- springs, and in salt-beds or salt-mines as rock-salt. 300. Free chlorine is commonly prepared by heating man- ganese dioxide, Mn0 2 > with hydrogen chloride, HC1 : Mn0 2 +4HCl=MnCl 2 +2H 2 0+2Cl. 301. Chemical Properties. Chlorine displays great chemical energy, which fact is usually expressed by the statement that 196 A CORRESPONDENCE COURSE IN PHARMACY it strongly attacks many other substances or has a destructive effect upon them. It unites with any one of all the other known elements (except those that form no compounds whatever, as is apparently the case with neon, argon, krypton and xenon). It displaces bromine and iodine from bromides and iodides. No one atom of any other element can unite with more than six atoms of chlorine. Noxious effluvia and other poisonous decomposition prod- ucts of organic matter are frequently unstable hydrogen compounds, and they may generally be destroyed by chlorine, because of the great affinity of chlorine for hydrogen. This explains the great disinfectant power of chlorine. 302. Hydrogen chloride, HC1, is commonly called "hydro- chloric acid." Being very unstable or easily decomposed when brought in contact with certain metals and other sub- stances, it is described as highly corrosive or destructive. Iron, zinc, aluminum and several other metals readily attack hydrogen chloride, from which they appropriate to them- selves the chlorine, thus liberating the hydrogen : Zn+2HCl=ZnCl 2 +2H. 303. Aqua regia is a mixture made of hydrogen chloride and nitric acid, and contains free CI together with nitrosyl chloride, ONC1. This so-called "nitrohydrochloric acid" dissolves gold and platinum, forming the chlorides of these metals. 304. Chlorides are the compounds of negative chlorine with any other elements or with certain positive compound radicals. Among the most common chlorides are : Hydro- gen chloride, HC1; sodium chloride, NaCI; ammonium chloride or "sal ammoniac" or "muriate of ammonia,' ' H 4 XC1; ferric chloride, FeCl 3 ; calomel, HgCl; and corrosive sublimate, Hg01 2 . FLUORINE, CHLORINE, BROMINE AND IODINE 197 305. Bromine is a dark-brownish-red, mobile, heavy liquid, which gives off suffocating yellowish-red vapors, intensely irritating to the eyes and the respiratory organs and extremely dangerous when inhaled. Its destructive action on organic substances, including clothing, wood, etc., render it imperative that bromine should be handled only with great caution. Bromine occurs in sea-water and in salt-springs chiefly in the form of magnesium bromide, MgBr 2 , from which the bromine is liberated by chlorine and in other ways. Bromine exhibits intense chemical energy. Potassium bromide, KBr, is the most common bromine compound. Hydrogen bromide is commonly called hydro- bromic acid. The binary compounds of the metals with bromine are called bromides. 306. Iodine consists of dry, brittle, purplish-black, rhombic crystal plates, having a shining appearance resembling metallic luster, a strong, characteristic, somewhat saffron- like odor, and an acrid taste. The specific weight of iodine is 4.948 at 17° C. It melts at about 114° C. and boils at 200°. Its vapor is of a beauti- ful violet or purple color. It is nearly insoluble in water but soluble in alcohol. Iodine occurs together with chlorine and iodine in sea- salts and salt-springs. It also occurs in the form of sodium iodate in the residuary liquors obtained in separating sodium nitrate from the saltpetre deposits of Chili. From sodium iodide leached out of the ashes of seaweeds the iodine is obtained in the same manner as chlorine and bromine may be liberated from chlorides and bro- mides : 2NaI+Mn0 2 +2H 2 S0 4 =MnS0 4 -f^"a 2 S0 4 +H 2 0+2I. The most common iodide is that of potassium, KI. 198 A CORRESPONDENCE COURSE IN PHARMACY XXI Sulphur, Selenium and Tellurium, Phosphorus, Arsenic and Antimony, Carbon and Silicon, Boron 307. Sulphur is at ordinary temperatures a light yellow, hard, odorless and tasteless solid. Its specific weight varies from 1.96 to 2.07. It melts at about 114° C. to an amber- colored liquid. When carefully fused sulphur is allowed to cool slowly it crystallizes, and if the still liquid portion be poured off before the whole mass solidifies long crystals can be obtained. Molten sulphur heated beyond 150° 0. darkens and thickens, and at nearly 200° it becomes almost black and so tough that it scarcely runs. Heated higher it gets thinner again, and if then poured into water and allowed to cool it forms a soft, tough, yellowish-brown solid. Sulphur boils at 446° C. Brimstone is impure sulphur molded into cylindrical sticks. Sublimed sulphur ', or "flowers of sulphur," is a light yellow crystalline powder. Precipitated sulphur is an extremely fine, pale, greenish- yellow powder, without odor and taste. When sulphur is ignited it burns with a blue flame, forming sulphur dioxide, S0 2 , which may be at once recognized by its pungent "sulphurous" odor and irritating effects upon the respiratory organs. Sulphur is insoluble in water and in alcohol, but readily soluble in benzin, benzol, oil of turpentine and several other oils, and in ether and chloroform. 308. Occurrence in Nature. Sulphur is found in immense quantities in Italy, South America, California, Louisiana and elsewhere. In combination with iron, copper, lead and zinc it occurs in great abundance. "Iron pyrites" is FeS 2 ; " copper SULPHUE, PHOSPHOKUS, ARSENIC, ANTIMONY, ETC. 199 pyrites" is CuFeS 2 ; "galena" is PbS; and "zinc blende" is ZnS. 309. Chemical Properties. Sulphur does not exhibit any- great inclination to form compounds with other elements except at high temperatures. Negative sulphur forms compounds whose structure is exactly analogous to that of the compounds of oxygen. These sulphur compounds are called sulphides when they correspond to the oxides; they are called "thio-salts" when analogous to oxygen salts. Positive sulphur is sulphur in direct combination with either oxygen or with one of the four halogens (fluorine, chlorine, bromine or iodine). One sulphur atom can hold in combination either two or three oxygen atoms, forming the two oxides, S0 2 and S0 3 . S0 2 forms sulphurous acid with water ; S0 3 forms sulphuric acid. 310. Selenium and tellurium are rare elements which form compounds exactly analogous to those formed by sulphur. ,311. Phosphorus occurs chiefly in the form of a soft white, or slightly yellowish, semi-translucent solid of a peculiar odor and taste. It emits white fumes when exposed to the air and on longer exposure it ignites spontaneously and burns with a fierce flame, forming phosphoric oxide, P 2 5 , which is a snow-white solid. Owing to the intense inflam- mability of phosphorus it must be kept under water in strong glass-stoppered bottles in a cool, secure place. It is very poisonous. Phosphorus is insoluble in water, but soluble in 350 parts of absolute alcohol at 15° C, in 80 parts of absolute ether, in about 50 parts of any fixed oil, and very freely in chloro- form and carbon disulphide. When the ordinary or waxy phosphorus is heated in a closed vessel to about 300° C. it is converted into red phosphorus, 200 A CORRESPONDENCE COURSE IN PHARMACY which is an amorphous dark-red powder, not poisonous nor self-inflammable. 312. Phosphorus occurs principally in the form of calcium phosphate in bones, and in the mineral called apatite. It is made from " bone-ash" or " calcined bone," which consists chiefly of calcium phosphate. 313. Arsenic is an element occurring chiefly in the form of sulphides. The so-called "cobaltum" of commerce is not cobalt but an impure arsenic. Arsenic is a dark steel-gray, brittle solid of a somewhat metallic luster. It is not a metal, because it combines directly with hydrogen to form H 3 As, and it does not per- form the basic function, so that oxygen salts with arsenic as the basic element do not exist. Chemically this element is closely related to nitrogen, phosphorus and antimony. 314. Compounds of arsenic are poisonous. Their structure is illustrated in the following examples : As 2 3 is arsenous oxide, commonly misnamed "arsenous acid." H 2 HAs0 3 is arsenous acid. K 2 HAs0 3 is potassium arsenite, contained in the medicinal preparation called "Fowler's Solution." Na 2 H As0 4 + 7H 2 is crystallized sodium arsenate. Na 4 As 2 7 is sodium pyroarsenate. 315. Antimony occurs in nature chiefly as antimonous sulphide, called antimonite. This element looks decidedly like a metal, having a high metallic luster. It is also very heavy, its specific weight being 6.8. But it combines with hydrogen to form H 3 Sb, and it performs the basic function but feebly if at all. The only water-soluble antimony compound is "tartar emetic," which has the composition 20SbKC 4 H 4 6 -f H 2 0. Sb 2 S 3 is antimonous sulphide. The "black sulphide of SULPHUR, PHOSPHORUS, ARSENIC, ANTIMONY, ETC. 201 antimony" is crystallized antimonous sulphide. Precipitated antimonous sulphide is yellowish-red. Sb 2 3 is antimonous oxide. Sb 2 S 5 is antimonic sulphide. SbCl 3 is antimonous chloride. 316. Carbon is an element common to all vegetable and animal substances. In its free state it exists in several forms, viz. : diamond, graphite, soft coal, hard coal and peat. Coke, wood charcoal, animal charcoal and lampblack are also carbon. Combined carbon is contained not only in all vegetable and animal substances but also in limestone, chalk, marble, magnesite, etc. In its ordinary forms carbon is a solid, inodorous, tasteless substance, insoluble in all liquids, infusible and non-volatile. When heated strongly in the air it ignites and burns, form- ing C0 2 if the supply of air or oxygen is abundant, but CO if the supply is deficient. 317. The chemical properties of carbon are extraordinary. At common temperatures it shows no chemical energy ; but at a high heat it readily combines with oxygen, forming either C0 2 or CO, according to whether the supply of oxygen is liberal or deficient. It, therefore, has two combining values, 4 and 2. But the valence of the carbon atom in nearly all known carbon compounds is 4. The most remark- able characteristics of carbon are that its atoms can hold each other in combination to form chains or rings which give character to innumerable organic substances, and that the same carbon atom can hold in combination with itself both positive and negative elements at the same time. Thus hydrogen, which is positive, and oxygen, which is negative, can both be held in combination with the same carbon atom, as in H 3 COH. 318. The compounds formed by carbon with hydrogen 202 A CORRESPONDENCE COURSE IN PHARMACY alone are called hydrocarbons. The simplest of these is H 4 C, because it contains but one carbon atom. Hydrocarbons containing a small number of carbon atoms are gases ; others, with a larger proportion of carbon, are liquid; and those containing much carbon are solids. Coal oil is a mixture of hydrocarbons. Benzin, gasolin, petrolatum, paraffin, naphthaline, terebene and benzol are all hydrocarbons. Nearly all volatile oils contain one or more kinds of hydrocarbons. The coal gas used for illumina- tion -and for fuel is a mixture of gaseous hydrocarbons of which the chief is H 4 C. Carton monoxide, or carbonous oxide, is CO— a colorless, odorless, tasteless gas which burns with a blue flame, forming C0 2 . The CO is poisonous when inhaled. When steam is blown through incandescent coal or coke, the water (steam) is decomposed and the products are H and CO, which together constitute the gaseous mixture called water gas. Carbon dioxide, C0 2 , is present in the air because animals exhale it. C0 2 is also produced in the decay of certain organic substances and by combustion. The C0 2 is com- monly called "carbonic acid gas," because when dissolved in water it forms a solution of carbonic acid, H 2 C0 3 . Carbonic acid water is a refreshing and not unwholesome drink; but- when inhaled the gas C0 2 is poisonous, and even a small pro- portion of it renders air unfit to be breathed. Effective ventilation is necessary to remove the air contaminated with the C0 2 injected into it by respiration. Men and animals inhale air and exhale carbon dioxide. Plants decompose the carbon dioxide, appropriating the carbon and restoring the oxygen to the air. Cyanogen, (CN) 2 , is a colorless gas of irritating odor and very poisonous. HCN is the fearfully poisonous hydrogen cyanide, commonly called "hydrocyanic acid," or "prussic acid." SULPHUR, PHOSPHORUS, ARSENIC, ANTIMONY, ETC. 203 319. Silicon is, next to oxygen, the most abundant of all elements. Silica, Si0 2 , and silicates of several kinds, con- stitute a large proportion of the rock, sand and clay forma- tions of the earth's surface. Quartz, flint, sand and agate are different forms of silicon dioxide or silica. Brick, earthenware, porcelain and glass are mixtures of silicon compounds. The chief constituents of glass are the silicates of potassium, sodium, calcium and lead. The pure silicates of potassium and sodium are water-soluble, but mixtures of them with the silicates of calcium and lead are not only insoluble in water but even resist the action of strong acids and alkalies to a remarkable degree. 320. Boron is an element that occurs chiefly in the com- pound called lorax, which is sodium tetraborate, Na 2 B 4 7 . Boric acid is H 3 B0 3 , or, rather, (HO) 3 B. Boric acid is a remarkable antiseptic and hence used in large quantities as a preservative of meats and other perish- able organic substances and also as a harmless and yet effective constituent of antiseptic lotions, dressings and powders. Test Questions 1. Name the halogens. 2. What is the correct scientific name for hydrobromic acid ? 3. What is the maximum number of chlorine atoms that can be contained in a chloride ? 4. What is the maximum number of atoms of the positive element in any true iodide ? 5. How can tri-iodide of chlorine be made ? 6. What is the most common fluorine compound in nature ? 7. What is the most abundant chloride ? 8. How is chlorine produced ? 9. How is the great power of chlorine as a disinfectant explained ? 204 A CORRESPONDENCE COURSE IN PHARMACY 10. What is formed when iron is dissolved in a solution of hydrogen chloride ? Write the equation representing the chemical reaction. 1 1 . What is the algebraic combining number of the nitrogen in nitrosyl chloride ? 12. Write the formulas for mercurous chloride and mer- curic chloride ; for ferrous chloride and ferric chloride. 13. What is the action of chlorine on water ? 14. Why is chlorine recognized as a powerful oxidizing agent ? 15. Write the formula for ammonium bromide. 16. How is bromine liberated from a bromide ? 17. Describe bromine. 18. How does it differ from chlorine and iodine ? 19. What are the sources of iodine? 20. What is the chemical action of bromine on potassium iodide ? 21. What is the percentage of bromine in a 10 per cent solution of hydrogen bromide ? 22. What is the percentage of bromine in potassium bromide ? 23. Which contains the greater amount of iodine, a syrup containing 10 per cent of hydrogen iodide or the compound known as potassium iodide ? 24. Which of the two compounds, potassium chloride and potassium chlorate, is best able to resist decomposition when exposed to strong heat ? 25. Describe S0 2 and state how it is produced. 26. What is the difference between a carbonate and a thio-carbonate ? 27. What is the difference between positive sulphur and negative sulphur ? 28. What is the difference between sulphuric sulphur and hyposulphurous sulphur ? SULPHUR, PHOSPHORUS, ARSENIC, ANTIMONY, ETC. 205 29. What is formed when S0 3 is added to water ? 30. Write the chemical reaction occurring when S0 2 is dissolved in water. 31. Name the several possible products formed from S0 3 and water. 32. Can you name any compound containing both positive sulphur and negative sulphur ? 33. Describe phosphorus. 34. What are the differences between the two allotropic modifications of phosphorus ? 35. What is the most common source of phosphorus ? 36. How many bonds has the phosphorus atom in HPH 2 2 ? 37. How many bonds has the phosphorus in H 3 P0 2 ? 38. How many bonds does the phosphorus have in HOP0 2 ? 39. How many bonds does the phosphorus have in H 2 PH0 3 ? How many in H 3 P0 3 ? 40. How many bonds does the phosphorus have in H 5 P0 5 ? InH 3 P0 4 ? InHP0 3 ? 41. Give the technical names of all the phosphorus com- pounds represented by the formulas in questions 36-40. 42. What is the difference between the phosphorus in a metaphosphite and the phosphorus in any phosphate ? 43. Write the molecular formula for nitrate of arsenic. 44. Write the molecular formula for arsenous hydroxide. 45. If hydrogen arsenide is H 3 As, what possible combining values can the arsenic have when united to oxygen ? 46. Why is the formula for arsenous acid written H 2 HAs0 3 instead of H 3 As0 3 ? 47. Can that formula be written more scientifically than it is in either of the forms given in the preceding ques- tion? 48. Why is As 2 3 not an acid? 49. Antimony is a very heavy, brilliantly metallic looking 206 A CORRESPONDENCE COURSE IN PHARMACY substance and forms several useful alloys. Why, then, is it not a metal, chemically as well as physically ? 50. What is an antimonide ? 51. What is the difference between antimonous oxide and antimonic oxide ? 52. Name several carbon compounds contained in the mineral world. 53. Mention several forms of free carbon found in nature. 54. What is the algebraic combining number of the carbon atominH 3 COH? 55. Why are the hydrocarbons so useful as fuel? 56. What is carbonic acid ? 57. What is carbonic acid gas ? 58. How is the 00^ exhaled by men and animals removed from the atmosphere ? 59. What is hydrocyanic acid ? 60. What is the algebraic combining number of the carbon in a molecule of the so-called hydrocyanic acid ? 61. What is silica? 62. What is the composition of glass ? 63. What are the principal uses of boric acid ? 64. What is the algebraic combining number of each boron atom in borax ? LESSON FIFTEEN To the Student: The section numbered XXIV, which treats of the solubilities of com- mon inorganic chemical compounds in water and in alcohol, is included in this lesson principally because of its value as a matter of reference for students. It is full of facts a knowledge of which the student should have, but as the mastering of it is a pure matter of memory, no questions are given upon it. It is not expected, moreover, that the student will memorize the chapter, but will keep it available for frequent reference in subsequent lessons, and it is certain that he will find the matter useful in examinations and in future work. XXII The Light Metals 321. The light metals are those whose specific weights are less than 5 and lower than the specific weights of their own oxides. The most important light metals are lithium, sodium, potassium, magnesium, calcium, strontium, barium and aluminum. All of these metals have a constant valence. 322. The alkali metals are lithium, sodium, potassium, rubidium and caesium. The two last mentioned are rare. Potassium and sodium are abundant. All of them are monads or have an atomic combining value of 1, for their oxides are Li 2 0, Na 2 0, K 2 0, Kb 2 and Cs 2 0. Their hydroxides are the true alkalies, which are freely water-soluble. The alkali metals have such an intense affinity for oxygen that they must be excluded from contact 207 208 A CORRESPONDENCE COURSE IN PHARMACY with air, and this is effected by keeping them immersed in kerosene or benzin. When put in water they decompose it, combining with hydroxyl and liberating one hydrogen atom from each molecule of water decomposed : HOH + K = KOH + H. 323. Potassium is a soft silver-white metal, lustrous when freshly cut but tarnishing rapidly in the air. It is kept immersed in benzin to prevent its oxidation. The specific weight of K is 0.86. 324. Occurrence. Potassium is a widely distributed metal. Potassium silicate occurs in granite rocks, and plants grow- ing in the soils derived from such rocks yield an ash contain- ing potassium carbonate. This is leached out from wood ashes with water and the solution boiled down to get the crude potassium carbonate which is called "potash." The metal itself derives its name from the potash. Potassium is also contained in "argols" or crude "tartar," which is the bitartrate of potassium deposited from the fermenting grape juice in the process of making wine. Purified by recrystallization, the crude tartar is called "cream of tartar." But the present source of potassium is the potassium chloride associated with other salts in the salt beds at Stassfurt, Germany. 325. Potassium compounds are white or colorless unless they contain other elements which impart color. They are nearly all very readily water-soluble, and several common potassium compounds are, in fact, deliquescent. Among the most common compounds of potassium are: KOH, potassium hydroxide, called "caustic potash." K 2 C0 3 , the carbonate of potassium, or "potash." KHC0 3 , bicarbonate of potassium. KBr, potassium bromide. KI, potassium iodide. THE LIGHT METALS 209 KN0 3 , potassium nitrate, or "niter," or " saltpetre." KCIO3, potassium chlorate. 326. Sodium is very like potassium, but does not decompose water so violently. Its specific weight is 0.97. It occurs abundantly in the form of common "salt," which is sodium chloride, in sea-water and in salt-springs and salt- beds. Sodium nitrate is found in Chili in the form called "Chili saltpetre." Common "washing soda" is sodium carbonate, which is manufactured on an immense scale from sodium sulphate made out of sodium chloride, or the carbonate may be made direct from sodium chloride. 327. Sodium compounds are white or colorless and generally very readily water-soluble. The most common include : NaOH, sodium hydroxide, or "caustic soda." Na 2 C0 3 -l- 10II 2 O, sodium carbonate, which constitutes "sal sodae" or washing soda. NaHC0 3 , sodium bicarbonate, or "baking soda." NaCI, "common salt." Na 2 SO 4 + 10II 2 O, sodium sulphate, or "Glauber's salt." Na 2 S0 3 S + 5H 2 0, sodium thio- sulphate, commonly but erroneously called "hyposulphite of sodium" (which is Na 2 S0 2 — quite another substance). NaN0 3 , sodium nitrate, or "Chili saltpetre." Na 2 HP0 4 -f 12H 2 0, sodium phosphate. Na 2 B 4 O 7 + 10H 2 O, sodium tetraborate, or "borax." NaC 18 H 33 2 , sodium oleate, the chief constituent of com- mon hard soap, such as "Castile soap." 328. Lithium is, like potassium and sodium, a soft silver- white metal. It is comparatively rare and costly. Its specific weight is 0.589. Its compounds are white or colorless. They are not as generally or freely soluble as the compounds of potassium 210 A CORRESPONDENCE COURSE IN PHARMACY and sodium. One of the most striking properties of lithium salts is the beautiful crimson color they impart to flame. 329. The Alkaline Earth Metals. These are barium, strontium and calcium. They have an atomic combining value of 2, for their oxides are BaO, SrO and CaO. The hydroxides of these metals are sparingly water-soluble, but the solutions have a strongly alkaline character. Like the alkali metals, they decompose water, but much more quietly. 330. Barium is a soft, yellowish metal of the specific weight 4. It occurs in "heavy spar," which is barium sulphate, in caves on Put-in-Bay Island, Ohio. The most common compounds of barium are : BaO, barium oxide, or "baryta." BaC0 3 , barium carbonate. BaCl 2 + 2H 2 0, barium chloride. Ba(N0 3 ) 2 , barium nitrate. BaS0 4 , barium sulphate. 331. Strontium is comparatively rare. It is a soft, yellowish metal having the specific weight 2.5. Its compounds are analogous to those of calcium and barium. 332. Calcium is a soft, yellowish metal of the specific weight 1.6. It may be kept in dry air without oxidation, but decomposes water rapidly : 2H 2 + Ca = Ca(OH) 2 + 2H. It occurs abundantly in the form of limestone, chalk and marble, all of which are calcium carbonate. Igneous rocks contain calcium silicate and other calcium compounds. "Gypsum" is calcium sulphate, and dried gypsum is nearly anhydrous or water-free calcium sulphate, which, when mixed with the proper amount of water, forms normal calcium sulphate, commonly called crystallized calcium sul- phate or "plaster of Paris." Quick lime, or building lime, is THE LIGHT METALS 211 calcium oxide, and slaked lime is calcium hydroxide. Hy- draulic cement is made by calcining limestone containing clay and silica; this cement hardens when mixed with water, forming calcium silicate and carbonate. 333. Calcium compounds are white or colorless. The car- bonate, phosphate and oxalate are insoluble ; hydroxide and sulphate are sparingly soluble. Among the most common calcium compounds are : CaO, calcium oxide, calx, or "lime." Ca(OH) 2 , calcium hydroxide, "slaked lime." "Lime water" is a solution of calcium hydroxide. CaCl 2 , calcium chloride. CaC0 3 , calcium carbonate, marble, chalk, limestone. CaH 4 S0 6 (or CaS0 4 4-2H 2 0), calcium sulphate or "gyp- sum." CaS0 4 , dried calcium sulphate, used for making "plaster of Paris" by mixing the dry powder with water. Oa 3 (P0 4 ) 2 , calcium phosphate, which is the chief inorganic constituent of bone. Ca(C10) 2 , calcium hypochlorite, the valuable constituent of the so-called "chloride of lime" or "bleaching powder," which also contains CaCl 2 . 334. Magnesium is a white metal which oxidizes but slowly in moist air. Can be made into wire and ribbons, and con- verted into coarse powder. Its specific weight is 1.74. It does not decompose water at the ordinary temperatures, but does so at the boiling point of. the water. The "flash-light" of photographers is produced by burning powdered magnesium. Magnesium occurs in large quantities, chiefly in the form of carbonate and silicate. Magnesite is magnesium carbonate. "French chalk" or "talcum," and also "asbestos" and "meerschaum," are magnesium silicate. 212 A CORRESPONDENCE COURSE IN PHARMACY 335. Magnesium compounds are white or colorless. The oxide, hydroxide, carbonate, phosphate and oxalate are insoluble in water. The citrate is also practically insoluble in water, but the " solution of citrate of magnesium" of the drug stores is made by adding a large excess of citric acid, which holds the magnesium citrate in solution in the water. Among the most common magnesium compounds are: MgO, magnesium oxide, commonly called "calcined magnesia." MgH 2 S0 5 + 6H 2 (commonly represented as MgS0 4 + 7H 2 0) is magnesium sulphate, or "Epsom salt." Mg 5 (OH) 2 (C0 3 ) 4 + 5H 2 is the common carbonate of mag- nesium. 336. Aluminum is a silver-white metal which is malleable, ductile and capable of high polish. It is not tarnished in dry, pure air. Its specific weight is 2.5. It is strong, tough, durable and light, and as it does not corrode in the air and is not easily affected by other substances except chlorides, it is an extremely useful metal. This metal occurs abundantly in combination with oxygen and silicon. Clay consists of aluminum silicate. Cryolite is 3XaF. A1F 3 . Beauxite is A1 2 3 + H 2 0. Aluminum oxide, commonly called "alumina," occurs as emery, corundum, sapphire and ruby Feldspar. and mica contain aluminum, and "thina clay" or "pipe clay" or "kaolin" are also aluminum compounds. The metal is named after "alum." 337. Aluminum salts are white or colorless. Those soluble in water are astringent. The structure of aluminum compounds is illustrated by the following common compounds: A1 2 3 , aluminum oxide. Al(OH) 3 , aluminum hydroxide, commonly misnamed "aluminum hydrate." A1C1 3 , aluminum chloride. THE HEAVY METALS 213 A1K(S0 4 ) 2 + 12H 2 0, aluminum and potassium sulphate, or alum, or " potash-alum." A1II 4 N(S0 4 ) 2 4- 12H 2 0, aluminum and ammonium sulphate, or "ammonia alum," the now common alum. XXIII The Heavy Metals 338. The heavy metals are those whose specific weights exceed 5 and are higher than those of their oxides. The heavy metals of great importance include zinc, iron, nickel, chromium, manganese, lead, copper, mercury, silver, gold, platinum, bismuth and tin. The compounds of the heavy metals are not as generally water-soluble as are the compounds of the light metals, and the compounds of metals of very high atomic weights as well as specific weights form very few water-soluble compounds. The light metals form more powerful bases than the heavy metals. 339. Zinc is a bluish-white, crystalline, lustrous, brittle metal of the specific weight 7.2. It melts at 412° C. It readily decomposes dilute acids, and also the alkalies in hot solutions. Zinc occurs as zinc Mende, which is sulphide of zinc, and also as calamine, which is composed of carbonate and silicate. 340. Zinc compounds are generally white or colorless. The water-soluble salts of zinc have a disagreeable, bitter, astringent, metallic taste, and are poisonous. Among the most common zinc compounds we have : ZnO, zinc oxide. ZnCl 2 , zinc chloride. ZnH 2 S0 5 + 6H 2 (commonly represented as ZnS0 4 + 7H 2 0) , zinc sulphate, or "white vitriol." 214 A CORRESPONDENCE COURSE IN PHARMACY 341. Iron is. light grayish, lustrous, hard, malleable, ductile, tenacious. Its specific weight is from 7.3 to 7.9. It melts at about 2000° C. Wrought iron, steel and cast iron all contain carbon and minute amounts of other elements. Wrought iron contains the smallest proportion of carbon ; cast iron the greatest. Iron occurs in very large quantities in the form of oxides, hydroxides, carbonates and sulphides. The best iron ore is "magnetic iron ore," which has a composition represented by Fe 3 4 . 342. Iron compounds are of various colors — white, gray, green, yellow, red, brown, blue, black, purple and rose. Ferrous compounds contain iron with a valence of 2. They are generally white or grayish-white when anhydrous, but green or greenish-blue when hydrous or in water solution. Ferric compounds contain iron with a valence of 3. They are usually nearly white or pale yellow when anhydrous, but red-brown when associated with water. The iron preparations used in medicine are numerous. Among the most common compounds of iron are the fol- lowing: FeCl 2 , ferrous chloride. Fel 2 , ferrous iodide. FeH 2 S0 5 + 6H 2 (commonly written FeS0 4 + 7H 2 0), ferrous sulphate, or "green vitriol." ' FeH 2 S0 5 , dried or anhydrous ferrous sulphate. Fe 2 3 , ferric oxide. FeCl 3 , ferric chloride. Fe(OH) 3 , ferric .hydroxide, commonly misnamed "ferric hydrate." Fe 2 (S0 4 ) 3 , ferric sulphate. 343. Nickel is a hard silver-white metal, tough, capable of high polish. Its specific weight is 8.9. The principal nickel ore is nickelic arsenide, NiAs. THE HEAVY METALS 215 344. Chromium is a hard, gray, crystalline, infusible powder of the specific weight 7.3. Chromous compounds contain the metal with a valence of 2, as in CrCl 2 . In chromic compounds the element has a valence of 3, as in Cr 2 3 . But potassium dichromate (com- monly misnamed "bichromate") has the composition K 2 Cr 2 7 , and "chromic anhydride" is Cr0 3 , which is commonly misnamed chromic acid. 345. Manganese is a hard, brittle metal, fusible with diffi- culty. It occurs in nature in combination with oxygen. Its specific weight is about 7.5. Manganese is remarkable because of its many different valences. It can apparently have a valence of either 2, 3, 4, 6 or 7. MnO is manganous oxide. Mn 2 3 is manganic oxide. Mn0 2 is manganese dioxide. MnS0 4 is manganous sulphate. K 2 Mn0 4 is potassium manganate. KMn0 4 is potassium permanganate. 346. Lead is a soft, gray or bluish- white metal of bright luster when untarnished. Its specific weight is 11.4, and its melting point 330° 0. The principal lead ore is galena, which is PbS. The only water-soluble lead compounds are the acetate and the nitrate. PbO is oxide of lead, familiar in the form of the red "litharge" and the yellow "massicot." "White lead" is a "basic carbonate of lead." "Red lead" or "minium" is Pb 3 4 . Lead compounds are poisonous. 347. Copper is reddish, softer than iron but harder than silver, malleable and ductile, capable of high polish. Its specific weight is 8.9, and its melting point about 1090°. 216 A CORRESPONDENCE COURSE IN PHARMACY It is found in large quantities, uncombined, in the great copper mines of the Lake Superior regions and in other places. Copper pyrites is represented by the formula CuFeS 2 and is common. Brass is an alloy of copper and zinc. 348. Copper compounds are generally green or blue, but some are white, red, brown or black. Cuprous copper is a monad; cupric copper a dyad. Soluble copper compounds have a nauseous, strongly "metallic" or "brassy," persistent taste, and are poisonous. Among the very common copper compounds are the following : Cu 2 0, cuprous oxide. CuO, cupric oxide. Cu 2 S, cuprous sulphide. CuS, cupric sulphide. Cu(N0 3 ) 2 , cupric nitrate. CuS0 4 , anhydrous cupric sulphate. CuS0 4 + 5H 2 0, crystallized cupric sulphate, or "blue vitriol." 349. Mercury is the only metal which is liquid at the ordinary temperatures. It is silver- white, lustrous, and so mobile that it is called "quick silver." Its specific weight is 13.6, and its boiling point 360° C. It freezes at about -40° C. Cinnabar is the crystallized mercuric sulphide found in nature and this constitutes the ore from which the metal is obtained. 350. Mercury compounds are of two classes, according to the valence of the element. Mercurous mercury is a monad, forming mercurous compounds; mercuric mercury is the metal with a valence of 2, forming mercuric compounds. The only water-soluble mercury compounds are mercuric chloride and mercuric cyanide; but the nitrates, both THE HEAVY METALS 217 mercurous and mercuric, can be dissolved in a mixture of nitric acid and water. Mercury compounds have a great variety of colors : color- less, white, scarlet, crimson, gray, yellow, orange red, black and brown. They are poisonous, except when absolutely insoluble. Among the most common mercury compounds are : HgOl, mercurous chloride or "calomel." Hgl, mercurous iodide. HgO, mercuric oxide, which is red if produced "in the dry way," but yellow if made by precipitation. Eed oxide of mercury is often called "red precipitate," but cannot be made by "precipitation" as we now understand that term. HgCl 2 , mercuric chloride or "corrosive sublimate." Hgl 2 , mercuric iodide, or "red iodide of mercury." HgS, mercuric sulphide, which is red when crystallized, but black when precipitated, although the black precipitated mercuric sulphide can be converted into a red powder called "vermilion." H 2 NHgCl is mercuric chloramide, commonly called "white precipitate. ' ' 351. Silver is a beautiful white metal, harder than gold, capable of very high polish, malleable and ductile. . Its specific weight is 10.6, and its melting point about 916° 0. It is the best known conductor of heat and of electricity. Pure silver is called "sterling silver." This metal occurs in nature in the free state, but more freely in the form of sulphide associated with the sulphides of lead and copper. 352. Silver compounds are colorless, white, black, yellow or brown. As silver is univalent, the structure of its compounds is simple : Ag 2 is silver oxide. AgOl, silver chloride. 218 A CORRESPONDENCE COURSE IN PHARMACY AgX0 3 , silver nitrate, which, when molded into pencils, is called "lunar caustic." 353. Gold is soft, yellow, capable of extremely high polish, remarkably malleable and ductile. Its specific weight is 19.3. It melts at about 1037° 0. Pure gold does not decompose acids, but it dissolves in the mixture called "aqua regia," which is made of nitric acid and hydrochloric acid, because that mixture contains free chlorine, with which the gold forms a soluble chloride. Gold occurs in nature almost exclusively in the uncombined state. The most common gold compound is the chloride, AuCl 3 , which is a light yellow, transparent, water-soluble, crystalline solid. 354. Platinum is a grayish-white, lustrous, hard, tough metal, fusible only at a strong white heat. Its specific weight is 21.46. It occurs in nature only in the free state. It dissolves in "aqua regia" to form platinic chloride, PtCl 4 . 355. Bismuth occurs in nature only in the uncombined state. It is a reddish-white, brittle metal of high luster and well defined crystalline structure. It is not malleable nor ductile. It has the specific weight 9.74. It is easily fused, its melting point being 270° 0. It readily decomposes nitric acid, forming nitrate of bismuth, which is soluble in water mixed with nitric acid, but converted into subnitrate of bismuth by water alone. Bi 2 3 is bismuth oxide. OBiCl is bismuthyl chloride. Bi(N0 3 ) 3 , bismuth nitrate. OBiN0 3 , bismuthyl nitrate, or "subnitrate of bismuth." (OBi) 2 C0 3 +H 2 0, "subcarbonate of bismuth," or bismuthyl carbonate. 356. Tin is a silver-white, lustrous, soft, malleable metal, of the specific weight 7.3, fusible at 228° C. It occurs in SOLUBILITIES OF COMMON INOKGANIC COMPOUNDS 219 nature in the form of "tin ore" or "tin-stone," which is stannic oxide, Sn0 2 . Tin is not easily oxidized, nor is it affected by organic substances which attack iron, copper, lead, zinc, etc. Hence its great usefulness. "Tin salt" is stannous chloride, SnCl 2 + 2H 2 0. XXIV Solubilities of Common Inorganic Chemical Compounds in Water and in Alcohol WATER SOLUBILITIES 357. Potassium Compounds. All are water-soluble and most of them are readily soluble. Deliquescent are the hydroxide, carbonate, cyanate, phos- phate, hypophosphite, acetate and the sulphated potassa. Readily soluble are the bicarbonate, chloride, bromide, iodide, ferricyanide, ferrocyanide, nitrate, tartrate, citrate, salicylate, benzoate and Rochelle salt. Less readily soluble are sulphate in 9.5 parts of water, dichromate in 10 parts of water, permanganate in 16 parts of water and chlorate in 16.7 parts of water. Very sparingly soluble is cream of tartar in 201 parts of water. Nearly insoluble is potassium-platinum chloride. 358. Sodium Compounds. All are soluble except anti- monite, which is nearly insoluble. Very freely soluble are the hydroxide, carbonate, chloride, bromide, iodide, chlorate, sulphate, sulphite, bisulphite, thio-sulphate, nitrate, nitrite, phosphate, hypophosphite, arsenate, acetate, tartrate, citrate, valerate, salicylate and benzoate and Rochelle salt. 220 A CORRESPONDENCE COURSE IN PHARMACY Less readily soluble are bicarbonate in 11.3 parts of water, pyrophosphate in 12 parts of water, borax in 16 parts of water and bitartrate sparingly. 359. Lithium Compounds. All freely soluble in water except the carbonate, which dissolves in 80 parts of water, and the phosphate, which is nearly insoluble. 360. Ammonium Compounds. All officinal ammonium compounds are readily water-soluble, the least soluble being the benzoate and the carbonate, which are soluble in 5 parts of water. 361. Barium Compounds. The nitrate, chloride, bromide, iodide, sulphide and acetate are readily soluble. The hy- droxide is soluble in 20 parts of water. Insoluble are the carbonate, phosphate, sulphate and oxalate. 362. Strontium Compounds. The chloride, bromide and iodide are deliquescent. The acetate, lactate and nitrate are readily soluble. The hydroxide is comparatively sparingly soluble. Insoluble are the carbonate, phosphate, sulphate and oxalate. 363. Calcium Compounds. Deliquescent are the chloride, bromide and iodide. Eeadily soluble are the nitrate, hypo- phosphite, sulphite, acetate, lactate and the sulphurated lime. Sparingly soluble is the hydroxide, which requires from 600 to 700 parts of water for solution, and the sulphate, which is soluble in from 300 to 400 parts of water. Insoluble are the carbonate, oxalate and phosphate. 364. Magnesium Compounds. Eeadily soluble are the chloride, bromide, iodide, nitrate, sulphate, acetate, lactate and the acid citrate. Insoluble are the oxide, hydroxide, carbonate, oxalate and phosphate. 365. Zinc Compounds. Deliquescent are the chloride, bromide and iodide. Eeadily soluble are the sulphate, SOLUBILITIES OF COMMON INORGANIC COMPOUNDS 221 nitrate, acetate, lactate and paraphenolsulphonate. Less readily soluble is the valerate. Insoluble are the oxide, sulphide, phosphide, hydroxide, carbonate, oxalate, phos- phate and oleate. 366. Cadmium Compounds. Soluble are the chloride, bro- mide, iodide, nitrate and sulphate. Insoluble are the oxide, hydroxide, sulphide, carbonate, oxalate and phosphate. 367. Aluminum Compounds. Eeadily soluble are the chloride, bromide, iodide, nitrate, sulphate, acetate, potash alum and ammonia alum. Insoluble are the oxide and hydroxide. 368. Cerium Compounds. Soluble are the chloride, nitrate and sulphate. Insoluble are the oxide, hydroxide, carbonate and oxalate. 369. Cobalt Compounds. The cobaltous salts and halides are deliquescent. Insoluble are the oxides, hydroxides and sulphides. 370. Nickel Compounds. Mckelous sulphate and nickel- ous chloride are soluble. The oxides, hydroxides and sul- phide of nickel are insoluble. 371. Iron Compounds. Very readily water-soluble are ferrous chloride, bromide and iodide, ferrous sulphate and nitrate, ferric chloride and bromide, ferric nitrate, subsul- phate, sulphate, acetate and citrate, and iron alum. The scale-salts of iron are all freely soluble. Less soluble is ferrous lactate, requiring 40 parts of water for solution. The insoluble iron compounds are ferrous and ferric oxides, hydroxides, sulphides, carbonates, oxalates, phos- phates, pyrophosphates, metaphosphates andhypophosphites. 372. Chromium Compounds. Water-soluble are the chlo- rides, chromium sulphate, chromic anhydride, commonly called chromic acid, potassium chromate, potassium dichro- mate and chrome alum. 222 A CORRESPONDENCE COURSE IN PHARMACY 373. Manganese Compounds. Soluble are manganous chloride, bromide, iodide, nitrate and sulphate; also potas- sium manganate and permanganate and sodium perman- ganate. Insoluble are the oxides, hydroxide, carbonate, oxalate, phosphate and sulphide. 374. Lead Compounds. The only readily water-soluble lead compounds are the nitrate, acetate and subacetate. Lead chloride is sparingly soluble. 375. Copper Compounds. The only water-soluble cupric compounds are the chloride, nitrate, sulphate and acetate. 376. Mercury Compounds. All mercurous compounds are insoluble in water, but mercurous nitrate is soluble in a mixture of water and nitric acid. The only water-soluble mercuric compounds are the chlo- ride, which is soluble in 16 parts of water, and the acetate and cyanide. The bromide is soluble in about 200 parts of water, but mercuric nitrate is soluble in a mixture of nitric acid and water. 377. Silver Compounds. The only water-soluble salts are the nitrate and acetate. 378. Gold Compounds. The only water-soluble gold com- pound much in use is the trichloride. 379. Bismuth Compounds. The only water-soluble bismuth compound is citrate of bismuth and ammonium. But the nor- mal bismuth nitrate which is decomposed by water is soluble in glycerin and also in glacial acetic acid without decomposi- tion. It is also soluble in a mixture of nitric acid and water. 380. Antimony Compounds. The only water-soluble anti- mony compound is tartrate of antimonyl and potassium, commonly called tartar emetic. But chloride of antimony is soluble in a mixture of hydrogen chloride and water. 381. Arsenical Compounds. Sodium arsenate is readily soluble. Potassium arsenite is also soluble, as is iodide of arsenic. Arsenous acid is only sparingly soluble. SOLUBILITIES OF COMMON" LSTOKGANIC COMPOUNDS 223 382. Oxides. No metallic oxides are water-soluble, except chromic anhydride and other oxides that react with the water to form either acids or bases. These dissolve by "chemical solution. " 383. Hydroxides. The only freely water-soluble metallic hydroxides are those of the alkali metals. The hydroxides of barium, strontium and calcium are comparatively sparingly or very sparingly soluble. All other metallic hydroxides are insoluble. 384. Chlorides. All metallic chlorides are water-sol- uble except those of silver and lead, mercurous chloride and the chloride of antimony (which is decomposed by water, but soluble in a mixture of hydrochloric acid and water) . Deliquescent chlorides are those of calcium, zinc, ferric chloride and platinic chloride. Eeadily soluble are the chlorides of potassium, sodium, lithium, ammonium, barium, strontium, magnesium, alumi- num and gold. Less readily soluble is mercuric chloride, soluble in 16 parts of water. Nearly insoluble is lead chloride. Insoluble are silver chloride and mercurous chloride. Decomposed by water is antimony trichloride. 385. Bromides. Eeadily soluble are the bromides of potas- sium, sodium, lithium, ammonium, barium, strontium, calcium, magnesium, zinc, aluminum and ferrous and ferric bromide. Soluble, though rather sparingly, are mercuric bromide and bromide of gold. Insoluble are the bromides of silver, lead, and mercurous bromide. 386. Iodides. Freely soluble are the iodides of potassium, sodium, lithium, ammonium, barium, strontium, calcium, 224 A CORRESPONDENCE COURSE IN PHARMACY magnesium, zinc, cadmium, ferrous iodide, manganous iodide and arsenous iodide. Insoluble are the iodides of silver, lead and mercury. 387. Cyanides. Those of the alkali metals are freely soluble. Mercury cyanide is soluble. Silver cyanide is insol- uble. 388. Ferrocyanides and Ferricyanides of the alkali metals are water-soluble. 389. Sulphides. Those of the alkali metals and the alkaline earth metals are freely water-soluble. All sulphides of the heavy metals are insoluble. 390. Hypochlorites of the alkali metals and alkaline earth metals are soluble. 391. Chlorates of potassium and sodium are soluble. 392. Sulphites of potassium and sodium are readily soluble. Those of calcium and magnesium are soluble. 393. Sulphates. All metallic sulphates are soluble, except those of barium, strontium, calcium, lead and mercury. Readily soluble sulphates are those of sodium, ammonium, aluminum and ferric sulphate, also the alums. Soluble are the sulphates of potassium, lithium, magnesium, zinc, ferrous sulphate, manganous sulphate and copper sulphate. Very sparingly soluble is calcium sulphate. Insoluble are the sulphates of barium, strontium and lead. Decomposed by water is sulphate of mercury. 394. Thio-sulphates of potassium and sodium are freely soluble. 395. Sulphated potassa and sulphurated lime are freely soluble. 396. Nitrates. All are water-soluble except those of mercury and bismuth, which are decomposed by water. 397. Nitrites of the alkali metals are soluble. 398. Phosphates, Pyrophosphates and Metaphosphates. The only water-soluble phosphates are those of potassium, SOLUBILITIES OF COMMON INORGANIC COMPOUNDS 225 sodium and ammonium, but some phosphates of the heavy metals, also the phosphates of the alkaline earth metals and magnesium, are soluble in phosphoric acid. 399. Orthophosphates of iron are soluble in orthophosphoric acid, but insoluble in pyrophosphoric or metaphosphoric acid. Pyrophosphates and metaphosphates of iron are insoluble in orthophosphoric acid, but soluble in meta- phosphoric acid. 400. Hypophosphites. Those of the alkali metals and of calcium are water-soluble. Those of the heavy metals are insoluble, or .nearly so. 401. Carbonates. The only water-soluble carbonates are those of potassium, sodium and ammonium. That of lithium is but sparingly soluble. 402. Borates. Borax is soluble. 403. Acetates of the metals are all water-soluble. 404. Valerates. Those of potassium, sodium,, lithium and ammonium are soluble. Valerate of zinc is sparingly so. 405. Oxalates. Only those of the alkali metals and ammo- nium are soluble. 406. Tartrates. The normal tartrates of the alkali metals and ammonium are soluble. Their bitartrates are sparingly soluble. The tartrates of ferryl and potassium, and ferryl and ammonium, and antimonyl and potassium are soluble. 407. Citrates. Those of the alkali metals, ammonium and iron are soluble. Magnesium citrate is soluble in water con- taining much citric acid. Bismuth citrate is insoluble, but citrate of bismuth and ammonium is soluble. 408. Lactates of the alkali metals, calcium, strontium, magnesium, zinc and iron are water-soluble. 409. Salicylates. Those of the alkali metals are alone water-soluble. 410. Phenol Sulphonates. Those of the alkali metals and of barium, calcium and zinc are water-soluble. 22G A CORRESPONDENCE COURSE IN" PHARMACY 411. Benzoates. Those of the alkali metals and of ammo- nium and calcium are water-soluble. 412. Oleates. Only the soaps are water-soluble. 413. The student will find it very useful carefully to memorize the following: All of the officinal compounds of potassium, sodium and ammonium are water-soluble, but cream of tartar is only very sparingly soluble. The hydroxides of potassium, sodium and ammonium are freely soluble. The oxides, hydroxides, sulphides, carbonates, oxalates, phosphates (including pyrophosphates, metaphosphates and orthophosphates), hypophosphites, arsenates, arsenites, sali- cylates, benzoates and oleates of the heavy metals are all insoluble. ALCOHOL SOLUBILITIES 414. A very large proportion of the inorganic chemical compounds are insoluble in alcohol, and especially those that contain much water. Inorganic chemical, compounds which are insoluble in water are also, with scarcely any exception, insoluble in alcohol, but even a large number of the water- soluble inorganic chemicals are insoluble in alcohol. 415. Very soluble (in less than 5 parts of alcohol) are: Hydroxides of potassium, sodium and ammonium. Chlorides of magnesium, zinc, iron and mercuric chloride. Bromides of lithium, barium, strontium, calcium, mag- nesium and zinc. Iodides of lithium, sodium, barium, calcium, magnesium and zinc. Acetate of potassium. Valerates of potassium, sodium, ammonium and iron (ferric). Salicylates of potassium, sodium, lithium and ammonium. Ferric sulphate. SOLUBILITIES OV COMMON INORGANIC COMPOUNDS 227 416. Soluble in from 6 to 30 parts of alcohol : Iodine, 1 in 10. Boric acid, 1 in 15. Chloride of lithium, 1 in 10; of strontium, 1 in 6; of calcium, 1 in 8. Bromide of sodium, 1 in 13; of ammonium, 1 in 30. Iodide of potassium, 1 in 18 ; of ammonium, 1 in 9. Mercuric cyanide, 1 in 15. Nitrate of ammonium, 1 in 20. Hypophosphite of potassium, 1 in 7.3; sodium, 1 in 30. Acetate of sodium, 1 in 30; lead, 1 in 21. Lactate of strontium. Benzoate of lithium, 1 in 12, and ammonium, 1 in 28. 417. Sparingly soluble (in from 36 to 200 parts of alcohol): Bromide of potassium, 1 in 200. Iodide, mercuric, 1 in 130. Chlorate of sodium, 1 in 100. Nitrate of sodium, 1 in 100. Phenolsulphonate of sodium, 1 in 132. Acetate of zinc, 1 in 36. Valerate of zinc, 1 in 40. Benzoate of sodium, 1 in 45. 418. Insoluble, or nearly so, in alcohol are: All metallic carbonates, oxalates, phosphates, pyro- phosphates, metaphosphates, arsenates, arsenites, citrates and tartrates. All metallic sulphates except ferric sulphate. All the scale-salts of iron. Chlorides of potassium, sodium and ammonium and mercurous chloride. Iodide of lead and mercurous iodide. Cyanide of potassium. Nitrates of potassium, lead, copper and mercury. Chlorate of potassium. 228 A CORRESPONDENCE COURSE IN PHARMACY Nitrate of sodium. Sulphite of potassium. Thio-sulphate of sodium. Borax. Potassium dichromate. All the ferrocyanides and ferri cyanides. Ammoniated mercury. Ferrous lactate. Test Questions 1. Write the chemical reaction which takes place when sodium is placed in water. 2. What is the most common potassium compound with which you are acquainted ? Give the molecular formula for that compound. 3. What is the difference between washing soda and bak- ing soda ? Give the molecular formulas of both. 4. What is cream of tartar ? 5. What is the color of sodium thio-sulphate ? 6. What kind of a salt is Castile soap ? 7. What is the percentage of bromine in potassium bro- mide and in lithium bromide ? 8. Give the molecular formula of strontium sulphate. 9. Give the molecular formula of barium hydroxide. 10. Describe calcium. 11. What is the difference between CaS0 4 + 2H 2 and CaH 4 S0 6 ? 12. What is the difference between quick lime and slaked lime? 13. What is chloride of lime ? 14. What is talcum ? 15. Give the molecular formula of magnesium hydroxide. 16. What is the difference between MgS0 4 + H 2 and MgH 2 S0 5 ? SOLUBILITIES OF COMMON INORGANIC COMPOUNDS 229 17. What kind of a sulphate is MgS0 4 and what kind of a sulphate is MgH 2 S0 5 ? 18. How many aluminum atoms are contained in 3NaF.ALF 3 ? 19. How many different systems of atomic linking do you find in the foregoing formula ? 20. What is the molecular formula for alum ? 21. Write the molecular formula for aluminum and sodium sulphate. 22. What is the most common source of aluminum ? 23. Can you mention any property by which the light metals differ chemically from the heavy metals ? 24. What is zinc blende ? 25. What is formed when zinc is dissolved in diluted sul- phuric acid ? Write the reaction. 26. What is formed when zinc is dissolved in so-called hydrochloric acid ? Write the reaction. 27. What is the difference between ferrous phosphate and ferric phosphate ? 28. What is the difference in color between a solution of ferric chloride and a solution of ferrous chloride ? 29. Can you trace the atomic linking in the substance represented as Fe 3 4 ? 30. What is the difference between FeO + Fe 2 3 and Fe 2 Fe0 4 ? 31. What is FeH 2 S0 5 ? 32. WhatisFe(N0 3 ) 2 ? 33. What is Fe(N0 3 ) 3 ? 34. What is FeO ? 35. What is the algebraic combining number of each of the two elements in nickelic arsenide ? 36. What is the difference between chromic anhydride and chromic acid ? Write the molecular formulas for both. 37. What is the difference between potassium dichromate 230 A CORRESPONDENCE COURSE IN PHARMACY and potassium bichromate ? Write the molecular formulas for both. 38. WhatisMn0 2 ? 39. If such a compound as MnMn0 4 exists, what is it, and how does it differ from Mn0 2 ? 40. What is the difference between basic manganese and acidic manganese as to valence ? 41. What is galena ? 42. What is Pb0 2 ? 43. Can you trace the atomic linking in Pb 3 4 ? 44. Can you trace the atomic linking in Pb 2 Pb0 4 ? 45. If Pb 2 Pb0 4 exists, what is its technical title ? 46. What is the highest valence possible to lead, as indicated by its position in the periodic system ? 47. Give the molecular formula for sulphate of copper. 48. What are the differences between mercurous com- pounds and mercuric compounds ? 49. How can you distinguish between them when you see their molecular formulas ? 50. How is mercury obtained ? 51. What is the difference between calomel and corrosive sublimate ? 52. Silver nitrate being soluble in water, how would you make it ? 53. Silver chloride being insoluble in water, how would you make it ? 54. What is the combining value of silver ? 55. Why is it that aqua regia dissolves gold but does not dissolve silver ? 56. What is the algebraic combining number of the bismuth in OBiCl ? 57. Write the formula for bismuthic oxide. 58. Write the formula for bismuthous sulphide. 59. Write the formula for stannic chloride. LESSON SIXTEEN XXV Weights and Measures 419. Three different systems of weights and measures are at the present time in use in medicine and pharmacy, although the metric system is exclusively employed in all pharmacopoeias except the British, and the British phar- macopoeia uses both the metric system and the imperial system. Physicians who write prescriptions employ the metric system exclusively in all countries except Great Britain and America. In Great Britain they use partly the imperial system and partly the old apothecaries' system, while in the United States the apothecaries' system is generally used. Pharmacists in this country must therefore understand all the three systems — the imperial system, the apothecaries' system and the metric system. It is also necessary that pharmaceutical students understand the relations of weight and volume to each other and the principles of metrology. 420. The metric system is the most scientific and simple system of weights and measures in use. Its chief merit is that it is decimal, and therefore in perfect harmony with our arithmetical notation. We count from 1 to 10 and the number 10 is expressed by two numerals. When we reach 100 we use three numerals, and for 1000 we use four. In other words, the periodic number of our arithmetic is 10. 231 232 A CORRESPONDENCE COURSE IN PHARMACY No mathematician believes that 10 is the most convenient periodic number; on the contrary, either 8 or 12 would be far superior to 10, because 8 can be subdivided successively by 2 until unity is reached, and, moreover, the number 8 contains the cube of the smallest number that can be cubed. It is evidently most natural to men to divide numbers into halves and quarters, eighths, sixteenths, thirty-seconds, etc. It is not natural to divide by 10 and 5. The number 12 can be divided by either 6, 4, 3 or 2, but cannot be divided successively by 2 without striking fractions. Hence, although 12 is preferable to 10, it is probably not so convenient as 8. The only reason advanced against the introduction of the metric system which has any weight or deserves any atten- tion is the argument that our system of arithmetic is unnatural and will probably be changed in the course of time; but it has been admitted by those who advance this argument against the metric system that probably centuries will elapse before a more natural system of arithmetical notation is adopted. Every one competent to express an opinion will readily admit that whatever our system of arithmetic may be, our weights, measures and money ought to agree with it. Since, therefore, our arithmetical notation is decimal, it follows that our weights, measures and money should also be decimal, in order that computations may be rendered as simple as possible; and if we are going to continue to use decimal arithmetic for centuries, we certainly should in the meantime use decimal weights, measures and money instead of waiting for reform in weights and measures until a new system of arithmetic has been introduced. 421. The metric system was devised a little over one hundred years ago. Many of the world's scientific men were concerned in constructing it. It was first decided that it should be decimal. Next, it was decided that it should be based upon some linear unit, and that measures of surface, WEIGHTS AND MEASURES 233 volume and weight should be based upon the linear unit primarily. Next, it was decided that the linear unit chosen should be an aliquot part of some physical constant. The physical constants that have been thought of are the length of the polar axis, the length of the equator and the length of the meridian, also the length of the seconds pendulum — a pen- dulum of such length that it swings in seconds of time at a given latitude — or the length of the seconds rod, which is exactly 50 per cent longer than the seconds pendulum. The idea involved in the selection of a physical constant as the natural basis of a universal system of weights and measures was that the dimensions and movements of the earth can be measured at any time, so that if the material standard made to represent the natural standard should ever be lost, it could be replaced with absolute certainty of perfect sameness. In devising the metric system, the length of the meridian was chosen as the primary natural standard, and the length of the seconds pendulum was chosen as a secondary standard to serve as a check upon the other. But the length of the seconds pendulum is hardly ever mentioned in connection with the metric system any longer, and the length of the meridian has now but a theoretical and sentimental connec- tion with the metric system based upon the meter. The original meter was intended to be identical with the forty- millionth part of the length of the meridian, or the ten- millionth part of the quadrant, and in order to arrive at this unit of length an arc of the meridian was measured from Dunkirk to Barcelona, and a platinum bar was constructed and called the meter. Upon the length of this meter the whole metric system was based. It has since been held by some that the platinum meter is not exactly identical with the ten-millionth part of the quadrant. At all events, the question is a disputed one. 234 A CORRESPONDENCE COURSE IN PHARMACY Whether the theoretical meter, which is the forty-millionth part of the meridian, and the actual meter made of platinum are identical is of no consequence whatever, for there are now extant in the world a large number of meter bars made of platinum alloyed with 10 per cent of iridium which are microscopically accurate, and as these several meter bars are kept in various parts of the world and are so constructed that they will resist any injury, we shall never lose all of them. Any meter bar lost can be readily replaced with the absolute certainty that the new one will have precisely the same value as the one lost. Hence, there will never be any occasion for measuring the meridian again for the purpose of constructing a new meter bar. 422. The original platinum meter is preserved in the archives of France, and is universally called the " Metre des Archives." It is believed to be porous and inferior in other ways to the irido-platinum meter bars now used, so that the Metre des Archives is merely an interesting historical relic. It is never used. 423. The modern meter bars are constructed by the Inter- national Metric Bureau, an institution established by the civilized nations of the world, who all contribute toward its maintenance. The International Metric Bureau is located near Paris. It has supplied standard meter bars and stand- ard kilogram weights to all countries, and is engaged in investigations and scientific, determinations connected with weights and measures for the benefit of the civilized world. 424. The units employed in the metric system for the measurement of surfaces are simply the squares upon the meter and upon decimal multiples and subdivisions of the meter. For the measurement of bulk the cubes upon the meter and its decimal multiples and subdivisions are used. In order to obtain a unit of mass, the scientific men who devised the metric system decided that the mass of a given WEIGHTS AKD MEASUEES 235 volume of water at the temperature of the maximum density of that liquid should constitute that unit. Hence, the weight of a cubic centimeter of water at 4° C, weighed in vacuo, was called a gram, and that gram is the unit of weight of the metric system. In France there is, further, a simple relationship between the metric unit of weight and the weight of the silver coinage. 425. The important units of the metric system for the measurement of linear measure, square measure, cubic measure and weight are the meter, the are, the stere, the liter and the gram; the meter for long measure, the are for land measure, the stere for the measurement of large bulks, the liter, or cubic decimeter, for capacity measure for smaller volumes, and for weight the gram, and one thousand grams make the so-called kilogram represented by the mass standards of metric countries. 426. One of the defects of the metric system is the redundance of units it provides. A new unit with a new name has been provided for each successive decimal multiple and for each successive decimal subdivision of each of the principal units. The multiples are indicated by Greek prefixes; namely, the word deka, which means ten; the word liehto, which means one hundred; fcilo, which means one thousand; and myria, which means ten thousand. A dekagram, therefore, means a ten-gram, and hektometer means a one-hundred-meter; three kiloliters means three thousand-liters, and a myria- gram means one ten-thousand-gram. The subdivisions are named with the aid of Latin prefixes ; namely, deci, which means one-tenth; centi, which means the one-hundredth part; and milli, which means a one- thousandth. A milliliter, therefore, is a one-thousandth- liter; a centigram is a one-hundredth-gram, and a decimeter is .a one-tenth-meter. 236 A CORRESPONDENCE COURSE IN" PHARMACY It is not only unnecessary but burdensome to use so many different units. The superfluity of these many units is well exemplified by the following illustration : In America the monetary unit is called the dollar. In common speech we speak of ten dollars as an eagle, of the tenth of a dollar as a dime, the one-hundredth part of a dollar as a cent, and the one-thousandth part of the dollar as a mill. But no sensible person would count money in eagles, dollars, dime's, cents and mills. We find the dollar and the cent amply sufficient for all purposes. In the metric system the only necessary linear units are the kilometer, the meter and the millimeter. For capacity measures the liter and the milliliter are sufficient, and for weights, the kilogram, the gram and the milligram. 427. The following tables of the weights and measures of the metric system are sufficient for purposes of study: Linear Measure 1 kilometer = 1,000 meters 1 hektometer = 100 meters 1 dekameter = 10 meters 1 meter = 1 meter 1 decimeter = 0.1 meter 1 centimeter = 0.01 meter 1 millimeter = 0.001 meter 1 meter is equal to 39.37 inches, and 25 millimeters nearly equal inch. Square Measure 1 square kilometer = 1,000,000 square meters 1 square meter = 100 square decimeters 1 square meter = 10,000 square centimeters 1 square meter = 1,000,000 square millimeters Land Measure 1 square meter is called a centiare 100 square meters is an are 10,000 square meters is a hektare. WEIGHTS AND MEASURES 237 Cubic Measure 1 cubic meter = 1,000 cubic decimeters 1 cubic decimeter = 1 ,000 cubic centimeters The cubic meter is called a Stere. Capacity Measures 1 kiloliter = 1,000 liters 1 hektoliter = 100 liters 1 dekaliter = 10 liters 1 liter = 1 cubic decimeter 1 deciliter = 0.1 liter 1 centiliter = 0.01 liter 1 milliliter 0.001 liter One liter is equivalent to about 33.8 U. S. fluid ounces. Weight Units 1 kilogram = 1,000 grams 1 hektogram = 100 grams 1 dekagram = 10 grams 1 gram = 1 gram 1 decigram = 0.1 gram 1 centigram = 0.01 gram 1 milligram = 0.001 gram One gram is equivalent to 15.432 grains (nearly). 428. The system of weights and measures in the United States is an incongruous mixture of old standards which were introduced into this country during colonial times. Several of the units we employ have been abolished in Great Britain, and the values of our customary weights and measures are probably not absolutely identical with the original English values, which they are supposed to represent. Our linear units are squared and cubed, but our unit of land measure, the acre, does not bear a simple relationship to the standard yard ; nor do the bushel and gallon measures bear a simple relationship either to the yard or the pound. We have several kinds of gallons and several kinds of pounds, although only two of the gallons are actually used. 429. The original theoretical yard was of such length that the length of the seconds pendulum at Greenwich, England, 238 A CORRESPONDENCE COURSE IN PHARMACY was expressed by 39.1393 inches, each inch being the thirty- sixth part of the standard yard; but it is not absolutely certain that either the British yard or the American yard is now identical with the value just stated, for when the original British standard yard was lost and a commission was ap- pointed to remeasure the length of the seconds pendulum and to construct a new standard yard from the results, the task was abandoned as impracticable and an extant copy of the old standard yard was chosen and adopted as the new standard, and in our country the length of the yard is now !$£$ °f the length of the meter. The present American yard may or may not be absolutely identical with the present British yard. 430. Our customary capacity measures are not based upon the linear unit, but upon weight. Our bushel measures, gallon measures and their subdivisions are, in other words, constructed and verified by weight. Originally the gallon employed for the measurement of liquids (the Old English wine gallon) was 231 cubic inches, but the American gallon of to-day is the volume of 3785.434 grams of water at 4° 0., weighed in vacuo. Whether or not that volume is 231 cubic inches is doubtful. The National Bureau of Standards of America adjusts the liquid gallon by weight, on the assumption that 252.892 grains of water at its maximum density, weighed in vacuo , measures one cubic inch. If the theoretical kilogram, which is the weight of one cubic decimeter of water at its maximum density in vacuo, is identical with the actual international standard kilogram, which is assumed to be equivalent to 15432. 35G39 grains, then, as 39.37 inches is equal to one meter, the weight of a cubic inch of water at its maximum density in vacuo is 252.892 grains, and from this value the weight of 231 cubic inches of water at its maximum density in vacuo must be 3785.434 grams. But many authorities WEIGHTS AND MEASURES 239 declare that the weight of one cubic inch of water at its maximum density, weighed in vacuo, is not 252.892 grains. If so, onr liquid gallon is not 231 cubic inches. The gallon for dry measure in America is supposed to be the old English Winchester gallon of 268 cubic inches. 431. The commercial pound of this country is assumed to be identical with the British imperial pound, but we also employ in America the old English Troy pound, and a copy of the old British Troy pound is kept in the custody of the United States Mint at Philadelphia for the purpose of regu- lating the coinage of the United States, in accordance with a resolution of Congress. The Troy weight is used also for weighing gold and silver bullion, gold and silver ware and jewelry. The Troy pound is subdivided into 12 Troy ounces, and each Troy ounce is subdivided into 20 pennyweights, and each pennyweight into 24 grains. It will be seen, there- fore, that the subdivisions of the Troy pound are not identical with the subdivisions of the commercial pound, called the avoirdupois pound, nor is it identical with the subdivision of the apothecaries' pound. The value of the Troy ounce is not identical with the value of the avoirdupois ounce, but it is identical with the value of the apothecaries' or medicinal ounce. The only unit of avoirdupois weight, Troy weight and apothecaries' weight having the same value is the grain. 432. The customary weights and measures of America are as follows : Linear Measure 1 league = 3 miles, or 5,280 yards 1 mile = 8 furlongs, or 1,760 yards 1 furlong = 40 poles or rods 1 pole or rod = 5 \ yards 1 yard = 3 feet, or 36 inches 1 foot =12 inches 240 A CORRESPONDENCE COURSE IN PHARMACY Surface Measure 1 square mile = 640 acres 1 acre = 4 roods, or 4,840 square yards 1 rood = 40 square poles 1 square pole= 30 \ square yards 1 square yard = 9 square feet 1 square foot = 144 square inches Cubic Measure 1 cubic yard = 27 cubic feet 1 cubic foot = 1,728 cubic inches Capacity Measure Dry "Measures 1 bushel = 4 pecks, or 32 dry quarts 1 peck = 2 dry gallons, or 8 dry quarts 1 dry gallon = 4 dry quarts, or 8 dry pints 1 dry quart = 2 dry pints Liquid Measures 1 liquid gallon (wine gallon) = 4 liquid quarts 1 liquid quart = 2 liquid pints 1 liquid pint = 4 gills American Medicinal Fluid Measures 1 liquid gallon = 4 liquid quarts 1 quart = 2 pints 1 pint = 16 fluid ounces 1 fluid ounce = 8 fluid drams 1 fluid dram = 60 minims Weights Commercial or Avoirdupois Weights 1 ton = 20 hundredweights, or 2,000 pounds 1 hundredweight =100 pounds 1 pound = 16 ounces, or 7,000 grains 1 ounce = 16 drams, or 437£ grains 1 dram (now obsolete) = 27£$ grains Troy Weights 1 troy pound = 12 troy ounces, or 5,760 grains 1 troy ounce = 20 pennyweights, or 480 grains 1 pennyweight = 24 grains WEIGHTS AND MEASURES 241 Apothecaries' Weights 1 pound = 12 ounces, or 5,760 grains 1 ounce = 8 drams, or 480 grains 1 dram = 3 scruples, or 60 grains 1 scruple = 20 grains 433. The imperial system of Great Britain was adopted in 1824, to take effect January 1, 1825. The imperial gallon is the volume of 10 imperial pounds of pure water at 62° F., weighed in air of the same tempera- ture. Therefore the imperial gallon is based upon weight and not upon any linear unit. It is true that the British Par- liament has also declared that the imperial gallon is equal to 277.274 cubic inches, but the volume of 10 pounds of water under the British standard conditions must depend upon natural laws, without reference to legislation by Parliament. If 277.274 cubic inches of water at 62° F., weighed in air, does not weigh 10 pounds, Parliament cannot alter the fact. As the British pound is subdivided into 7000 grains and into 16 ounces, each equivalent to 437.5 grains, and as the imperial gallon is subdivided into 8 pints, and each pint into 20 fluid ounces, it follows that the imperial weight ounce and the imperial fluid ounce are commensurate units, with regard to water, under the British standard conditions. In other words, an imperial fluid, ounce of water weighs one imperial ounce, or one imperial ounce of water measures an imperial fluid ounce. But the imperial minim of water does not weigh one grain. 434. The capacity measures of the imperial system are shown in the following table : 1 bushel = 4 pecks, or 32 quarts 1 peck = 2 gallons, or 8 quarts 1 gallon = 4 quarts, or 8 pints, or 160 fluid ounces 1 quart = 2 pints, or 40 fluid ounces 1 pint = 20 fluid ounces 1 fluid ounce = 8 fluid drams 1 fluid dram — 60 minims 242 A CORRESPONDENCE COURSE IN PHARMACY 435. The linear measure of the British imperial system is the same as prior to 1825 and practically identical with the American customary long measure. The surface measures are the same as those used in this country The only weights which may be legally used in Great Britain are the avoirdupois weights, and the only liquid measures are the imperial measures referred to in the preceding paragraph. 436. From the foregoing, the student will see that the theoretical meter is the forty-millionth part of the length of the meridian, while the actual meter is the length of the material prototype meter of the International Metric Bureau. The theoretical liter is one cubic decimeter, but the actual liter is the volume of one kilogram of water at 4° C, weighed in vacuo, because capacity measures must of necessity be constructed by and based upon weight and not upon linear measure. The theoretical kilogram is the mass of one cubic decimeter of water at 4° C, but the actual kilogram is the mass of the piece of irido-platinum of the International Metric Bureau, called the standard kilogram. The standard kilogram of the International Metric Bureau is probably too light. In other words, the true mass of one cubic decimeter of water at 4° 0. is probably more than one standard kilogram. 437. In the metric system the liter is subdivided into 1000 milliliters, but the milliliter is very generally referred to as a cubic centimeter, and in tables of weights and measures it is stated that one liter is equivalent to 1000 cubic centimeters. But the student should observe that the one-thousandth part of one cubic decimeter, which is of course one cubic centi- meter, cannot be one milliliter unless the liter is exactly equivalent to one cubic decimeter. The actual liter in use is the volume of one kilogram of water at 4° C, weighed in vacuo, and as the kilogram upon which the liter is based WEIGHTS AND MEASURES 243 and by which it is standarded cannot be the theoretical kilo- gram but is instead the actnal kilogram, which is too light, the actual liter must be less than one cubic decimeter. 438. The relations between the various units of weight and measure in use by civilized nations are shown in the following tables : Long Measure 1 league = 4,828 meters 1 mile = 1,609.3 meters 1 furlong =» 201.2 meters 1 rod = 5.03 meters 1 yard = 36 inches = 0.914 meters 1 foot = 30.48 centimeters 1 inch = 25.4 millimeters 1 kilometer = 0.6213 mile 1 meter = 1.0936 yards 1 meter = 3.28 feet 1 meter = 39.37 inches Surface Measure 1 square mile = 259 hektares 1 acre =40.47 square meters 1 square yard = 0.8361 square meter 1 square foot = 9.29 square decimeters 1 square inch = 6.452 square centimeters 1 square meter = 1.196 square yards 1 square meter = 10.764 square feet 1 hektare = 2.471 acres Measures of Capacity 1 bushel = 35.24 liters 1 peck = 8.81 liters 1 dry gallon = 4.40 liters 1 dry quart = 1.10 liters 1 American liquid gallon = 3,785.4 liters 1 American liquid quart = 0.946 liter 1 American liquid pint = 473 milliliters 244 A CORRESPONDENCE COURSE IN PHARMACY 1 American fluid ounce 1 American fluid dram 1 American minim 29.57 milliliters 3.697 milliliters 0.0616 milliliter 1 British Imperial gallon 1 British Imperial quart 1 British Imperial pint 1 British Imperial fluid ounce 1 British Imperial fluid dram 1 British Imperial minim 1 American liquid gallon 1 American liquid quart 1 American liquid pint 1 American fluid ounce 1 American fluid ounce 1 British Imperial gallon 1 British Imperial gallon 1 British Imperial pint 1 British Imperial fluid ounce 1 British Imperial fluid ounce 4.543 liters 1.136 liters 0.568 liter 28.39 milliliters 3.55 milliliters 0.059 milliliter 0.833 British Imperial gallon 0.833 British Imperial quart 0.833 British Imperial pint 1.04 British Imper'l fluid ounces 500 British Imperial minims 1.200 American liquid gallons 9.601 American liquid pints 1.200 American liquid pints 0.96 461 American fluid ounce American minims 1 liter = 0.2642 American liquid gallon 1 liter = 1.0567 American liquid quarts 1 liter = 33.81 American fluid ounces 1 liter = 0.220 British Imperial gallon 1 liter = 0.881 British Imperial quart 1 liter = 35.23 British Imperial fluid ounces Measures of Weight 1 kilogram = 2.205 avoirdupois pounds 1 gram = 15.432 grains 1 milligram = g 1 ^ grain 1 avoirdupois pound = 453.6 grams 1 avoirdupois ounce = 28.35 grams 1 grain = 64.8 milligrams WEIGHTS AND MEASURES 245 1 American medicinal pound = 373.243 grams 1 American medicinal ounce = 31.10 grams 1 avoirdupois pound = 1.215 Troy pounds 1 avoirdupois ounce = 0.911 American medicinal ounce 1 American medicinal pound = 0.823 avoirdupois pound 1 American medicinal ounce = 1.097 avoirdupois ounces Convenient Approximate Equivalents 1 kilogram =32 medicinal ounces 1 milligram = -^ grain 1 grain = 64 milligrams 480 American minims = 500 Imperial minims The weight of 96 American medicinal fluid ounces of water is 100 avoirdupois ounces. 439. The differences between the values of the theoretical and the actual units of the metric system and the differences between the actual and theoretical values of some of the customary units of weights and measures are so insignificant that in actual practice they are ignored. In fact, it is sufficient in all ordinary operations to employ approximate equivalents. For example, it is sufficient to consider one meter as equivalent to 40 inches and one inch as equivalent to 25 millimeters. It is quite sufficient to consider one liter as equivalent to 34 apothecaries' fluid ounces. It is even perfectly allowable to consider one apothecaries' fluid ounce as equivalent to 32 cubic centimeters, although it is more nearly 30 cubic centimeters. If one fluid ounce be con- sidered as equivalent to 32 cubic centimeters, then one fluid dram is equivalent to 4 cubic centimeters, and one cubic centimeter is equivalent to 15 American minims. It is sufficient to consider one apothecaries' ounce as equivalent to 32 grams, although it is a little over 31 grams. If the 240 A CORRESPONDENCE COURSE IN PHARMACY apothecaries' ounce be considered as equivalent to 32 grams, then one dram is equivalent to 4 grams, and one gram is equivalent to 15 grains. But in the pharmaceutical labora- tory and at the dispensing table it matters little whether one gram be considered equivalent to 15 grains or 15.432 grains or 16 grains, and it is immaterial whether the cubic centimeter be considered as equivalent to 15 minims or 16 min- ims. It makes no difference whether a certain amount of medicine be divided into 31 equal doses or into 32 equal parts, for a dose of medi- glass meas- cine of any kind is of necessity an arbitrary one, representing simply the best judgment of the medical man in each instance. It would be impossible to observe any difference between the medicinal action of 30 grains and the medicinal action of 31 grains of the same substance. In chemical analysis the conditions are of course altogether different. The most accurate balances and weights are necessary in chemical determinations, while in the weigh- ings at the dispensing table a balance sensitive to two or three milligrams is sufficient, and more durable than a bal- ance sensitive to the fraction of one milligram. Thirty-two Troy ounces or apothecaries' ounces of water at ordinary room temperatures is equal to one liter, and 32 apothecaries' ounces is equal to one kilogram. One grain is equal to 64 milligrams, or, in other words, ^ of a grain is equal to one milligram. As 6 American liquid pints of water weighs 100 avoirdupois ounces, it follows that the weight of 6 pints of anything else in avoirdupois ounces must be 100 times its specific gravity. To convert any number of kilograms into the correspond- ing number of avoirdupois pounds, multiply by 2.2. To find the weight in grams of any number of cubic centimeters, multiply the cubic centimeters by the specific weight. To WEIGHTS AND MEASURES 247 find the volume in cubic centimeters of any number of grams, divide by the specific weight or multiply by the specific volume. To find the volume of any number of apothecaries' ounces in American fluid ounces, divide by the specific weight, or multiply by the specific volume, and then add 5 pei cent. To find the weight in apothecaries' ounces of any number of fluid ounces of any liquid, multiply by the specific weight and deduct 5 per cent. This is because one fluid ounce of water weighs .95 of an ounce. Test Questions 1. In what countries are the weights and measures of the imperial system used ? 2. In what countries are the weights and measures of the apothecaries' system used ? 3. In what countries is the metric system employed ? 4. Why is a decimal system of weights and measures pref- erable to any other ? 5. What was the object of making the length of the meridian the basis of the metric system ? 6. What is the length of the quadrant ? 7. What is the difference between the theoretical meter and the actual meter ? 8. What is the difference between the theoretical liter and the actual liter ? 9. What is the difference between the theoretical kilogram and the actual kilogram ? 10. Where are all the standard prototypes of weights and measures made and adjusted ? 11. How is the permanent loss of the metric standards prevented ? 12. How many cubic millimeters are contained in one cubic decimeter ? 248 A CORRESPONDENCE COURSE IN PHARMACY 13. How many cubic centimeters in one cubic meter ? 14. How many square centimeters in one square decimeter ? 15. Do you know any other name for the cubic centimeter ? 16. Do you know any other name for the liter ? 17. What is a myriameter ? 18. What is a decigram ? 19. What one name is given to ten liters ? to one hundred grams ? to one thousand liters ? to the tenth of a gram ? to the hundredth part of a liter ? to the thousandth part of a kilogram ? to the thousandth part of a gram ? 20. What is the difference between a milliliter and a cubic centimeter ? 21. What is the difference between a liter and a cubic decimeter ? 22. What is the exact value of the American yard ? 23. What is the exact value of the wine gallon now in use for commercial purposes ? 24. Is any other gallon used for commercial purposes than the wine gallon ? 25. What is the difference between the old English wine gallon and the American wine gallon ? 26. What is the ultimate standard for the adjustment of our bushel measures and gallon measures in America ? 27. What is the ultimate standard which fixes the present value or size of an acre ? 28. What is the weight of a cubic inch of water at 4° 0. in vacuo , according to the Government authorities of the United States ? 29. What is the difference between a Troy ounce and an apothecaries' ounce ? 30. What is the difference between an avoirdupois ounce and an imperial ounce ? 31. What is the difference between an apothecaries' grain and an imperial grain ? WEIGHTS AND MEASUEES 249 32. What is an imperial gallon ? 33. What is the origin of the American liquid gallon ? 34. Has the American liquid gallon ever been used in any- other country, and is it now in use in any other country ? 35. What is the volume of ten pounds of water at 62° F. in air, measured in cubic inches ? 36. What is the equivalent of the apothecaries' pound in grains ? 37. What is the equivalent of the English commercial pound in grains ? 38. Into how many drams is the Troy ounce subdivided, and into how many scruples is the Troy dram divided ? 39. How many drams are there in an avoirdupois ounce ? 40. Which has. the greater mass, the actual kilogram or the theoretical kilogram ? 41. Which is greater, the actual liter or the theoretical liter ? 42. What is approximately the equivalent of one kilogram in apothecaries' ounces ? 43. How many milligrams equal one-half grain ? 44. How many grams approximately equal one dram ? 45. If you had a prescription for one powder with the quantities of the ingredients for that powder stated in grains, how would you convert that prescription into metric terms and increase the quantities so that fifteen powders can be made, each containing the same dose as in the original pre- scription ? 46. An average adult dose of opium is considered to be one grain. What would it be set down to be in an ordinary dose table if our grain were 10 per cent larger than it is, and how much would it be set down to be if our grain were 10 per cent lighter than it is ? 47. What is the equivalent of two American fluid ounces in British minims ? 250 A CORRESPONDENCE COURSE IN PHARMACY 48. What is the weight of one quart of a liquid having the specific weight 1.800 ? 49. What is the equivalent of an American fluid ounce in cubic centimeters and what is its equivalent in milliliters ? 50. Which is larger, an imperial pint or an American pint ? 51. Which is larger, an imperial fluid ounce or an Ameri- can fluid ounce ? 52. Which is larger, an imperial minim or an American minim ? 53. Which is larger, an imperial grain or an American grain ? 54. What is the ultimate standard by which the weight of American coins is regulated ? LESSON SEVENTEEN XXVI Specific "Weight and Specific "Volume 440. The specific weight of any substance is the relation of its mass to its volume. A substance having great weight in proportion to its volume is said to have a large specific weight, and a substance of which the same volume weighs less has a smaller specific weight. The specific weight of different substances must be con- veniently and intelligently expressed, and this is accomplished by stating specific weights in numbers referring to the specific weight of water as the unit. In other words, the relation of the weight of water to its volume under standard conditions is arbitrarily called 1, and the specific weight of any substance a given volume of which is heavier than the same volume of water is expressed by a number greater than 1, while the specific weight of any substance a given volume of which weighs less than the same volume of water is expressed by a number less than 1. The number expressing the specific weight of any solid or liquid is the number of times the weight of that solid or liquid contains the weight of the same volume of water. In other words, it is ex- pressed by the number obtained by dividing the weight of a given volume of that solid or liquid by the weight of the same volume of water expressed in the same kind of weight units. The specific weight of chloroform is 251 252 A CORRESPONDENCE COURSE IN PHARMACY 1.5, because a liter of chloroform weighs 1.5 kilograms; and the specific weight of ether of a certain strength is .750 if 1000 cubic centimeters of it weighs 750 grams, for 1000 cubic centimeters of water weighs 1000 grams, and 750 -*■ 1000 is .750. In the pharmacopoeia and most of the technical works specific weights are expressed to the third decimal. Hence, the specific weight of chloroform is given as 1.500 and not as 1.5. 441. Specific volume is the relation of the volume of a sub- stance to its mass. Accordingly, the specific volume of any substance is expressed by a number which is the reciprocal of the number expressing its specific weight. In other words, if the specific weight is 2, the specific volume must be -J. If the specific weight is f, the specific volume must be |. If the specific volume of any substance is |, then the specific weight must be J . Specific weights and specific volumes, when expressed by numbers with fractions, are expressed decimally, but if the specific weight is expressed by a common fraction, then the corresponding specific volume is found by simply inverting the fraction. For example, as the specific weight of chloro- form is 1.500, or stated in the form of a common fraction, io£o> ^ follows that the specific volume of chloroform is •TTnrij. As the specific weight of glycerin is 1.250, its specific volume must be 0.800, for 1.250 multiplied by 0.800 gives the product 1. The specific volume is found from the specific weight by dividing 1 by the specific weight, and the specific weight can be found from the specific volume by dividing 1 by the specific volume. The specific volume of any liquid is found also by dividing the volume of a given weight of the liquid by the volume of the same weight of water, expressed in the same units. The use of the term specific volume to indicate the relation SPECIFIC WEIGHT AND SPECIFIC VOLUME 253 of the volume of a liquid to its weight as here explained was first proposed by the writer of this book in 1883. Its practical value depends upon the fact that multiplication is an easier operation than division. In converting weight into volume we multiply the weight by the specific volume, if the weight units and the volume units are commensurate. 442. Several pairs of commensurate units exist. The avoirdupois ounce and the imperial fluid ounce are commen- surate, because an avoirdupois ounce of water measures an imperial fluid ounce. The gram and the cubic centimeter are commensurate units, because a cubic centimeter of water weighs a gram ; and the liter and the kilogram are com- mensurate, because the liter is the volume of a kilogram of water. A kilogram of any liquid having the specific volume 0.800 must measure 800 cubic centimeters. As 6 wine pints of water weighs 100 avoirdupois ounces, it follows that 96 American fluid ounces of any liquid having the specific weight 0.960 must weigh 96 fluid ounces. The specific weight of castor oil is 0.960; hence an American fluid ounce of it weighs one avoirdupois ounce. 443. How the Specific Weight is Found. As the specific weight of any solid or liquid is the number of times the weight of a given volume of water is contained in the weight of the same volume of the solid or liquid, it follows that a simple method of finding the value sought is to divide the weight of the solid or liquid by the weight of the same volume of water. But the specific weight of a solid or liquid may be found in several other ways, directly or indirectly. The weight of 1000 cubic centimeters of any liquid stated in kilograms at once expresses the specific weight of that liquid. Hence, if we have a flask with a long neck graduated by means of an etched line around the neck indicating the point to which one kilogram of water reaches at the standard temperature, 254 A CORRESPONDENCE COURSE IN PHARMACY we may fill that flask up to the mark on the neck with any other liquid, take the weight of it, and thus at once find its specific weight. Graduated flasks of other capacities can, of course, be used for the same purpose. 444. A pycnometer, or specific gravity bottle, is a flask con- structed to hold a given quantity of pure water at standard temperature when completely filled. The size of the flask is such that the weight of the water can be expressed in a simple number of weight units, such as will be an easy divisor, as, for instance, 50 or 100 or 500 or 1000 units. This bottle is then used in the same manner as the graduated flask already described. The most complete pycnometers made are glass-stoppered bottles provided with thermometers, so that the temperature of the liquid may be conveniently observed in the same operation with the determination of the weight of the contents. A counterpoise representing exactly the weight of the empty pycnometer accompanies the apparatus. The filled pycnometer is then placed on one pan of the balance and the counterpoise on the other, after which it is only necessary to restore the equilibrium of the balance by placing the requisite weights on the pan with the counterpoise. If the pycnometer is so made as. to hold 50 grams of water, we can take the weight of the other liquid in grams, multiply that by 2 and divide the product by 100, when the quotient will be the specific weight sought. Any glass-stoppered bottle may be used for the same pur- pose, the weight of the water it will hold being taken and the weight of the other liquid required to fill the bottle also determined, after which the division follows. But when an ordinary bottle is used, the divisor, or the weight of the water the bottle holds, will not be a simple number of weight units, and the division will consequently not be so easy. Another way of finding the specific weight of a liquid is based upon the law of Archimedes. SPECIFIC WEIGHT AND SPECIFIC VOLUME 255 445. The law of Archimedes may be stated as follows: Any solid immersed in a fluid is buoyed up by that fluid with a force measured by the weight of the fluid displaced by the solid. If, for instance, a cubic inch of lead rests upon the table, it does not press upon its support with its whole mass, but with its mass minus the weight of a cubic inch of air, in which the piece of lead is immersed. The difference between the weight of that cubic inch of lead in a vacuum aud its weight in air must be, according to the law of Archimedes, the weight of one cubic inch of air. If the same cubic inch of lead be weighed suspended in water, the difference between its weight in air and its apparent weight when suspended in water will be the weight of one cubic inch of water. If it be weighed suspended in olive oil, then the difference between its weight in air and its weight in olive oil will be exactly measured by the weight of one cubic inch of olive oil. If a piece of glass or any other solid be weighed first in air and then in water while suspended from a balance by means of a wire or thread, the difference between its weight in air and its weight in water must be the weight of the same volume of water. If, now, the same piece of glass be weighed in any other liquid, the difference between the weight of the glass in air and its weight in the liquid must be the weight of the same volume of the other liquid. We then have the necessary factors from which to find the specific weight of the second liquid, namely, the weight of a definite volume of water and the weight of the same volume of the other liquid. We then divide the weight of the water into the weight of the other liquid. If the piece of glass used for this purpose be of such size that it displaces a simple number of weight units of water, as for instance 5 grams or 10 grams, and the number of grams it displaces be known, it need not be weighed in waier again, but only in the liquid the specific weight of which is to be ascertained. 250 A CORRESPONDENCE COURSE IN PHARMACY 446. The specific weight of a solid heavier than water may be found by submerging the solid in water in a gradu- ated cylinder, as follows: If the cylinder is graduated in grams and fractions of grams and a solid whose weight in air is known in grams be dropped in the water contained in the graduated cylinder, then, as the solid sinks below the surface of the water, the level of the water necessarily rises to correspond with exactly the volume of the solid. If the solid weighs 10 grams in air, and when dropped in the water in the graduated cylinder causes the level of the water to rise 2 grams, according to the graduated scale, then the same volume of water weighs 2 grams, and the specific weight of the solid must be 5. 447. Any solid having a specific weight greater than that of water must sink below the surface of the water when placed in it, and any solid having a less specific weight floats in water, and only descends into the water far enough to dis- place its own weight. Any solid having precisely the same density as that possessed by water may be placed in any position in the body of the water and will neither sink nor rise. Lard is lighter than water, but heavier than alcohol. The specific weight of lard may therefore be found by putting a piece of it in a vessel of water and then adding gradually enough alcohol, mixing the two liquids cautiously until the piece of lard may be placed in any part of the mixed liquid and will remain in its position without sinking or rising. The specific weight of the liquid is then taken and must, of course, be identical with the density or specific weight of the lard. 448. Specific gravity beads are hollow glass beads the specific weights of which have been ascertained and etched upon them. If a handful of such beads be thrown into any liquid, the beads having a greater density than the liquid SPECIFIC WEIGHT AND SPECIFIC VOLUME 257 will sink to the bottom and those having a less density will float at the surface, but any bead having the same density as the liquid may be made to swim about in the body of the liquid in any position. The density of the liquid in this case is, of course, that marked upon the bead that neither sinks nor floats. This fact is taken advantage of for the purpose of finding deviations from the normal density of urine, for if a glass bead or bulb so made that it has precisely the specific weight of normal urine be put in a sample of urine, it will sink if the urine is abnormally light, or it will float if the urine is abnormally heavy. 449. A hydrometer is a float of nearly cylindrical form loaded at one end with shot or mercury so as to bring the center of gravity of the whole instrument to that end, in order that when the hydrometer is placed in a liquid it may assume a vertical position. If the whole instrument weighs more than its own volume of the liquid in which it may be placed, it will, of course, sink below the surface of that liquid. If it weighs less than its own volume of that liquid, it will sink down into the liquid just far enough to displace its own weight of the liquid. The floating hydrometer, therefore, sinks farther down in a light liquid than in a heavy one, and the tube or stem of the hydrometer may be graduated, or provided with a graduated scale indicating the density of the liquid in which it may be placed. If the hydrometer is constructed especially to take the specific weights of heavy liquids, then the point to which it sinks in water is marked by the figure 1 at the top of the scale, and the point to which it sinks in a liquid having, for instance, a density twice as great as that of water would be marked 2, after which the distance between the two gradu- ation marks is accurately divided into equal spaces indicating the densities of liquids between ths specific weight 1 and the specific weight 2. 258 A CORRESPONDENCE COURSE IN PHARMACY If the hydrometer is to be used to find the densities of liquids lighter than water, then the instrument is so made that it descends into the water only to the lower end of the scale. We shall then have the unit at the bottom of the scale and the densities of the lighter liquids graduated above as far as may be necessary. The most common hydrometers are of two kinds — one for densities ranging from 1.000 up to 1.300 and the other for densities ranging from 1.000 down to 0.700. Test Questions 1. Define specific weight. 2. What is the difference between specific weight and specific gravity ? 3. Define specific volume. 4. How are specific weights expressed ? 5. What is the unit of expression for the specific weights of gases ? 6. What is the unit of expression for the specific weights of liquids ? 7. What unit is employed for expressing the specific weights of solids ? 8. What is the quotient obtained when 1 is divided by the specific weight ? 9. What is the quotient obtained when 1 is divided by the specific volume ? 10. What is the specific volume of a liquid the specific weight of which is 1.111 ? 11. What is the specific weight of a liquid the specific volume of which is 1.111 ? 12. What is the product obtained from multiplying the specific volume of a substance by its specific weight ? 13. What practical uses are made of specific weight ? 14. What are the practical uses of specific volume? SPECIFIC WEIGHT AND SPECIFIC VOLUME 259 15. What is meant by commensurate units of weight and volume ? 16. Name several pairs of such units. 17. When it is stated that hydrochloric acid has the specific weight 1.160, what does that number mean ? 18. What is the standard temperature adopted by the pharmacopoeia for finding and expressing specific weights ? 19. Mention a convenient method of taking the specific weight of a fluid extract. 20. Give a method of finding the specific weight of lead. 21. What is a pycnometer ? -" 22. State the law of Archimedes. 23. What are specific gravity beads ? 24. Describe a hydrometer. 25. A piece of metal weighs 8. 3 ounces. The same volume of water weighs 1 ounce. What is the specific weight of the metal ? 26. A bottle holds 480 grains of water, but 576 grains of nitric acid. What is the specific weight of the acid ? 27 If 20 imperial fluid ounces of a liquid weigh 1\ avoir- dupois pounds, what is the specific weight of the liquid ? 28. A one-thousand-grain pycnometer holds 735 grains of ether. What is the specific weight of that ether ? 29. A fluid ounce of alcohol at 22° 0. weighs 373 grains and a fluid ounce of water at the same temperature weighs 455 grains. What is the specific weight of that alcohol referred to water at 22° 0. as unit ? 30. Is the specific weight of that alcohol greater or less referring to water at 15° as unit ? 31. A liter of diluted alcohol weighs 925 grams. What is its specific weight ? 32. A liter of glycerin weighs 1250 grams. What is its specific weight ? 33. A bottle which holds \ ounce of water holds 5 drams 260 A CORRESPONDENCE COURSE IN" PHARMACY of a certain solution. What is the specific weight of that solution ? 34. If 1 gallon of ether and \ gallon of chloroform have the same weight and 2 pints of chloroform weigh the same as 3 pints of water, what is the specific weight of the ether ? 35. I have a solid weighing 13 grams in air. I drop it into a graduated cylinder containing 30 cubic centimeters of water and find that the level of the water rises to 40 cubic centimeters when the solid sinks to the bottom of the cylinder. What is the specific weight of the solid ? 36. The weight of 3 gallons of water is 400 avoirdupois ounces and the weight of a gallon of alcohol is 109 avoir- dupois ounces. What is the specific weight of the alcohol ? 37. An imperial gallon of oil of peppermint weighs 9 avoirdupois pounds. What is its specific weight ? 38. Six pints of solution of zinc chloride weigh 155^- avoirdupois ounces. What is its specific weight ? 39. A mass of thirteen grams of a certain solid has a volume of 10 cubic centimeters. What is its specific weight ? 40. A solid weighs 4.75 grams In air and 4 grams in water. What is its specific weight ? 41. A piece of metal of the bulk of 161.7 cubic inches weighs 347624.55 grains in air and 306839.75 grains in water. What is the weight in grains of 231 cubic inches of water ? 42. A crystal weighs 10 grams in air and 9 grams in oil of turpentine. The specific weight of the oil of turpentine is 0.860. What is the specific weight of the crystal ? 43. One cubic centimeter of a certain solid weighs 870 milligrams. What is its specific weight ? 44. A piece of cork weighs 0.732 grams in air. A piece of metal weighs 7.7 grams in air, but only 6.6 grams in water. Cork and metal tied together and weighed in water are found to weigh 4.182 grams. What is the specific weight of the cork ? SPECIFIC WEIGHT AND SPECIFIC VOLUME 261 45. A piece of lard is put in a vessel of water, and alcohol is gradually added and mixed with the water until the piece of lard instead of floating on the surface may be placed at will in any position in the body of the liquid. A fifty-gram pycnometer is now filled with the liquid and the contents of the pycnometer found to weigh 46.9 grams. What is the specific weight of the lard ? 46. If a piece of metal weighs 9 ounces in air, 8 ounces in water and 8.1 ounces in oil, what is the specific weight of the oil? 47. A solid measuring 10 cubic centimeters when immersed in oil of turpentine is found to displace 8.6 grams of the oil. What is the specific weight of the oil ? 48. Glycerin has the specific volume 0. 800. The weight of three volumes of glycerin is the same as that of five volumes of ether. What is the specific weight of the ether ? 49. Fifty cubic centimeters of nitric acid weigh 71 grams and 50 cubic centimeters of hydrochloric acid weigh 58 grams. The specific weight of the hydrochloric acid is 1.160. What is the specific weight of the nitric acid ? 50. A certain bottle holds 100 ounces of glycerin, the specific weight of which is 1.250. How many ounces of water will it hold ? 51. How much will the same bottle hold of ether having the specific weight 0.720 ? 52. How much will it hold of chloroform of the specific weight 1.470? 53. How much will it hold of syrup having the specific weight 1.330? 54. A solid weighs 3 ounces. It has the specific weight of 8. 300. When weighed in a certain liquid its apparent loss of weight is \ ounce. What is the specific weight of the liquid ? 55. The specific weight of water is 1. What is its specific volume? 262 A CORRESPONDENCE COURSE IN PHARMACY 56. One thousand avoirdupois ounces of a liquid measure 60 pints. What is the specific volume ? 57. If 300 grams of a liquid measure 280 cubic centi- meters, what is its specific volume ? 58. One kilogram of a liquid measures 755 cubic centi- meters. What is the specific volume ? 59. If 4 imperial pints of a liquid weigh 6 pounds, what is its specific volume ? 60. What is the weight of 255 cubic centimeters of a liquid having the specific weight 1.100 ? 61. What is the weight of 30 cubic centimeters of a liquid having the specific weight 0.700 ? 62. What is the weight in avoirdupois ounces of 100 imperial fluid ounces of a liquid having the specific weight 1.960? 63. What is the weight in pounds of an imperial gallon ? 64. What is the weight in avoirdupois ounces of 96 American fluid ounces of a liquid having the specific weight 1.820? 65. What is the weight in avoirdupois ounces of 16 United States fluid ounces of a liquid having the specific weight 1.260? 66. If a cubic inch of water weighs 252.5 grains, what is the weight of 231 cubic inches of a liquid having the specific weight 0.900? 67. If an American fluid ounce of water weighs 0.95 apothecaries' ounce, what is the weight of 1 American fluid ounce of a liquid having the specific weight 0.860 ? 68. What is the volume of 3 kilograms of nitric acid having the specific weight 1.420 ? 69. What is the volume of 5 pounds of a liquid having the specific volume 1.111 ? Give the answer in pints. 70. Castor oil has the specific volume 1.042. What is the volume of 6 pounds stated in American fluid ounces ? SPECIFIC WEIGHT AND SPECIFIC VOLUME 263 71. A piece of metal weighs 6445.380 grains in air. When suspended in water, its apparent weight is 5585.996 grains. Its bulk is 3.40 cubic inches. What is the specific weight of the metal, and what is the weight of a cubic inch of water ? 72. A piece of metal weighs 480 grains in air, 420 grains in water and 400 grains in a solution of sugar. What is the volume of 500 grams of that solution ? 73. A kilogram weight of brass and a kilogram weight of platinum balance each other perfectly in a vacuum. Which has the greater mass ? 74. Which has the greater volume ? 75. Which of them seems to weigh more in air ? 76. You weigh in the usual manner a pound of wood and a pound of lead. Which is really the heavier of the two ? 77. A solid measuring 0.1 cubic decimeter is weighed first in vacuo, then in air, and lastly in water.' One cubic inch of air weighs 0.3 grains and a cubic inch of water 252.50 grains. Find the difference between the weight of that solid in vacuo and its weight in air; the difference between its weight in air and its weight in water. 78. A ten-dollar gold coin weighs 258 grains in air. Assuming its specific weight to be 18.300, what is its apparent loss of weight when weighed suspended in water ? 79. If an imperial gallon of sulphuric acid weighs 18.35 avoirdupois pounds, what is the volume of 1000 grams of that acid expressed in cubic centimeters ? 80. If the specific weight of oil of vitriol be twice that of olive oil, and if 1. liter of olive oil weighs 917. grams, what is the weight of 500 cubic centimeters of oil of vitriol ? 81. If a solid weighs 75 ounces and the same volume of water 10 ounces, what is the apparent weight of that solid when weighed suspended in water ? 82. If a bullet weighs 13 ounces in air and 12 ounces in 264 A CORRESPONDENCE COURSE IN PHARMACY water, what will it appear to weigh in a liquid having 1.400 specific weight ? 83. If a pound of water measure 15f fluid ounces and a pound of a certain solution 7^ fluid ounces, what is the specific volume of the solution ? 84. What number of cubic centimeters expresses the volume of 85.33 grams of a liquid having 1.01 specific volume ? 85. The specific weight of solution of mercury nitrate being 2.100, what is the weight of one liter of it ? 86. Solution of citrate of iron has the specific weight 1.260. What is the weight of one American pint in avoir- dupois ounces ? 87. The specific weight of oil of turpentine is 0.860. What is the weight of 96 American fluid ounces of it in commercial ounces ? 88. Which is greater, the number expressing the specific weight of acetic acid referring to water at 4° 0. as unit, or the number expressing the specific weight of the same acid referring to water at 15° C. as unit ? 89. A certain liquid at 39.2° F. has the specific weight 1.200 referring to water at 22° C. as unit. Will the number expressing its specific weight at 60° F. referring to water at 4° C. as unit be greater or less than 1.200 ? 90. The weight of one liter of water at 4° 0. is 15,432 grains, but the weight of 500 cubic centimeters of water at 22° C. is 7696 grains: (a) What is the specific weight of water at 22° C. referring to water at 4° C. as unit? (b) What is the specific weight of water at 4° C. referring to water at 22° C. as 1 ? 91. An imperial gallon of water at 62° F., barometer at 30 inches, weighs 70,000 grains: (a) Does it weigh more or less at 15° C. ? SPECIFIC WEIGHT AND SPECIFIC VOLUME 265 (b) Does it weigh more or less when the atmospheric pres- sure is greater ? 92. A cubic inch of water at 22° 0. weighs 252.5 grains. What is the weight of 231 cubic inches of an alcohol having 0.860 specific weight, referring to water at 22° C. as 1 ? 93. What is the volume of 100 apothecaries' ounces of oil of 0.900 specific weight, if one cubic inch of water weighs 250.5 grains? 94. What is the specific volume corresponding to each of the following specific weights, respectively: (a) 1.000; (#) 1.250; (c) 1.333; (d) 0.500; (e) 0.750; (/) 0.800; (g) 2.000; (70 0.720; (i) 0.820; (/) 0.950; \k) 1.500; (J) 1.300; (m) 1.320? 95. What is the volume of 1000 grams of a liquid having the specific volume 1.200 ? 96. What is the volume in imperial fluid ounces of 100 avoirdupois ounces of a liquid having the specific volume 0.800? 97. What is the volume in United States fluid ounces of 25 avoirdupois ounces of a liquid having the specific volume 1.000 ? 98. What number of cubic centimeters expresses the volume of 85 grams of a liquid having the specific weight 1.010 ? 99. What number of cubic centimeters expresses the volume of 85 grams of a liquid having the specific volume 1.010? 100. What number of grams expresses the weight of 85 cubic centimeters of a liquid having the specific weight 1.010 ? 101. What number of grams expresses the weight of 85 cubic centimeters of a liquid having the specific volume 1.010? 102. The total weight of a bottle filled with water is 30 266 A CORRESPONDENCE COURSE IN PHARMACY ounces. The same bottle filled with olive oil weighs 28 ounces. What is the weight in ounces of the water the bottle is capable of holding ? How many ounces of oil will it hold ? What is the weight of the bottle itself ? 103. A bottle filled with water weighs 16 ounces ; filled with chloroform having the specific weight 1.470 it weighs 19.877 ounces; filled with acid it weighs 17.32 ounces. How much does it hold of water, of chloroform and of acid, respectively, and what is the specific weight of the acid ? 104. A solid measuring 2 cubic inches weighs 6000 grains in air, but only 5400 grains when weighed suspended in a certain liquid. What is the specific weight of that liquid ? 105. A solid measuring one cubic centimeter and weighing 10 grams loses one gram in weight when weighed in a certain liquid. What is the specific weight of that liquid? 106. Alcohol has the specific weight 0.820 at 15.6° C. The net weight of a barrel of alcohol at that temperature is found to be 300| pounds. How many gallons of the alcohol does that barrel contain ? 107. A certain mixture of water with a syrup of the specific weight 1.330 is found to have the specific weight 1.200. What are the proportions of syrup and water in the mixture ? LESSON EIG-HTEEN XXVII in Pharmaceutical Operations 450. Heat for pharmaceutical purposes may be obtained most conveniently by means of gas burners, but where gas is not available, coal oil and alcohol lamps or burners are used. The Bunsen burner is the most approved gas burner for pharmaceutical and chemical purposes. It is a tube which the gas is mixed with air admitted near the bottom of the \ tube, and the mixture ignited at / i the top. The flame of the gas / A \ ! { burner is bluish when sufficient air is mixed with the gas so that the combustion is complete, but when the gas supply is too abun- dant or the amount of air insuffi- cient, the flame is yellow and deposits unconsumed carbon upon the vessels heated over the flame. 451. The sand bath is an iron dish containing a layer of sand which may be used for the purpose of distributing the heat of the flame. The flask, dish or other vessel to be heated is placed in the sand. A water bath is a vessel of water intervening between the flame and the vessel to be heated. The object of the water bath is to prevent the temperature from rising above the boiling point of water. The contents of vessels heated upon 267 BUNSEN BURNER, CONTRASTING THE PROPER FLAME WITH ONE THAT RESULTS WHEN THE GAS IS "LIGHTED BACK" INTO THE TUBE 2G8 A CORRESPONDENCE COURSE IN PHARMACY the water bath rarely attain a higher temperature than a little above 90° 0. To control the temperature when substances must be heated above 100° 0., glycerin baths, oil baths and solution baths are employed. 452. Exsiccation is a term used to express the heating of chemical compounds for the purpose of expelling water of crystallization. Sulphate of iron, alum, sodium carbonate, sodium phosphate, magnesium sulphate and various other salts containing large quantities of water of crystallization may be dried so as to expel all water or a portion of it. 453. Calcination is the process of converting metallic carbonates and other metallic salts into metallic oxides by heat. Strong heat is usually required for this purpose, and the by-products formed are volatile. When a carbonate is calcined, the by-products are 00 2 and water, or C0 2 alone, according to the composition of the carbonate decomposed. Nitrates and sulphates can also be calcined. The word calcination is derived from the Latin calx, which means lime, because lime is produced by strongly heating limestone or calcium carbonate in kilns. 454. Dry distillation, or "destructive distillation," is a term employed to express the decomposition of organic substances by strong heat, resulting in the formation of new products, some of which are volatile and others fixed. For example, when oak billets are heated strongly in closed iron cylinders provided with an outlet for the volatile products, the oak wood undergoes decomposition, and, among the volatile products which distill over, acetic acid is one of the most valuable, and the residue in the cylinder is a tarry mass of mixed composition. 455. Sublimation is the distillation of solids; in other words, volatile solids are vaporized, and the vapor conducted into condensing vessels in which they reassume a solid form. The product is called a sublimate, and is generally of PHAEMACEUTICAL OPERATIONS 269 crystalline character. Sublimation is employed as a method of separation of volatile substances from fixed substances for purposes of purification. 456. The coarse mechanical division of drugs is an im- portant pharmaceutical operation. For the preparation of mixed teas, drugs are required to be very coarsely comminuted. If they are flexible, they may be cut with sharp-edged tools so as to produce pieces free from dust or powder, but if they are hard so that they cannot be cut, they are comminuted by crushing, in which case more or less powder is unavoidably produced. The crushing of plant drugs is best accomplished in an iron mortar with an iron pestle, but smaller pieces of drugs can be crushed also in hand-mills of iron. 457. An iron mortar used for crushing and powdering drugs must be very large in proportion to the amount of drug operated upon in order to do effective work. It should be solid, heavy, and placed upon a solid block, which, if possible, should rest upon the ground instead of upon the floor. The crushing of drugs in a mortar by means of blows with the pestle is technically called contusion. 458. The iron mill used by druggists for making coarse powders of drugs is similar to the mill used by grocers for grinding coffee, but there is an essential difference in the construction and position of the grinding plates, so that the hand drug-mills are not identical with coffee mills and spice mills. There are several makes of hand drug-mills, and the best forms are those which have the grinding plates in a nearly horizontal instead of vertical position. These hand-mills are provided with set-screws which enable the operator to move the grinding plates nearer to each other or farther apart at will, to make coarser or finer powder, as may be desired. It is usually necessary to pass a drug through the hand-mill more than once, if a com- A SMALL PORCE- LAIN MORTAR 270 A CORRESPONDENCE COURSE IN PHARMACY paratively fine powder is required ; in other words, the drug is first crushed, then passed through the mill to make a coarse powder, then the mill is set finer and the coarse powder passed through the mill again, this operation being repeated until the required fineness is attained. But very fine powder cannot be made with the hand drug-mill. A coarse powder can, however, be easily enough made very fine by contusion in the iron mortar. 459. Trituration is the grinding produced in the mortar by a rotary motion of the pestle accompanied by pressure. When trituration is performed, the pestle is grasped firmly by the whole hand in order to apply sufficient force to crush the parti- cles of substance triturated. Comparatively brittle substances can be powdered by tritu- ration, but in order to do effective work the trituration mortar should be large in proportion to the quantity of substance triturated, for if too deep a layer of powder is operated upon at one time, the operation is necessarily slower. Trituration is also employed for mixing powders, but if the ingredients of the mixture are already sufficiently fine, no pressure is required 'n mixing them. The spatula is usually necessary, in ac- complishing trituration, to scrape the substances from the end of the pes- A steel spatula tie and the bottom and sides of the mortar, in order to do rapid and effective work. Trituration mortars are generally made of porcelain or of Wedgewood ware. 460. Levigation is the trituration of substances in a fine state of division, either upon a slab with the muller or in a mortar with the pestle, with the addition of some liquid to PHARMACEUTICAL OPERATIONS 271 the solid substance to aid in its further division. Water, alcohol and oil are all used for such purposes. Sometimes the levigation has for its object not only the production of a very fine powder, but also the removal of impurities with the aid of the liquid added. For example, calomel is levigated by trituration with water in order to wash out from it the corrosive sublimate which may be con- tained in sublimed calomel and which is soluble in water. When purification of calomel is effected by levigation, several successive portions of water must, of course, be used until all of the corrosive sublimate has been finally removed. 461. Elutriation is also a process employed for the purpose of producing very fine powders of insoluble substances. The finely powdered solid is put in water, with which it is well mixed by stirring. The mixture is then allowed to stand at rest until the coarser and heavier particles have subsided, while the finer particles still remain suspended in the liquid, which is decanted, after which the finer powder is allowed to settle to the bottom. When this process is repeated several times an almost impalpable powder can be produced. Prepared chalk and purified antimony sulphide are prepared by elutriation, according to the directions of the pharmacopoeia. 462. Powders, however they may be made, are never perfectly uniform. To render them as nearly uniform as practicable they are passed through sieves made out of sieve-cloth of various grades of fineness. The fineness of sieves is indicated in the pharmacopoeias according to the number of meshes in the sieve-cloth. Sometimes the number of meshes is counted according to linear measure, but a better way is to count the number of meshes per square measure. In the United States pharmacopoeia the fineness of sieves and powders is indicated by the number of meshes to the linear inch. Thus, a No. 60 sieve means a sieve Z72 A CORRESPONDENCE COURSE IN PHARMACY having sixty meshes to the linear inch, and a No. 80 sieve *s one having eighty meshes to the linear inch. But the meshes of sieve-cloth are not always square, so that a different number of meshes may be counted to the linear inch, according to whether the count is made along the woof or along the warp. Moreover, the wire or silk thread or hair out of which the sieve-cloth is made may be of varying caliber, so that this method of determining the fineness of powders is very uncertain. The student will readily understand this by an extreme example: Suppose a sieve has one hundred meshes to the linear inch and is made of brass wire. If the wire cloth is made of wire one one-hundredth part of an inch in diameter, it follows that there would be no openings in the sieve-cloth at all. 463. While the pharmacopoeias always prescribe a method of expressing the fineness of powders, they do not all of them prescribe a given degree of fineness for each individual drug. In the American pharmacopoeia, for instance, there is no information given as to how fine powdered digitalis should be when ordered by the physician, although the powder to be used of digitalis for the preparation of the tincture, the fluid extract or the extract is specifically prescribed. Very full directions are given in some pharma- copoeias, stating how fine the powder should be of any important drug prescribed by a physician to be used in powder form or in pill-masses, and to fail to give such directions would seem to be a serious omission. 464. By "dusted powders" is meant powders so fine that when made in a mill constructed expressly for the purpose, they rise in the mill-box like dust, which settles upon shelves along the walls of the mill-box or on the floor of that box away from the circle in which the millstones run like wheels. 465. Colored substances become lighter when reduced to PHARMACEUTICAL OPERATIONS 273 fine powder, and the color grows lighter as the powder gets finer. 466. The solution of soluble substances may be effected in many different ways, but most quickly by reducing the substance to be dissolved to a more or less fine powder, except in cases where the fine powder would be- come agglutinated by the action of the solvent. A solution mortar is a deep mortar provided with a lip. A salt or other substance to be dissolved in water may be put in the solution mortar and there crushed, after which one portion after another of solvent is added and poured off as solution results, until all of the solvent to be used has been employed and the solid substance liquefied. A PORCELAIN SOLUTION MORTAR A BEAKER WITH LIPS, USED IN MAKING SOLUTIONS A BEAKER WITHOUT LIPS, USED IN MAKING SOLUTIONS 467. Circulatory displacement consists in placing a soluble substance on a strainer at the top of a vessel containing the solvent, just below the surface of the liquid; the solution 274 A CORRESPONDENCE COURSE IN PHARMACY formed, being denser than the solvent itself, then runs down to the bottom of the vessel so that fresh portions of solvent come in contact with the solid matter, and the solution is thus more rapidly effected. This method is a very useful one, and if a strainer of the right kind is employed the solution obtained by circulatory displacement may be rendered so clear as not to require further clarification. 468. Extraction methods by which soluble substances contained in plant drugs are extracted and separated from the insoluble substances are of great importance. The solvents employed are called " menstrua,' ' and the most common menstrua are alcohol and water and mixtures of these. The extraction methods are maceration, digestion, infusion, decoction and percolation. 469. Maceration consists in placing the comminuted drugs in the menstruum and permitting them to remain in contact with each other a sufficient length of time at the ordinary room temperature, after which the solution obtained is separated from the undissolved residue, which is called the "marc." But maceration may be varied so as to be rendered more effective, by using several successive portions of menstruum upon the undivided amount of drug to be exhausted of its soluble matter. If, for instance, a pound of drug be mixed with enough diluted alcohol to produce a thick mixture, and this mixture be allowed to stand a day or two, after which the solution formed is expressed by means of a hydraulic press or other effective pharmaceutical press, the press-cake can then be disintegrated again and mixed with another portion of fresh menstruum to produce a thick mixture as before, allowing this new portion of menstruum to extract as much of the remaining soluble matter as it may, after which this second solution is separated by expression as before. These successive macerations with new portions of PHARMACEUTICAL OPERATIONS 275 menstruum may be repeated until absolutely no more soluble matter remains in the drug. If at the same time the several macerates or solutions obtained by maceration be kept separate from one another, these several macerates may be employed over again as menstrua upon a fresh portion of drug, the drug being macerated first with the first macerate from the preceding portion of drug and then with a second and third and fourth macerate, and finally with a fresh portion of previously unused menstruum, until this second portion of drug has also been completely exhausted, the object being to use each portion of menstruum over and over again as long as it still retains any solvent power, in order to effect the extraction of all the soluble matter with the smallest possible amount of menstruum, so as to obtain as concentrated a solution as may be made. [This is also the object of percolation and re-percolation, as will be seen later on.] A very common form of maceration when employed in the preparation of tinctures is to use two-thirds of the whole amount of menstruum upon the whole amount of drug in the first period of maceration, and then, after separating the solution formed, to use the remaining third of the menstruum to finish the exhaustion of the drug. 470. Digestion differs from maceration in one particular only, namely, the temperature. While maceration is per- formed at any ordinary room temperature, or, in other words, without the application of artificial heat, digestion is performed at any temperature above that of the work- room, or, in other words, with the application of more or less heat. The temperature of digestion may be any degree of heat from 25° 0. up to nearly 90° 0. The effectiveness of digestion as compared with maceration is great, and the employment of even a comparatively 276 A CORRESPONDENCE COURSE IK PHARMACY moderate degree of heat generally increases the solvent power of the menstruum so greatly that digestion ought to be employed more largely than it is, for it accomplishes in great part the same object as is gained by percolation and re-percolation, namely, the exhaustion of the drug with a minimum amount of menstruum. 471. Infusion is a process consisting of putting boiling water upon a plant drug and letting the hot water exert its solvent action upon the drug without taking any measures to maintain the temperature, but allowing that to gradually fall even to the temperature of the atmosphere of the room, after which the solution formed is separated from the marc by straining and expression. But the process of infusion is at the present time most frequently performed by means of a water bath or "digestorium," and when this is the case, the temperature is maintained at such a high degree that che result is very different from that obtained by the old method of infusion. The products or preparations made by the process of infusion are generally called infusions. 472. Decoction is a process of extraction consisting of boiling a drug in the menstruum for a given length of time. This process is rarely applicable except when water is the menstruum and the drug contains no substance of value liable to be injuriously affected by the high temperature. The products made by decoction are called "decoctions," and decoctions are rarely made of potent drugs. 473. Percolation is an effective method of extraction which is extremely useful when concentrated liquid extracts are to be made or when it is desired to exhaust the drug with a minimum amount of menstruum. These objects are gained in the process of percolation by using the same quantity of solvent over and over again on successive portions of drug, until the solvent is so charged with soluble matter or so nearly saturated that it is no longer capable of doing PHARMACEUTICAL OPERATIONS 277 effective work. This can be accomplished in various ways. The simplest form of percolation consists in moistening the drug in the form of powder with a sufficient amount of menstruum to dampen it, after which the dampened powder is allowed to lie long enough thoroughly to absorb the menstruum, so that each particle of powder may be soft- ened and permeated by the solvent as far as it can be. The dampened drag is then packed more or less firmly in a tall cylindrical tube called a perco- lator, the form of which is indicated by the illustration on this page. If the drug is uniformly and not too firmly packed in the percolator by means of the plunger or packer, the descent of the menstruum, afterwards poured upon the drug, will be very regular. A sufficient quantity of men- struum is poured upon the drug in the percolator completely to saturate the packed drug from top to bottom, leaving a layer of menstruum above the surface of the drug, after the packed mass has been filled and satu- rated. The apparatus is closed so that no liquid can pass out from it. In the percolator described in the pharma- copoeia and figured in the text, a rubber tube is attached to the lower end of the percolator, and when this tube is raised and tied to the side of the percolator so that the end of the tube is above the level of the liquid, the atmospheric pressure will prevent any portion of liquid from passing out. The apparatus is left in this condition a greater OLDBERG'S PERCOLATOR 278 A CORRESPONDENCE COURSE IN PHARMACY or less period of time, according to circumstances, in order that the menstruum may have time enough to act upon the drug and to dissolve the soluble substances in it. The tube is then lowered and the displacement of the liquid from the mass of drug in the percolator is allowed to proceed. The liquid or solution flowing out of the percolator is called the percolate, and the rate of its flow is regulated so that it may pass out slowly, the object being to permit the liquid in the percolator to gather up more soluble matter as it passes through successive layers of the packed drug. The student can readily see that when the menstruum is poured upon the drug in the percolator, each drop of liquid passes through the entire distance from the top to the bottom, first taking up soluble matter from the upper layer and then from the next layer of drug, and so on, so that if the column of drug is tall enough, it may happen that the solution formed will finally be so thick that it can pass no further. This, of course, is to be avoided, but the column of drug is always made sufficiently tall to insure that the menstruum may form as saturated a solution as can readily pass down and out. If the process is successfully performed, the percolate passing out from the percolator will be clear or free from solid particles. Fresh menstruum is added from time to time, being poured into the percolator at the top and allowed to percolate through the drug, following the preceding portions until finally no more soluble matter remains in the marc. If the percolator is put in a warm place, the effectiveness of this operation is very much increased. When liquid preparations are made of such strength that they represent more than one-fifth of their weight of the drug, percolation is unquestionably the best method of extraction, but most of the pharmacopoeias of the world PHAKMACEUTICAL OPEEATIOKS 279 order maceration for making tinctures of 20 per cent, strength or less. Percolation is a difficult process, which should never be undertaken by inexperienced operators without constant supervision exercised by persons familiar with the necessary conditions- of success. In other words, it requires con- siderable practice and close attention to perform percolation successfully. Maceration, on the other hand, is a very simple process, and this undoubtedly is the reason why most of the pharmacopoeias prefer it to percolation, except in cases where maceration proves insufficient. 474. By re-percolation is meant a process of percolation in which one portion after another of the drug is subjected to displacement or percolation in the manner described, using part of the same menstruum for the second portion of drug as for the first, and part of the same menstruum for the third portion of drug as for the second. This plan is adopted for the purpose of further increasing the effective- ness of the process. In simple percolation the last portion of the percolate is a comparatively diluted solution, which can readily be used again as an effective menstruum, and it is so used when re-percolation is employed. (See p. 275.) 475. The clarification of liquids is accomplished in various ways. Sometimes clarification is effected by subsidence, the solid particles suspended in the liquid being simply permitted to sink to the bottom, forming a sediment from which the clear "supernatant liquid" may be decanted by means of a siphon. The decantation of liquids from sediments and precipitates and the transfer of liquids from one wide-open vessel to another may also be effected in the manner shown in illus- trations on page 280. Another method of clarifying a liquid is by passing it through a straining cloth or bag. This is called eolation. 280 A CORRESPONDENCE COURSE IN PHARMACY and the strained liquid obtained by eolation is called the colature. 476. Another and still more effective method of clarification wherever practicable is to pass the liquid through a paper DECANTATION BY A GUIDING ROD DECANTATION OVER A GREASED RIM filter. Paper is manufactured expressly for this purpose and called filter paper. It is usually obtained in circular disks of various diameters, and these disks, when folded, form the paper filters which are placed in glass funnels in order to perform the filtration. A simple paper filter is one so folded that when bent in the funnel it lies close against the sides of the funnel all around, leaving no channels through which the liquid can pass out. Such filters are useful in washing precipitates, but as the liquid can pass out of the paper filter only at the apex in the throat of the funnel, the process of filtration with simple filters is very slow. Plaited filters are so folded as to leave channels between the filter paper and the funnel all around, and such filters, of course, permit of rapid filtration. The pores of the filter paper are close enough or small enough to arrest the passage of all solid particles, so that the filtrate is usually perfectly clear. However, some substances in a very fine state of A PLAITED PAPER FILTER PHARMACEUTICAL OPERATIONS 281 A PLAIN PAPER FILTER IN POSITION division pass through the pores of filter paper so readily that they cannot be separated by this method. In such cases double or triple filters may sometimes prove effective, or the unclear liquid first may be mixed with magnesium carbonate or calcium phosphate, or some other insoluble filtering medium in the form of powder, through which the liquid must pass before it can run out of the filter. The use of a layer of wetted magnesium carbonate, calcium phosphate or other filtering medium put in the paper filter often proves sufficient to clarify liquids which cannot be rendered clear by paper alone. 477. The process of evaporation as carried out for pharma- ceutical purposes is comparatively simple. "Evaporating dishes," or vessels in which liquids are heated to evaporate them, are shallow, in order that the liquid contained in them may present a large surface exposed to the air. The rate of evaporation is further facilitated or increased by stirring, which causes the vapor formed in the body of the liquid to be more readily disentangled so that it can escape. Eapid evaporation is called vaporization. The term "spontaneous evaporation" means the slow evaporation of liquids which takes place at ordinary temperatures, or, in other words, without the application of artificial heat. 478. Distillation is the vaporization of liquids in an apparatus so constructed that the vapor is again condensed to a liquid form and the distilled liquid, called the distillate, collected. 479. Pharmaceutical stills are usually made of copper or tinned iron, and they are also usually provided with water A PORCELAIN EVAPO- RATING DISH 282 A CORRESPONDENCE COURSE IN PHARMACY baths or doable bottoms' so that they can be used with water-bath heat. Water stills for making distilled water are not provided with water baths, because the heat applied to them must be sufficient to produce rapid distillation of the water. But when alcohol and other more volatile liquids are to be dis- tilled, water-bath heat is not only sufficient but also much safer, if the liquid contains in solution substances liable to be injured by high temperatures. Stills of the most simple construction are the best, because they can be most readily cleaned and kept in order. Manu- facturers of pharmaceutical apparatus have various kinds to offer, and students as well as pharmacists are freely supplied with illustrated descriptive catalogues of such apparatus, from which they may learn about the various forms of construction. 480. Condensers used in connection with stills are also of various kinds. The usual condensing worm, or worm-condenser, consists of a spirally bent block-tin tube or glass tube, placed in a vessel of water so that it may be surrounded by cold water, called the condensing water, which is intended to absorb the latent heat given up by the vapor as it reverts to the liquid form. Liebig^s condenser consists of two tubes, one without the, other. The inner tube is the one through which the vapor is conveyed, while the outer tube holds the condensing water. The outer tube is, of course, open at both ends, so that the condensing water may pass through it. The condenser is placed in a slanting position and the condensing water is admitted at the lower end and runs out at the upper end. Mitscherlich's condenser consists of three tubes. The outer tube is a large tank containing the condensing water. In this is placed a double cylinder, composed of two tubes PHARMACEUTICAL OPERATIONS 283 soldered together at the ends. An opening into the space between the two tubes is made both at the top and at the bottom. The space between the tubes is the condensing space, and the condensed liquid runs out at the bottom of the apparatus, through a tube leading from the lower open- ing of the double cylinder through the wall of the tank. The student will see that the vapor to be condensed, being contained in the space between the two tubes constituting the double cylinder immersed in the tank, must form a thin sheet surrounded by water on both sides, for the condensing water passes all around the outer one of the two tubes forming the double cylinder and fills the inner tube com- pletely. This is the most effective condenser that can possibly be constructed. The dome-shaped condenser has a funnel-shaped still-head, or top of the still. This funnel-shaped top constitutes the bottom of a water vessel. In other words, the inverted funnel is surrounded along the lower edge by a wall so that the water can be kept on top of the funnel. The liquid heated in the still below forms vapor, which rises to the dome-shaped top and condenses against the sides of the dome or inverted funnel, and then runs down the sides to a gutter running along the inner and lower edge of the funnel. This gutter is lower at one point than elsewhere, so that the liquid runs out at that point through a tube. This dome-shaped condenser, in combination with the body that belongs to it, is one of the most useful pharmaceutical stills. Condensers made of glass are also in various forms, and are used in connection with flasks and retorts employed in distilling comparatively small quantities of liquids. 481. Crystallization is the formation of regular geometric solids resulting from the arrangement of the molecules in accordance with inherent natural laws. Solid substances 284: A CORRESPONDENCE COURSE IN PHARMACY assume the crystalline form most readily when passing from a liquid form in the state of solution, or from a state of vapor, back to the solid condition; but crystallized and crystalline substances are also obtained by precipitation and in other ways. The most common method of making crystals is to dissolve the crystallizable substance in a suitable solvent, after which the solvent is separated from the solution by evaporation. As soon as the solution becomes supersaturated, the dissolved substance separates in the form of crystals. A saturated solution may also be made at a high temper- ature, and then cooled to a lower temperature, at which the amount of solvent present is no longer sufficient to hold the substance in solution. Large and well-defined crystals are most readily obtained by slow concentration of solutions, for crystals grow by deposition of more of the solid matter on the surface of the smaller crystals, or nuclei, first formed. Special vessels for making crystals from solutions are called crystallizers. As the crystals are formed from solutions, on account of the deficiency of solvent, it follows that the liquid remaining after the crystallization must always be a saturated solution. This saturated solution in which crystals are being formed is called the "mother- liquor." When crystals are formed very rapidly and when the liquid in which the crystals are being formed is agitated in any way, the crystals are necessarily small and not well- developed. The formation of small crystals obtained by rapid evaporation accompanied by stirring or by rapidly cooling a hot saturated solution is called granulation. Pharmacists are sometimes required by physicians' pre- scriptions to make saturated solutions of medicinal sub- stances. When such solutions are dispensed, it happens that if the liquid is placed in a cold room, some of the dis- solved matter separates in crystalline form; to prevent PHAEMACEUTICAL OPERATION'S 285 this, directions should be given to keep this preparation in a warm place. Crystals obtained by sublimation are usually quite small, especially if the vaporized substance is condensed at a temperature considerably below that at which the vapor was formed. A cake, or large crystals, may be obtained when the vapor is slowly condensed at a temperature but little below the heat required for the sublimation. Crystals can also be obtained by fusing crystallizable solids and permitting the fused substance to cool gradually. 482. Precipitation is the formation of insoluble solids in liquids. It takes place in a liquid previously free from undissolved matters, and consists in the formation of solid particles insoluble in that liquid. It # is caused by a change in the relation of the solvent to the matter held in solution. It may, therefore, result from a change in the solvent or by a change in the substances dissolved in the liquid. Physical precipitation results when a non-solvent is added to the solution, as, for instance, when water is added to an alcoholic solution of a resin. The resin precipitates because it is insoluble in a mixture of alcohol and water. Alcohol precipitates mucilage from a water-solution for a similar reason, mucilage being insoluble in alcohol. Many metallic salts which are soluble in water are insoluble in alcohol, and for this reason strong water-solutions of such salts cannot be mixed with alcohol without causing the separation of the salts. Chemical precipitation results from the formation of new substances insoluble in the liquid. It is, in other words, the result of chemical reaction. When physical precipitation takes place, the molecules at the end of the process are the same as at the beginning, but in chemical precipitation the 286 A CORRESPONDENCE COURSE IN PHARMACY molecules present at the beginning give place to entirely new molecules. In most cases the reaction which takes place is one of double decomposition. When precipitates are intentionally made, the product sought may be either the insoluble substance itself or the soluble substance remaining in solution in the liquid. The "supernatant liquid" standing over the precipitate is called the mother -liquor. When the principal product consists of the precipitate, the latter must be washed with pure water until free from mother- liquor, when it is collected and dried. Heavy precipitates which readily subside in the liquid are easily washed, but light and P^bulky precipitates which remain suspended 3njar in the liquid longer are sometimes difficult to handle. In cases of double decomposi- tion, coarser and heavier precipitates may often be obtained by using strong, hot solutions of the factors of the reaction, while more finely divided and bulky precipitates are formed when the solutions used are cold and diluted. Precipitates unintentionally formed in certain pharmaceutical preparations are often troublesome, and they always indicate that a change has taken place which may lessen the value of the preparation. The process of precipitation em- precipitation flasks, J- ^"""» ^ if ^ F CALLED ERLENMEIER FLASKS ployed for the production of chem- ical compounds is, of course, intentional, and can gen- erally be regulated so as to give entirely satisfactory results. PHARMACEUTICAL OPERATIONS 287 Test Questions 1. Describe a Bunsen burner. 2. What is the object of the sand bath ? 3. For what purposes is the water bath used ? 4. What other means are employed to prevent the temperature from rising too high in pharmaceutical oper- ations requiring high heat ? 5. What is exsiccated alum ? 6. What is calcined magnesia? 7. By what means can volatile substances be separated from fixed substances in a solid condition ? 8. By what means is the coarse comminution of plant drugs effected ? 9. By what means can the druggist make fine powder of roots and barks ? 10. What is the difference between contusion and trituration ? 11. What is levigated calomel and what is the difference between it and sublimed calomel ? 12. How is prepared chalk obtained in such extremely fine powder ? 13. What is a No. 50 powder ? 14. Are all powders that pass through a No. 80 sieve of the same degree of fineness ? 15. What is meant by dusted powders ? 16. Why is powdered guaiac resin almost white, although the resin in the whole piece appears almost black ? 17. For what reasons can soluble salts be dissolved more quickly with the aid of the solution mortar ? 18. Describe circulatory displacement. ■ 19. What are the most common pharmaceutical menstrua ? 20. What is the difference between maceration and digestion ? '288 A CORRESPONDENCE COURSE IN PHARMACY 21. What is the most effective method of maceration ? 22. What is meant by the term marc ? 23. Which is the more effective method of extraction, maceration or digestion ? State the cause of the difference, if any. 24. What is meant by the process of infusion ? Describe it. 25. Describe decoction. 26. For what purposes is percolation employed ? 27. Describe succinctly the various steps of the process of percolation. 28. Describe a percolator. 29. Why is the drug moistened before being packed in a percolator for percolation ? 30. How tall can the column of packed drug be in the percolator without disadvantage ? 31. What is meant by re-percolation ? 32. Why is percolation more effective than maceration ? 33. What results can be accomplished by percolation which cannot be accomplished by ordinary maceration ? 34. Can all drugs be subjected to percolation ? If not, what drugs cannot be so treated ? 35. Name the several means commonly employed for rendering liquid preparations clear. 36. Make one plain filter and one plaited filter and return both with your recitation paper. 37. By what means can the passage of fine particles of powder through paper filters be prevented in certain cases ? 38. For what purposes is evaporation employed in pharmaceutical processes ? How is it rendered most effective ? 39. What are the practical uses made of distillation in pharmacy ? 40. What kind of a still is best for distilling volatile liquids ? PHARMACEUTICAL OPERATIONS 289 41. What is the difference between the Liebig condenser and the Mitscherlich condenser ? 42. Describe the worm-condenser. 43. Can a still be so made that a separate condenser is not necessary ? If so, how ? 44. By what several means can solids be made to assume a crystalline form ? 45. What is meant by granulation ? 46. What is the technical term used to designate the liquid from which crystals are deposited ? 47. Define precipitation. 48. What are the practical uses of crystallization ? 49. What are the practical uses of precipitation ? 50. What is meant by the term supernatant liquid ? 51. How long should a precipitate be washed before it is dried? 52. How is the washing of a precipitate effected ? 53. What is the difference between physical precipitation and chemical precipitation ? 54. By what means can precipitations be rendered heavy instead of light, or fine instead of coarse ? 55. Draw a figure showing the construction of a Liebig condenser. 56. Make an outline drawing showing the construction of a Mitscherlich condenser. 57. What would you call the kind of chemical reaction by which precipitation is produced ? 58. What are the usual means adopted to produce large crystals of water-soluble salts ? 59. By what means can very small crystals of water-soluble salts be secured ? 60. How would you produce crystals of insoluble volatile substances ? 61. Give three examples of physical precipitation. 290 A CORRESPONDENCE COURSE IN PHARMACY 62. Give ten examples of chemical precipitation. 63. What is contained in the liquid in which a precip- itate is produced by chemical reaction, and how can the sub- stance contained in that liquid be recovered from it, if desired ? LESSON NINETEEN XXVIII The Chemical Constituents of Plant Drugs 483. The substances contained in plant drugs may be classified into groups, as follows: 1, water; 2, cellulose in its various forms, the principal of which is woody fiber; 3, starch in its many forms; 4, pectinous substances; 5, vegetable mucilage; 6, sugars; 7, albuminoids; 8, fixed oils and fats; 9, organic acids ; 10, tannin; 11, bitters, called in Latin amara; 12, volatile oils; 13, resins; 14, glucosides; 15, alkaloids. 484. Water is contained in all plants. Some fresh plants contain over 90 per cent., others much smaller amounts. Plant drugs must be dried in order to preserve them. The condition in which they are ordinarily employed is that called "air-dry." An air-dried drug contains no more moisture than it necessarily must contain as usually kept, exposed as it is to the ordinary atmosphere. If dried beyond that point, it absorbs moisture again ; if it contains more than that amount of moisture, it is liable to be damaged by mold or fermentation. Fresh drugs are also used for making pharmaceutical preparations, but whenever this is done, the amount of moisture contained in the undried drug must be considered in connection with the method of preparation adopted. 485. Cellulose, starch, pectin, mucilage and sugar are all so-called carbohydrates. By the term carbohydrate is 291 '-202 A CORRESPONDENCE COURSE IN PHARMACY meant an organic substance having the formula or com- position C 6 H 10 O 5 , or a multiple of that formula. Some carbohydrates differ from this formula, but only by two hydrogen atoms and one oxygen atom, added or deducted. The carbohydrates have no medicinal action of great importance, but some drugs containing starch, and others containing mucilage, are employed for the purpose of pre- paring demulcent or mucilaginous liquids, to serve as vehicles for more potent remedies, or to protect local mucous surfaces. 486. Cellulose, which exists in plant drugs chiefly as woody fiber, is entirely insoluble in all ordinary solvents, such as water, alcohol, glycerin, etc. Therefore, cellulose con- stitutes a large proportion of the undissolved residue obtained when extracts are made of plant organs. 487. The various classes of constituents of plant drugs are contained in the cells and the intercellular spaces in the tissues. These cavities are bounded by the cell walls, made of the insoluble cellulose. Hence, the cellulose offers more or less obstruction to the extraction of soluble substances contained in the drugs. This fact renders it necessary to grind or powder the plant drugs sufficiently to break down the obstruction. 488. Water has the power to pass through vegetable membranes, even when the pores in those membranes are extremely minute. This power of liquids to pass through vegetable membranes is called osmosis. Its passage out- ward is called exosmosis. The current inward is called en- dosmosis. We make use of this property of water in our pharmaceutical operations, as will be explained in the next paragraph. 489. Certain substances soluble in water may pass through vegetable membranes in a state of solution, and this phenomenon is called dialysis. Other substances soluble in water cannot pass through vegetable membranes, or do THE CHEMICAL CONSTITUENTS OF PLANT DEUGS 293 it so slowly as to be practically undialyzable. We are there- fore able to separate dialyzable substances from the undia- lyzable substances, even in drugs so coarsely powdered that only a small proportion of the cells and intercellular cavities are broken into. Therefore, whenever the valuable con- stituents of a drug are best dissolved in water, it is not necessary to powder the drug finely. Even a piece of whole drug will give up a good deal of its dialyzable constituents when put in water. For instance, a piece of gentian placed in water will very quickly make all of that water bitter. 490. Alcohol passes through plant membranes so extremely slowly that we cannot take any advantage of its slight power to do so. We consider it practically unable to penetrate plant membranes. Whenever, therefore, the valuable constituents of a plant drug are such as require alcohol for their solution and extraction, it is necessary that the drug shall be powdered finely so that the alcohol may come in actual contact with the substances to be dis- solved, for the alcohol will only wash off what is on the surface of the particles of powder, and will extract nothing from the interior of cellular structures. 491. Starch in its normal condition is entirely insoluble in alcohol and in water, but the starch 'in plant drugs is often altered starch. It has been changed under the influence of heat, moisture and the action of various substances contained with the starch in the drug, in such a way that it is not insoluble. Altered or partially altered starch is sometimes soluble in water to such an extent that when extracted from the drug by a very diluted alcohol, it may form a consider- able deposit on the bottom of the bottle upon standing for some time; for the altered starch, although soluble in water and very diluted alcohol, reverts to its normal insoluble condition when long in contact with alcohol. Hence, when sarsaparilla or licorice root is extracted by percolation with 291 A CORRESPONDENCE COURSE IN" PHARMACY a very diluted alcohol, the liquid extract, although perfectly clear or free from solid particles, will, in the course of a few weeks, deposit a large layer of white or nearly white starch. Starch is altered by water having a temperature above 60° C. , so that the starch granules burst and a mucilage results. From this starch -mucilage the starch cannot be recovered in its normal condition. Yet the starch held in the mucilage is not, strictly speaking, dissolved; it is simply held in suspension, distributed through the liquid uniformly. To make starch-mucilage, it is customary to employ one part of starch to one hundred parts of water ; but to make a starch- paste, one part of starch is necessary with ten parts of water. 492. To illustrate how the constituents of drugs guide us in making pharmaceutical preparations, I may mention that some drugs containing a large amount of starch in addition to their more important constituents may be treated in different ways, according to whether or not we desire the product to contain the starch. The pharmacopoeias contain an infusion of calumba and also a decoction of calumba. The infusion is made with hot water, but the temperature is not maintained and hence the starch is not extracted and rendered mucilaginous. But the decoction is made by boiling the drug in water, and that preparation accordingly is thick and demulcent, because it contains the starch. Barley, rice, oats and wheat consist largely of starch, and decoctions are made of them. Whenever a decoction of starch or a starchy drug is made, it is intended that so much drug shall be used that the preparation will be sufficiently thick. Other preparations are scarcely ever made from starchy substances. 493. Pectin and pectinous substances are water-soluble. They resemble mucilage in many respects, but have the characteristic property of forming jellies. Apples, currants and other fruits form jellies because they contain pectin. THE CHEMICAL CONSTITUENTS OF PLANT DRUGS 295 Some other fruits, like cherries, do not form jelly because they contain an insufficient amount of pectin. The forma- tion of the jelly requires the presence of a sufficient amount of pectin, and the formation of the jelly is aided by the addi- tion of much sugar. Some drugs contain pectin. As an example, we may mention kino, which contains so much pectin that a tincture of kino made with diluted alcohol sometimes changes to a solid jelly in the bottle. Pectin is insoluble in alcohol, and is therefore not contained in pharmaceutical preparations made with strong alcohol. 494. Mucilage is contained in nearly all plants. It may be normal or physiological mucilage, formed in the natural growth and life of a plant, or it may be pathological mucilage, formed by the breaking down of plant tissues, caused by injury. We see physiological mucilage in many leaves and in the inner bark of plants. We also find it covering the seed-coat of flaxseed, quince-seed and some other seeds. Pathological mucilage occurs in masses on the trunks and branches of certain trees and shrubs, when the bark has been perforated by insects. Apple tree gum, peach tree gum, cherry tree gum and gums upon other trees of the same natural order are familiar. These solid gums are formed by the evaporation of the plant-juice exuding through the wound made in the bark of the tree by an insect. 495. There are two classes of gums — the arabin gums and the bassorin gums. The arabin gums are completely soluble in water; the bassorin gums simply absorb water and swell in it to form translucent jellies, but do not dissolve. Gum arabic is a typical example of the arabin gums. Tragacanth is a typical example of the bassorin gums. A piece of gum arabic put in water dissolves completely, forming a mucilage, but a piece of tragacanth put in a large amount of water 296 A CORRESPONDENCE COURSE IN PHARMACY simply swells and softens until it has taken up all the water it is capable of absorbing, and then forms a gelatinous mass, the outlines of which can be readily seen in the water, and this gelatinous mass remains distinct from the water about it. If the mixture is stirred actively, the jelly is, of course, disintegrated, but it does not dissolve, and if the mixture is thoroughly shaken in a bottle and then allowed to stand at rest, the gelatinous tragacanth separates again. 496. The word "gum" is so much misused that it perhaps ought to be discarded from technical nomenclature. Tech- nically, gum is dry mucilage. It is either perfectly soluble in water or forms a mucilage with water, even if it is not really soluble. Hence, no substance insoluble in water, or nearly so, can be a gum. Nevertheless, many resins which are entirely insoluble in water are called gums, as, for instance, shellac, benzoin, copal, mastic, etc. Gums are entirely insoluble in alcohol. For this reason, when alcohol is added to a water-solution of any gum, the gum separates from the solution, or is precipitated. Aloes, kino and catechu are extract-like drugs soluble in diluted alcohol. They are therefore not gums, although frequently called so. There are, in fact, only two kinds of gums in the pharma- copoeia, namely, acacia and tragacanth. When a gum or dry mucilage is heated, it becomes drier and harder instead of fusing, and when the temperature is sufficiently high, the gum is charred but does not ignite so as to burn with a flame. Compare this behavior of the gums with the properties of resins. Dried mucilage or gum undergoes no change when kept with ordinary care, but moist gum or a solution or mucilage undergoes fermentation when exposed to the air, and muci- lage ferments so readily that it can be kept unaltered only a few days. Acacia and tragacanth are employed pharmaceutically in THE CHEMICAL CONSTITUEKTS OF PLANT DRUGS 297 making pill-masses and other masses cohesive, and also in making emulsions. The pharmacopoeias contain mucilages made of sassafras pith, slippery elm bark, flaxseed, quince-seed and other plant drugs containing mucilage of the arabin type. When bassorin gum is heated twenty-four hours in water, it is rendered soluble. The mucilage of acacia of the pharmacopoeia is made by dissolving one part of whole acacia in two parts of water. 497. Sugars of various kinds are contained in many plants and plant drags. All sugars are water-soluble. They are also soluble, though less freely, in alcohol. A weak sugar-solution made with water undergoes fer- mentation when exposed to the air, forming alcohol. Hence, a small amount of sugar present in an aqueous liquid preparation invites fermentation, but when so much sugar is added to a watery solution that the solution acquires great density, it acts as a preservative, because it excludes air. Air is soluble in water, but is not sol able in a dense water-solution of other substances. Sugar is used to a great extent to sweeten certain pharma- ceutical preparations. Medicated syrups are both sweetened and preserved by sugar. Fresh plant substances and animal substances placed in a large amount of sugar are in a measure preserved, especially plant tissues, because the sugar takes up the water, and water is essential to the changes that cause organic matter to decompose. Sugar is also used in pharmacy and in medicine as a diluent. One class of dilutions ordered by the pharmacopoeia is called triturations. These preparations are composed of one part of some active medicinal agent mixed with nine parts of milk sugar. 498. The principal sugars of interest to pharmacists are 298 A CORRESPONDENCE COURSE IN PHARMACY cane sugar and milk sugar. Cane sugar, or ordinary white sugar, is extensively used. Milk sugar, which is much less readily soluble, is employed as a diluent mainly for insoluble substances. Starch-sugar, or glucose, is employed in the form of a solution, called glucose syrup. Other saccharine substances used in pharmacy and medicine are honey and manna. 499. When sugar ferments, it forms alcohol, as has already been mentioned, but the process of fermentation ceases as soon as 14 per cent of alcohol is contained in the liquid. Accordingly, when wine is made from grape juice, the prod- uct cannot naturally contain more than 14 per cent of alcohol. Any wine containing a larger percentage of alcohol has been fortified by the addition of alcohol after the process of fermentation. Alcohol acts as a preservative. For this reason, many liquid pharmaceutical preparations are made with alcohol. The principal preparations of this kind are the tinctures and the fluid extracts, but other liquid pharmaceutical prepara- tions are also preserved by the addition of smaller quantities of alcohol. From what has already been said, it is evident that any liquid containing fermentable matter must have at least 14 per cent of alcohol in it in order to be proof against fermentation. Usually 15 per cent or more is added for this purpose. 500. Albuminoids, or vegetable albumins, are contained in many plants and drugs. Vegetable albumin is much like animal albumin, and the most familiar and striking type of animal albumin is the white of egg. It is a colorless, water- soluble substance, insoluble in alcohol, and coagulated by heat. When an egg is boiled or heated to a temperature above 60° C, the white of the egg becomes a solid, white, insoluble substance, which cannot again be changed back to its original THE CHEMICAL CONSTITUENTS OF PLANT DRUGS 299 soluble condition, and we say that it is coagulated. Alcohol has a similar effect upon the white of egg. Albumin, when exposed to the air in the presence of moisture, putrefies; that is, it undergoes decomposition, resulting in the formation of ill-smelling sulphur compounds, because all albumin contains sulphur, together with carbon, hydrogen, oxygen and nitrogen. The fact that albumin so easily undergoes decomposition renders it desirable that most pharmaceutical preparations shall not contain it. Moreover, if the albumin is present in any considerable quantity, it dilutes the preparation unnecessarily. There- fore, in making aqueous extracts of plant drugs, the watery liquid containing the soluble matters is brought to the boil- ing point, or at least to a temperature above 60° C, in order to coagulate the albumin, when it forms solid flocculi that can be removed by straining, after which the liquid is concentrated by evaporation to obtain the solid substances free from the water used. Preparations of plant drugs, if made with alcohol, cannot contain albumin, since it is not soluble in that liquid. 501. Fixed oils, fats and waxes are contained in seeds and various other plant parts. The student will probably be surprised to learn that fats and oils and waxes are salts ; yet, such is the case. They are compounds formed by certain acids with certain bases. The principal acids form- ing fats are called oleic acid, palmitic acid and stearic acid. The basic function in a fat is performed by an atomic group composed of three atoms of carbon and five atoms of hydro- gen, C 3 H 5 , called glyceryl. Our familiar glycerin is the hydroxide of glyceryl. Other basic groups may also form fats. When a strong alkali like potassium hydroxide or sodium hydroxide is added to a fixed oil or fat, a soap is formed. The fat-acid forms a potassium salt or sodium salt, which constitutes the soap, in place of the glyceryl salt, which con- 300 A CORRESPONDENCE COURSE IN PHARMACY stituted the fixed oil or fat. If potassium hydroxide is used, soft soap is formed ; if sodium hydroxide is used, hard soap is formed. Castile soap consists almost entirely of sodium oleate. Oleate of glyceryl is called olein. Palmitate of glyceryl is palmitin, and stearate of glyceryl is stearin. Olein is per- fectly liquid. Olive oil and almond oil consist very largely of olein. Palmitin is like a soft ointment and palm oil con- tains a good deal of it, so that palmitic acid and palmitin are named after palm oil. Stearin is hard. Solid fats are solid because they contain a considerable amount of stearin, and their hardness is in direct ratio to the percentage of stearin. Fixed oils are called so because they are not volatile; they cannot be distilled. If heated strongly enough, they decom- pose. They burn with a smoky flame if the supply of oxygen is insufficient, but with a smokeless flame if arrange- ments are made to supply an abundance of the oxidizing agent. Fixed oils, fats and waxes are all absolutely insoluble in water. They are all lighter than water. They are soluble to some extent in alcohol, more soluble if the alcohol is strong. They dissolve freely in ether, chloroform, liquid hydrocarbons and volatile oils. Pure fixed oils and fats are odorless and colorless, but many of these substances are more or less impure, or contain naturally other substances that impart color and odor. Fixed oils have no action whatever upon vital organs of the body, and therefore are very harmless when taken internally. In fact, it may be said that their only use medicinally depends upon their emollient effect. They soften and penetrate the skin so that certain medicinal agents can be administered through the medium of ointments and cerates applied to the skin, or ointments and cerates are THE CHEMICAL CONSTITUENTS OF PLANT DRUGS 301 used as local dressings for protection, etc. Castor oil has a laxative effect, but that effect is not due to the fixed oil as such, but to some other substance held in solution in it. This laxative or cathartic substance contained in the castor oil abounds in the whole castor oil plant, so that the bruised leaves are far more active than castor oil. When strong alcohol is used as a menstruum in making a pharmaceutical preparation of a plant drug, any fixed oil contained in the drug is dissolved by alcohol and may after- wards separate, at least in part, from the alcoholic solution on standing, and if the alcoholic liquid extract is evaporated until a solid mass remains, the fixed oil or fat may be readily seen to constitute a part of the residue, and if there is a large amount of fat present, it should be removed. There are several methods by which fixed oil can be removed in preparing solid extracts. One method consists in dissolving out the fixed oil with ether before using any other solvent. This can be done whenever the valuable constituent of the drug is not soluble in ether. Another method consists in using as a menstruum or solvent a liquid which, while extracting the valuable constituents, will not dissolve the fixed oil or fat. A third method consists in extracting the grease, together with the active constituents, and then separating the grease afterwards. 502. Organic acids occur in abundance in some fruits. Small amounts of numerous kinds of organic acids occur very generally in plants. There is probably not a plant growing that does not contain one or more kinds of organic acid. Among the organic acids that occur in fruits and other plant parts in considerable quantities, we may mention oxalic acid, tartaric acid, citric acid and malic acid. None of these acids has any important medicinal action, and probably not one plant drug owes its medicinal value to any organic acid, unless it be what is called a * 'resin-acid." 302 A CORRESPONDENCE COURSE IN PHARMACY 503. We have now enumerated all the classes of plant constituents without decided medicinal action. They are commonly referred to as inert constituents of the plant drugs. In making pharmaceutical preparations and partic- ularly in making solid extracts, the aim of the pharmacist is to eliminate from his products all the inert constituents, or as great a proportion of them as possible, in order that the preparation may be as concentrated as practicable. 504. Tannin is a peculiar substance contained in almost every growing plant, and, therefore, also in almost every plant drug. When extracted from the plant and separated from other substances, tannin is a dry solid of a very light yellow color. It is soft, friable, and soluble in water, alcohol and glycerin. It is insoluble in absolute ether, but soluble in ether saturated with water ; in fact, it is usually extracted from nutgall with an ether containing 10 per cent of water in solution. Tannin is astringent, and all drugs containing a sufficient amount of tannin are also astringent and used for their astringent properties, unless they also contain other and much more important constituents. An astringent drug, in order to be effective, ought to contain not less than 10 per cent of tannin. Several astringent drugs contain more than 20 per cent and nutgall contains from 50 to 60 per cent. Tannin is named so because it has the property of tan- ning raw hide, converting it into leather. But there are two classes of tannins, and only the tannins of one of those classes will make leather. Physiological tannins are the tannins naturally contained in live plants. It is found chiefly in barks. Physiological tannin has the property of forming leather. Pathological tannin is the tannin formed in large quantities in galls or excrescences on the barks and leaves of trees when stung by insects. The nutgall is formed in such a way. When the insect stings through the bark, there THE CHEMICAL CONSTITUENTS OF PLANT DRUGS 303 is a flow of sap to the spot, and a gall is gradually formed surrounding the egg laid I t the insect. Tannin forms insoluble compounds with a large number of other substances. It therefore makes precipitates in solutions containing gelatin, mucilage, alkaloidal salts, metallic salts, etc. With iron compounds dissolved in water, liquids containing tannin form ink. Hence, the tincture of chloride of iron which is so much used by physicians always forms an inky mixture with the tinctures of nearly all plant drugs, because the tinctures of plant drugs contain tannin. Tannin in water-solution rapidly undergoes decomposition, but alcoholic liquid preparations containing tannin can be kept a reasonable length of time without serious deteriora- tion. Fluid extracts and tinctures made out of astringent drugs are all made with diluted alcohol containing a certain amount of glycerin, because the tannin compounds insoluble in water and in alcohol are many of them soluble in glycerin, so that the addition of glycerin to the preparation prevents precipitation. 505. Amara, or bitters, are a miscellaneous class of plant constituents of no great importance. They are sometimes called neutral principles, simply because they are neither acids nor bases. It is impossible to describe them, because they have few properties in common. Many of them are water-soluble, but scarcely soluble in alcohol. Others are freely alcohol-soluble and scarcely soluble in water. Most of them dissolve sufficiently well in a mixture of alcohol and water, or, in other words, in diluted alcohol. Hence, both tinctures and fluid extracts of bitter drugs or simple stomachic tonics are made with diluted alcohol, and some of the solid extracts of such drugs are made with diluted alcohol, while others are made with water. The dose of an amarum may be said to be altogether indefinite. A quantity sufficient to produce a bitter impres- 304 A CORRESPONDENCE COURSE IN PHARMACY sion to the taste is usually a sufficient dose, and a much larger dose will probably produce no greater effect. Hence, a very large dose of a simple bitter stomachic tonic cannot do any harm, beyond the inconvenience of the bitter taste. 506. Volatile oils are a very miscellaneous class of sub- stances, too. The name volatile oil is quite misleading. The word volatile usually suggests that volatile oils are excep- tionally volatile, whereas they are much less volatile than water, for water boils at 100° C, whereas the average boil- ing point of volatile oils is above 120° 0. The term "vola- tile oil" suggests that these substances resemble fixed oils, whereas they do not resemble fixed oils any more than they resemble a great many other liquids. Volatile oils are in fact radically different from fixed oils, not only in that the volatile oil is distillable while the fixed oil cannot be distilled, but also in that volatile oils are always odorous, whereas fixed oils, when pure, are odorless. The volatile oils have a pungent or hot taste, whereas fixed oils have a very bland taste, if any. Volatile oils burn fiercely with a smoky flame, even in an abundant supply of air or oxygen. Volatile oils dissolve to a slight extent in water, while fixed oils are insoluble in water. The volatile oils dissolve very freely in alcohol, whereas fixed oils dissolve only to a limited extent in that solvent. Volatile oils do not contain any fat-acids nor any glyceryl compounds, whereas fixed oils are composed of nothing else. The most common constituents of volatile oils are hydro- carbons of the formula C 5 H 8 or a multiple of 5 H 8 , such as O 10 H 16 or C 15 H 24 or C 20 H 32 . The hydrocarbons having the formula C 10 H 16 are called terpenes ; those of the composition C 5 H 8 are called semi-terpenes ; those having the formula C 15 H 24 are called sesqui-terpenes, and those of the composition C 20 H 32 are called diterpenes or double terpenes. These hydrocarbons are liquids. They are oxidized on exposure THE CHEMICAL CONSTITUENTS OF PLANT DRUGS 305 to air and form oxidation products which are also usually contained in greater or less proportion in all volatile oils. The oxidation products are some of them camphors, while others are resins. Volatile oils are nearly all liquids at common temperatures, but some of them solidify at but a few degrees below the ordinary room temperature. When a volatile oil is placed in a cold room, a solid substance may crystallize out from it. In other words, some volatile oils are separable into a liquid portion called the elaeopten and a solid portion called the stearopten. The elaeopten contains most, if not all, of the hydrocarbons, while the stearopten contains most, if not all, of the oxidation products, or compounds containing oxygen. Scarcely a single plant or flower having a distinctive odor is free from volatile oil, to which that odor is due. The odorous substance in sweet clover is not a volatile oil, but contains the odorous crystallizable substance called coumarin. But odorous substances of plant origin that are not volatile oils are rare. The odors of volatile oils are so powerful that an extremely minute amount will impart a characteristic odor to the plant, flower or drug. Aloes is a drug having an intensely strong, disagreeable odor, and that odor is due to volatile oil. The amount of volatile oil in aloes is so small that it takes three hundred pounds of the drug to make a single ounce of the volatile oil. Some flowers having a powerful and agreeable fragrance contain so little volatile oil that it is extremely difficult to extract it, and perfumes of such flowers are made not from the volatile oils, but from the flowers themselves. It has been found that volatile oils containing oxygen com- pounds have more pronounced odors than volatile oils that do not contain them, or that contain smaller amounts of the oxygen compounds. It is said that certain volatile oils con- 306 A CORRESPONDENCE COURSE IN PHARMACY sisting almost entirely of hydrocarbons without any oxygen have no odor at all, although they are generally believed to be very fragrant. It is thought, for instance, that oil of lemon has no odor, but that when the vapor of oil of lemon mixes with air before it reaches the nostrils, the odor perceived is created by the oxidation resulting from the admixture of air. Oil of cloves has a powerful odor because it contains a considerable quantity of oxygen compounds. Certain other volatile oils contain sulphur compounds, and also cyanogen compounds, and they have very strong, disagreeable odors. All volatile oils are stimulants. All of them are diuretics. Some of them are anthelmintics. Many oils are so irritant as to be rubefacient when applied externally. Other medicinal uses of volatile oils are comparatively unimportant. Water-solutions of volatile oils contain usually much less than one-tenth of 1 per cent, of volatile oil, although they are saturated, but this small amount of volatile oil renders the water both fragrant and pungent. All of our spices contain volatile oils and most of them contain, in addition, resins formed by the oxidation of the volatile oils. Since alcohol is the most effective solvent for volatile oils, the pharmaceutical preparations made out of plant drugs containing volatile oils are generally made with a strongly alcoholic menstruum, and diluted alcohol is used only when the quantity of volatile oil in the drug is comparatively small. Drugs containing volatile oils as their only valuable medicinal constituents are called aromatic stimulants. If a mixture of alcohol and volatile oil is put in a gradu- ated glass tube and water is added in large quantity, the alcohol leaves the volatile oil and enters solution in the water, so that the volume of the volatile oil is diminished by j ust the amount of alcohol it contained. The adulteration of volatile oils with alcohol is easily detected in this way, THE CHEMICAL CONSTITUENTS OF PLANT DRUGS 307 and even the quantity of adulterant may be accurately determined. 507. Resins are oxidation products of volatile oils, and as the volatile oils are usually mixtures of several substances, the resulting resins are also mixtures. Most of the resins are dry solids, but some of them are soft solids, or semi-solids. All resins are insoluble in water, but perfectly soluble in alcohol. Some resins are also soluble in ether and in chloro- form, and all resins are soluble in volatile oils. Eesins are in some respects like feeble acids. While not exhibiting strongly acid properties, they form water-soluble compounds with the alkalies and with the alkaline earths. Eesin soaps are made from alkalies and resin instead of alkalies and fats. The resin-soaps have detergent properties like the true soaps, but they are easily decomposed in boiling water. Eesins ignite readily and burn with a smoky flame, owing to the large amount of carbon they contain which is not consumed. They melt when heated and do not decompose until ignited. Soft resins are usually acrid, but some dry resins are also acrid to such an extent that when applied to the skin they raise blisters. The soft resins cannot be dried so as to become hard. Pharmaceutically, the resins are used in making plas- ters, cerates and ointments. Industrially, the resins are used in making varnishes, sealing wax and various other products. Irritant resins usually have a cathartic action, and most, if not all, of the plant cathartics contain either resins or resin-compounds, to which their medicinal action is due. Some resins which are hard and dry do not dissolve in the stomach, but pass beyond it and are dissolved only when they come in contact with the alkaline bile. For this reason 308 A CORRESPONDENCE COURSE IN PHARMACY physicians sometimes order hard, dry, inert resins added to pills in order to make them slowly active. Tinctures and fluid extracts of resinous drugs are, of course, prepared with strong alcohol. 508. Glucosides are named after glucose, and they have received the name glucoside because, when they decompose, one of the products of the decomposition is sugar. They are very unstable as a rule, decomposing easily when heated in water in the presence of a little acid or in the presence of certain kinds of ferments. The first glucoside to be definitely described as a typical substance of this class was amygdalin. Amygdalin is the bitter substance contained in bitter almonds, and it is decomposed when water is added to the bitter almond, the decomposition being effected through the action of the white fleshy substance of the almond, which is called emulsin or synaptase, which is a nitrogen compound acting as a ferment. As long as the bitter almond is dry, the amygdalin remains intact, but upon the addition of water, it all decomposes within twenty or thirty minutes, and then splits up into volatile oil of bitter almond, hydrocyanic acid and sugar. Amygdalin exists also in peach kernels, cherry seeds and a number of other seeds, which are therefore poisonous. They do not contain any poison, but they contain the glucoside amygdalin, which gives rise to the formation of the highly poisonous hydrocyanic acid as soon as wetted with water. No general description of glucosides beyond what little has already been mentioned can be made, because they are so miscellaneous in character. Some of them are soluble in water, but not in alcohol, while others are soluble in alcohol, but not in water. A large number of the glucosides are either poisonous or form poisons when decomposed. In fact, two-thirds of all poisonous plant drugs contain alkaloids, and the remaining one-third contain glucosides. THE CHEMICAL CONSTITUENTS OF PLANT DRUGS 309 Many of the glucosides contained in drugs have a decided action on the circulatory system, affecting the heart strongly. Tinctures and fluid extracts are made of drugs containing glucosides, but solid extracts are not made of all glucosidal drugs, because of the unstable character of the glucosides. 509. Alkaloids are chemical compounds containing carbon, hydrogen and nitrogen, or carbon, hydrogen, nitrogen and oxygen, having the power of neutralizing acids to form salts and of turning certain red vegetable colors blue. They are called alkaloids because they resemble the alkalies in the properties just mentioned. They are also called vegetable bases. When the alkaloids form salts with acids they act in the same manner as ammonia, in that the entire molecule of the alkaloid enters into combination with the entire molecule of the acid by a rearrangement of the atomic linking. When ammonia, H 3 N, reacts with hydrogen chloride, HC1, the compound formed is H 4 NC1, from which it will be seen that the hydrogen and the chlorine of the hydrogen chloride are separated from each other by the nitrogen of the ammonia. When ammonia reacts with nitric acid in ammonium nitrate, H 4 NN0 3 , it will also be seen that the nitrogen of the ammonia separates the hydrogen of the nitric acid from its N0 3 . Alkaloids and acids form salts in a similar way. For this reason alkaloids have sometimes been called compound ammonias. Alkaloids are always poisonous, and some of them are so potent that the customary dose may be less than the two- hundredth part of a grain. Examples of alkaloids are found in quinine, morphine, strychnine, cocaine and caffeine. It is true that quinine and caffeine and some other alkaloids are not generally looked upon as being poisonous, but if a considerable quantity be 310 A CORRESPONDENCE COURSE IN PHARMACY taken internally of either of them, alarming effects will undoubtedly be produced. From what has been said, it will be apparent that a very large number of our most important plant drugs contain alkaloids as their principal active constituents. The English names of alkaloids are in this country given the ending ine, and the corresponding Latinic titles in the pharmacopoeias have the ending ina. There are two classes of alkaloids — the ternary alkaloids and the quaternary alkaloids. The ternary alkaloids are called so because they contain only the three elements carbon, hydrogen and nitrogen. They are volatile, so that they can be distilled or vaporized without decomposition, have a strong odor and are generally liquid. The quaternary alkaloids are called so because they contain four elements, carbon, hydrogen, nitrogen and oxygen. These are solids. Very few of them can be vaporized without decomposition, and they have no odor. The volatile alkaloids are few in number in comparison with the solid alkaloids. The volatile alkaloids are soluble in water as well as in alcohol, and hence preparations of plant drugs containing volatile alkaloids may be made either with alcohol or water, or a mixture of the two. But the alkaloids containing oxygen usually require a strongly alcoholic menstruum, because they are rarely soluble in water. Alkaloids seldom occur in the plants and plant drugs uncombined with acids. They are usually found in com- bination with peculiar organic acids which, like the alkaloids themselves, are rarely found in more than one plant genus. The salts which the alkaloids form with the organic acids referred to are generally alcohol-soluble, and to a much less extent water-soluble. But the alkaloids can be extracted from the plant drugs and separated from all other substances and then converted into salts witli the ordinary acids. These salts are frequently freely water-soluble. From what has THE CHEMICAL CONSTITUENTS OF PLANT DRUGS 311 been said it will be understood that the alkaloids of plant drugs may be extracted with water to which has been added some acid forming a water-soluble salt with the particular alkaloid to be dissolved, or the drug may be mixed with an alkali which liberates the alkaloid from its natural salt, after which alcohol, ether, chloroform, petroleum spirit or some other suitable solvent for the free alkaloid may be used. But these are chemical methods of extracting alkaloids. The pharmaceutical method of extracting them consists in using an alcoholic menstruum which will extract the natural alkaloidal compound without chemical alteration. 510. The active principles of plant drugs belong to the classes described as tannins, bitters, volatile oils, resins, glucosides and alkaloids, and any plant drug containing no substance belonging to either of those classes is not likely to possess any medicinal value. The activity of any particular drug may be due to only one substance or it may be due to two or three or several substances. 511. The chemical constituents found in plant drugs are generally formed in the plant during its life, but several important valuable constituents of drugs are formed after the death of the plant, by chemical changes in the natural constituents. Opium, for instance, is a drug formed by drying the fluid that exudes from poppy capsules when full grown and just before they ripen, through incisions made in the capsules. No morphine or only traces of it or of any other alkaloids have been found in the poppy capsules, but the opium, when finished by drying the poppy juice in the sun, may contain over 20 per cent, of total alkaloids. Another illustration is furnished by the common drug called frangula, which, when just gathered, is a violent griping cathartic and even emetic, but which after having been kept for a year or two becomes a mild laxative, the cathartic substances being decomposed and giving place to decom- 312 A CORRESPONDENCE COURSE IN PHARMACY position products having a milder action. Some drugs are used in the fresh condition before the natural constituents undergo alteration, while other drugs are not used until after they have become modified by the chemical changes referred to. It is further to be understood that these chemical changes in the constituents of drugs continue through a long time, so that probably all plant drugs deteriorate when kept too long, and many of the plant drugs contain such unstable active principles that they cannot be preserved unaltered even for a few months. A fresh supply of an unstable plant drug can, of course, be obtained only once a year, and such drugs should accordingly be procured by the pharmacist at the right season, that is, immediately after the new crop comes into the market. Such drugs should be preserved with the greatest care. Very few drugs are comparatively permanent, so that they remain in good condition as long as two years. Test Questions 1. What is a carbohydrate ? 2. Which of the class of carbohydrates are water-soluble ? 3. What is exosmosis ? 4. What advantage can be taken of dialyzation in the extraction of the constituents of drugs ? 5. Which of the several classes of chemical constituents of drugs are dialyzable ? 6. Name a solvent for starch in its normal condition. 7. What is meant in pharmacy by the expression * 'altered starch"? 8. What kinds of drugs are employed for making demulcent decoctions and what drugs for mucilaginous infusions ? THE CHEMICAL CONSTITUENTS OF PLANT DRUGS 313 9. Name some substances containing normal starch and some other substances containing altered starch. 10. What kind of a menstruum can be used on plant drugs which will not extract carbohydrates ? 11. What is the cause of gelatinization in certain liquid pharmaceutical preparations ? 12. What is a gum ? 13. Name all of the gums you can think of. 14. What is the difference between arabin and bassorin ? 15. Can you name some gums soluble in alcohol ? 16. If you have a liquid extract containing mucilage in solution, how can you remove that mucilage from the liquid ? 17. What are the pharmaceutical uses of the official gums ? 18. In what parts of plants is physiological mucilage usually found ? 19. In view of the fact that mucilage ferments so easily, how can drugs containing mucilage be preserved ? 20. In what manner does sugar act as a preservative of water-solutions of fermentable substances ? 21. What are the pharmaceutical uses of sugar? 22. What proportion of alcohol must be contained in a solution of fermentable matter in order to prevent fer- mentation ? 23. Mention some plant constituents contained in aqueous liquid extracts which are not contained in alcoholic liquid extracts. 24. Name some plant constituents contained in alcoholic liquid extracts which are not contained in aqueous extracts. 25. Name some plant constituents which are soluble both in water and in alcohol. 26. At what temperature does starch become pasty in water ? 27. At what temperature does albumin coagulate ? 28. Which kind of a liquid extract contains the most 314 A CORRESPONDENCE COURSE IN PHARMACY albumin, a liquid extract -made with cold water or with boiling water or with alcohol ? 29. Which preparation contains the most starch, one made with cold water, boiling water or alcohol ? 30. Can albumin in solution be separated from a liquid extract ? If so, how ? 31. What is glyceryl hydroxide commonly called ? 32. Can you mention any other common glyceryl com- pounds ? 33. What is hard soap and what is soft soap ? 34. Name the most common fat-acids. 35. What is the chemical composition of olive oil, lard, tallow and cottonseed oil ? 36. What is stearin ? 37. What are the principal physical differences between olein, palmitin and stearin ? 38. What liquid pharmaceutical preparations are most liable to contain fixed oils, those made with water, with diluted alcohol, with strong alcohol or with ether ? 39. What are the pharmaceutical and medicinal uses of fixed oils ? 40. What parts of plants contain fixed oil more frequently than other plant parts ? 41. Can a solid extract be made from a plant drug con- taining fixed oil without obtaining a product mixed with grease ? If so, how ? 42. What are the best solvents for fixed oils ? 43. What is tannin ? 44. What are its most characteristic properties ? 45. Name three different solvents for tannin. 46. What is the most notable difference between physio- logical tannin and pathological tannin ? 47. What kinds of fluid extracts and tinctures are most liable to contain precipitates formed on standing ? THE CHEMICAL CONSTITUENTS OF PLANT DEUGS 315 48. What is meant by an amarum ? 49. What menstruum is commonly employed in making tinctures of drugs containing amara ? 50. What menstruum is commonly employed in making fluid extracts of drugs containing volatile oils ? 51. What menstruum is commonly employed in making fluid extracts of drugs containing tannin ? 52. Enumerate the differences you can think of between volatile oils and fixed oils. 53. How would you make a solid extract of a drug con- taining volatile oil as its only active constituent ? 54. What are the most common constituents of volatile oils ? 55. Do you think you can discover tannin in a plant drug without a chemical examination of it ? 56. Do you think you can discover volatile oil in a plant drug without separating the volatile oil or detecting it by chemical means ? 57. What is the difference between a carbohydrate and a hydrocarbon ? 58. What volatile oils have the strongest odors? 59. What is the general physiological and therapeutic action of volatile oils ? 60. What volatile oils produce a grease spot on clean white unsized paper ? 61. What are the best solvents for volatile oils ? 62. What are volatile oils liable to contain besides hydro- carbons and camphors ? 63. What are the constituents contained in aromatic astringents ; in astringent bitters ; in aromatic bitters ? 64. By what means can you detect alcohol in a volatile oil adulterated with that liquid ? 65. What are the solutions of volatile oils in water called ? 316 A CORRESPONDENCE COURSE IN PHARMACY 66. Why are resins usually found together with volatile oils in plants ? 67. What are the differences between gums and resins ? 68. What are the pharmaceutical uses of inert resins ? 69. What are the medicinal effects most common in resins and resin compounds ? Why does potash lye dissolve resin ? 70. Bitter almond is the source of expressed oil of almond, as well as of volatile oil of bitter almond and amygdalin. The amygdalin is soluble both in hot alcohol and in water. W r hat is the best way to extract the amygdalin from the bitter almond ? What is amygdalin ? 71. How can you separate the fixed oil of bitter almond without having that fixed oil contaminated with amygdalin ? 72. How can you make volatile oil of bitter almond and subsequently also amygdalin out of the same lot of bitter almonds ? 73. What are usually the active constituents of poisonous plant drugs ? What makes peach kernels poisonous ? 74. What differences can you mention in the chemical properties of glucosides and alkaloids ? 75. Give the origin of the words glucoside and alkaloid. 76. In what respects do the alkaloids resemble ammonia? 77. What is the difference between a ternary alkaloid and a quaternary alkaloid ? 78. Are any alkaloids in the free state water-soluble ? 79. What class of alkaloids are alcohol-soluble ? 80. What are the best solvents for making liquid extracts of alkaloidal drugs ? 81. What are the most common chemical processes of extraction of alkaloids from drugs ? 82. In what form do the alkaloids usually occur in plant drugs ? How long should plant drugs be kept before they are used ? LESSON TWENTY XXIX Pharmaceutical Preparations -512. The materials out of which pharmaceutical prepara- tions are made may be definite chemical compounds or simple elements, or they may be mixtures of two or more substances. Chemical preparations are those made by processes result- ing in the formation of new substances, or, in other words, processes involving chemical reactions. Galenical preparations are preparations made by processes not involving any chemical changes. The Galenical prepara- tions may be simply mechanical mixtures of the ingredients, or they may be solutions or extracts. Organic drugs are of such a complex character that their pharmacy is much less simple than that of definite chemical compounds. The Galenical preparations of plant drugs generally take the form of liquid or solid extracts, the object being to present the medicinal constituents of the drug in the most concentrated and convenient form. 513. The classification of pharmaceutical preparations may be based upon various considerations. Probably the most practical and convenient classification is the following: 1. Dry and semi-solid preparations for internal use, made by processes not involving extraction. These preparations include species, powders, triturations, confections and electu- aries, masses, troches and pills. 317 318 A CORRESPONDENCE COURSE IN PHARMACY 2. Dry and semi-solid preparations for external use, includ- ing poultices, ointments, cerates, plasters and suppositories. 3. Liquid preparations for internal use, not made by proc- esses of extraction, including solutions, waters, mucilages, syrups, glycerites, mixtures, emulsions and spirits. 4. Liquid preparations for external use, including lotions, gargles, injections, liniments, etc. 5. Liquid extracts, including infusions, decoctions, vine- gars, tinctures, wines and fluid extracts. 6. Solid and semi-solid preparations made by processes of extraction, including solid -extracts, oleoresins and pre- cipitated resins. XXX Solid Preparations Not Made by Extraction 514. Species are teas made of mixed plant drugs, very coarsely cut or crushed. Such preparations are not common in America. Breast teas, laxative teas, bitters and stimu- lant teas are among the most common. 515. Powders. Compound powders are made by triturat- ing together two or more substances, so as to obtain a prod- uct in the pulverulent form. If the ingredients can be each in fine powder before being mixed, the process is very simple. But when one of the substances is a liquid or moist solid, it must be triturated with one or another of the dry ingredients in order to reduce it to a state of powder. When there is not a sufficient quantity of dry substance, it may be necessary after making the mixture to subject it to a drying process before finishing the pulverization. If the ingredients are nearly equal proportions, they may be mixed all at once, but if one ingredient is to be used in very small quantity and the other is several times as bulky, the ingredients used in large proportion should be divided and an intimate mixture SOLID PREPARATIONS NOT MADE BY EXTRACTION 319 made after adding each consecutive portion to the other ingre- dient before the next portion is added. When one or more of the ingredients are of such character as to adhere to the mortar and pestle when triturated under pressure, the trituration should be effected with as little force as possible. When the ingredients are such as have a tendency to act upon each other chemically, they should also be mixed lightly or without pressure, in order to avoid the chemical reaction as far as practicable. When potent substances are to be diluted in the form of powder, the diluents employed may be cane sugar, milk sugar, starch, acacia, tragacanth, marshmallow root, or other inert powders. 516. Triturations are powders made out of potent remedies with nine times their weight of milk sugar. 517. Confections and electuaries are soft solid mixtures, made by mixing powders or solid extracts, or both, with syrup or honey. These preparations are intended to be sufficiently sweetened so that they may be taken without difficulty. Very few such preparations are now used. 518. Masses. Confections and electuaries are, of course, masses, but the title massa used in the pharmacopoeia means a mass of such consistency that pills can be made out of it. The manner in which ingredients are massed for making pills and troches will be described later. 519. Troches or lozenges or tablets are hard, dry pieces of medicinal substances weighing from two or three grains up to thirty grains. They contain either a large amount of sugar or in its place a sufficient quantity of extract of licorice to make them less disagreeable to the taste than the unsweet- ened medicinal agents usually are. In the preparation of troches, etc., the ingredients are, if possible, first reduced to a uniform mixture in the state of powder. A moist excipient is then added to mass the powder together, or to make it cohere so as to form a well-mixed mass which can be rolled 320 A CORRESPONDENCE COURSE IN PHARMACY out into a cake of uniform thickness, out of which the tablets or troches are cut by means of a lozenge-cutter. The troches are most commonly circular disks, but they may be oblong, octagonal and of various other forms. They are usually dried so as to become hard, unless they contain extract of licorice, in which case they are not always entirely dry. Troches are often flavored with volatile oils or with aromatic waters. 520. Pills are small masses of mixed medicinal agents, usually of spherical form or oval, weighing from one grain to five grains, or from sixty to three hun- dred milligrams. In making pills, the ingredients are mixed uniformly in the same manner as medicinal substances are mixed in mak- ing compound powders, confections, sectional view of masses and troches, and the massing is A PILL MORTAR 1 ° accomplished in such a way that the pills when formed out of the mass may be sufficiently firm to retain their shape. The pills when finished should be either entirely soluble in the fluids of the stomach or they should contain enough soluble matter to become disintegrated when wetted. Pills which are very hard and almost insoluble are use- less, and the pharmacist must choose his excipients for pill- masses in such a way as to avoid the formation of insoluble pills. 521. The excipients employed in making pill-masses include both solids and liquids. If. the other ingredients make a soft mass, it is, of course, necessary to add a dry excipient to give the mass the right consistence. While the mass should be somewhat plastic in order that it may be comparatively easy to form it into perfectly round pills, it is also necessary that the mass shall be sufficiently cohesive SOLID PREPARATIONS NOT MADE BY EXTRACTION 321 and firm so that the pills may not flatten after they have been finished. To stiffen a soft mass, the following dry excipients will be found most useful: Powdered slippery elm lark is useful, because it is highly absorbent and fibrous and contains very little soluble matter. Poivdered licorice root and powdered altlma are also fibrous and absorbent, but less useful than the slippery elm bark, because they contain considerable amounts of soluble constituents. Starch may also be used to stiffen pill-masses, but it is not absorbent and hence somewhat larger quantities must be employed of starch than are necessary of such a substance as slippery elm bark. Magnesium carbonate is an entirely insoluble but absorbent substance that can be used to advantage in soft pill-masses containing volatile oils or oleoresins. None of the dry substances so far mentioned are adhesive. The adhesive dry excipients most suitable for making pill- masses are powdered tragacanth and powdered extract of licorice, but tragacanth Ms so far superior to all other dry substances rendered adhesive when moistened that it is almost invariably used. Very small amounts of traga- canth are usually sufficient to render a pill-mass cohesive, when the mass contains enough moisture to develop the adhesive quality of the tragacanth. Tragacanth acts slowly, so that the operator should add it very gradually and take time to observe the results before adding any more. A pill- mass that is but very slightly too soft can generally be rendered firm by the addition of a very small amount of tragacanth. When acacia enters into pill-masses and the quantity used is considerable, the result is usually a mass that becomes very hard on drying. Milk sugar is sometimes introduced into pill-masses to give 322 A CORRESPONDENCE COURSE IN PHARMACY bulk to them or to dilute some very potent substance, but it is not enrployed to stiffen soft masses. The wet or moist excipients most common are water, alcohol, glycerin, glucose, syrup and mucilage of tragacanth. When the dry ingredients of a pill-mass contain any sub- stance which becomes adhesive as soon as moistened with its appropriate solvent, then the addition of that solvent is generally sufficient to mass the whole mixture. Extractive matter when moistened is always adhesive. Hence, when the extractive is water-soluble, the addition of a little water will suffice to form the mass, or if the extract is alcohol- soluble, we may add alcohol or diluted alcohol, instead of water, to develop sufficient adhesiveness to make the mass cohesive. Glycerin is added in pill-masses solely to prevent them from becoming too dry and hard. When too small an amount of glycerin is added and the mass contains water, the water and glycerin evaporate together, and the pill may after all become hard. But a mixture of equal parts of water and glycerin or of two parts of water and one part of glycerin may be advantageously employed, because when the water evaporates enough glycerin will remain to keep the pills from becoming too hard. Glucose-syrup is so sticky that it is employed in cases where the ingredients of the mass are of such a nature as to form crumbly masses with less adhesive excipients. The student will understand that moist ingredients require dry excipients, and dry ingredients require moist excipients, and that adhesive materials require only non-adhesive excip- ients, while non-adhesive materials require adhesive ex- cipients. 522. Pills should never be less than one grain in tveight. If the materials ordered in a prescription are insufficient to give each pill the requisite weight, inert excipients are added SOLID PREPARATIONS NOT MADE BY EXTRACTION 323 to increase the mass so that each pill will weigh at least one grain. Pills of the size of from two to three grains are more readily swallowed than either smaller or larger ones. It occasionally happens that a presciiber inadvertently orders pills too large to be conveniently taken. In such cases, the pharmacist should consult the prescriber and obtain permission to divide the mass into twice as many pills or even three times as many, in order to obviate the difficulty. Pills weighing only one grain are generally called granules. Pills coated with sugar or various kinds of gelatin coating are now manufactured on a large scale, and all the pills commonly prescribed can be had already prepared and coated. The coatings should either be completely soluble in tepid water or should at least become disintegrated, and the pill- mass itself should also be either soluble or should fall apart when put in tepid water. 523. Cataplasms, or poultices, are not often prepared by the pharmacist. The most common cataplasms are flaxseed poultices and mustard plasters. Flaxseed poultice is made by first mixing the ground flaxseed with a little cold water, mixing well so as to break up all lumps, then adding the requisite amount of boiling water and heating the mixture until the starch in the flaxseed becomes sufficiently pasty so that the resulting cataplasm has the right consistence. Mustard plaster is best made by mixing the ground mustard by trituration with tepid water. The water causes the formation of the irritant volatile oil which renders the mustard plaster, effective as a rubefacient. If it is desired to make the mustard plaster milder in its action, the ground mustard is diluted with white flour, corn meal, or ground flaxseed before being made into a cataplasm, or a cataplasm of pure ground mustard and tepid water is mixed with a 324 A CORRESPONDENCE COURSE IN PHARMACY separately prepared poultice of flaxseed or corn meal. In making a mustard plaster, boiling water should never be used, because it coagulates one of the constituents of the mustard which causes the formation of the volatile oil, and moreover causes the volatile oil to vaporize and be lost. Neither should alcohol be used in making mustard plaster, because that, too, coagulates the ferment which causes the formation of the valuable volatile oil. 524. Ointments. Ointments are soft solids intended to be applied externally for the purpose of causing the absorption of certain medicinal agents through the skin, or to soften the skin or protect it, or as a soothing and healing appli- cation to denuded surfaces, etc. They are usually made of fatty substances, but they may also be prepared out of soft soap or of glycerite of starch or soft paraffins. The most common ointment bases are lard, the so-called simple ointment made out of lard and wax, lanolin or sheep's wool fat, petrolatum and glycerite of starch. Ointments may be divided into two classes, according to their medicinal application; namely, perfectly Hand oint- ments^ containing no active medicinal agent, and medicated ointments. The simple ointment of the pharmacopoeia is a mixture of four parts of lard and one part of yellow wax, melted together, and the melted mixture stirred until it congeals. When fats of low melting point are mixed with fats of high melting point, such as wax and spermaceti, the whole mixture must be stirred during the process of cooling to prevent the separation of the fat of higher fusing point. The stirring not only prevents that separation, but it also makes the ointment bulkier and softer and lighter in color. At the same time the process of stirring undoubtedly intro- duces air into the finished product, and the presence of air detracts from the keeping qualities of the preparation. SOLID PREPARATIONS NOT MADE BY EXTRACTION" 325 Ointments made by fusion sometimes contain resins added to the fats, and liquid fixed oils are also employed in making certain ointments. The fusing point of a finished ointment is intended to be very nearly that of the temperature of the body. 525. Medicated ointments are usually mixtures made out of the bland ointments with the finely powdered or semi-fluid medicinal agents. Solid extracts to be thoroughly incor- porated in ointments must first be rendered semi-fluid by trituration with water or diluted alcohol, after which they can be easily mixed with the fatty base or any other soft ointment base. Solid substances that cannot be reduced to a semi-fluid condition must be in the form of impalpable powder, which is first mixed with a small portion of the ointment base, the remainder of which is afterwards added gradually, and trituration is continued until the mixture is perfectly uniform. When an ointment is well made, a small amount of it spread very thinly on a piece of white paper with the spatula will show no lack of uniformity, no lumps or streaks. A good ointment feels perfectly smooth when rubbed between the fingers. One of the essentials in the preparation of good ointments is the employment of perfect materials. Lard and other fats are so liable to become rancid and irritating that only perfectly fresh lard or fat can be used. Eancid lard applied is much more likely to cause inflam- mation than to be soothing in its action. When soft soap is used in ointments, no fat is used with it, but sometimes it is necessary to add a little hot water to give the ointment the proper soft consistence. Glycerite of starch has the advantage of being water- soluble, so that an ointment made with that base is easily 326 A CORRESPONDENCE COURSE IN PHARMACY washed off with tepid water and, moreover, glycerite of starch does not become rancid or change in any other unfavorable manner. / Petrolatum keeps a long time without alteration, but it is far less suitable for the preparation of ointments than animal fats, because petrolatum does not soften and penetrate the skin, but is suitable only for local dressings. When watery liquids are to be introduced into ointments, lanolin is very useful as an addition to the preparation, because very large quantities of water can be mixed with lanolin and the mixture is sufficiently firm; in fact, when water is added to lanolin, the mixture becomes more and more firm until as much water has been added as the lanolin can hold. Glycerin, also, when added to lanolin makes it stiffer instead of softer. 526. Cerates are altogether like the ointments, with the exception that they have a higher melting point and are somewhat firmer. The simple cerate of the pharmacopoeia is a mixture of seven parts of lard and three parts of white wax, mixed together by fusion. Other cerates contain, in addition, resin. Cerates are used mainly as dressings. They may be medicated in the same manner as ointments. 527. Plasters are still firmer external preparations, intended to be applied to circumscribed areas of the body. Plasters are made of metallic oleates, resins, gum-resins and wax. The most common simple plaster is called lead plaster, which consists of a mixture of oleate of lead and stearate of lead. This is made by boiling lead oxide and olive oil together, adding a small quantity of water. The water changes the lead oxide to lead hydroxide, which reacts with the oleate and stearate of glyceryl so that lead oleate and lead stearate are formed, together with glyceryl hydroxide or glycerin The glycerin is then washed out of the finished SOLID PREPARATIONS NOT MADE BY EXTRACTION 327 plaster mass, and the latter is rolled into sticks ready for use in the preparation of medicated and adhesive plasters. Lead plaster is too hard and non-adhesive to be used alone. To render it adhesive, resins are added, the lead plaster and resin being melted together and the mix- ture stirred until cold. Wax is also added to adhesive plaster. When gum-resins are introduced into plasters, the best plan is to emulsionize the gum-resin by beating it up with diluted acetic acid until converted into a thick, uniform liquid, free from lumps. This liquid, strained, is then added to the melted plaster and the whole mixture kept warm and liquid, stirring it constantly until the diluted acetic acid has evaporated, so that the plaster becomes sufficiently firm on cooling. When soap is introduced into plasters, the soap is preferably mixed with hot water first, and the uniform soft soap mixture is then added to the plaster and the plaster-mass kept hot until the water added has been evaporated. •When solid extracts are added to plasters, the extracts must first be rendered semi-fluid by trituration with water or diluted alcohol, after which they can be added to the melted plaster, which is kept at a temperature barely sufficient to keep it fluid to permit of the requisite stirring. Plasters made by fusion are always stirred constantly during the process of cooling, until they become so firm that further stirring is impossible. This is to insure uniformity of composition. When volatile substances like camphor or menthol are introduced into plasters, the plaster is first melted and then allowed to cool until barely fluid before the volatile sub- stance is added, after which the mass is diligently stirred and cooled as rapidly as possible, to prevent the loss of any portion of the volatile medicament. 328 A CORRESPONDENCE COURSE IN PHARMACY 528. Suppositories are solid bodies with or without active medicinal ingredients, and they are intended to be intro- duced into cavities of the body for the purpose of local medi- cation. They are usually made of oil of theobroma, or cacao butter. This substance is peculiarly useful for this purpose, because it is a solid fat which does not soften gradually with an increase of temperature, but remains firm up to very nearly the temperature at which it suddenly liquefies. When suppositories are ordered to be made with oil of theobroma as the base, the operation is somewhat difficult, because the oil of theobroma liquefies so readily when handled, its melting point being about the temperature of the body. From the nature of the substance, it will be readily understood that it is likely to be either too hard or too soft to be easily formed into cones or globular bodies, such as constitute ■ the so-called suppositories. But no addition must be made to the oil of theobroma to lower its fusing point or increase it, because the superiority of oil of theobroma over all fatty bases that can be used for making suppositories depends upon its property of suddenly liquefy- ing at the right temperature. Suppositories are made to weigh from one to four grams or from fifteen to sixty grains, according to their uses. Bougies are long, slender pencils made out of materials similar to those employed in making suppositories, and are also employed for local medication of cavities and passages. Medicaments to be added to suppositories and bougies should, of course, be in a semi-fluid condition before they are incorporated with the base, or they should be in the form of impalpable powders. The mass for making suppositories may be mixed on a board with the spatula, or it may be made in a mortar with the pestle, or the oil of theobroma may be melted in a por- celain dish and the medicaments added to the melted base, SOLID PREPARATIONS NOT MADE BY EXTRACTION 329 the mixture being stirred until it congeals, or stirred until barely fluid enough to be poured into suitable molds. 529. Suppositories are formed either by hand or by mold- ing them in special molds. To make suppositories oy hand, the oil of theobroma may be cut into thin shavings with the spatula and the shavings worked with the spatula on the board until sufficiently soft and plastic and free from lumps, after which the medicaments can be easily incorporated, the mass scraped together, rolled out in a cylinder, and the cylinder cut into the requisite lengths, according to a scale prepared for the purpose. Rectal suppositories are usually about one inch in length and three-eighths of an inch in diameter at the base, while the apex is bluntly pointed, the shape being nearly conical. In fashioning suppositories in this manner, the mass should come in contact only with the board and spatula ; if the mass is touched with the fingers, it is apt to become smeary so that it cannot be formed at all. To prevent the mass from sticking to the board and spatula, a very small amount of lycopodium is dusted on the board, and the mass rolled on the dusted surfaced Molds are made in such a way at present that the mass can be pushed from a cylinder by, means of a piston into molds of any shape or size. These suppository machines can be used with a cold mass, and are the best because when the mass is not melted there can be no separation of the ingre- dients from one another. Molds intended to be used with a melted mass are much more difficult to manage. If the medicaments are not soluble in the melted oil of theobroma and especially if they are solid and heavy, they sink to the bottom of the melted oil and it is difficult even with constant stirring to keep the mixture uniform. Separation cannot be prevented when the stirring ceases and the mixture is poured into the molds. All that can be done is to stir the mixture 330 A CORRESPONDENCE COURSE IN PHARMACY and allow it to cool off until barely fluid enough to be poured, and to have the molds so well chilled with ice that the mixture congeals rapidly when the molds have been filled. But there is another difficulty attending this operation. If the mold contracts at the low temperature more readily than the contents, and if the congealed mass does not contract in the same ratio, the suppository will be held so firmly in the mold that it cannot be removed, but will be broken in the attempt to extract it. Test Questions 1. What is meant by a Galenical preparation ? 2. By what methods are Galenical preparations made, as distinguished from the methods by which other preparations are made ? . • • 3. What is the difference between an organic preparation and an inorganic preparation ? 4. How would you mix one milligram of strychnine with one gram of sugar ? 5. How would you mix one ounce of opium, one ounce of ipecac and eight ounces of milk sugar ? 6. How would you mix five grains of a tough, moist extract with sixty grains of sugar ? 7. How would you mix ten grains of a moist, tough extract with ten grains of sugar, the mixture to be divided into ten- powders ? 8. How would you make a compound powder consisting of two chemical compounds ? What precautions are neces- sary to prevent any chemical changes of the ingredients ? 9. How much morphine is contained in one and one-half grain of trituration of morphine ? 10. What are the usual ingredients of medicinal con- fections ? SOLID PREPARATIONS NOT MADE BY EXTRACTION 331 11. What ingredients are common to all kinds of troches ? 12. What is an excipient ? 13. If a pill-mass is to be made containing four medicinal ingredients, two of which are powders, one a tough, moist solid, and the third a volatile oil, how would you make the mass? 14. What would you add to a solid extract of the con- sistence of thick honey to make a pill-mass of it ? 15. What are the chief differences between acacia and tragacanth as excipients in pill-masses ? 16. Which takes the longer time — to stiffen a pill-mass with powdered slippery elm or to stiffen it with starch ? 17. What are the essential characteristics of a good pill- mass ? 18. When is water used as an excipient in pill-masses ? 19. W^hen is alcohol a better excipient than water ? 20. Name two of the stickiest moist excipients. 21. Name one of the best absorbent fibrous excipients and one of the best absorbent inorganic excipients. 22. What is a granule ? 23. What would you do when a prescription calls for pills and the ingredients prescribed for each pill weigh ten milligrams ? 24. What is the proper way to make a flaxseed poultice ? 25. What is the proper way to make a mustard plaster ? 26. How would you make suppositories of oil of theobroma? 27. What is simple ointment ? 28. How does simple ointment differ from simple cerate ? 29. How would you make an ointment of tar and tallow ? 30. How would you make an ointment of cottonseed oil and hard paraffin ? 31. What are the principal differences between lard and vaseline as ingredients of ointments ? 332 A CORRESPONDENCE COURSE IN PHARMACY 32. How would you make an ointment of resin, wax and lard ? 33. How would you mix lard with a solid extract ? 34. How would you test or examine an ointment to see whether or not it is well mixed ? 35. What are the advantages of petrolatum over lard as an ointment base ? 36. What are ointments used for and what are cerates used for ? 37. What is lead plaster ? 38. What is adhesive plaster ? 39. How would you make a plaster of extract of henbane ? 40. How would you mix adhesive plaster, camphor, olive oil and oil of lavender to make an ointment ? 41. What are suppositories ? 42. Why do the pharmacopoeias generally order oil of theobroma as the chief material out of which suppositories should be made ? 43. How would you make suppositories of extract of stramonium ? 44. How would you make suppositories of camphor ? 45. How would you make suppositories containing lead iodide? * LESSON TWENTY-ONE XXXI Liquid Preparations Not Made by Processes of Extraction 530. Water-solutions of inorganic chemical compounds are to be found in all pharmacopoeias. In the American pharmacopoeia they are called solutions, in English, and are given the title liquor in the Latinic nomenclature. The definition of the title liquor most frequently given in text-books is "a water-solution of a non-volatile substance," but mucilages, syrups, infusions and decoctions are also water-solutions of non-volatile substances. Among the "liquores" of our pharmacopoeia there are not now any prep- arations other than water-solutions of non-volatile inorganic chemical compounds, so that this group of preparations is at present well defined. Some of the official liquores are used only as materials out of which other preparations are made, but most of them are intended for medicinal use, external or internal. The waters or aquae of the pharmacopoeia are commonly defined as " water-solutions of volatile substances, "but while it is true that all of the preparations given the title "aqua" in the American pharmacopoeia are really water- solutions of volatile substances, it is equally true that there are other water-solutions of volatile substances not called by that title, as, for instance, several of the acids. 531. A great majority of the aquse are water-solutions of 333 334 A CORRESPONDENCE COURSE IN PHARMACY volatile oils, and a scientific classification of the pharma- ceutical preparations would seem to require that the aromatic waters should be made to constitute a class by themselves and should not be grouped together with such solutions as ammonia water, chlorine water and solution of hydrogen dioxide, which are chemical preparations. The aromatic waters are nearly or quite saturated solutions of volatile oil, made by triturating the volatile oil with talcum or with calcium phosphate and then with water, after which the mixture is filtered, two cubic centimeters of volatile oil being generally used to prepare 1000 cubic centimeters of the finished product. But rose water and orange flower water are made by distillation, and bitter almond water is made by dissolving the volatile oil of bitter almond in the water without the aid of trituration with calcium phosphate. Chloroform water is prepared by adding enough chloroform to a convenient quantity of distilled water to maintain an excess of chloroform at the bottom of the bottle, so that when the contents are thoroughly shaken together, the excess of chloroform will sink to the bottom of the bottle and the saturated solution standing over the undissolved chloroform is poured off as required. The aromatic waters are employed chiefly as flavoring agents or as vehicles for more important substances. 532. Mucilages are water-solutions of vegetable mucilage. The mucilage of acacia of the pharmacopoeia is made by dissolving 340 grams of acacia in small fragments in enough water to make the finished solution weigh 1000 grams. The acacia is first washed with cold water to remove dust, and then dissolved in the necessary amount of water to form the preparation, which must be kept in completely filled bottles in a cool place, in order to prevent fermentation. Mucilage of tragacanth is prepared by mixing G parts of LIQUID PREPARATIONS NOT MADE BY EXTRACTION 335 tragacanth with a mixture of 18 parts of glycerin and 75 parts of water, and letting the mixture stand twenty-four hours, stirring occasionally. The glycerin and water are first mixed and the mixture heated to boiling, after which the tragacanth is added. After twenty-four hours, the mix- ture is beaten until of uniform consistence and enough water is added to make the whole product weigh 100 grams, and the thick mucilage is forcibly strained through muslin. This mucilage, too, is likely to undergo fermentation and should therefore be prepared in quantities so small that they will be consumed in a short time. Mucilage of slippery elm bark is made by digesting bruised slippery elm in water over a water bath for one hour, after which the liquid is strained. Mucilage of sassafras pith is made by macerating sassafras pith with the prescribed quan- tity of water for three hours. All mucilages are liable to undergo fermentation and hence cannot be kept in stock more than a few days. 533. Syrups are water-solutions of medicinal substances, sweetened with considerable quantities of sugar. The "syrupus," or simple syrup of the pharmacopoeia, is a water-solution of sugar made by dissolving 850 grams of coarsely powdered sugar in enough water to make the finished solution measure 1000 cubic centimeters. The sugar is either dissolved with the aid of heat and the solution raised to the boiling point, after which it is strained, or the sugar is dissolved by percolating water through it in an ordinary percolator. Simple syrup has a specific weight of about 1.317, and is an almost saturated solution at ordinary temperatures, so that it crystallizes if placed in a cold room. Several of the medicated syrups of the pharmacopoeia contain inorganic chemical compounds, as, for instance, syrup of hydriodic acid, syrup of calcium lactophosphate and syrup of ferrous iodide. Other medicated syrups of the 336 A CORRESPONDENCE COURSE IN PHARMACY pharmacopoeia contain organic medicinal substances, usually added in the form of fluid extracts. Several of the pharmacopceial syrups are used as flavoring ingredients or agreeable additions to mixtures. The presence of considerable quantities of inorganic chemical compounds in syrups tends to preserve them, so that such syrups may be made with a smaller quantity of sugar than is necessary to preserve syrups containing fer- mentable organic matter. 534. Glycerites are solutions of pharmaceutical and medicinal substances in glycerin. Glycerin solutions are more permanent than water-solutions of the same substances. Medicated glycerites are few in number, and those contained in the pharmacopoeia are the glycerites of carbolic acid, tannic acid, boroglycerin and hydrastis. The glycerite of starch is a thick, translucent, jelly-like preparation made out of 1 part of starch, 1 part of water and 8 parts of glycerin, heated together at the temperature of from 140° to 144° 0. It is used mostly as an ointment base. The glycerite of yolk of egg, sometimes called glyconin, is a mixture of yolk of egg and glycerin, intended to be used in preparing emulsion-like mixtures, the yolk of egg acting as an emulsifying agent. 535. Emulsions are liquid mixtures containing insoluble substances in a fine state of division, suspended uniformly throughout the whole liquid. The undissolved, finely divided substances may be volatile oils, fixed oils, oleoresins, resins, gum-resins or inorganic powders. Emulsions may be classified as follows: Seed emulsions, gum-resin emulsions, emulsions of fixed oils, emulsions of volatile oil and oleoresins, quasi-emulsions of inorganic powders. 536. Emulsions of seeds are formed when the seeds are beaten and thoroughly triturated with water, because all LIQUID PREPARATIONS NOT MADE BY EXTRACTION 337 seeds contain fixed oils, and they usually contain emulsin, which acts as an emulsifying agent. The only very common seed emulsion is the emulsion of almond, which is prepared as follows : Sweet almonds are blanched by first placing them in tepid water for a few minutes to loosen the seed-coat, which is then easily removed. The seed-coat of almonds can also be loosened by putting the almonds in cold water, but it takes much longer time. Boiling water should never be used, because it unfavora- bly affects the result, since the emulsin of the almond is coagulated by temperatures exceeding 60° 0. The blanched almonds are put in the emulsion mortar and beaten to a coarse powder. Sugar and acacia, previously mixed in the proportions ordered by the pharmacopoeia, are then added and mixed with the coarsely crushed almond. Enough water is then added and the whole mixture beaten into a smooth pulp or paste, free from lumps. More water is gradually added and the mixture triturated thoroughly until finally all the water to be used has been added, after which the emulsion is strained and is then finished. Sweet almond beaten up with water will form an emulsion without the addition of acacia and sugar, but such an emulsion of almond is thin and poor. The amount of fixed oil contained in the almond is so great and the emulsin in the almond is so insufficient as an emulsifying agent, that in order to get a rich emulsion it is necessary to add acacia, which is one of the most effective emulsifying agents we have. Sugar is added to sweeten the preparation. Emulsion of almond is used sometimes as a ' 'placebo," by which is meant a pharmaceutical preparation ordered by physicians in cases where no active medicinal agent is necessary, the ailment of the patient being one of imagina- tion. Emulsion of almond may also be used as a pleasant vehicle for medicinal substances of not too decided flavor. 338 A CORRESPONDENCE COURSE IN PHARMACY A preparation called liydrocyanated emulsion is used in several countries of Northern Europe, and occasionally in other countries. This preparation when ordered by a physician is usually prescribed in heroic doses and in cases where life or death depends upon prompt administration of the preparation. Hence, hydrocyanated emulsion must be dispensed by the pharmacist with the least possible delay. It is a mixture of emulsion of sweet almonds with a certain quantity of amygdalin. In order to avoid unnecessary delay, the emulsion of sweet almond required for the preparation of hydrocyanated emulsion is made without first blanching the almonds. 537. Gum-resin emulsions are formed when gum-resins are triturated with water. Two such emulsions are contained in the pharmacopoeia — emulsion of asafetida and emulsion of ammoniac. The gum-resin must be clean, and to that end should consist of selected pieces. These are crushed in the mortar, reduced to coarse powder and then beaten with a small amount of water until a perfectly smooth pasty pulp is obtained, free from lumps. More water is gradually added and the trituration continued until all of the water pre- scribed has been used. The mixture is then strained, and if the work has been well done there should be little if any residue left on the strainer. 538. Emulsions of fixed oils, volatile oils and oleoresins are made with acacia, according to the so-called "Hager's rules." Hager's rule fixing the proportions of the materials required to make emulsions of fixed oils is as follows: Take 4 parts of fixed oil, 2 parts of acacia in powder and 3 parts of water of emulsification. For emulsions of volatile oils and oleoresins, Hager's rule is: Take equal parts, by weight, of the volatile oil or oleoresin, powdered acacia and water of emulsification. LIQUID PREPARATIONS NOT MADE BY EXTRACTION 339 The manipulations are as follows : Mix the oil thoroughly with the powdered acacia, then add the "water of emulsifi- cation" all at once, and immediately stir the mixture with the pestle in the mortar as rapidly as possible, until the mixture becomes as light colored as it can be made, thickens and crackles under the pestle, and the globules of oil or oleoresin entirely disappear. The emulsification is then finished. If any additional water is ordered to be added, it must be gradually added after the completion of the emul- sification, and finally the emulsion is thoroughly shaken in a bottle. Another method is to mix the powdered acacia and water first, which requires considerable dexterity and rapidity of motion, to avoid the formation of lumps. When a uniform mixture of the acacia and water has been made, the oil or oleoresin is then added, a little at a time, and the emulsifica- tion of each portion completed before another portion is added. A third method is to put the powdered acacia on the bottom of the mortar in the center, covering the acacia after- wards with the oil or oleoresin, and then adding the water of emulsification so carefully that the layer of oil covering the acacia is not disturbed, in order that the water may not come in contact with the acacia until the trituration begins. If the water should come in contact with the powdered acacia before brisk stirring begins, lumps would be formed, which it is afterwards extremely difficult to crush. Having now all the necessary ingredients in the mortar in the right proportions, the operator grasps the pestle and with an extremely rapid rotary motion in one direction accomplishes the emulsification, after which any additional quantity of water required may be gradually stirred in. The most common emulsions of fixed oils are made of cod- liver oil, castor oil, olive oil and oil of almond. The most 340 A CORRESPONDENCE COURSE IN PHARMACY common emulsion of volatile oils is made of oil of turpentine. The only common emulsion of oleoresin is an emulsion of copaiba. Yolk of egg is also an effective emulsifying agent, employed in making emulsions of fixed oils and occasionally other emulsions. When the yolk of egg is used for this purpose, the oil is mixed with it before the water of emulsification is added. Powdered tragacantli can also be used, and is quite as effective as powdered acacia, but a much smaller amount of tragacanth will prove sufficient. The tragacanth, however, works slowly, so that it takes a longer time to finish the emulsion, which, however, when finished, holds together remarkably well. Irish moss jelly is also used as an emulsifying agent for fixed oils, but it is not so effective in reducing the oil to an extremely fine state of division, although the emulsion when finished is comparatively permanent. Unless the Irish moss used in preparing the jelly is carefully selected so that the jelly is nearly colorless, the emulsion made with this emulsifying agent is unsightly, whereas emulsions made with acacia or tragacanth have a much better and cleaner appearance. Another emulsifying agent sometimes used is tincture of soap bark, but tincture of soap bark contains an extremely active medicinal substance called saponin, and hence this emulsifying agent should never be used unless ordered by a physician, and no intelligent physician is ever likely to order it. The only reason why it has been employed is its wonderful emulsifying power and the ease with which the emulsification is effected by it. 539. Chloroform and ether may be incorporated in mixtures with the aid of tragacanth. It is, in fact, a very easy task to make such mixtures. All that is necessary is LIQUID PREPARATIONS NOT MADE BY EXTRACTION 341 to place the required quantity of powdered tragacanth in a dry, clean bottle, add the chloroform or ether, and shake the mixture so as to disintegrate any lumps of the powdered gum; then add the water required and shake the bottle vigorously, when a uniform emulsion will soon be formed. The emulsion of 'chloroform of the American pharmacopoeia contains oil of almond as well as chloroform. The best way to make it is to add the chloroform to the oil, then add the powdered tragacanth and finally the water of emulsification, stirring vigorously as in other emulsions and finally shaking the mixture. The chalh mixture of the pharmacopoeia is a quasi- emulsion obtained by triturating prepared chalk with acacia and sugar and then with water and cinnamon water. The insoluble prepared chalk is held in suspension in the mixture temporarily by the acacia, which dissolves in the water, but as the chalk is only temporarily sus- pended, the mixture must be shaken each time it is to be taken. Precipitated sulphur can also be held in suspension with the aid of acacia, and then triturated a sufficiently long time with the requisite amount of water. 540. Spirits are defined as alcoholic solutions of volatile substances. They are mostly alcoholic solutions of volatile oils, which are very simple preparations. 541. Liquid preparations for external use are generally simple solutions or mechanical mixtures. The ingredients are extremely varied. Therapeutically, the external liquid preparations are chiefly stimulants, rubefacients, lubricants, astringents and cooling or soothing applications. Antiseptic and disinfectant lotions are also very much used. Lotions may be water-solutions of inorganic or organic 342 A CORRESPONDENCE COURSE IN PHARMACY substances, or they may even be alcoholic liquids. Lotions are for local use externally. Eye washes are technically known as colly via, while those used for nasal difficulties are called collunaria. Gargles are mostly water-solutions, but they, too, fre- quently contain alcoholic ingredients. Gargles, technically known as gargarismata, are used as washes for the throat. Injections are so miscellaneous in their character that it is impracticable to give any general description of them. They are aqueous, mucilaginous, oily or even alcoholic. They are injected by means of syringes into the body cavities through the rectum, ear or other openings. A rectal injection is called an enema. Liniments usually contain some fixed oil, volatile oil or soap, but may also be composed of other ingredients in liquid form, as, for instance, tinctures. Liniments are for external use, and are applied as washes or rubbed in by gentle friction. Collodions are solutions of so-called soluble guncotton or pyroxylin in a mixture of alcohol and ether. Simple col- lodion contains nothing else, but medicated collodions contain tannin, cantharidin and various other medicinal substances. When collodion is applied to the skin or to a wound, the alcohol and ether evaporate, leaving a continuous film of the pyroxylin. If the collodion is of suitable density, the film is sufficiently strong and elastic to form an effective covering. The lips of wounds may be held together by applications of collodion, but if the application is too thick, the contraction of the film may be painful. For this reason various additions to collodion are made to render the film elastic so that it may be less painful. The most common additions made for this purpose are glycerin, castor oil and Venice turpentine. LIQUID PREPARATIONS NOT MADE BY EXTRACTION 343 Test Questions 1. Mention several kinds of liquid preparations for external use. 2. What is collodion made of and how is it made elastic ? 3. What is the meaning of the title liquor in the Ameri- can pharmacopoeia ? 4. What several kinds of water-solutions of non-volatile substances are common in pharmacy ? 5. How are the aromatic waters made ? 6. How is mucilage of acacia prepared ? 7. How is mucilage of tragacanth prepared ? 8. What proportions of sugar and water, by weight, are required to make just six pints of simple syrup ? 9. How do you find these proportions most easily ? 10. What quantity in cubic centimeters of mucilage of acacia can be made from 340 grams of acacia, assuming that the specific weight of the mucilage is 1.31 ? 11. How much sugar is necessary in a medicated syrup ? 12. How is glycerite of starch made ? 13. What is an emulsion ? 14. What substances will form emulsions when beaten with water without the addition of any other substance ? 15. Describe how a good emulsion of almond is made. 16. Describe how a good emulsion of ammoniac is made. 17. What is Hager's rule for the production of fixed oil emulsions ? 18. State Hager's rule for making emulsions of oleoresins. 19. What is Hager's rule for the production of emulsions of volatile oils ? 20. What are the principal emulsifying agents ? 21. How would you make an emulsion containing one-half its volume of almond oil ? 22. How would you make an emulsion containing oil of turpentine and olive oil together ? 344 A CORRESPONDENCE COURSE IN PHARMACY 23. How can an emulsion of ether be made ? 24. Describe in detail how you would make an emulsion containing one-eighth of its volume of volatile oil of copaiba. 25. What is the object of the acacia in chalk mixture ? 26. What would you call an alcoholic solution of oil of peppermint ? LESSON TWENTY-TWO XXXII Extracts 542. Infusions are ordered by the American pharmacopoeia to be made in accordance with the following general direc- tions, unless specially otherwise ordered: "An ordinary infusion, the strength of which is not directed by the physician nor specified by the pharmacopoeia, shall be pre- pared by the following formula: Take of the substance coarsely comminuted 50 grams, boiling wat