WITHDRAWN Bowdoin College Library —— i ee — i‘ i he ae ; Meas ee ey ; ert b> : c ie ee s peers trey | PE CRUNES ON ILLUMINATING ENGINEERING K ; a : - } 4 WA 3 AVI 4A OVUITA ie } LECTURES ON ILLUMINATING ENGINEERING DELIVERED AT THE JOHNS HOPKINS UNIVERSITY October and November, 1910 UNDER THE JOINT AUSPICES OF THE UNIVERSITY AND THE ILLUMINATING ENGINEERING SOCIETY VOLUME | THE JOHNS HOPKINS PRESS BALTIMORE, Mb. ve) sent OB keen th 423 SS Seren, ~~ } ~~ < eed ; — coe | A? » > ~ + XN “x Be oy ws : Lars - ox i ‘ f he ioe ee rr f bi ae : “ ies - " alge . = i i 4 > t ‘ ' ue. Se r F f wy f Z f i. } f we; eo é id a ry i y Be ae eee yo FS ; # t w tJ eet a ris eiatasty rie Weer 4 , J . 64 6! Pg PSS. £ t 6 ie ate : : we — Aap rss COLA Grier a’ ao wy PREFACE This Course of Lectures on Illuminating Engineering was given at the Johns Hopkins University, Baltimore, between the dates October 26 and November 8, 1910, under the joint auspices of the University and the Illuminating Engineering Society. The origin and objects of the lectures are clearly stated in the preliminary announcement of the course, from which the following quotation is made: “The Illuminating Engineering Society recognizing the fact that there is an increasing demand for trained illuminating engi- neers, and that the present facilities available for the specialized instruction required are inadequate, determined, through an act of the Council of the Society, to encourage the establishment of a course of lectures on the subject of illuminating engineering. This course should have three objects: (1) to indicate the proper codrdi- nation of those arts and sciences which constitute illuminating engi- neering; (2) to furnish a condensed outline of study suitable for elaboration into an undergraduate course for introduction into the curricula of undergraduate technical schools; and (3) to give practising engineers an opportunity to obtain a conception of the science of illuminating engineering as a whole. “Inasmuch as such a course is most appropriately given at a university where graduate instruction is emphasized, and as the Johns Hopkins University has regularly offered courses by non- resident lecturers as part of its system of instruction, and is now preparing to extend its graduate work into applied sciences and engineering, an arrangement has been effected by which the lectures will be given at this University under the joint auspices of the University and the Illuminating Engineering Society. The sub- jects and scope of the lectures have been proposed by the Society and approved by the University. The lecturers have been invited by the University upon the advice of the Society.” The lectures were attended by 240 men from various parts of the United States, many of them representatives of technical schools, gas and electric central stations, and manufacturing com- vl | PREFACE panies. A large number of the attendants at the lectures also followed the course of laboratory work which had been arranged. The general interest in the course encourages the hope that these published volumes may serve to advance our knowledge of this new and important branch of engineering. II. VII. IV. VI. VII. VIII. GENERAL CONTENTS VOLUME I LECTURES . THE PHYSICAL BASIS,OF THE PRODUCTION oF LiautT. Three et eee MIEN ie aoa cee Akad ab hoe hes Mee ne oh totem Bbiehaa are 8 oot JosEPpH S. AMES, PH. D., Professor of Physics and Direc- tor of the Physical Laboratory, The Johns Hopkins University. THE PHYSICAL CHARACTERISTICS OF LUMINOUS SourcES. TJ'wo eeu ae ee Ohare Foie. ot she a Pgh hile Gels mcs bi aiagiaese wine ee ye ea Epwarp P. Hypr, PH. D., President, Illuminating En- gineering Society; Director of Physical Laboratory, National Electric Lamp Association. THE CHEMISTRY OF LUMINOUS SouRcES. One léecture...... Wiuis R. Wuitney, Pu. D., Director of Research Labo- ratory, General Electric Co.; Past President, American . Chemical Society. ELECTRIC ILLUMINANTS, Two le€Ctures........ccccceeeeees CHARLES P. STEINMETZ, PH.D., Consulting Engineer, General Electric Co.; Professor of Electrical Engineer- ing, Union University. (1) Gas AND Om ILLUMINANTS, (2) INCANDESCENT GAS ame rr meee F400 LECTULES Joc tere ov ec ca 0 esa wo ROMER Ge © ea _ (1) ALEXANDER C. HuMPHREYS, M.E., Hon. Sc. D., Presi- _ dent of Stevens Institute of Technology; Past President American Gas Institute. (2) M. C. WHITAKER, B. S., M. S., Professor of Industrial Chemistry, Columbia University. PAGE 93 109 157 THE GENERATION AND DISTRIBUTION OF ELECTRICITY WITH . SPECIAL REFERENCE TO LIGHTING. Jwo léctures........... JOHN B. WHITEHEAD, PH. D., Professor of Applied Elec- tricity, The Johns Hopkins University. THE MANUFACTURE AND DISTRIBUTION OF acerca GAS WITH SPECIAL REFERENCE TO LIGHTING. Two lectures..... (1) Mr. E. G. Cownpery, Vice-President, Peoples Gas Light and Coke Company, Chicago, III. (2) Mr. Water R. Appicks, Vice-President, Consolidated Gas Co., New York. PHOTOMETRIC UNITS AND STANDARDS. One lecturé......... Epwarp B. Rosa, PH. D., Physicist, National Bureau of Standards. 237 277 387 Vili GENERAL CONTENTS IX. THr MEASUREMENT OF LIGHT. TZ'wo léectures......-..e000. CuLaytTon H. SHarp, Pu. D., Test Officer, Electrical Test- ing Laboratory, New York City; Past President, Illumi- nating Engineering Society. X. THE ARCHITECTURAL ASPECTS OF ILLUMINATING ENGINEER- ING. Ome TECtUTE oo Ss Se Re iin oa 3 5 ace we cue WALTER Cook, A. M., Vice-President, American Institute of Architects; Past President, Society of Beaux Arts Architects. VoLuME II LECTURES XI. THE PHYSIOLOGICAL ASPECTS OF ILLUMINATING ENGINEERING. PUO BOCTUPES: GeO vino a iaac SS ede hel a chal a ayers nee = eee P. W. Coss, B.S., M. D., Physiologist, Physical Labora- tory, National Electric Lamp Association. XII. THE PSYCHOLOGICAL ASPECTS OF ILLUMINATING ENGINEERING. One TECTUTE oe os oa eis one eb nies she ae 4,8 fe no cee ee ROBERT M. YERKES, PH. D., Assistant Professor of Psy- chology, Harvard University. , XIII. THE PRINCIPLES AND DESIGN OF INTERIOR ILLUMINATION. Six PECTULES. oo. ae oe 6 sie e se 010 ws. 0! sue vm 6.6 ape ieee tela leaiens gent (1) W. E. Barrows, Jr., Assistant Professor Electrical Engineering, Armour Institute of Technology, Chicago, Illinois. (2) L. B. Marks, B.S., M.M.E., Consulting Engineer, New York City; Past President, Illuminating Engineer- ing Society. (3) Mr. NorMAN Macsetu, Illuminating Engineer, The Welsbach Co. XIV. THE PRINCIPLES AND DESIGN OF EXTERIOR ILLUMINATION. TREE, LECTUTES 5. « pixce o.e-4 ¢ suve 4.0 gies le pile apaitec anata (1) Louis BELL, PH. D., Consulting Engineer, Boston, Mass.; Past President, Illuminating Engineering Society. (2) E. N. WricutTineton, A.B., Boston Consolidated Gas Co. XV. SHADES, REFLECTORS AND DirruSING MeEpIA. One lecture... VAN RENSSELAER LANSINGH, B.S., General Manager Holophane Co. XVI. LIGHTING“ FIXTURES. “One! lectures. 075 32% oe ee Mr. Epwarp F. CALDWELL, Senior Member of Firm and Designer, Edward F.. Caldwell & Co., New York. 507 525 575 605 795 931 XVII. AOVIEL Lists of experiments in connection with the Lecture Course, to- together with the necessary bibliographies CHARLES O. Bonp, Manager of Photometric Laboratory, United HERBERT E. Ives, Ph. D., Physicist, Physical Laboratory, GENERAL CONTENTS THE COMMERCIAL ASPECTS OF ELECTRIC LIGHTING. One SN tO gE eee eg GAME, Ghee yienas «dona e ohh im, soanle cceke a ders « is JOHN W. Lies, JR., M.E., Third Vice-President, New York Edison Co.; Past President, American Institute of Electrical Engineers. THE COMMERCIAL ASPECT OF GAS BUSINESS WITH SPECIAL REFERENCE TO GAS LIGHTING. One léecturé.........2scc0e: WALTON CLARK, M.E., President of The Franklin Insti- tute, Philadelphia; Third Vice-President, United Gas Improvement Co., Philadelphia. LABORATORY EXERCISES Gas Improvement Co., Philadelphia. National Electric Lamp Association. Preston S. Mituar, Electrical Testing Laboratory, New York. A. H. Prunp, Ph. D., Associate in Physics, The Johns Hopkins University. Dilelnu Sele aielial se) sdjese) eo) 9 0 6 s 0 6 (0: 6 |6 ‘© s 6 © 6 6 6 © 0 0m 10 ¢ © 0 0p «8 6 6 eo) 08 @ 08 8 6 eo 6 8 8 8 8 eee eee eee ee ee ee we we www 1x 945 1009 a . 7 4 be Foe te tk j 1 iy ea 4 2 | ran y 4 q ’ + Bie Marie Bhd | t A f 4 Ses? x4 >t Bea s¢ ‘<5 $ : a wes i ‘ hy x ( hs i” n ° + oe ’ - eae a b ; ‘ieee he TC , - * ' AC ~ i 7 4 a seat Gl ee TSM Ee WOT SE AS a - a) fey eps Ets hit eh Mt La J Ft i" ies . d a f « ‘ . i ; : j tan ’ - Z “ J vue! +t 5 [ THE PHYSICAL BASIS OF THE PRODUCTION OF LIGHT * By JoszepH S. AMES CONTENTS LECTURE I Physical Quantities and Measurements Objects and general principles of physics. Methods of assigning numbers to physical quantities. a. Measurement in terms of units. b. Indirect means, e. g., temperature. Simple ideas. a. Intuitive: space and time. b. Experimental: e. g., force (illustrated by properties of matter), Units of length, of time, of force; C. G. S.; English. Derived mechanical quantities, and their units; e. g., density, pressure. Measurement of length, volume, time, force, pressure. Errors of instruments. Discussion of observations. Definition of electrical quantities, and their units. Measurement of electrical quantities by portable instruments. LEcTURE II Energy and Thermal Phenomena Definition of work and energy: mechanical illustrations. Our temperature sense. Thermal phenomena. Thermal effects. ; Methods of producing these effects. Explanation in terms of energy. Meaning of ‘“ Conservation of Energy.” Illustrations: battery, dynamo, etc. Discussion of temperature and its “ measurement.” Discussion of modes of producing heat-effects: flames, friction, conduc- tion, radiation, ete. y Radiation and absorption: Kirchhoft’s law, “ Black Body.” Measurement of energy. a. Rise in temperature. b. Mechanical means. c. Electrical method: Bit. * The lectures are based upon the author’s text-book ‘“ General Physics,” published by the American Book Co., New York. 2 ILLUMINATING ENGINEERING LEcTURE III Radiation Spectra of radiation. Dispersive apparatus. Detecting and measuring apparatus. Visible, ultra-violet, infra-red radiation. Continuous, discontinuous and absorption spectra. Modes of producing radiation. a. “ Temperature-radiation.” b. Luminescence: fluorescence, electrical discharge, ete. Color sensation. Cause of color of natural objects. a. Body absorption. b. Surface absorption. c. Exceptional cases. Extension of temperature scales by radiation methods. Lecture I Physical Quantities and Measurements Matter. Through our various senses, such as those of sight and hearing, we are constantly receiving sensations which we interpret objectively; i. e., we locate the cause of a sensation in a definite portion of space. We picture to ourselves the existence there of something which we call “matter”; and to a limited portion of space which contains matter we give the name “physical body.” Matter may be divided into two great classes: that which is living, such as plants and animals, and that which is not, such as pieces of wood and glass, water and air. Physics is, broadly speaking, the science concerned with this second division of matter, which may be called “ ordinary matter ” ; and phenomena occurring in con- nection with matter of this kind are called “ physical phenomena.” The scientific study of a subject involves three distinct ideas; the discovery, the investigation, and the explanation of phenomena. The first two require no discussion here; but it may be well to state that by the words “to explain a phenomenon” is meant to determine its exact connection with other phenomena, to describe it in terms of simpler ones, and in this manner to reduce the number of fundamental ideas as far as possible. In seeking for explanations of phenomena we assume either directly or indirectly, that there is a definite connection between - consecutive events, of such a nature that if we are able to reproduce exactly a definite condition, the same effect will follow regardless Tue Puysicat BAsiIs or THE PRopucTION oF LIGHT? a of the epoch of time or the location in space. We are justified in this belief by all of our experience and observations. Ether. ‘The careful study of the phenomena of light led philoso- phers, many years ago, to believe that there is present in space another medium for phenomena than that furnished by ordinary matter. It has become an accepted fact that throughout the vast regions of space, in the solar system and beyond, there is a medium permeating all ordinary matter and having many properties in common with matter and yet not identical with it. This is called “the ether.” In order to explain many electrical and magnetic phenomena, and even to describe the phenomena of radiation, it is necessary to assume its existence.* Physics. ‘The object of physics may therefore be defined to be the attempt to determine the exact connection between phenomena, both in ordinary matter and in the ether, and to express these relations with as few hypotheses as possible concerning the nature and properties of either. Physical Quantities. A physical quantity is one which we can imagine as capable of changing in amount, something to which we can assign a numerical value. Some quantities can be measured, others cannot. ‘To measure a quantity, another similar one must first be chosen as a standard or rnit, and then the number of times this is contained in the original quantity is its measure. Thus, a length can be measured in terms of an inch, a yard, a centimeter, etc., depending upon the choice of unit. It is possible to understand the meaning of a zero value of any measurable quan- tity; further, two or more measurable quantities of the same kind, for instance two lengths, may be added. On the other hand there are many physical quantities which cannot be measured; and yet it is possible to give them numerical values. Thus, the temperature of a body cannot be measured, although it is possible by measuring the change in volume of mercury in a thermometer to give a num- ber to temperature. Simple Quantities. To most physical quantities exact definitions can be given, but there are a few for which this is impossible; there are no simpler ideas in terms of which we can describe them. The question as to the exact number of these need not be discussed here, and in what follows the philosophy based upon Kant will be * One should add that a new school of philosophy exists which looks .at nature from a different standpoint. 4 ILLUMINATING ENGINEERING accepted. According to this we divide our simple ideas into two classes; intuitive and experimental. The two intuitive ideas are those concerned with space and time. 1. A straight line, a polygon, or a solid figure bounded by plane faces, together with the ideas involved in assigning numerical values to lengths, areas and volumes are considered intuitive. That is, it is impossible to define what is meant by length; and the idea of two equal lengths admits of no ambiguity. We can choose a unit length arbitrarily and then, making use of a method of super- position, determine the number to be given any length. The same general method may be applied to areas and volumes. 2. In regard to time, we have a definite conception of what is meant by two equal intervals of time; certain physical phenomena appear to us to repeat themselves at intervals of time apparently equal, e. g., the vibrations of a pendulum or the balance wheel of a watch. ‘We have no way by which we can prove that these inter- vals are equal, yet there is every reason for believing that these motions of a pendulum and of the balance wheel of a watch are _ exactly periodic; for at any instant the external conditions affecting the motion are exactly the same, so far as we can tell, as they were at a definite interval of time before. In order to give a number to an instant of time one must choose some periodic motion such as just described, e. g., a certain pendulum vibrating under definite conditions, and some arbitrary epoch of time from which to count the number of vibrations; the number of vibrations between the epoch and the instant for which a number is desired is this number. Among the fundamental ideas of which we learn by means of our senses may be mentioned temperature, pitch of sound, and what we call “ force.” For instance, through our muscular sense we become conscious of certain definite sensations when with our hands or arms or bodies we perform certain experiments on matter. Thus, if a large stone is held in the hand we become conscious of a cer- tain property of matter called its “weight”; if we change the motion of a body by means of our arms, e. g., if we throw a ball or stop one in motion, we become conscious through the same chan- nel of a property of matter called “inertia.” It is possible, of course, to hold a body suspended from the earth and to set a body in motion or to stop it if moving, by other means than by our muscles; thus a weight can be suspended from a spiral spring and hang at rest with reference to the earth, a compressed spiral spring Tor PHysiIcAL BASIS OF THE PRODUCTION OF LIGHT 5 may, as in a toy gun, produce the acceleration of a bullet, etc. Under all these conditions which are in their nature identical with those brought about by our muscles we say, in ordinary language, that “a force is acting on” the body; but it should be borne in mind that this is simply a description, nothing more. In order to assign a numerical value to a force one follows the natural way of studying the simplest cases of forces one can have, and then usmng definitions and methods based upon these observations. The discussion of this subject forms that branch of mechanics known as dynamics. The simplest mode of obtaining a unit or standard force, at least from the standpoint of the inhabitants of this earth, is undoubt- edly as follows: 1. Select arbitrarily a certain piece of matter. 2. Suspend it from a fixed support by a cord. 3. Call the tension in this cord a unit force. It is easy to see how, by means of a pulley, it is possible to balance this force by an equal one obtained by suspending from the other end of the cord, passing over the pulley, another body which is added to gradually until there is a balance. Having thus obtained two equal forces one can obtain a force twice as great by balancing one body against the two used in the first experiment, etc. In this way a set of standard bodies may be obtained whose weights give forces equal to 1, 2, 3, 4, 5, ete., and then, if it is desired to give a number to an unknown force, this may be done by balancing it against a selection of these known forces. One can discuss in a similar manner methods of giving numbers to temperature, etc., and this will be done in a later lecture. ‘Units. The science of mechanics is based upon our ideas of length, time and of force, and methods have been discussed showing how we can give numbers to all these quantities. It is seen, how- ever, that in each of these methods certain steps are arbitrary, and that the number finally obtained depends upon the nature of this arbitrary step. | a. Length. In giving a number to a length the first step is to select a length to which we give the number 1 (if we use the inch, we have one value for the length, if we use the centimeter we have a different value, etc.). The scientific world agrees to adopt as its unit of length the one-hundredth portion of the length of a certain platinum rod, kept in Paris, when this rod is at the temperature of melting ice. The length of this rod under these conditions is 6 ILLUMINATING ENGINEERING called a “meter”; and one-hundredth of this length is called a “centimeter.” There are other unit lengths in daily use in this country and in England, but it is not necessary to discuss them. b. Time. In assigning a number to an instant of time we saw that it was necessary to select a “time-keeping mechanism,” such as a clock, and, secondly, to agree upon some definite instant from which to begin counting. The scientific world has agreed to adopt as its time-keeping instrument the earth itself as it rotates on its axis, and to use as the unit, in terms of which intervals of time are expressed, the “ mean solar second.” This quantity is the second of time referred to the “ mean solar day,” which is the average length for one year of the lengths of the solar days during that interval, a solar day being the interval of time between the two instants when the sun crosses the earth’s meridian at any point. It is known that solar days differ in length, but pendulums may be made whose periods are such that they agree exactly with the earth in its rota- tions at intervals a year apart, and these clocks are used ordinarily as time-keeping instruments. Different epochs are chosen in dif- ferent localities; these usually differ by one, two, etc., hours. e. Force. In assigning a number to a force it was seen that the essential step was to select an arbitrary piece of matter; and here the scientific world has agreed to use a certain piece of platinum kept in Paris. When this body is suspended and allowed to hang vertically there is said to be “a force” in the string equal to the “weight of one kilogram.” The thousandth portion of this. force is called the weight of “one gram.” In England and this country other unit forces are sometimes used, commonly what is called the weight of a “ pound.” The unit force on the “ centimeter-gram-second ” (C.G.S.) sys- tem, as used in all scientific laboratories, is the force required to pro- duce an acceleration of one centimeter per second per second in a piece of matter whose mass is one gram. ‘This force is called one “dyne.” The weight of one gram is very closely 980 dynes—it is not the same at all points on the earth. d. Pressure. From these fundamental properties—length, time and force—numerous other quantities are derived, one of which should be mentioned here: pressure. By pressure we mean the force per unit area, and, of course, the number we obtain for any pressure depends upon our selection of units of force and of area. THe Puysicat BAsis oF THE PRODUCTION oF LIGHT 4 Measurements. It is necessary to say a few words in regard to the actual measurement of, or methods of assigning numbers to, the physical quantities so far discussed; but it is easily understood that for any satisfactory discussion of the subject reference should be made to some laboratory hand-book. a. Length. In the measurement of small lengths two methods are in general use; one, depending upon.the use of a screw and divided head, the other upon the use of a vernier. In the measure- ment of greater lengths special precaution must be taken against changes due to temperature, flexure, etc. b. Volume. Measurements of volume are made in one or two ways; if the volume to be measured has the shape of a simple geo- metrical figure, its linear dimensions are measured and its volume calculated ; if the volume is irregular, or if it is that of an inacces- sible space, a method is used depending upon our knowledge of the volume of mercury which is required to produce a definite weight at a definite temperature; e. g., the volume of a bulb may be determined by filling it with mercury, expelling the mercury, noting its temperature, and then weighing it. ce. Time. Methods of accurate measurement of time are too complicated to be discussed here. It is sufficient to note that there are several methods which give an accuracy of a minute fraction of a second. d. Force. The general method of measuring a force is, as stated before, to balance it against a known force, or a combination of such forces. It is possible to buy sets of weights, or a spiral-spring balance, which will give results sufficiently accurate for all purposes. e. Pressure. It is customary to measure pressures such as those of the atmosphere, of boilers, of water mains, etc., by balancing the pressure against a vertical column of mercury. An illustration of this method is furnished by the ordinary mercury barometer. Since this is the accepted method, the unit in terms of which pressures are most often expressed is that of ‘ one centimeter of mercury,” by which is meant the vertical pressure required to balance a column of mercury, at the temperature of melting ice, one centimeter in height, when the force of gravity is that which exists at sea-level at latitude 45 degrees. This is a perfectly definite unit, and its value is known in terms of the other units. Errors of Instruments and Observations. In this brief refer- ence to the measurements of these five quantities it is seen that 8 ILLUMINATING ENGINEERING reliance must always be placed upon an instrument furnished by some instrument maker; e. g., a micrometer screw, a vernier scale, a set of weights, a clock, etc., and it should not be necessary to emphasize two facts in connection with these instruments. First, every instrument must, of course, be compared with the original standard, or with copies of it whose errors are known. It is for this purpose that in all, civilized countries Bureaus of Standards exist where such comparisons may be made. Thus every testing laboratory in America has or should have standards of length and of mass, whose values are known accurately in terms of the Paris standards. But, even granting that the testing laboratory has these standards, there are many errors or uncertainties inherent in the use of every instrument, and a thorough study must be made of it before it can be used for purposes of measurement. ‘Thus no screw has an absolutely uniform pitch, and the variations in this must be determined by known methods; no set of weights is ac- curate, and its errors must be learned; and similar statements are true in regard to every instrument. The first precaution therefore in the measurement of any quantity is to determine the true scale of the instrument, which is not by any means in all cases that assigned to it by the instrument maker, and also to learn the varia- tions in this scale in different parts of the instrument. Second, when an instrument is to be used for purposes of meas- urement it is not sufficient to simply make one observation, e. g., to observe once the reading on a micrometer of the diameter of a wire. It is necessary to repeat the measurement often. To begin with it is always possible that an error may be made in reading the figures on the. instrument or in recording them. Again, when the same measurement is repeated, the measuring instrument being removed and then. replaced, it is noted that as a rule a different reading is obtained. This does not mean that the quantity measured has changed or that the instrument used is defective, but simply that in the use of the instrument there are certain inherent errors which limit the accuracy to which it may be trusted, errors coming in part from the individual using the instrument, in part from the instrument itself, and in part from other causes. When a sufficient number of observations have been made one may calculate by known methods the most probable value to be attached to the quantity, and also learn something concerning the certainty with which this number may be regarded as approaching the true value. Tue Puysican BAsis of THE PRODUCTION oF LIGHT 9 The confidence felt in their measurements by certain observers, and their entire lack of appreciation of the need of ascertaining the probable errors and uncertainties involved, is little short of astound- ing to one accustomed to ordinary laboratory methods. 7 Electrical Quantities. It seems necessary in this, the first lecture of the course, to give a brief discussion of some quantities which will not be fully explained until later in the course. hese are the various electrical quantities ; and, of course, to most engineers they are all well known. In the history of electric currents many units have come to the front at different periods, and even at the present time the definitions are not the same in all countries. The differ- ences, however, are so slight as to justify us in neglecting them in all ordinary cases. The definitions given in what follows are those in terms of which practically all the measuring instruments now in use are calibrated. The unit of resistance—the ohm—is defined to be equal to the resistance of a column of mercury at zero degrees, of uniform cross-section, of length 106.3 cms., and having the weight of 14.4521 grams. (This column then has a cross-section of almost exactly one square millimeter.) The ampere—the unit of current—is defined to be such a current as flowing in a silver voltameter of a specified pattern deposits per second .001118 grams of silver. The volt—the unit of e.m. f.—is defined to be such a difference of potential as will produce, when applied to a conductor whose resistance is one ohm, a current of one ampere. One of the fundamental properties of current when flowing in a conductor is to develop heat in this conductor, and it is well known that a simple formula connects the heat developed and the electrical characteristics of the system. This matter wilt be discussed more fully in the second lecture. In order to. give numbers to the resistance of a conductor the current flowing in it and the difference of potential at any two points, various methods have been devised and instruments per- *fected. At the present time there are no instruments in common use in laboratories which have attained accuracy to such a remark- able degree as these. This is owing in large part to the epoch- making inventions of Siemens and Lord Kelvin in Europe, and of Weston in this country. Thanks to the efforts of these scientists we now have instruments for the measurement of volts, amperes and watts which are sufficiently accurate for most purposes. I may 10 ILLUMINATING ENGINEERING be pardoned if I again emphasize the fact, however, that all instru- ments are imperfect and that uncertainty is attached to every ob- servation. Lecture II Energy and Thermal Phenomena Work and Energy. We are all familiar with the use of the words “ work” and “energy” in every-day language. They have been adopted in physics as names of certain physical quantities which admit of exact definition. Naturally these definitions have been made so as to coincide as nearly as possible with those every- day experiences which gave rise to the names originally. Thus, if a man raises a weight vertically from the ground, if he com- presses a spring, if he throws a base-ball, he knows that he is doing work. The essential ideas in all cases of work are, first, the action of a force, and, secondly, a displacement in the direction of this force. Corresponding to these ideas the numerical value of work is defined to be the product of these two quantities, i. e., the value of the force by that of the displacement in the direction of the force. It is easily seen that in all cases in mechanics the results of a force are either to overcome another force or to produce accel- eration (i. e., change of velocity of a piece of matter). Correspond- ing to these two types of forces there are two ways in which work may be done; first, when a force or opposition is overcome, as when a weight is lifted, a spring is wound up, a bow is bent, ete.; second, when acceleration is produced, as when a ball is thrown, a fly-wheel or grindstone is set in motion, etc. It is common experience that in all cases when work is done on a body, as when a weight is raised from the earth, a spring is wound, a body given accelera- tion, the body as a result gains the power of doing work itself. It is said to have gained “energy.” If the work done on the body has been done in overcoming an opposing force, the body .is said to have gained “ potential ” energy; whereas, if the work has been done in producing acceleration, the body is said to have gained* “kinetic ” energy. Potential energy is therefore always associated with a body in a strained or “ unnatural” condition; kinetic en- ergy, with motion, either translation or rotation. It is a matter of common experience also that in all cases of mechanical work one body loses energy and a second body gains it. Thus, if a bullet is expelled from a toy gun by means of the sudden relaxation of a THe Puysicat Basis or THE Propuctivn or LIgut 11 compressed spring, the bullet gains energy and the spring loses it. It is easy to show that for all types of ordinary mechanical forces the amount of energy lost by one part of the system—namely, that which is doing work, is numerically equal to the energy gained by another portion of the system, that on which work is being done; and, as a consequence, therefore, the total amount of energy in the system remains unchanged. It was recognized many years ago that there were certain apparent exceptions which were associated with friction. Thus, if a fly-wheel in motion is disconnected from the driving shaft, its energy—as shown by its motion—gradually decreases, as it comes to rest under the action of friction. Here, then, is a case of an apparent disappearance of energy. It was noted, however, that in all cases like this there were certain heat- effects produced; and it has been established that there is an inti- mate connection between the loss of mechanical energy and the resulting heat-phenomena. Before stating this connection, how- ever, it may be well to say a few words in regard to our ideas of heat. Heat-Phenomena. Our attention is called to thermal phenomena by means of our temperature sense. We possess in certain portions of the surface of our bodies nerve endings which are sensitive to thermal changes in our environment. That is, if we expose our hands to sunshine or bring them near a stove in which there is a fire, or to a flame, we experience a definite sensation, and we say that we feel warm. Whereas, if we put our hands on a block of ice, or if we allow some volatile liquid to evaporate from them, we experience a different sensation and say that we feel cold. The first step in the scientific investigation of these phenomena must be taken by exposing a piece of inanimate matter, such as a rod of iron, to the same conditions as those under which we felt warm or cold. When this is done, it is found that the piece of matter undergoes various changes; and these are called thermal effects. In ordinary language we speak of a change from a condition when we feel cold to a condition when we feel hot as being a change from low “temperature” to high temperature. Experiments show that when the temperature of a body is changed, all of its physical properties, with the exception of its mass and weight, are also changed. We select ordinarily from these thermal effects a few of the most obvious and the most important for purposes of study and observation. Among these may be mentioned change in volume, change in electrical resistance, and change in state, as, for instance, 12 ILLUMINATING HNGINEERING when a piece of ice melts and becomes liquid. On examination it is found that whenever work is done against friction, heat-effects are produced, and the investigations of Joule led him to believe that the connection between these two phenomena was an exact one, which could be stated by saying that the amount of heat-effect produced depended simply upon the amount of work done against friction, i. e., upon the apparent loss of energy, and upon nothing else, not upon the time taken for the change, nor the temperature of the working parts, etc. As a matter of fact, if we consider various cases in which heat-effects are being produced, we see that in them all work is being done against the smaller parts of the body which experiences the heat-effect, in such a manner that the energy of these smaller parts is altered. As a consequence of various experiments, but notably those of Joule, the scientific world has accepted the belief that, when we are dealing with friction or similar phenomena, there is no loss of energy, but that simply the portions of matter with which it becomes associated are too minute for observation with our eyes, and therefore we do not observe by this means the effect produced, but that this effect is shown to us through our temperature sense or by some heat-effect. This state- ment means that one can apply a numerical value to the heat-effects produced, in such a manner that if it is introduced into the total value of the energy of a system, this total value remains unchanged no matter how much friction may take place in the system. Conservation of Energy. ‘This constancy of a certain number when applied to the energy of a system, including in that the proper figure to take into account heat-phenomena, is an illustration of what is meant by the principle of the conservation of energy. ‘This principle was extended by Joule, Mayer and Helmholtz to include other phenomena than those of mechanics and heat. For instance, we know that, if we place some granules of zine in a test tube and pour sulphuric acid upon them, there is a violent evolution of gas and the test tube gets warm. This experiment can be described in terms of energy by saying that the internal energy of the molecules of the zinc and of the acid furnish the supply necessary for the formation of the new molecules and also for the production of the rise in temperature. ‘This experiment forms one of thousands coming under the head of Thermo-Chemistry, and all of these have - resulted in justifying the above description of the experiment in terms of the internal energy of the various substances. We also Tue PuHysicat Basis oF THE PRODUCTION oF Licgut 13 know that, if we take a test tube containing sulphuric acid and insert into it a strip of zinc and a strip of some other metal like copper, the two being joined outside the test tube by means of some wire, we shall then have what we call an electric current. This is an illustration of a primary cell. In this particular type of cell the zinc dissolves in the acid, and there is an evolution of gas; the chemical side of the experiment is exactly the same as in the previous test-tube experiment just described. It is observed, however, that in the second experiment, that with the primary cell, there is practically no change in temperature of the test tube. This means, in general language, that the energy previously used in causing a change in temperature is consumed in this case in producing the electric current. As a matter of fact, we all know that, when an electric current is passing in a conductor, the tem- perature of the latter is raised; and, if the conservation of energy can be extended to the phenomena of electric currents, we would expect to find on investigation that the energy consumed in the heating of the conductor by the current is exactly the same as that which is not accounted for in the heating of the test tube where the chemical reactions are going on. Complete investigations on this point justify this belief. Joule performed many interesting experiments to see if in return for a given amount of work he always obtained the same heat-effect regardless of the method and mechanism by which the latter was caused by the former; thus, by means of a steam engine, it is possible to turn a paddle in water and one can note the rise in temperature of the water, or by means of the same engine one can turn a dynamo, thus producing a cur- rent which can be made to flow in a wire immersed in water, and again the final effect is the rise in temperature of water. In all cases like this it is found that the conservation of energy is fully justified. As a consequence of these and countless other experi- ments it has become an accepted belief that the conservation of energy can be extended to all phenomena of both matter and ether. Temperature and Thermometers. Before discussing questions of radiation and absorption as heat-phenomena it is necessary to say something in regard to temperature and the methods by which we are able to give a number to the temperature of a body. As we use the words hot and cold and speak of high temperature and low temperature in ordinary language, we are making use of ideas which come from our temperature senses, and therefore the tem- 14 ILLUMINATING ENGINEERING perature of a body is.a term which refers to its relatwe hotness. It is easily seen that this quantity cannot be measured, i. e., we cannot regard otherwise than as absurd such an idea as selecting a unit of hotness and determining how many times it is contained in the hotness to which we wish to give a number. The words themselves are nonsense, It is, however, evident that we can choose such a measurable property of some body as changes when the tem- perature of the body changes, and make use of the measured change in this as a means of giving a number to the temperature itself. For instance, we can select arbitrarily a certain copper rod, measure its length under some condition which can be easily repeated, such as at the temperature of melting ice, again measure its length when — it is as another definite temperature, for instance, when it is 1m- mersed in steam under standard conditions, then measure its length at the temperature for which a number is desired. We can assign arbitrarily a certain number of steps or degrees to the interval between the temperatures of melting ice and of steam, say, 100; then an obvious method of giving a number to the temperature would be to take a proportion of 100 equal to the ratio of the change in length of the rod between melting ice and the unknown tempera- ture to the change in length between melting ice and steam, i. e., ae Vs Lioo— Jo which are justified by observations; namely, that the temperature of melting ice and of boiling water under standard conditions are the same at all points on the earth’s surface, and at all times (this may ~ be shown by proving that a body will always return to the same length when placed in a bath of ice and water, ete.) ; further, that the copper rod we have selected always attains the same length under the ‘same thermal conditions. It should be noted, too, that this scale gives the number 0 to the temperature of melting ice and 100 to that of boiling water. (It is clear that this method of giving a number to temperature is practically the same as that which anyone would follow if called upon to give a street number to a house erected at some point in a block otherwise vacant.) It can- not be emphasized too often that we have devised a method for giving a number to temperature, and that we have not in any sense tried to measure temperature. Some other observer might decide to take as his thermometer, or instrument for numbering temperatures, an iron rod and meas- t = 100 This system is based upon several assumptions Tue PuystcaL Basis oF THE PRODUCTION OF LIGHT 15 ure its change in length; or a glass bulb containing mercury and measure the apparent change in volume of the mercury; or a glass bulb containing some gas and measure the change in pressure of the gas, its volume being kept constant; or a platinum wire and measure the change in its electrical resistance; and so on. One of these methods is as good as another; each gives consistent re- sults by itself; and, if several observers use instruments of the same kind, their readings are concordant. But the readings obtained for any one temperature by the use of different methods and instru- ments would all be different; and it is necessary for workers in scientific laboratories to come to an agreement as to which instru- ment they will use. The scientific world has agreed to adopt as the instrument for giving numbers to temperature the constant volume hydrogen thermometer. In various bureaus of standards throughout the world ordinary mercury thermometers may be com- pared with the standard instruments, so that the former may be used for ordinary purposes, as they are much more convenient. It is clear that this definition of temperature applies only through the range of temperature over which we can make use of the hydro- gen thermometer. When we come to temperatures so low or so high that there are serious defects in the use of the instrument, it is necessary to define other scales of temperature. For instance, at extremely low temperatures a helium thermometer may be used, or a platinum resistance instrument; and at high temperatures a scale of temperature based upon certain empirical laws of radiation may be adopted. In both these cases of the introduction of new scales of temperature the attempt is made to define them so that they agree with the gas temperatures at those moderately low and moderately high temperatures over which this gas scale can be used at the same time as the two new ones. In this way a certain continuity is obtained, but it must not be thought that we are extending the hydrogen-gas scale; on the contrary, we are intro- ducing new scales. | Radiation and Absorption.—In text-books on physics one finds a full description of methods of producing heat-effects such as flames, friction, etc., and also a description of the various methods by which in general these effects are distributed from one point to another, as by conduction or radiation. In this course of lectures special emphasis must be laid upon the radiation process. This is illustrated when we expose our hands to sunshine and in many 16 ILLUMINATING ENGINEERING other similar ways. It is known as a result of experiments, which need not be discussed here, that the essential features of the process are: first, an emission from one body of energy in the form of ether disturbances, second, the absorption of this energy by another body. It is known further that all bodies in the universe are emitting this energy. As a consequence, therefore, of these two facts the question as to whether there will be any heat-effect pro- duced in'a body owing to radiation processes depends upon two things ; first, how much energy the body is losing; second, how much it is gaining. The phenomena of radiation and absorption of many bodies under different conditions have been carefully studied by many observers, and in the middle of the last century at about the same time a very important law was announced by Balfour Stewart in England, and by Kirchhoff in Germany. ‘The statement is ordinarily called “ Kirchhoff’s Law.” One form of it is to say that the radiating power and absorptive power: of a body are iden- tically the same in all respects at any one temperature; i. e., if a body under certain conditions radiates a certain type of energy more intensely than a second body, then the first body under the same condition will absorb that same type of energy more intensely than the second. (In the end this principle is an illustration of resonance.) In connection with this discussion of radiation and absorption Kirchhoff introduced the idea of a “ black body,” mean- ing by that a body which absorbs completely all radiations falling upon it; for, of course, in general, when radiation is incident upon a body part is reflected, part is transmitted, and only part is absorbed. : Temperature Radiation. When the radiation from bodies was more carefully studied it was found necessary to make certain limi- tations in the application of Kirchhoff’s law. Kirchhoff himself applied it only to those cases where radiation was to be considered simply as a heat process, not as a chemical or electrical one, and recent experiments appear to prove that we are justified in using Kirchhoff’s law only in the case of certain particular bodies under definite conditions. One way of defining this is to say that, if there is no. change in the molecular constitution of a body when it is radiating energy, its temperature being maintained constant, then it obeys Kirchhoff’s law; and the radiation from it is called “pure temperature radiation.” Other types of radiation will be discussed in: the following lecture. | Tuer PuHysicat BAsIs 0F THE PRODUCTION oF Liagut 17 It follows, then, that since a “black body” is the best absorber spossible it is also the best radiator; i. e., at a given temperature it radiates more energy of any particular kind than any other radia- tor which obeys Kirchhoff’s law; and it also follows, therefore, that all “black bodies” radiate alike and obey the same laws. If we can secure such a body, then, we have an instrument of great im- portance. Kirchhoff himself showed that, if a hollow body, such as a cast-iron shell, be maintained at a constant temperature, the radiation inside the space was that which is characteristic of a “lack body” at the given temperature. If a small opening is made from without to the interior of such a shell, some radiation will escape; but the type of radiation inside will not be seriously affected ; and, since, through the opening we receive on the outside the random radiation which is characteristic of the interior, we can secure in this manner what is practically a “ black-body ” radiator. The various laws which have been deduced for the radia- tion from such a body will be discussed in the next lecture. Measurement of Energy and Power. So far nothing has been said in regard to the measurement of energy or the units in terms of which it is expressed. If we use the C.G.S. system of units, the standard of energy or its units is called the “ erg ”—i.e., the work done by a force of 1 dyne acting through 1 cm.—which is an extremely small quantity, so small that it is more customary to use 10° ergs as the unit. This amount is called a “Joule.” If we are interested not simply in the amount of energy but in the rate at which it is delivered, we introduce the word “power” to signify the energy delivered per unit of time, and if the amount of work is one Joule per second the power is said to be one “ watt.” (On the English system the unit of work is the “ foot-pound ” ; and the unit of power is a “horse-power,” which is defined to be 33,000 foot-pounds per minute—this equals approximately 746 watts. ) There are three standard ways of measuring energy; by rise in temperature, by mechanical means, by electrical methods. A few words should be said in regard to the first and third. By experi- ments performed by Joule, by Rowland and by others we know accurately the amount of energy required to raise the temperature of water; and by the experiments of Regnault and many others we know the ratio between the amount of energy required to. raise the temperature of water and that required to raise the temperature. 18 ILLUMINATING ENGINEERING of other substances. Consequently, if we can observe the rise in temperature owing to heat-causes of any body of known character,, and of known weight, we know accurately the amount of energy supplied. Thus, if radiation falls upon a body and is totally absorbed, we have a means of measuring the amount of energy received. In the case of experiments with electric currents we know that the energy consumed per second is equal to the product of the electro-motive force and the current; and the units of the ampere, the volt and the watt are so chosen that, if the electro-motive force as measured in volts is multiplied by the value of the current in amperes, the product is the number of watts of power furnished by the current. It is easy to see how by having this simple means of determining power through the operation of the electric current, we can make use of it for the general measurement of energy. Lecture III Radiation Radiation. By radiation we mean those disturbances. in the ether which are being emitted by matter of all kinds and at all times. For a proper study of its nature we require instruments which analyze the radiation and which measure the quantity of © energy in the radiation. It was observed by Newton that when the radiation from a small source of light was allowed to pass through a prism of glass it was broken up or “ dispersed,” so that the white light of the sun, for instance, was divided into many colors, each particular color corresponding to radiation leaving the prism in a definite direction. This process of analysis of radiation by means of a prism is called “ dispersion”; and the investigations of Fresnel and others showed that what takes place is this; the prism transmits in definite directions trains of waves of definite wave-length; so that, whatever the nature of the incident radiation, that which is transmitted is distributed into regular groups, each group having a definite wave-length and leaving the prism in a definite direction. It was shown by Fraunhofer and others that one could secure dispersion by other means than by the use of a prism, as, for instance, by the use of a dispersion grating. The Bil ate by which the dispersion of light is atid taal is called a “spectroscope.” It consists essentially of three parts: THe PrystcaL BAsis oF THE PRODUCTION oF LiaHT 19 narrow slit through which the light enters; a prism or grating to cause the dispersion; a lens or concave mirror to focus the different streams of radiation on a suitable screen, where the detecting or measuring instrument is placed. Spectra. When the radiation from any very hot source such as the sun or the carbons in an arc light is thus analyzed and spread out according to its wave-lengths, it is observed that only a-small portion affects the eye. This is called “ the visible spectrum.” We see a broad band of light, colored red at one end, and violet at the other. In between these there are different colors, each merging imperceptibly into its neighbors. Certain colors have definite names; and we often speak of red, orange, yellow, green, blue, indigo, violet, as being the “ colors of the spectrum”; yet we must remember that these colors are not isolated; the transition from red to violet is a gradual one. If a photographic plate is held in the region beyond the violet, it is affected intensely; and, if a thermometer is held in the region beyond the red, it shows by its rise in temperature that energy is falling upon it. We are thus accustomed to speak of the “ ultra-violet spectrum ” and the “ infra- red.” When the wave-lengths of the radiations causing in our eyes the color sensations are measured, it is found that a definite color is associated with a definite wave-length; and so we often speak of “ red-light,” etc., meaning radiation of such a wave-length as produces in our eyes the sensation of red, etc. The wave-length of the radiation in the extreme ultra-violet is the shortest of all; then, as the wave-lengths become longer, the blue end of the spec- trum is approached; as it becomes still longer, the color gradually changes from blue to green, to red, etc., down into the infra-red. Recording Instruments. It is not easy to find an instrument which will respond to waves of all wave-lengths, i. e., which will absorb them or will indicate the amount of the incident energy. For waves which are extremely short, much shorter than those which affect our sense of sight, we may use a photographic or a photo- electric process; through the visible spectrum we may also use a photographic process for the detection of the radiation, but for its quantitative measurement, either here or in the infra-red, we must use some modification of a thermometer. Various types of instru- ments have been devised and the problems are now fairly well un- derstood. The four forms of instruments in general use are: a, the bolometer, which is a thin strip of blackened platinum whose 20 ILLUMINATING ENGINEERING change in electrical resistance produced by the radiation is meas- ured; b, the thermo-couple, or junction of two metals forming a closed circuit, whose E. M. F. as altered by the radiation is: meas- ured; c, the radio-micrometer, an instrument in which the thermo- electric current produced by the radiation flows through a .small circuit suspended between the poles of a magnet, and can therefore be measured by the deflection. produced; d, the radiometer, a modi- fication in Crookes’ original form of the instrument, depending upon the repulsion produced by incident radiation in a blackened disk suspended in a partial vacuum. Any one of these instruments, when properly calibrated, may be used to measure the energy of radiation. | | Classes of Spectra. If the spectra of solids and liquids are studied, it is found in almost every case that there is a continuous spectrum, having its maximum in a: region depending primarily upon the temperature of the source. On the other hand, if a gas is made luminous by the discharge through it of an electric current or by any other means, it is noted that its spectrum is discon- tinuous, i. e., is made.up of isolated trains of waves. When the light from a white-hot solid is allowed to fall upon any body such as a piece of glass or a tank containing some liquid, a certain amount of the radiation is absorbed by the body, and if the trans- mitted radiation is analyzed by a prism or a grating the resulting spectrum is called “the absorption spectrum” of the body. It is obvious that the nature of this spectrum depends not simply on the body itself but also on the character of the source. : Temperature Radiation. In the preceding lecture some time was devoted to the discussion of the conditions under which Kirchhoff’s law of radiation and absorption could be applied. It may be re- membered that these conditions were as follows: If a body is emitting radiation and if its temperature is maintained constant by suitable means, then, provided there are no permanent changes produced in the body, it obeys Kirchhoff’s law and. the radiation which it emits is called “pure temperature radiation.” ‘The im- portance of this discussion and definition comes from the fact that for bodies which are emitting such radiations it is possible by apply- ing certain general principles of physics to deduce theoretically certain relations between the temperature of the body and its radia- tion. Further, if the radiation from a “black body” is studied experimentally, certain empirical laws connecting gas, temperature THe PHysicAL BAsts oF THE PRODUCTION oF LiacutT 21 and energy of radiation may be learned, and all “black bodies ” radiate alike. This matter will be referred to more in detail to- wards the end of the lecture. It is extremely difficult to obtain pure temperature radiation, though we can approximate closely to it by the use of a “ black body ” such as described in the last lecture. Luminescence. In general, however, when a body is emitting radiation there are changes going on in it even if its temperature is maintained constant by heating it from without; such bodies are said to: be “ luminescent.” ‘We have many types of luminescence and it may be worth while to say a few words concerning some of these. ‘There is what is called ‘ chemical luminescence,” which is illustrated by the slow oxidation of phosphorus; there is “ electro- luminescence” which we have when a gas is made luminous by an electrical discharge; there is “ fluorescence,” which is observed in many bodies and consists in the absorption of light of a certain wave-length, and in the emission of light of a different wave-length. The exact energy relation for the various cases of luminescence are not clear in all cases; nor is it possible to state any relations which connect the radiation with the physical properties of the source. ‘Photometry. The most obvious property of radiation is, of course, its power to affect our sense of sight in case the source has a temperature sufficiently high, or in case it is emitting waves suf- ficiently short. As has been said, we associate different colors with different wave-lengths, and the question therefore as to our color sensation depends primarily upon two things; the nature of the radiating source and the power of our eyes to recognize color. The physiological action of the eye is to be discussed in later lectures ; and it may be sufficient to note here that the eyes of most people are competent to distinguish colors with great accuracy, provided the illumination is sufficiently intense. The most important matter connected with radiation is the ques- tion of the energy carried by the trains of waves of definite wave- length. This can be investigated obviously by means of a suitable dispersive apparatus and a sensitive recording instrument, such as a bolometer or radio-micrometer properly standardized. But this is largely of theoretical importance. What we are most closely concerned with is the question as to the intensity of the effect of radiation upon our eyes. The investigation of the various problems connected with this forms the science of photometry. We must - find suitable methods of comparing the efficiency of various sources 22 ILLUMINATING ENGINEERING of light in producing light sensation; this implies a study of the intensity of the light sensation, of the energy required for this, and of that portion of the energy of the source which is radiated in the invisible portions of the spectrum. Colors of Objects. We are concerned most often, however, not with the color of the source of light itself but with the color which natural objects appear to have when viewed in a certain. light. ‘We ordinarily call a leaf green, a brick red, ete., meaning simply that when viewed.in sunlight these objects have these colors. If we study carefully many cases of colored objects we soon recognize that their color is in general due to one of two causes. The com- monest of all causes is what is called “ body absorption,” and is illustrated perfectly by a piece of colored glass, a tank of colored water, flowers, etc. The process is as follows: The incident light penetrates into the body, where certain trains of waves of definite wave-lengths are absorbed, and where the rest of the light is either transmitted or is scattered in all directions by small inequalities or dust particles. Consequently, if one looks at the object either by transmitted light or from any direction, he will receive in his eye only that portion of the incident light which is left over after the absorption in the interior of the body. If the incident lght is white, and if red light is absorbed by the body, it will appear blue, because when white light loses its red constituent it becomes blue. It is evident therefore that the nature of the color which an object appears to us to have depends vitally upon the nature of the hght in which it is viewed, because we see in the end that light which is the result of subtraction from the incident light owing to ab- sorption. The same body will appear to us of a different color, if the color of the source is changed. If the light after passing through one colored object is allowed to fall upon a second, and if we view this transmitted light we have, of course, a double sub- traction. ‘This is the process which we have ordinarily in the mixing of paints. The explanation of the color of a painted object is ex- actly that just given; the light enters a short distance and is scattered out, so that if two paints are mixed we have a double subtraction. It is hardly necessary to emphasize the importance of this general discussion of color in the question of the illumination in a room, 1. e., the effect of the color of the wails, curtains, etc., upon the Pensell illumination, etc. CI THer PuHysiIcaL BASIS oF THE PRODUCTION oF LIGHT 23 There are certain objects, however, which owe their color to a process different from this, as, for instance, metals and the aniline dyes. In their case the incident light suffers absorption at the surface, not in the interior, and so their color is said to be due to “surface absorption.” There are many other exceptional cases of color about which noth- ing need be said at the present time, such as the colors associated with luminescence, interference, the scattering th to fine parti- cles, ete. . Laws of Temperature Radiation. The most important type of radiation is, as has been said repeatedly, pure temperature radia- tion; and for many years many competent observers have been in- vestigating the connection between the temperature of the “ black body ” emitting such radiation and the nature of the spectrum and the amount of the energy. It has been shown that, if all the energy emitted is measured by using a suitable absorbing instru- ment, the connection between the temperature of a source and the total quantity of the energy may he expressed by an extremely simple formula, namely, energy emitted=a(t+273)4, where t is temperature on the gas scale, and:a is a measurable con- stant, independent of temperature. This is called “ Stefan’s Law.” This evidently furnishes a means of defining a scale of temperature in a region where a gas thermometer could not be used, since we can measure the energy emitted by bodies at all temperatures. The method, of course, is to take the law as given, which states the relation between gas temperature and energy over the extreme range to which a gas thermometer can be used, and define the tempera- ture for regions of higher temperature by the formula itself. That is, we would measure the energy from a certain source and by the use of the formula deduce the value of the temperature. It should be clearly understood that there is no assumption involved in this; it is a matter of definition. It has been found further that, when the energy of a “ black body ” has been dispersed into its spectrum, and the amounts of energy carried by trains of waves of definite wave-length are meas- ured, there is also a connection between the distribution of this energy as a function of the wave-length and the temperature of the source, as measured on the gas scale. Several formulas have been > +4 24 ILLUMINATING ENGINEERING derived from these experiments; and here again we have a means of defining a temperature scale which can be applied to extremely high temperatures. All these scales defined by radiation formulas seem to agree to a high degree of accuracy. One of these relations, known as Planck’s law, may be written where E, is the energy carried by waves whose wave-lengths lie between A and A+dA, T is written for t+273,'e is the base of the natural system of logarithms, C, and C, are constants. Two other relations are: : Anie Usaconst: = = const. where T is again written for t+273; Amaw is the wave-length cor- responding to the maximum value of E, for the temperature T; and E, is the value of E, at this wave-length Amac- II THE PHYSICAL CHARACTERISTICS OF LUMINOUS SOURCES By Epwarp P. Hypsg CONTENTS LECTURE I 1. Introduction. A. What is light? B. The conditions to be fulfilled by light sources. C. The sources of supply and loss of energy. 2. Luminous efficiency. A. Sensibility of the eye to energy of different wave-lengths. a. Time relation between stimulus and sensation. b. Sensibility a function of absolute intensity of illumination (Purkinje effect). Luminosity curves for various illuminants. . Mechanical equivalent of light. a. Unsatisfactory nature of ordinary definition. b. Mechanical equivalent of most efficient monochromatic radia- tion (M= 800 lumens per watt). D. Highest possible efficiency of white light (about 300 lumens per watt). E. Highest possible efficiency of black body radiation (about 140 lumens per watt). F. Quantities entering in discussion of efficiency. a. Power supplied to lamp (Q). b. Power radiated by lamp (R). c. Power dissipated by convection (C,). d. Power dissipated by conduction (Cy). e f on . Power radiated in visible spectrum (L). . Luminous flux in lumens (¢). 3. Quality of light. A. Integral color of composite light. B. Spectral distribution. 4. Temperature radiation. A. Black body radiation. a. Properties of the theoretical black body. b. Quantity and quality of black body radiation at various temperatures. 26 B. ILLUMINATING ENGINEERING c. Ratios of energy radiated in visible spectrum to total energy L radiated Ge at various temperatures. d. Ratios of luminous flux to energy radiated in visible spec- trum (+) at various temperatures. e. Ratios of luminous flux to total energy radiated (x) at various temperatures. f. Temperature of highest possible efficiency of black body about 6000° absolute. Selective radiation. a. No natural body is absolutely “ black.” 1. Difference in emissivity—‘ gray ”’ bodies. 2. Difference in spectral distribution—“ selective ’’ bodies. b. Gray bodies have same efficiency as black bodies at same temperature. c. Selective bodies may have higher efficiency than black body at same temperature. d. Metallic filaments as a rule owe efficiency in part to selectivity. 5. Luminescence. A. B. C. De Accepted definition of luminescence. Query as to significance of term “ luminescence.” Employment of terms in present lectures. Types of luminescence. a. Chemi-luminescence. b. Photo-luminescence or phosphorescence. c. Electro-luminescence. LECTURE II 1. Introduction. 2. The physics of the electric incandescent lamp. A. DB: C. D. C’?R loss in leading-in wires. Loss by thermal conduction and convection of gas negligible in commercial lamps. Relation between loss through gas and pressure of gas for special platinum filament lamp at about 1700° absolute. Loss by thermal conduction along leading-in wires and anchor wires not more than 5% for commercial tungsten and 7% for tantalum lamps. . Radiation arises from temperature and not iuminescence. . Efficiency of metal filament lamp partly due to temperature of operation and partly to favorable selectivity. Osmium prob- ably most selective of ordinary filaments. L . Values of R for incandescent lamps. . Relations between voltage, current and candle-power for in- candescent lamps. PHYSICAL CHARACTERISTICS OF LUMINOUS SOURCES BY 3. The physics of the arc lamp. A. B. C. : : L . Data on conduction and convection losses, and on values of =- Definition of “arc.” Characteristics of arc discharge. Distribution of potential in the arc. a. Fall of potential at anode. b. Fall of potential along vaporous path. c. Fall of potential at cathode. . Sources of luminous flux in the arc. a. Anode principal source of luminous flux in direct current open and enclosed arcs. b. The two electrodes equally the principal sources of luminous flux in alternating current open and enclosed arcs. c. The luminous vapor the principal source of luminous flux in “luminous” and “ flaming” arcs. . The difference between “luminous” and “ flaming” ares im- portant from physical standpoint. . Is luminosity of gas to be ascribed to selective temperature radiation or to so-called ‘“‘ luminescence ’’? . Probable temperatures of anode, cathode and vapor in open carbon arcs. . Conduction and convection losses in arc lamp not accurately known. L . Values of and ae for various types of arc lamps. physics of low pressure arcs and vacuum tubes. . Distinction between arc and vacuum tube discharge. . The ordinary mercury vapor lamp an enclosed luminous arc at low pressure. a. Efficiency ascribed to luminescence with large percentage of radiation in the visible spectrum. . The mercury arc in quartz tube operated at higher current density and increased efficiency. a. Temperature radiation supposed to supplement luminescence in quartz mercury arc. R for mercury arcs meager. . In vacuum tube discharge the character of the light depends on nature of gas between electrodes. . Owing to distribution of potential in vacuum tubes, long tubes are necessary for high luminous efficiency. . Luminous efficiency of vacuum tube sources ascribed to lumi- nescence. physics of open flames, and of the incandescent mantle. . The ordinary open flame owes its luminosity to the temperature of carbon particles heated to incandescence. . The temperature of Bunsen flame about 2100° absolute at its hottest part. 28 ILLUMINATING ENGINEERING . The peculiar radiating properties of rare earths and their mixtures. . Hypotheses that have been advanced to account for high effi- ciency of mantles. ’ a. Luminescence. b. Localized high temperature due to catalysis. c. Selective emission at temperature consistent with that of Bunsen flame. . Most generally accepted theory at present that given under D—c, but question still in doubt. . Peculiar phenomena of mixtures of thoria and ceria explained on basis of relative emissivities and selectivities of the two substances. . Estimates of temperature of incandescent mantle. L . The luminous efficiency of mantle and values of se . Temperature of acetylene flame. L . The luminous efficiency of acetylene, and the value of a physics of the Nernst glower. . The glower a “solid electrolyte,’ composed of oxides of rare earths. . Conduction, convection and other losses. . Probable temperature of glower. if . The luminous efficiency of the glower and the value of “hs physics of the fire-fly and other light-producing organisms. . The high efficiency of the fire-fly due to extremely selective luminescent radiation. . Light-giving properties of bacteria and other organisms. distribution of energy in the spectra of the various luminous sources. . Spectra of gases, liquids and solids. a. Unique spectra of rare earths. . Energy distribution in visible spectrum of ordinary illuminants. . Energy distribution in infra-red spectrum of ordinary illu- minants, quality of light from the various luminous sources. . Integral color and continuity of visible spectrum. . Colorimetric measurements of ordinary illuminants. Lecture I 1. Introduction The sensation of light is produced normally when radiant energy transmitted through the luminiferous ether in electro-magnetic waves of sufficient amplitude, and within certain limits of wave- length impinge upon the retina of the eye. It is necessary to $ PHYSICAL CHARACTERISTICS OF LUMINOUS SOURCES 29 keep in mind that the ultimate object of every luminous source is to produce the sensation of light, and that therefore the relation between the psycho-physiological sensation and the physical stimulus furnishes a fundamental criterion in an analysis of the physical characteristics of luminous sources. However, the first condition to i fulfilled by a luminous source is that it radiate energy within the limits of the visible spectrum. This is the initial condition, but there are many other conditions, physical and non-physical, scientific and aesthetic, which determine the real efficiency of a luminous source, where by efficiency is meant the degree of adaptability to the required end. From a physical standpoint, the energy relations in the production of luminous energy are of prime importance. The interest centers in the ef- ficiency of the transformation of the energy supplied to the lamp into the light received from it. A definite amount of what is familiarly termed ichematdd: energy is stored up.in the molecules of acetylene and oxygen. After com- bustion a smaller amount of energy is stored up in the resultant molecules of CO, and water vapor, a part of the residue becoming available as light. The gross efficiency of the combustion of acety- lene as a source of light is the ratio of the light produced to the energy stored up in the molecules of acetylene and oxygen before combustion, the two being measured in appropriate units. The energy stored up in the resultant molecules of CO, and water vapor may be considered as waste so far as the present transformation is concerned. This example illustrates chemical rather than physical relations in transformation of energy, but serves to show that in many cases the two are intimately interconnected. Judged from a purely physical | aspect the efficiency of the acetylene lamp depends en- tirely upon the ratio of the light produced to the energy liberated in the chemical transformation. Thus some of the energy is dis- sipated by conduction, some by convection and some by radiation. Of the latter a relatively small part is available as light. The matters of fundamental importance to the physicist, therefore, are the relations of the energy dissipated by conduction and convection to that radiated, the spectral distribution in the radiant energy, and the causes which determine these relations, The incandescent electric lamp furnishes an interesting illustra- tion. A definite amount of energy per second i is supplied electrically 30 ILLUMINATING ENGINEERING to the terminals of the lamp. A part of this is transformed into heat by the C?R loss in the leading-in wires and junctions. The remainder is transformed into heat by the passage of the current through the high-resistance filament. That which is transformed into heat by the C?R loss in the leading-in wires is completely lost, as far as its direct influence on the luminous efficiency of the lamp is concerned. This loss in the ordinary types of lamps manufac- tured at the present time is negligibly small, amounting in most cases to less than 1 per cent. The energy which is transformed into heat in the filament is dissipated in various ways, only a small part of it ultimately be- coming available for the production of light. A part of the energy is dissipated by conduction and convection by the gases in the bulb in cases where the vacuum is not high, but this loss in a good lamp is entirely negligible. Another portion of the energy is dissi- pated through heat conduction by the leading-in and anchoring wires. Thus, owing to the high temperature of the filament com- pared with that of the leading-in and supporting wires with which it comes into contact, there is a continual heat conduction away from the filament at these points, thus cooling the filament locally and decreasing its luminous efficiency. The remainder of the energy transformed in the filament is radiated, the spectral distribution depending upon the temperature of the filament. Only that portion which is radiated in waves within the limits of wave-length of the visible spectrum is pro- ductive of light. As stated above, the loss due to conduction and convection by the gas in a normal lamp must be neglgibly small. It is quite a simple matter, however, to show what a saving is effected in the case of an ordinary incandescent lamp through the use of an evacuated bulb. If a lamp is constructed having a fila- ment of some material, such as platinum, which can be operated either in air or in a vacuum, the difference in power supplied to the lamp when evacuated and when filled with air, the temperature of the filament being the same in the two eases, is quite large. — Thus a platinum filament of 0.1mm. diameter and 15 cm. length, mounted in a pear-shaped bulb of 8cm. maximum diameter and 13 cm. length, when operated at a temperature of approximately 1700° Abs. (Centigrade+ 273°), requires 4.75 watts when the bulb is evacuated, and 24.3 watts when filled with air at atmospheric pressure. In other words, the loss by convection and conduction PHYSICAL CHARACTERISTICS OF LumMINous SourRCcES 31 of the gas is 400 per cent of the total power he ahi to operate the filament in a vacuum. The losses by conduction at the leading-in and anchoring wires have been variously estimated, the values found ranging from an almost negligible quantity to as high as 25 or 50 per cent in various types of standard lamps.’ Attempts at direct measurement of the energy radiated seem to indicate comparatively high figures for the thermal conduction losses, whereas the conclusion from prac- tical experience in lamp manufacture points to rather small losses. Preliminary measurements by a new direct method gave for these losses for normal carbon, tantalum and tungsten lamps values in all cases of the order of magnitude of 5 per cent, which would seem to be more consistent with the experience of lamp manufacturers than the much larger losses found by other investigators. If then the losses by convection and conduction amount to but a small percentage of the total energy supplied to the filament, ex- planation of the relatively low luminous efficiency of the lamp must be sought.in the spectral distribution of the radiated energy. 2. Luminous Efficiency Of the energy radiated by a luminous source only that portion which lies within the wave-length limits of visibility produces the sensation of light. Even within these narrow limits the intensity of the sensation varies greatly with the wave-length when the retina is excited with equal quantities of energy. Thus a quantity of energy which in the deep red or extreme violet is scarcely sufficient to be visible, would in the yellow or green regions of the spectrum produce a moderately strong sensation. The extreme wave-lengths which mark the limits of the visible spectrum are somewhat variable, depending on the individual. For normal eyes radiant energy between the limits of wave-lengths of 0.8 » (4=0.001 mm.) on the red side to a little less than 0.4 » on the violet side produces the sensation of light. With moderately intense sources the eye can perceive rays of wave-lengths down to 0.38 », but there is no sense of color beyond 0.4 p. The energy contained in the visible spectrum of the radiation from an ordinary solid at ordinary temperatures comprises but a very small fraction of the total energy radiated. Beyond the visible on the red side, the infra-red spectrum extends from 0.8» to in- definitely longer wave-lengths, which have been isolated and studied 32 ILLUMINATING ENGINEERING up to 96.7 uw. It is in this region that in most cases the great bulk of radiant energy is emitted. Thus, in the case of the tungsten lamp about 95 per cent of the energy radiated by the filament is emitted in the form of heat rays of wave-lengths too long to excite the human retina. | Beyond the visible spectrum on the violet side the ultra-violet spectrum extends from about 0.4 » or 0.38 » to indefinitely shorter wave-lengths which have been isolated and studied down to 0.1 np. The energy radiated in the ultra-violet region of the spectrum is for all ordinary sources very small, even compared with that radiated in the visible spectrum, and may generally be neglected in the fol- lowing discussion. It has been stated that the energy radiated in the infra-red and ultra-violet regions of the spectrum does not conduce to the sensa- tion of hght, and that even within the narrow limits of wave- length comprising the visible spectrum: equal quantities of energy in different portions of the visible spectrum do not produce the same intensity of sensation. It is of much interest, therefore, and most pertinent to the question of the efficiency of light sources, to consider briefly the relation between the energy of the stimulus and the intensity of the resultant sensation for the various wave-lengths lying within the limits of the visible spectrum. At the outset it is necessary to note that the intensity of the sensation does not depend solely on the intensity of the stimulus, even for any one wave-length. The time interval during which the stimulus acts determines, to some extent, the intensity of the sensation. There is a lower limit to the duration of the stimulus, below which no sensation is produced. As this time interval is increased the sensation rises rapidly for some wave-lengths even beyond that of permanent régime and then falls again to what has been termed the permanent régime, or normal sensation. All of this occurs within a fraction of a second. After the retina has been exposed for a long time to a constant stimulus, the sensation gradually decreases owing to fatigue. The element of time, there- fore, plays an important role in determining the intensity of sen- sation for a given stimulus. There is a second element which should be mentioned at the beginning as determining the relation between the intensity of the sensation and the intensity of the stimulus for different wave- lengths. If there have been found two quantities of energy in the PHYSICAL CHARACTERISTICS OF LuMINOUsS SouURCES 33 red and blue ends of the visible spectrum, respectively, which pro- duce equivalent intensities of sensation where the absolute intensity of sensation is low, it does not follow that the two sensations will remain equivalent if the quantities of energy are greatly increased, even though each is increased by the same relative amount. The red sensation. at the higher intensity would be relatively larger. This phenomenon is familiarly known as the Purkinje effect, and ’ may be stated in general as follows: The relative intensities of sensation for equal energy excitation in different portions of the visible spectrum depend upon the absolute magnitude of the energy stimuli. In other words, the relation between the increase in sen- sation and the increase in stimulus is not the same for different wave-lengths in the visible spectrum. In addition to these two elements of interval of duration and absolute magnitude of the stimulus in determining the relative sensations produced by equal quantities of energy in the different portions of the visible spectrum, there are other psycho-physiological elements which will not even be mentioned here. Moreover, the two elements which have been described briefly will not be con- sidered further in the discussion. It will be assumed, (1) that in every case the stimuli act over a sufficiently long interval to produce the normal sensations of permanent régime; (2) that the absolute magnitudes of the stimuli are always moderately large, since it is only at relatively low intensities of illumination that the Purkinje effect is distinctly noticeable. What, then, under normal conditions, is the relation between the intensity of the stimulus, and the intensity of the sensation in different portions of thé visible spectrum? The answer is given in Figure. 1. The so-called sensibility curve which gives this relation is com- monly obtained by determining the quantity of energy per second necessary in different portions of the spectrum to produce the same luminosity, i. e., the same intensity of sensation. The reciprocals of these quantities of energy are then plotted as the sensibility curve. The curve obtained-in this way is shown in [Figure 1. Neglecting the variations caused. by the Purkinje phenomenon, the relative candle-powers of two sources may be computed by multi- plying the ordinates of the spectral energy curves of the two sources by the ordinates of the sensibility curve, and comparing the areas _ enclosed by the two luminosity curves thus obtained. 34 ILLUMINATING ENGINEERING Luminosity curves obtained in this way for a number of common light sources are given in Figure 2. Curves a, b, c, ete., are the spec- tral-energy curves for the 3.1 w. p.c. carbon lamp, the 1.25 w. p. c. tungsten lamp, the Nernst lamp, and the Welsbach mantle (99.25° per cent thoria, 0.75 per cent ceria) and curves a’, b’, c’, etc., are the corresponding luminosity curves, i. e., the curves showing the relative intensities of sensation produced in different parts of the spectrum. The energy curves are so drawn that the total energy in the visible spectrum (taken arbitrarily for this particular il- lustration as extending between the limits of wave-length A=0.70 pu Vit esl) ei i el i lap tee . BEECHER | LT oe andaun ra | “RBIS S SBA SE Se ~ a wi | bd || wa \ ma | IAI Reciprocals of intensities of radiation A slestea holed et i rebate ae SN eee dX in ie Fiq. 1.—So-Called Sensibility Curve. (Luminosity Curve for Equal Energy Distribution. ) AGRE REGRMaGANS Se Ae Ve wise {ive (RSC aenees See. eome JERE @ on the red side to A=0.48 » on the violet side) is the same for all. In other words, the areas enclosed by the energy curves and the axis of abscissas, between the two limiting ordinates, are equal. It is seen from an inspection of the luminosity curves a’, b’, etc., that although the eye has its maximum sensibility at A=0.545 p, the wave-length of maximum luminosity for most sources is shifted well toward the red end of the spectrum, owing to the predominance of energy in the longer wave-lengths. Moreover, the wave-lengths of maximum luminosity for the various sources are somewhat differ- ent, as are also the shapes of the luminosity curves, owing to the different distributions of energy in the spectra of the various sources. | PHYSICAL CHARACTERISTICS OF LUMINOUS SOURCES 35 The literature on the efficiency of various light sources contains many reports of determinations of the mechanical equivalent of light* where by this term is meant the energy per second within the limits of the visible spectrum which will produce a unit flux of light, measured photometrically—in other words the watts per ECAH pal od Sa I a ass ae \ cov iaas ce RiieRe d\ in p. Fig. 2.—Energy and Luminosity Curves for Various Light Sources. lumen. The determination of the mechanical equivalent of light is an attempt to correllate flux of energy, measured in watts, with the resultant sensation produced, measured in light units. As ordi- narily determined, however, it is subject to criticism in two re- spects: (1) the value found for any light source depends upon the wave-lengths arbitrarily chosen as limiting the visible spectrum ; (2) for any definitely chosen limits of wave-length, the value de- 36 ILLUMINATING ENGINEERING pends on the light sources used. Both deficiencies arise funda- mentally from the same cause, viz., that the mechanical equivalent of light is different for every color or wave-length, and therefore has definite significance only as applied to light of some one wave- length. TABLE I MECHANICAL EQUIVALENTS OF LIGHT AS GIVEN FOR SEVERAL ILLUMINANTS (Wave-length limits taken as 0.38 uw and 0.76 “.) Source Authority bd heed oo HIGIneT ) BEE EEE REE ho JS Sa ee Sane Ree SEE eee eee eter ep N ee a Seimei ore ttt tS eer ie eae tet lel eT | TAS ET TT eet ee eee AA Sipe seme ion eile eb poet fab Peleg rN) Ben img Ae Fig. 10.—Energy Distribution for Acetylene Flame—According to G. W. Stewart. ments carried out with the F. E. Ives colorimeter have been pub- lished by H. E. Ives” for a number of illuminants. These results are given in Table II. White light is taken as that emitted by a black body at 5000° Abs., for which the sensation values are red 33.3 per cent, green 33.3 per cent and blue 33.3 per cent. The color values of the various illuminants are expressed in terms of red, green and blue sensations, such that the three values given add up to 100 per cent. From a consideration of this table it is seen that the carbon- dioxide vacuum tube approaches most nearly to average daylight. 84. ILLUMINATING ENGINEERING Although the spectrum of the vacuum-tube source is always dis- continuous, the number of bright lines in the spectrum of carbon dioxide is very large, and the lines are distributed throughout the entire visible spectrum, being thus equivalent for practical purposes to a continuous spectrum. The other sources which show discon- tinuous spectra, as stated in the discussion of spectral energy dis- tributions, are the low-pressure mercury are and the ordinary lumi- nous and flaming arcs. In the case of the mercury arc the effect of the visible spectrum being composed of a few lines widely sep- arated is plainly shown in the unnatural appearance of certain colored objects illuminated by its light. One significant feature in regard to the integral color of hght sources is the relatively different impressions produced by two lights, each slightly different from average daylight, when the direction of the difference is one way or another. If the color of a light is approximately that which a black body gives at some temperature, it does not appear nearly so strikingly different from daylight, although the hue may be distinctly reddish, as a hght which differs from daylight in such a way as not to lie on the scale of color which a black body assumes as the temperature is varied. The explanation of this phenomenon comes rather within the province of physiological optics than that of physics. TABLE II CLASSIFICATION OF LIGHT SOURCES ACCORDING TO COLOR VALUES Sensation values. SEES Red. Green. Blue. 1. Blacksbody>at/5000° "Abs? 7 7.022 33.3% 33.3% 33.3% 2. Bluevsky ws. 46 the os ee eee 32.0 32.2 35.8 3, Overcast sky! esac Lene ee SHGNiEE LE SRO 31.5 4, Afternoon Aut 2 oa ban tae ee eee olan 3f.3 25.0 GS, FLGINGT ny coe here ccs Giese ee 55.0 38.8 6.2 6°31 we Dd. ‘e.vearbon Wamp ..'). eee dL 40.4 8.3 1 Acetylene) 3363. ORastes 2 lekk eee ee 49.1 40.5 10.5 S.« Tungsten ol 25 nWadid.. 26tt ). ae eee 48.7 40.5 10.9 Dep NOTUS la css be Ee ec ee 49.2 40.7 a Fi 10. Welsbach, 42 Oo" Cerlas wav. st eens 42.5 40.8 16.7 11: “Welsbach "97%, ceria” <2... eae 45.5 42.0 12.5 12.) Welsbach, 14496 ceriadea. Jia gee 47.2 41.8 14.0 13. Direct’ current atemew....... eee 41.0 36.3 oouD 1d) Mercury, ALC hese bes wetnke ee 29.0 30.3 40.7 15. Yellow flame arc. ua0.. a... en eee 52.0 31.0 10.5 16. Moore carbon dioxide tube......... 5a Ne 31.0 one PHYSICAL CHARACTERISTICS OF LUMINOUS SOURCES 85 BIBLIOGRAPHY 1. R. Von Helmholtz, Beiblaetter, 74, p. 589, 1890. 3. L. Hartman, Phys. Zeit. 5, p. 579, 1904. L. Hartman, Phys. Rev. 20, p. 322, 1905. H. Lux, Ill. Eng..(Lond.) J, p. 98, 1908. C. V. Drysdale, Proc. Roy. Soc. A. 86, 1907. Féry et Chéneveau, Bul. Soc. Int. des Elec., 2d Ser. 9, p. 683, 1909. G. Leimbach, Zs. f. wiss. Photog. 8, p. 333, 1910. . H. Rubens and H. Hollnagel, Preuss. Akad. Wiss., Berlin, Sitz. 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Chemie, 38, p. 60, 1904. H. Schmidt, Ann. der Phys. 29, p. 355, 1909. E Bauer, C. R. 148, p. 908, 1909. . Jour. Gas Lt. Lond., p. 318, 1850. . Jour. Gas Lt. Lond., p. 1002, 1887. . vour. Gas Lt. Lond., p22, 1836. . Vienna Pharma. Centische, 2, 1886. Beiblaetter, 19, p. 423, 1895. . R. Bunsen, Liebig’s Ann. d. Chem. u., Pharm. 131, p. 255, 1864. . J. Bahr, Liebig’s Ann. d. Chem. u. Pharm. 135, p. 376, 1865. J. Bahr and R. Bunsen, Liebig’s Ann. d. Chem. u. Pharm. 137, p. 1, 1866. . W. Huggins, Proc. Roy. Soc. 18, p. 546, 1870. See also: Phil. Mag. (4) 30, p. 30251570: L, Haitinger, Monats. f. Chemie, 12, p. 362, 1891. E. L. Nichols and B. W. Snow, Phil. Mag. 33, p. 19, 1892. Ch. St. John, Wied. Ann. 56, p. 433, 1895. C. Killing, Jour. f. Gasbeleuch., p. 697, 1896. V. B. Lewes, Jour. Gas Lt. (Lond.), p. 1104, 1896. 45. 46. 47. 48. 49. 50. dl. 52. 53. 54. D5. PHYSICAL CHARACTERISTICS OF LUMINOUS SOURCES Drossbach, Jour. f. Gasbeleuch. 40, p. 174, 1897; 4/4, p. 352, 1898. H. Bunte, Ber. Chem. Gesell. 31, p. 5, 1897. Moschell, Zeit. f. Beleuch. 11, 1897. H. Le Chatelier et O. Boudouard, C. R. 126, p. 1861, 1898. Bei. zu den Ann. der Phys. 22, p. 313, 1898. A. A. Swinton, Proc. Roy. Soc. 65, p. 115, 1899. W. Nernst and E. Bose, Phys. Zeit. 1, p. 289, 1900. H. Thiele, Ber. Chem. Gesell. 33, p. 183, 1900. H. Kayser, Spectroscopie, 2, p. 161, 1902. C. Féry, C. R. 184, p. 977, 1902. M. Solomon, Nature, 67, p. 82, 1902. H. Bunte, Ber. Int. Cong. d. Chemie, Berlin, May, 1903. St. Clair Deville, C. R., 1903. H. Rubens, Phys. Zeit. 6, p. 790, 1905. J. Swinburne, Elec. (Lond.) 57, p. 744, 1906. H. Kayser, Spectroscopie, p. 452, 1906. Foix, C. R. 144, p. 685, 1907. R. J. Meyer and A. Auschiitz, Sci. Abs. 10 A, p. 588, 1907. Ill. Eng. (Lond.) 17, pp. 173 and 958, 1908. A. Simonini, Trans. Ill. Eng. Soc. 4, p. 647, 1909. H. Le Chatelier et O. Boudouard, C. R. 126, p. 1861, 1898. A, White and A. Travers, Jour. Soc. Chem. Ind. 27, p, 1012, 1902. Holborn u. Kurlbaum, Ann. der Phys. 10, p. 237, 1903. H. Rubens, Phys. Zeit. 7, p. 187, 1906. H. Rubens, Ann. der Phys. 20, p. 5738, 1906. -H. Lux, Zeit. f. Beleucht. 33, p. 375, 1909. 89 A. White and A. Travers, Jour. Soc. Chem. Ind. 21, p. 1012, 1902. H. Lux, Zeit. f. Beleucht. 33, p. 375, 1909. Le Chatelier, C. R. 121, p. 1144, 1895. V. Lewes, Chem. News, 71, p. 181, 1895. Smithells, Jour. Chem. Soc. 67, p. 1050, 1895. . L. Nichols, Phys. Rev. 10, p. 234, 1900. . Ladenburg, Phys. Zeit. 7, p. 697, 1906. . Nichols, Phys. Rev. 11, p. 215, 1900. Aha & 8, p. 257, 1902. . Nichols and W. Coblentz, Phys. Rev. 17, p. 267, 1903. . Stewart, Phys. Rev. 16, p. 126, 1903. . Liebenthal, Praktische Photometrie, p. 357, 1907. . Lux, Ill. Eng. (Lond.) /, p. 99, 1908. J. Morehead, Acet. Jour. 1/, p. 261, 1910. Te 2 _ Angstrém, Astrophys. Jour. 15, p. 223, 1902. See also Phys. Zeit. Bussman und Boehm, EHlek. Zeit. 24, p. 281, 1903. See also EH. De- Fodor, Sci. Abs. 2, p. 713, 1899. M. C. Beebe, Sci. Abs. B, 8, p. 398, 1905. Elec. World, 43, p. 981, 1904. H. N. Potter, Proc. Inter, Elec. Cong., St. Louis, 2, p. 852, 1904. AS, Wurtz, Trans fAul. E B..738iipreslip too. L. Hartman, Phys. Rev. 22, p. 353, 1906. 90 ILLUMINATING ENGINEERING H. Lux, Zeit. f. Beleuch., 1907. G. Leimbach, Zeit. f. wiss. Phot. 8, p. 395, 1910. 56. F. Hirschauer, Elek. Zeit. 29, p. 87, 1908. 57. 58. 59. W. Nernst and W. Wild, Zs. f. Elektrochem, 7, p. 373, 1900. Herzog, u. Feldman, Handbuch d. Elek. Beleuch., p. 70, 1907. W. Wedding, Elek. Zeit. 22, p. 631, 1901. Zeit. f. Instr. 23, p. 178, 1903. Elec. World, 43, p. 981, 1904. M. C. Beebe, Hlec. Rev. 46, p. 657, 1905. J. Herzog u. C. Feldmann, Handbuch der Elek. Beleuch., p. 144, 1907. O. Lummer u. E. Pringsheim, Verh. der Deutsch. Phys. Ges. 1, p. 235, 1899. F. Kurlbaum und G. Schulze, Ber. der Deutsch. Phys. Ges. 1, p. 428, 1908. L. R. Ingersoll, Phys. Rev. 17, p. 376, 1903. L. Hartman, Phys. Rev. 22, p. 353, 1906. Mendenhall and Ingersoll, Phys. Rev. 24, p. 230, 1907; 25, p. 12, 1907. W. Coblentz, Bul. Bur. of Stds. 4, p. 536, 1907. - W. Coblentz, Bul. Bur. of Stds. 5, p. 183,.1908. 60. L. R. Ingersoll, Phys. Rev. 17, p. 371, 1903. 61. 62. 63. 64. 65. Drude, Lehrbuch der Optik, p. 474, 1906. W. W. Coblentz, Bul. Bur. of Stds. 4, p. 553, 1907. W. W. Coblentz, Bul. Bur. of Stds. 5, p. 184, 1908. C. Drysdale, Ill. Eng. (Lond.) 7, p. 648, 1908. S. Langley and F. Very, Phil. Mag. 30, p. 260, 1890. Broomall, Sci. Amer. Nov. 5, 1898. H. E. Ives and W. Coblentz, Trans. Ill. Eng. Soc. 4, p. 657, 1909. A. Krug, Astrophys. Jour. 28, p. 300, 1908. M. E. Bauer, C. R. 130, p. 1747, 1910. E. Nichols and Franklin Amer. Jour. of Sci. 38, p. 100, 1889. ¥. Gaud, C. R. 129, po759;/1899; Blaker, Phys. Rev. 73, p. 345, 1901. P. Vaillant, C. R. 142, p. 81, 1906. E. Nichols, Trans. Il]. Eng, Soc. 3, p. 322, 1908. H. Kayser, Spectroscopie, 3, p. 427, 1905. E. Kottgen, Ann. der Phys. 53, p. 801, 1894. Nernst and Bose, Phys. Zeit. 1, p. 289, 1900. H. E. Ives, Bul. Bur. of Stds. 6, p. 284, 1909. G. Stewart, Phys.. Rev. 16, p. 125, 1903. L. Hartman, Phys. Rev. 17, p. 65, 1903. E. Nichols, Phys. Rev. 30, p. 333, 1910. Kurlbaum und Schulze, Ber. d. Deutsch. Phys. Ges. 1, p. 428, 1903. S. P. Langley, Phil. Mag. 29, p. 52, 1890. . H. E. Ives, Trans. Il]. Eng. Soc. 5, p. 208, 1910. E. Nichols, Phys. Rev. 2, p. 260, 1894. E. P. Hyde, Trans. Ill. Eng. Soc. 4, p. 334, 1909. W. Coblentz, Bul. of Bur. of Stds. 5, p. 360, 1908. W. Coblentz, Jour. Frank. Inst. 170, p. 174, 1910. 66. PHYSICAL CHARACTERISTICS oF LUMINOUS SOURCES ou Le Chatelier et Boudouard, C. R. 126, p. 1861, 1898. O. Lummer and G. Pringsheim, Verh. d. Deutsch. Phys. Ges. 1, p. 235, 1899. Rubens, Phys. Zeit. 6, p. 790, 1905. Rubens, Phys. Zeit. 7, p. 186, 1906. W. Coblentz, Bul. Bur. of Stds. 6, p. 173, 1910. G. Stewart, Phys. Rev. 16, p. 125, 1903. W. Coblentz, Bul. Bur. of Stds. 4, p. 533, 1907. W. Coblentz, Bul. Bur. of Stds. 5, p. 184, 1908. E. Drew, Phys. Rev. 17, p. 321, 19038. W. Voege, Jour. f. Gas Beleuch. 48, p. 513, 1905. H. E. Ives, Trans. Ill. Eng. Soc. 5, p. 208, 1910. D. McF. Moore, Trans. Ill. Eng. Soc. 5, p. 209, 1910. “Eh pera Oe ati RTS & . t a y : = OO er TaaL wet STO Pn fe A me) eat) Aa EE PS | oh ot ORS ne Vel Ge 1 Se oe Ee ae . eh 19 — : 8 \ F * iig ’ &¢ iss ok a - wie: BER Tah, haat 2c Fae a ae % Pr SPAy y ee - a 4 Pt; res 5 ee = LEP? F je | ‘ a ve i pehs fe s \ K ; es ha n oe is be 9 s y . . . 5 s } , * ‘ + eit III THE CHEMISTRY OF LUMINOUS SOURCES By Wiis R. WHITNEY CONTENTS Introduction. Peculiar position of the element carbon in almost all lighting systems. Carbon heated to luminescence in oil, illuminating gas and acetylene flame. Are lighting and incandescent lighting. Substitution of other materials for luminous carbon in flames. Drummond light. Welsbach mantle. Carbon arc lighting—History of. Electrochemistry of the arc. Combustion and electrical migration. Enclosed are and air control. Direct and alternating current arcs. Arcs of other material than carbon. Solids heated by arc. Non-carbon arcs. Iron, magnetite, titanium carbide arcs. Efficiency and size of light unit. ‘The mercury are. Its ultra-violet light and production of ozone. ‘Vacuum tube lighting. The incandescent lamp. Carbon filament. Chemistry of the methods of manufacture. Forming, baking, firing, coating and metallizing. Osmium filament. Tantalum filament. Tungsten filament. Only a few years ago anyone studying the chemistry proper of the sources of artificial illumination might well have been led to conclude that he could confine his efforts to a single element, i. e., carbon. This was owing to its general and peculiar applicability in all types of artificial lighting, no matter how widely they differed in their methods of employment of this interesting element. I even 94 ILLUMINATING ENGINEERING think he might have been forgiven for assuming that in relation to light carbon occupied some such particular place among the ele- ments, as it does in the chemical relations of life. Carbon, of all the elements, is the basis of organic chemistry and the one funda- mental element without which organic substance and life itself are impossible. All artificial hght was at that time due to carbon heated to incandescence. The efficiency of the light sources de- pended on the efficiency of maintaining carbon at a high tempera- ture. In the various types of oil lamps which were in use several thousand years ago, the light is due to the incandescence of carbon. This carbon is a product of decomposition of the vapors of the oil. It can easily be deposited from the flame and be kept from burning by introducing a cooled surface into the flame. This service of the carbon is a double one in the case of oil and ordinary gas illumination. Here an element is needed which forms readily vaporizable compounds or gases, and compounds, too, which are decomposed by the moderate heat produced by the reaction of the compound with the air, and, finally, the element must itself be non- vaporizable at the temperature of the continuing reaction. In these respects carbon is apparently the only element which possesses the needed properties. It did not follow of necessity that this same element should be best suited for electric are lights and for incan- descent filaments, and yet for half a century it was the mainstay for both methods of illumination. Possibly it is this apparent selective fitness of carbon among the 77 elements that caused post- ponement of attempts at discovery of other methods of illumination. In an address of this kind on the chemistry of luminous sources (a subject selected to properly fit into a comprehensive scheme covering illuminating engineering), it seems best to spare special emphasis of selected kinds as much as possible, and to consider in something of a co-ordinating way the chemistry of all the prac- tical methods of lighting. In such a consideration one is soon impressed with the fact that the several different types of illumination differ relatively little in their net efficiency. The labor and material involved in the pro- duction of the light of a candle does not seem to differ much by whatever methods one employs to produce the light. A candle- power from a modern oil lamp, an alcohol lamp, from a gas lamp, or from an electric lamp is, speaking quite generally, a matter of about the same order of magnitude of cost. This would not THE CHEMISTRY OF LUMINOUS SouURCES 95 be so remarkable if they were all nearly perfect illuminants, or if they were all of very high degree of energy efficiency—i. e., if they were all nearly perfect—but they are not. That they are nearly alike in cost is due to the fact that they are all so far removed from the perfect artificial illuminant that the large proportion of wasted energy practically determines the cost. ‘The kerosene oil lamp uses a few tenths of 1 per cent of the energy of the combustion of the oil in the production of visible light waves. The temperature at which the carbon is heated in this flame is so low that almost any other way of heating the carbon will give more light. In the case of the very intense acetylene flame we probably see the effect of much higher temperature of the carbon particles, as this is a hotter flame than that produced by common gas. It is known that the luminous radiation rises ex- ceedingly rapidly with rise of temperature at burning tempera- tures, so that the carbon does not have to be heated very much hotter in order to give off a very much greater light. Probably the range of temperature within which carbon is heated in the various kinds of lamps, excepting the arc and acetylene flame, lies below 1800° C. When ordinary illuminating gas is used, the maximum light is gained by a selected composition of the gas and construction of the burner. This is almost equal to saying that the gas is so mixed with the air which combines with it that none of the carbon produced by ~ decomposition of the gas is allowed to escape as soot, but is, on the other hand, kept heated without combustion within the flame as long and at as high a temperature as possible. If more air were introduced into the flame, less light would be produced, but a locally higher temperature. This is due to the increased rapidity of combustion of the carbon. This fact led to the introduction of other materials than carbon into the flame to be heated by the burning gas. Naturally, very little advance was made along this line until a scheme for making total and rapid combustion of the gas was developed. This was the work of Bunsen, who found that air mixed with the gas in suitable proportions brought about the effect of raising the temperature of the gas flame. In this appli- cation the carbon is immediately consumed and does not lend any luminosity to the flame. The industry waited at least a decade for some suitable substitute for the luminous carbon. It was the 96 ILLUMINATING ENGINEERING exhaustive work of Dr. Auer von Welsbach which produced the mantles of metallic oxides which we know to-day. These, when heated to the high temperature produced by the combustion of mixed air and gas, give a much greater light for a given rate of gas supply than the previous method of use of the same gas. This increased light efficiency is also greatly augmented by the proper selection of the components of the mantle mixture. It would, at first thought, seem probable that any white mantle capable of with- standing the high temperature of the flame would give the same definite, constant quantity of light under the same conditions of heating gas flame. That this is not so is readily shown by a study of the efficiency of various oxide mixtures when used as mantle compounds. There are a number of metallic oxides which do not melt or vaporize at the temperature of the flame, but the most refractory is not the most satisfactory. Each mixture of oxides seems to have its own characteristic light-giving power, and to possess also some considerable selective power in producing color differences. This has led to an immense quantity of purely experimental research, in order to discover what particular compound or mixture would give the most efficient and satisfactory light. As an illustra- tion of this fact, it is worth noting that Welsbach discovered that pure thorium oxide, when used in a mantle, will not give a tenth of the light that will be produced under the same conditions by a mantle made of a mixture of 99 parts of thorium oxide and 1 part of cerium oxide. This very interesting phenomenon will doubtless be taken up by Mr. Whitaker, and is therefore only referred to at this point. An instructive article on this subject was published in the April, 1909, number of the Journal of Industrial and Engi- neering Chemistry. It is the one discovery which has apparently given the illuminating-gas industry the help it needed to keep in competition with methods of electric lighting. Just as no story of incandescent electric lighting can be properly started without at least a reference to the enormous contribution of Edison, so also any history of are lighting properly commences with Sir Humphry Davy. In 1809 he was experimenting with phenomena produced by a battery of 2000 primary cells, and pub- licly showed that a very luminous are was produced when the cur- rent passed across the gas between carbon points. While he may not have been the discoverer of the arc, he was one of the first to THE CHEMISTRY OF LuMINOUS SouURCES 97 see a use for it. For a great many years thereafter no practical application was made of this discovery, because there had not been developed any satisfactory devices for generating the large amount of electrical energy consumed by even a small carbon are. In 1870 the Gramme generator was devised. Carbon are lamps were oper- ated from this machine, in place of batteries. Some of the first attempts at practical use of these machines and lamps were made in connection with light-houses on the English and French coasts. Soon thereafter the Jablochkoff electric candle came into use. This is an arc lamp with parallel carbons. These were kept separated by a thin wall of clay, or a mixture of sand and glass, which gradually vaporized during the burning of the are. At one time several thousand of these were in use in Europe. At the Paris Exhibition, in 1878, the illumination produced by these candles, operated by Gramme machines, marked an epoch in lighting which the previous 30 years of laboratory experiment with arcs had but dimly fore- shadowed. Somewhat later the simple carbon arc was commercially realized, and the clay part of Jablochkoff candles disappeared from the elec- tric lamp for a time. The phenomenon of this direct-current carbon arc is still quite far from being perfectly understood. From the chemical stand- point, the are presents two pure carbon pencils, each of which is slowly consumed. In the ordinary lamp the consumption of the positive, which is usually the upper electrode, is much more rapid than that of the lower or negative electrode. It was long evident that the wasting away of the carbon electrodes was largely due to simple combustion by the air, and many attempts were made to prevent this combustion, while retaining the characteristics of the carbon arc. This Jed to the discovery that the upper electrode is heated much hotter than the lower during the passage of the cur- rent, that carbon actually distills from this positive electrode, and when this carbon cannot burn it will deposit upon the cooler parts of the electrode. This property of building out mushroom growths on the electrodes when operated in vacuo or in inert gases seemed to stand in the way of economizing in such a lamp by practically separating the ordinary combustion of the electrodes from the proper electric-are phenomena. It was finally found, however, that by properly controlling the current and voltage, and by admitting only a very small quantity of air to the globe of a carbon arc lamp, 98 ILLUMINATING ENGINEERING the combustion of the electrodes could be greatly reduced. This air rate, which is controlled by the openings in the supports of the inner globe of the enclosed arc lamp, so greatly reduces the burning of the electrodes that the life is increased ten-fold or more. This gives us, then, the two primary types of carbon are lamps, the open and enclosed. In the closed, as in the open, it is the positive electrode which wastes or burns away the more rapidly of the two; it is the hotter and is the source of most of the light from the are. In the pure carbon arc only a few per cent of the light is due to the flame or are proper. This are stream is far from dense, and most of the carbon in the space is already present as carbon monoxide. While it is out of place here to go very deeply into the con- ceptions of theories which have been formed to cover the action in the arc, it may not be amiss to point out that the simplest ideas are not applicable. For example, it is quite apparent that a motion of positively charged particles across the gap of the are does not account for all the phenomena. As will be seen more clearly later, the negative electrode, at least in most cases, is the one which determines the character of the arc, and a carbon are is still a carbon are when the positive electrode is some other con- ducting substance, while it is usually no longer a characteristic carbon are when the negative electrode is another substance. There is no simple quantitative relation known between the current car- ried in an are and the waste or loss at either electrode. In this respect the arc differs from the passage of current through a gap within a solution, for example. Attempts made to determine the minimum loss of electrode for a given are current have only led thus far to the conclusion that if any quantitative consumption of electrode takes place of necessity when an arc is passing, the quan- tity of material corresponding to a given current is at least a thou- sand times smaller than migrates when equal current passes through a solution or an electrolyte. Moreover, it seems that this motion within the arc is usually, if not always, made up of material from the negative electrode. This general subject has led to a great deal of quantitative work in which are electrodes of other mate- rials than carbon have been used. In: most cases, as with carbon, the results are affected by the simultaneous oxidation of the elec- trodes. Copper and iron electrodes, when used as are terminals, show such irregularities that it has been impossible to accurately THE CHEMISTRY OF LUMINOUS SOURCES 99 determine values of loss at cathode or anode which might corre- spond in some way to the Faraday equivalents in electrolysis. Even when such arcs are operated in inert atmosphere or under water, one usually finds that the material of either electrode has passed in some irregular degree to the other electrode and deposited upon it. Such effects may be largely accredited to simple distillation. Some cases have, however, been found in which the processes of combustion may be fairly well separated from those of current action, and here again it seems proven that in an arc it is essential that material pass from the cathode into the arc space only, and that a consumption of the anode or positive electrode is always an accidental accompanying effect. ‘This will be referred to later. ‘We have thus far considered only the chemistry of the pure carbon arc. Modification of this are of interest to illuminating engineers have been many. It seems necessary to refer briefly to a few of them before considering other arcs. The direct-current carbon arc owes its efficiency to the highly heated crater or arc terminal on the positive carbon. When an alternating-current carbon lamp was measured, it was found that not quite so great efficiency was possible, though by the alternating position of the crater with each change in current direction, the distribution of the light is somewhat improved. Many inventors have attempted to increase the light from a given are energy by introduction of suitable chemical compounds into the arc. Some of these have led to successful commercial lamps. If a small piece of a very refractory material, such as zirconia, be brought into the carbon arc, it is heated to a tempera- ture at which it is very luminous. This is quite like the use of a rod of lime in the Drummond gas lamp. The difficulties in the way of stability, of mechanism, ignition and control, may account for the failure to develop this device in its simplest form. A small zirconia rod placed between the two carbon electrodes (when arranged as ordinarily, one above the other), although patented as an arc lamp, has not been commercially developed. A modification of this scheme, whereby a special form of Welsbach mantle is placed about the carbon arc to be heated by the arc, has also not advanced very far. A considerable difficulty in such schemes lies in the fact that the hot path of the are stream is usually of very small cross-section, and in lamps of moderate energy consump- tion is not easily confined to a limited position, so that it is not 100 ILLUMINATING ENGINEERING easy to keep interposed material heated to incandescence by this means. Countless schemes for continuously introducing powders or va- pors into the are have also been tried. It was found many years ago that the addition of such salts as carbonate of soda to carbon- are electrodes gave added luminosity to the are, reduced the volt- age across the arc and also permitted the arc to be lengthened with- out extinguishing it. Very small quantities of such salts are effective. This general knowledge did not produce the modern flame arcs at once, as the effect of such salts as were used a quarter of a century ago was probably not greatly marked or appreciated. About 10 years ago inventions involving this principle became quite common. Perhaps best known among them are those of Blondel in France and Bremer in Germany. They and others made use of very considerable proportions of salts added to the carbon during the manufacture of the electrode. Usually 10 per cent or more of mineral substance was added, and many different salts were pro- posed. Most successful seem to be the fluorides and chlorides of calcium and magnesium. Some inventors found they were able to construct an operative electrode by using a homogeneous rod of carbon and the salts. Others preferred to confine the salt to a core inside one or both electrodes. In most cases this core also contained some special form of carbon, and in some cases there were two concentric cylinders of various composition about the central core. It has been quite common to use carbon electrodes with a core of soft carbon, as the arc by this means is kept centered on the elec- trode. The present so-called carbon flame arcs, which are usually characterized by great luminosity, with predominance of reddish- yellow color, are made in the above way. ‘The electrodes usually contain so much mineral matter that they cannot be used in en-. closed lamps of the ordinary types. The mineral matter, after passing into the arc, must be carried from the lamp by a good draught, otherwise it will deposit on the globe and soon greatly reduce the luminosity of the lamp. The necessary draught involves also the rapid consumption of the electrodes, so that such lamps usually have to be trimmed or supplied with new electrodes daily. The presence of the salts insures low voltage for the lamp, so that they are usually burned two in series on the 110-volt circuit. The most useful future application of chemistry to this type of flame are lamp will doubtless be along the hnes of producing as THe CHEMISTRY OF LUMINOUS SOURCES 101 great an efficiency in white light as is now produced in the reddish tint. ‘Taken as an electric-light source alone, these reddish-flame arcs are the most efficient of any of the commercial lamps. I attach a table of efficiencies of various kinds of electric lamps for com- parison. Such a table, taken alone, may be very misleading. No indication of color, convenience, size of unit, and other practical considerations, appear in such a table. W.P.C. Carbon (open arc) ..... DC; 10 A. 43 V. 1.43 (spherical) ce (enclosed) ..... Ww AKGS 5 (CA. 80 V. 2.27 ‘ i. (enclosed) ..... A.C. (Doe. 80 V. 2.47 a Sw ervor tame arc ...... Dio: TOP A. 45 V. 42 "s Maenetite are bee oo... DiC: 4 A, 80 V. 1.25 cs BLOUAS GUN pac whe tee ee ara DAC. 5 110 V. 1.7 (horizontal) Metallized carbon ...... 2D 110 V. 2.6 i Se 0 es On a 5 110 V. Pal vs RS Rc oO es D.C, 35D 6 . 3 (pressure) ..... D.C. 3 i: WO RCS re gos p sials 6 3 AO. 1.6 a PE es ye ew vs ss Both 20 Le x Cee Be ee. mi 45 art "s eterno ETT Ls. 243 1.25 * It is particularly in the arcs that the chemical nature of the electrodes plays a determining part. When a ‘simple carbon arc is considered, the quality of the carbon is of the greatest im- portance. Pure graphite is not acceptable, but a hard, dense carbon, quite low in ash and of very fine physical structure, is most satis- factory. For many years these were imported from Germany, and they still are to some extent. In the introduction of new substances to the carbon arc there are many chemical and physical properties which unite to determine the value of the added substance. The salts of many elements add more or less intense colors to the arc, in accord with the spectrum lines of the particular element. This effect is greatly influenced by the degree of volatility of the salt and by the nature of the other elements or compounds vaporizing at the same time. Calcium oxide does not greatly affect the luminosity of the carbon-are stream, while calcium fluoride does. During the past 10 years some advances have been made in the practical use of other arcs than carbon. The best known are the magnetite and the mercury arcs. 102 ILLUMINATING ENGINEERING The magnetite differs chemically from the carbon in being much less combustible, as it burns only in changing from Fe,0, to Fe,O., in giving non-volatile oxides and in giving to the are flame, to a high degree of intensity, the characteristic colors of the iron spec- trum. The iron spectrum is one of those metal spectra which, while made up of defined lines, contain such a great number of them (over 2000 have been mapped) that the effect is practically that of a continuous spectrum. In the magnetite are practically all of the light is due to the are or flame. The luminous positive of the carbon arc is in this lamp replaced by a large block of copper or other metal, which does not contribute to the consumption in the arc, so that this lamp is an are lamp with only a single consuming electrode. The quality of the arc is greatly influenced by the quality of the magnetite electrode. It might seem probable at first that iron itself would be preferable to magnetite, but long series of experiments seemed to show that a compound and rather complex mixture, containing large proportions of pure magnetite, gave the best results. Such arcs must burn steadily and the electrode must contain a small amount of relatively volatile matter, such as the common salts of potash or soda. For a given current the rate of waste of the electrode can be very materially altered by the addi- tion of otherwise inactive materials, such as alumina and chromium oxide, without any considerable reduction in the light produced. This effect is probably due to the reduction of vapor pressure of the iron oxide in the molten top of the electrode. This corre- sponds to vapor-pressure reduction in case of simple solutions. Finally, it was found that the intensity of the arc is greatly in- creased by the addition of another element which has its own rich spectrum, such as titanium. So that the magnetite arc is really the are spectra of iron and titanium superposed. Such strictly are flames have one advantage over carbon arcs, in that they can operate economically in small units. The efficiency of the carbon arc is greater the larger the unit within a wide range, but units below 500 watts begin to be relatively inefficient. On the other hand, the efficiency of the strictly luminous arcs is maintained high as low as 250 or 300 watts. This, to the illuminating engineer, means that he has greater elasticity in the distribution of his lighting energy. The mercury arc may be said to differ but little from the other ares. It is greatly lengthened by being confined to a glass tube, and thus any combustion or loss of material is obviated. Its color THE CHEMISTRY OF LumMINOUS SouRCES 103 and light are determined as in the case of other arcs, by the nature of its cathode electrode. ‘The anode, as in the other arcs, may be made of almost any conductirig material. The vapors which are produced at the cathode condense to liquid state and return by gravity to the cathode. If the chemical elements had more fluid members among those of highly luminous spectra, the principle of the enclosed mercury lamp would probably quickly yield more new and useful lighting methods. The light of the mercury lamp, when broken down by the prism, is seen to be composed of only a few widely separated lines. Among them is no red. For this reason red articles appear black under this light, and, for this reason, many other colors fail to appear natural under the mercury arc. There are two interesting facts concerning the mercury are which may well ultimately be utilized in a practical manner. The are is very rich in ultra-violet light. This is not particularly noticeable when the arc is surrounded by glass, but when pure quartz is sub- stituted for the glass the ultra-violet light penetrates into the sur- rounding air. This produces ozone in a very marked manner, and this unfiltered light has a very serious and injurious effect on the eyes. It is highly probable that this modified mercury lamp is to be the most readily applicable form of ultra-violet light for thera- peutic purposes. Secondly, it has been discovered that when the are is operated under two or three atmospheres of mercury pressure the efficiency is high and the color more nearly approaches day- light. Glass tubes will not withstand the temperature of the arc at this pressure, but quartz will. Such. quartz mercury lamps are being made and sold abroad at the present time. Any considerable practical improvement in the color of the mer- cury arc has not been made by the amalgamation of other elements with the mercury. An element like copper or iron fails to vaporize from the cathode of the mercury are. Some of the alkali metals somewhat alter the light, but most of them also attack the glass of the lamp. It is worthy of note that some fluorescent dies, rhoda- mine, for example, are capable of absorbing the green and blue spectral lines and returning in their place some considerable red, but this has not proven an efficient process. The luminosity of gases and vapors has always. seemed a very promising field of artificial illumination. In the case of heated solids, the laws of radiation, convection and conduction are well enough known, so that a field in which less is known is apt to seem — 104 ILLUMINATING ENGINEERING promising. The Geissler or Pliicker tubes, in which attenuated gases are rendered luminous by relatively high voltage and low- current discharge, are well known to all. It seems very probable that future developments of importance will be made, and already, in the McFarlane-Moore System, very considerable advances have been made. Here the chemical composition of the gases and their pressure are the determining factors of the color and efficiency. A peculiar phenomenon in these lamps is the apparent consumption of the gas or air in the tubes. Gradually, in such apparatus, the gas disappears, as though driven into or combined with the glass. For this reason the inventor of this system has devised an automatic _ inlet valve which operates to let gas into the lamp when the vacuum rises to a certain degree. This seems to be a similar effect to the well-known “ hardening ” of X-ray bulbs from continued use, which is an improvement in vacuum, and is also noted in the case of the vacuum of an ordinary incandescent lamp. Without wishing to go deeply into the history of the incandescent lamp, it is necessary to point a moment to the work of Mr. Edison. The fact that electric current flowing through a conductor could heat it to incandescence had long been known. ‘That carbon in filament form, when preserved from combustion by a vacuum, would make a lamp was clear. J. W. Starr had patented such a lamp in 1845, and Swan, in England, had exhibited one in 1879. But between this point and a satisfactory incandescent lamp was a great eulf, which needed the untiring energies of such an inventor as Mr. Edison to help bridge. , A piece of carbonized thread, confined in such a vacuum as was known when he undertook the work, did — not constitute a practical lamp at all. In the poor vacuum produced by methods used in those days, even a good filament of the present time would have produced but a very imperfect lamp. The simpler methods of producing carbon filaments are capable of yielding only very imperfect lamp filaments. There are few artificial products which excel the filament in the divergence between apparent sim- plicity and actual complexity. ; The choice of elements for incandescent-lamp filaments may be said to be more nearly a physical than a chemical problem, but in the manufacture of all of them chemistry plays a dominant role. The best carbon filaments now in use may be described as con- sisting of a core of pure carbon, not graphite, covered with a coat or shell of pure graphite, which has been so changed by an electric- THE CHEMISTRY OF LUMINOUS SOURCES 105 furnace treatment, under atmospheric pressure, that it has a posi- tive-resistance temperature coefficient instead of a negative one. This graphite coating, to which the name metallized graphite has been given, has the appearance of having been melted or sintered together, and thus differs from all other graphite. The chemical and physical processes by which these carbon fila- ments are produced are as follows: High-grade cotton is dissolved in a strong solution of zinc chloride, which is then squirted through a small hole into dilute alcohol. The alcohol coagulates the viscous solution of cellulose so that a trans- parent thread is the product, and by washing this in running water the zine chloride is removed. Another equally satisfactory method for reaching the same end is to squirt a thick solution of nitro-cellulose, dissolved in acetic acid, into a container holding water. Washing with ammonia sulphide and water changes the nitro-cellulose into non-explosive hydro-cellulose. This product is then dried in the air while stretched on drums. It is then cut to desired lengths, formed into the nec- essary loops on brass frames, and finally packed in graphite boxes in a packing material such as baked peat, and very gradually heated until carbonization takes place. In this process the carbonized filaments are heated to as high a temperature as can be obtained by gas or oil-heated muffles. The product at this point is dense, hard carbon, A even under the microscope, is far from having the appearance of charcoal, and seems almost free of pores. The carbon filament in this form would make a very inferior lamp. The color or quality of its sur- face, and probably the volatility of its material, is not nearly so fa- vorable to lamp making as the corresponding properties of graphite. At any definite operating energy the amount of light produced by a gray-graphite surface is greater than that produced by a black-carbon surface, so that the carbon filaments are graphite- coated. This is done by heating them by the current in an atmos- phere of hydro-carbon, such as benzine, at low pressure. The quality and thickness of the coat may be controlled by the duration and temperature of the treatment. Until a few years ago the greater part of all carbon filaments were made in this way. It was then found that the effect of subjecting the graphite-coated filaments to temperatures above 3000° C. for a few minutes changed the graphite very materially in its properties. ‘Those which are of interest to 106 ILLUMINATING ENGINEERING us now are the resistance, its temperature coefficient and the sta- bility at operating lamp temperatures. Briefly, the resistance of the graphite coat is reduced to about 20 per cent of its original re- sistance. Its temperature coefficient is reversed and its lasting powers in the lamp increased nearly three-fold. This point seems a proper one at which to mention the standard of use for incandescent lamps as determined by practical conditions. Burning at a low efficiency, an incandescent lamp has practically an indefinite life. At 3 watts per candle-power it may have 1200 hours’ life and at 2.5 about 500 hours to 80 per cent of its original candle-power. It has been found by use that about 500 hours’ life for a carbon lamp is most practical, this 500 hours being the length of time the lamp remains above 80 per cent of its starting candle- power. ‘The metallized filament lamps, therefore, instead of being burned at the former efficiency of 3.1 watts per candle, are made to burn at about 24 .w.p.c., at which they have about 500 hours’ life. Evidently the higher the cost of the lamp the more stress has to be laid upon long life, while with very cheap lamps there is an advantage gained by burning them at unusually high efficiency and replacing them at the end of much less than 500 hours. The history of the development of the various metallic filament lamps is particularly interesting from the chemical standpoint. In the early days of incandescent lighting Mr. Edison and others rec- ognized the peculiar value of metallic filaments because of their flexibility and electrical conductivity. At that time platinum and iridium were the metals which offered most promise. ‘They were the metals of highest melting point, so far as then known. It was soon apparent that these metals could not be run at high enough temperature to make a practical lamp, though they were very nearly suitable. Mr. Edison then carried out a great number of experi- ments in an attempt to raise the melting point of the platinum. The effect of the occluded gases was carefully studied, but a com- mercial lamp did not result. For over a quarter of a century there- after, it remained unknown that at least six or seven of the then known metals had higher melting points than platinum. The en- tering wedge into this field was driven by Dr. Auer von Welsbach, who had acquired a personal and almost exclusive knowledge of a large group of more or less rare chemical elements in connection with his extensive researches, which were crowned by his gas-mantle inventions. At this time probably none of the metals which melt. THE CHEMISTRY OF LUMINOUS SouRCES 107 higher than platinum had ever been produced in any other form than that of a fine black powder. Osmium was the first of a trio of metals to become a nearly practical filament. It occurs in nature in metallic state, usually alloyed with iridium, platinum, rhodium and ruthenium. It is found only as very small grains or plates, and nowhere in any considerable quantity. By mixing powdered metallic osmium with a suitable starch or sugar binder, Welsbach squirted a thread which, after drying and baking, could be freed of carbon by heating in a mixed atmosphere of hydrogen and water- vapor. The resulting metallic filament was quite soft when hot, but was well suited for incandescent lamps, as it withstood tem- peratures necessary to produce a lamp burning satisfactorily at about 1144 watts per candle-power. The world’s known supply of osmium is very small, and to conserve this supply the lamps were usually rented instead of being sold. In 1901 Dr. Werner von Bolton announced the discovery of ductile tantalum. Operating in an incandescent lamp, it could be burned at about 1.7 watts per candle-power for a thousand or more hours. The metals tantalum and niobium are a pair usually occur- ring together and formerly quite difficult of separation. They occur in small quantities in Connecticut, in the Black Hills of Dakota, in Sweden and in Australia, the mineral being usually tantalite (a compound of the oxides of tantalum and iron, with or without manganese or tin) or some combination of tantalum and niobium oxides with iron, etc., as columbite, samarskite, fergu- sonite, etc. It was necessary’ first to perfect methods of preparing the pure metals, and of these the tantalum was found to have the higher melting point. It is about 3100°, while that of niobium is about 2900°, or still well above platinum. Until this investigation it had apparently been known only as powder. This powder was melted together into large buttons in an electric are and then drawn to wire in the usual manner through diamond dies. | Probably most, if not all, of the tungsten filaments in the lamps on the market are made by some method of squirting through a die tungsten powder mixed with a binding agent. The metal, in finely divided state, is usually obtained by the reduction of tungstic oxide at a red heat by hydrogen. This oxide is in turn obtained from the minerals Wolframite, which is a tungstate of iron or iron and manganese, and Scheelite, a tungstate of calcium. Several 108 ILLUMINATING ENGINEERING thousand tons of ore, averaging over 50 per cent tungstic oxide, are mined annually, largely for use in high-speed tool steel. Some of the successful processes for making the filaments are as follows: The powdered metal is mixed with a proper carbonaceous binder, then formed into threads by being forced through a suitable die, dried and baked at about red heat. They are then heated by pas- sage of current through them in a suitable atmosphere of hydrogen or mixture of hydrogen and nitrogen. By this treatment a shrink- age of the filament takes place, it becomes dense and metallic in appearance, and at the same time the carbon present is removed.. The product is, therefore, pure tungsten. Similarly, a metallic binding agent may be used. The finely divided metal in one such process is mixed with a cadmium-bismuth amalgam and the resulting mixture is pressed through a die. A thread not unlike a fine, lead fuse wire is the result. On heating this in in vacuo all metals but the tungsten are vaporized, and at the final temperature this is also sintered together into a compact filament. In the case of tantalum, nature seems to supply just about enough of the ore to satisfy the demand, and probably this element would have been a more successful competitor in the incandescent-lamp field if it only had to contend against carbon and osmium. It was more efficient than the former and much more plentiful than the latter. It is interesting to recognize the fact that the most recent successful metal filament, tungsten, occurs in nature in abundance. It was discovered by Scheele in 1781. For over 200 years it was. known in the pure state only as an infusible gray and heavy metallic powder. Its melting point, as determined by Pirani, is 3350°, and is the highest melting point of which we have measurement. The only measurement of higher temperature on the earth is that of the carbon-are crater, said to be about 3500° C., by Burgess and ‘Waid- ner. In all types of incandescent lamps there lies a promise that continued study will give continued advance in the art. This is sought usually as higher efficiency. A carbon lamp will burn a few moments at an efficiency 10 times as great as its normal value. In other words, from the materials at hand, this increase in efficiency is possible for a short time. It seems, therefore, not impossible. that this limiting time feature may be better controlled when better understood. Jia ELECTRIC ILLUMINANTS By CHARLES PROTEUS STEINMETZ CONTENTS GENERAL . The different forms of radiators and different kinds of radiation. Classification of electric illuminants. . Importance of the volt-ampere characteristic and the resistance- temperature characteristic of the conductor used in electric illuminants. Discussion of the multiple or constant potential, and the series or constant-current electric distribution system. SoLip CONDUCTORS . Volt-ampere and resistance-temperature characteristic of incandes- cent lamp filaments. Positive and negative temperature coeffi- : d Se ; : cients, — >0. Stability of operation on constant potential and on constant current circuits. [Fig. 1: Volt-ampere characteristics of incandescent lamp filaments. Fig. 2: Resistance-character- istics of incandescent lamp filaments. | . Volt-ampere characteristic of pyroelectrolytic conductors. The Nernst lamp glower as pyroelectrolyte. The instability range, d aH <0, of pyroelectrolytes on constant potential supply, and the necessity of steadying resistance or reactance. The Nernst lamp. [Fig. 3: Volt-ampere characteristic of low resistance pyroelectro- lyte. ] . The light radiation of solid conductors, as incandescent lamps and the Nernst lamp glower. Black-body, gray-body and colored- body radiation. Effect on the efficiency of the incandescent lamp filament and the Nernst lamp glower. Limitation of efficiency. . Relation of refractoriness and vapor tension or disintegration, to the possible efficiency of the incandescent lamp. Comparison of the carbon filament with the metal filaments. . The production of the carbon filament lamp. Base carbon and treated carbon, and their stability. . Metallized carbon, its resistance and temperature coefficient, and the gem lamp. . Metal-filament incandescent iamps. Osmium lamp, tantalum lamp, tungsten lamp. Their efficiencies. 110 ILLUMINATING ENGINEERING 10. Be 12. 13. 14. 15. 16. 17. 18. a9: 20. 21. 22. The manufacture of the tungsten lamp. Thinness and length of metal filaments. Fragility. Efficiencies of the different incandescent lamps. Conventional rat- ing in horizontal candle-power. Relation of efficiency to useful life. Relation of the efficiency of the incandescent lamp to the size of the unit, or the power consumption. Limitation by supply voltage at small units, by size of the lamp globe at large units. Wide range of units with fairly uniform efficiency. Inferiority of the incandescent lamp in efficiency, to the flame arc and luminous arc.. Superiority in small units. Main field of application of incandescent lamps and Nernst lamps in small units, where no other electric illuminant exists. GASEOUS CONDUCTORS . Difference between disruptive or Geissler-tube conduction, and con- tinuous or are conduction. ' GEISSLER-TUBE CONDUCTION Electric characteristics of Geissler-tube conduction: total voltage, terminal drop and stream voltage as function of gas pressure. [Fig. 4: Volt-pressure characteristic of Geissler tube with air as conductor. Fig. 5: Volt-pressure characteristic of the Geissler tube with mercury vapor as conductor.] Performance. efficiency and color of light. The Moore tube Arc CONDUCTION Nature of the are conductor. The are as unidirectional conductor. Rectification by the are. The alternating current arc. Constant- pressure and varying-pressure arcs. d Volt-ampere and volt-length characteristics of the arc: =: ee th [Fig. 6: Volt-ampere characteristic of magnetite arc of .5, 1.5 and 2.5 cm. length. Fig. 7: Volt-length characteristic of magnetite are at 2, 4, 8 and 16 amperes. ] Dependence of the arc voltage on two independent variables, current and are length. Instablity of the are on constant voltage supply. Necessity of steadying resistance or reactance. The stability curve of the are. [Fig. 8: Stability curve of the 1.5 cm. magne- tite arc.] Instability of parallel operation of arcs without steadying resis- tances. Instability due to non-inductive resistance shunt. Ex- tinction by shunted capacity. The arc as interrupter. The singing arc. Stream voltage and terminal drop of the arc. Heating of the termi- nals by the terminal drop. The carbon arc as incandescent radi- ator. Relation between the efficiency of the carbon arc, and the size and the life of the terminals. 23. 24, 25. 26. 27. 28. 29. 30. 31. 32. 33. ELEctTRIC ILLUMINANTS Ttt The open carbon arc or short burning are lamp. The enclosed carbon arc or long burning lamp. Its inferiority in efficiency. Uneconomical operation of. continuous-current series arc circuits. The series alternating enclosed arc lamp. Its very low efficiency. Replacement of the enclosed alternating carbon are by the magnetite arc lamp in street lighting, by the intensified are or the tungsten incandescent lamp in indoor lighting. The intensified arc lamp. The luminous are and the flame are. Their characteristic differ- ences, advantages and disadvantages. The magnetite arc. The flame carbon arc. Relation between size of electrodes and effi- ciency. The short-burning and the long-burning flame carbon are. The yellow color of the flame carbon are. Titanium, calcium and mercury as the three most efficient arc stream radiators. The mechanism of the arc lamp: starting device, feeding device, steadying device, shunt protective device, damping devices. Series lamp, shunt lamp, differential lamp. The effective resistance of the arc. Relation between arc length and efficiency. The short carbon arc and the long luminous and flame arcs. Regulation of are lamp for constant light flux. The floating system of control of the carbon arc and its advantages. Fixed are length required by the luminous arc. Its difficulties in constant potential lamps. The compromise control of the flame carbon lamp. Classification of arc lamps; the most important forms of arc lamps: The open carbon are on 9.6 amperes series direct current circuits. The enclosed carbon arc, for multiple and series circuits, on alternating and on direct current. ; The intensified carbon arc, on alternating and on direct cur- rent circuits. The vellow flame carbon arc, on alternating and on direct current circuits. The magnetite arc. The mercury arc. Increase of the efficiency of the arc with increasing size of the light unit. Relation between the efficiency of the arc lamp and the current, arc length and power, at constant arc length, con- stant current and constant power. The condition of maximum efficiency. [Fig. 9: Efficiency and power consumption of the 4- ampere magnetite arc for different arc lengths. Fig. 10: Effi- ciency and power of the .7-inch magnetite are for different cur- rents. Fig. 11: Efficiency, arc length and voltage of the 300-watt_ and the 500-watt magnetite arc, for different currents. Fig. 12: Relation between voltage, current, arc length and efficiency of the magnetite arc, under the condition of maximum efficiency, for various powers. ] Comparison of the arc lamp and the incandescent lamp. 113 ILLUMINATING ENGINEERING Vacuum ARCS 34. The low-pressure mercury arc in the glass tube. The high-pressure mercury arc in the quartz tube. Their characteristics. SENSITIVITY TO VARIATIONS OF THE ELECTRIC POWER SUPPLY 35. Comparison of various forms of incandescent lamps and arc lamps . regarding their sensitivity to variations of the electric power supply. GENERAL 1. The Different Forms of Radiators and Different Kinds of Radi- ation. Classification of Electric Illuminants In the production of light from electric power, solids, liquids or gases (the latter including vapors) may be used as conductors of electric power, and the radiation may be due to incandescence of the radiator, that is, temperature radiation (black-body, gray-body or colored-body radiation), or it may be the result of a more or less direct conversion of the electric power into radiation, as luminescence. | Solids as conductors of electric power are used in the various forms of incandescent lamps: the different types of carbon-filament lamps and the metal-filament lamps, as the osmium lamp, the tantalum lamp and the tungsten lamp, and also in the Nernst lamp. liquids are not used as conductors, due to their difficulty of application, but gases and vapors are extensively used in the various forms of arc lamps, as the open and the enclosed carbon arcs, the flame arcs and the luminous arcs, which latter include the vacuum arcs, and in the Geissler tube as illuminant (Moore light). In the former, the arc lamps, the vapors of the electrode material are used; in the latter, the Moore light, the gas which fills the space between the electrodes. In all solid conductors, and also in the plain-carbon arc lamp, the light production is due to temperature radiation or incandes- cence, either black-body or gray-body radiation, or colored-body radiation. In the flame arcs, luminous ares (including vacuum ares) and Geissler tubes luminescence plays an essential part in the light production. ELECTRIC ILLUMINANTS 113 2. Importance of the Volt-Ampere Characteristic and the Resist- ance-Temperature Characteristic of the Conductor Used in EHlectric Illuminants. Discussion of the Multiple or Con- stant Potential, and the Series or Constant-Current Electric Distribution Systems Since in electric illuminants the light is given by electric con- duction, the properties of the electric conductor, which is used in the illuminant, are of the foremost and fundamental importance, that is, the relation of current and voltage to each other, or the so-called “-volt-ampere characteristic” of the conductor; and the relation of the ratio of volts and amperes, that is, the effective resistance, to the temperature, that is, the “ resistance character- istic ” of the conductor. This is obvious, since the illuminant must be capable of use in the existing electric-power distribution systems. Electric power is distributed in two different forms: by the con- stant-potential or multiple-distribution system, that is, at the con- stant voltage of 110 or 220 volts,* or by the constant-current or series system. In the constant-potential system all apparatus are connected in parallel between the same supply mains, and thereby receive the same voltage, but each takes a different part of the supply current. All the illuminants must therefore be designed to operate at the same constant-terminal voltage of 110 or 220, and within such variations of this voltage as may be met in a constant-potential distribution system, which varies from 1 per cent to 5 per cent or more, depending on the character of the system. The different illuminants, however, may be designed for different currents. The multiple system has the advantage of permitting practically un- limited extension: with increase of the number of illuminants, the current in the supply feeders and mains increases, and larger con- ductors become necessary, but the voltage remains the same. When the number of illuminants becomes so large that the size of supply conductors becomes uneconomical, more sources of supply become necessary. Since, however, these sources of supply are usually sec- * 110 volts here means any constant voltage between about 105 and 125, and 220 volts twice this value: not the same voltage is used in dif- ferent distributing systems, but slightly different voltages, for the purpose of making the economical production of exactly rated incandes- cent lamps possible. (See ‘‘ General Lectures on Electrical Engineer- ing,” by the author, p. 12.) 114 ILLUMINATING ENGINEERING ondary stations, that is, transformers or converters receiving their power from a primary generating system at high voltage, this intro- duces no serious limitation. The constant-potential system of dis- tribution therefore is now generally used, with the exception of those few cases, where it is not economical: at the low voltage of 110 or 220 volts, the distance to which electric power can be sent is rather limited. When numerous illuminants are scattered over a wide area this difficulty is met by secondary stations, as trans- formers, as stated above. If, however, individual illuminants are scattered over a wide area, as in street lighting, the individual illuminants cannot be reached from one 110- or 220-volt feeding point, while the installation of a transformer at every lamp is uneconomical, and in this case the constant-potential system becomes uneconomical and the constant-current system is used. For street lighting the series system is therefore universally employed, with the exception of those few places in large cities where the street lamps can be reached by a multiple system installed for general distribution. In the constant-current or series system all apparatus are con- nected in series with each other, and thereby receive the same current, and the voltages consumed by the different illuminants add. The illuminants therefore are designed for the same current, but may consume different voltages. Since the voltage of a dis- tribution circuit cannot be indefinitely increased without involving difficulties with insulation and danger to life and fire risks, the number of apparatus which can be connected into one series circuit is rather limited; a series circuit is a very small unit of electric power, from our present point of view, and as economy requires the use of the largest possible units series circuits are used only in those cases where they are economically necessary, that is, for street lighting. It was, however, with series arc circuits that electric lighting started in the early days. Series circuits are usually operated at 4, 5, 6.6 or 7.5 amperes, some of the old open carbon are circuits at 9.6 amperes, and with voltages ranging usually from 4000 to 6000. Not all conductors, and therefore not all illuminants, can be connected promiscuously into multiple circuits or into series cir- cuits, even if designed for the proper voltage respectively current, and the study of the electric characteristics of the conductors which are used in illuminants is therefore of importance for their design and operation. ELEctric ILLUMINANTS 115 SOLID CONDUCTORS 8. Volt-Ampere and Resistance-Temperature Characteristic of In- candescent Lamp Filaments. Positive and Negative Tem- perature Coefficients, e >0. Stability of Operation on Constant-Potential and on Constant-Current Circucts The conductors of incandescent lamps are ohmic resistances, that is, conductors in which the resistance does not directly de- pend on current or voltage, but is constant at constant tempera- ture, and if it varies with a change of temperature, in case of a negative temperature coefficient, that is, a decrease of resistance with increase of temperature, the decrease of resistance with in- crease of temperature is less than the increase of current required to cause the increase of temperature. That is, such conductors are characterized by the relation: de di. In other words, an increase of current always causes an increase of terminal voltage. If the resistance were perfectly constant, that is, the temperature coefficient zero, the voltage would be pro- portional to the current, and the volt-ampere characteristic given by a straight line going through the origin, I in Fig. 1, and the resistance characteristic given by a horizontal straight line, I in Fig. 2. No conductor exists which has zero temperature coefficient over more than a limited range of temperature. If the temperature coefficient is positive the resistance increases with increase of temperature, and the voltage thus increases more than proportional to the current; that is, an increase of current 1 causes an increase of temperature and thereby of resistance r, and thus an increase of the voltage e=ir, which is greater than pro- portional to i, as shown in curves II to IV in Figs. 1 and 2. Inversely, if the temperature coefficient is negative the resistance decreases with increase of current, and therefore of temperature ; but the voltage still increases with increase of current, though less than proportional to the current, as shown in curves V and VI in Figs. 1 and 2. As illustrations are shown in Fig. 1 the volt-ampere character- istic, and in Fig. 2 the resistance characteristic of the conductors or filaments of various types of incandescent lamps. In Fig. 1 0; 116 ILLUMINATING ENGINEERING the co-ordinates have been chosen so as to start all curves at the slope of 45° at the origin. In Fig. 2 the co-ordinates have been chosen so as to give 10 at the operating point of the lamp. In Ra Gia aa f° psa | + fda ia) Solos VA 2h 28 ARORA 7 a eg Tee aR Ee 7 shou uon oy So | yaad loa CO i ch A il Fig. 1.—Volt-Ampere Characteristics of Incandescent Lamp Filaments. Fig. 2 as abscissae have been used \w, which with a black-body radiator would be proportional to the absolute temperature (for high values of w). It is: I. The theoretical conductor of constant resistance. II. The tungsten lamp filament. ELECTRIC ILLUMINANTS Tt? III. The osmium lamp filament. IV. The metallized carbon, or gem lamp filament. V. The treated carbon, or 3.1-watt carbon-filament lamp. VI. The untreated carbon, or base filament. Such a conductor, which fulfils the conditions, 6 >0, can be ha SRR Saas mess itl calles — Oa \ Re Resistance Fig, 2.—Resistance-Temperature Characteristics of Incandescent Lamp Filaments. operated satisfactorily on constant-potential as well as on constant- current circuits, provided, obviously, that its resistance is chosen so as to consume the rated power at the constant voltage respectively current of the circuit; on constant-potential supply the current, and thereby the power consumed by the conductor, is limited to 118 ILLUMINATING ENGINEERING that corresponding to the supply voltage; on constant-current supply the terminal voltage, and thus the power consumed by the conductor, is limited to that corresponding to the supply current. 4. Volt-Ampere Characteristic of Pyroelectrolytic Conductors. The Nernst Lamp Glower as Pyroelectrolyte. The Insta- bility range, “© tial Supply, and the Necessity of pane Resistance or Reactance. The Nernst Lamp <0, of Pyroelectrolytes on Constant-Poten- Very different are the conditions in the conductor of the Nernst lamp, the Nernst lamp glower. This belongs to a class of con- ductors, the pyroelectrolytes, in which the temperature coefficient within a certain range of temperature, and thus of current, is so greatly negative, that with increase of current the terminal voltage decreases. That is, with increase of temperature the resistance drops faster than the increase of current required to produce the increase of temperature, and the voltage e=ir thus decreases with increase of i. In this range, it therefore is: Such pyroelectrolytic conductors are many metal oxides, silicates, sulphides, ete. A typical volt-ampere characteristic of such a con- ductor (magnetite) is given in Fig. 3, with Vi as abscissae,* the terminal voltage e as ordinates. As seen, from i=0 to i, it is ee >0; from 1, tons is 2 <0, and for i>1, it is again Se >0. With most pyroelectrolytes the voltage peak at i, is so high that the conductor cannot be carried beyond it by the mere application of voltage, but artificial heating is required, and the resistance below i, is usually extremely high, usually near i, fusion occurs, and beyond that the conductor is an ordinary electrolytic con- ductor. The operating point of the Nernst glower is in the range between d ° . e i, and i,, where a ~<" i * For the purpose of better showing the initial part of the curve, Vi is used as abscissae, instead of i. + See “ Electric Conduction,’ paper read before the Hiectrochemicat Society, 1907, by the author. ELECTRIC ILLUMINANTS 119 A conductor, in which 2% <0, can be operated on constant- current supply, but cannot be operated on constant-voltage supply ; but at constant terminal voltage it is unstable within the entire range from i, to i,, in Fig. 3; on constant-voltage supply an in- crease of current, by lowering the voltage consumed by the con- ductor, causes a further increase of current and power, and thus further decrease of voltage, increase of current and power, etc., ye Arya ae fag EETS 1SCIC {ee | | | /é Cai Cs Low-Resistance Fyroelectrolyle a fpere Fie. 3. and the conductor destroys itself by melting; a slight decrease of current causes an increase of the voltage required by the con-_ ductor, and since this is not available on constant-voltage supply a still further decrease of current, increase of required voltage, ete., and the conductor open-circuits, that is, the lamp goes out. On constant-potential supply, such a conductor therefore either open-cirecuits or short-circuits, and to operate it at constant power on a multiple circuit a resistance or reactance is required in series 5 120 ILLUMINATING ENGINEERING to the pyroelectrolyte sufficiently large so that the voltage consumed by pyroelectrolyte (glower) plus steadying resistance increases with increase of current, that is, fulfils the conditions of operation de di seat The Nernst lamp thus requires a ‘‘steadying resistance” in series to the glower. To reduce this resistance, and thereby the waste of power caused by it, to a minimum, iron wire is used, operated in hydrogen or in a vacuum at that range of tempera- ture at which the temperature coefficient of the iron is abnormally high, and with increase of the current i the resistance r very rapidly increases, thus causing an abnormally rapid increase of ir. In arc- and Geissler-tube conduction, a similar instability on constant potential will be discussed. on constant-potential supply, 5. The Inght Radiation of Solid Conductors, as Incandescent Lamps and the Nernst Glower. Black-Body, Gray-Body and Colored-Body Radiation. Effect on the Efficiency of the Incandescent Lamp Filaments and the Nernst Glower. Limi- tation of Efficiency The light production by solid conductors as radiators is tempera- ture radiation. That is, by the resistance of the conductor, the electric power i’r is converted into heat, causing a rise of tempera- ture which produces the radiation. Normal-temperature radiation, that is, black-body or gray-body radiation, as given very closely by the various types of carbon- filament lamps, is a very inefficient light producer. The efficiency of ight production increases with increase of temperature, but is still very low at the highest temperatures at which solids can be operated. The selective radiation of a colored body which is de- ficient in radiating power in the ultra-red gives a higher efficiency of light production. The radiation of some of the metal filaments, and that of the Nernst lamp glower, is such a colored-body radia- tion, and thereby gives a light efficiency higher than corresponds to the temperature of the radiator. However, the selectivity seems to decrease with increase of temperature, that is, with increasing temperature the body seems to approach more a gray body. Yor — instance the Nernst glower radiates strongly selective at low tem- perature, at its operating temperature the radiation curve has ELECTRIC ILLUMINANTS 121 greatly smoothed out,* and while there is probably a gain in efficiency in some metal filaments and the Nernst glower over normal-temperature radiation, the gain does not seem to be so large as to bring the efficiency of light production much beyond that reached by normal-temperature radiation, and it does not appear probable that we shall be able to reach very much higher efficiencies by colored-body temperature’ radiation. 6. Relation of Refractoriness and Vapor Tension or Disintegra- tion to the Possible Efficiency af the Incandescent Lamp. Comparison of the Carbon Filaments with the Metal Fila- ments. Since temperature radiation reaches fair values of light efficiency only at very high temperatures, only the most refractory bodies come into consideration as radiators in incandescent lamps. The most refractory substances are carbon, tungsten, osmium, tantalum, ete.t However, refractoriness is not the only requirement, but the vapor tension, or rate of disintegration of the material below the melting point, is equally of importance, since on it depends how far we can, in the operating temperature of the radiator, approach its melting point. This is well illustrated by the relation between tungsten and the different forms of carbon.§ Carbon is the most refractory body, and has been the first em- ployed in commercially successful incandescent lamps, and the carbon-filament lamp still is the one used in the largest quantities. Carbon has the disadvantage of a relatively rapid evaporation or — disintegration far below its boiling point, and this limits the oper- ating temperature of the carbon filament so that we cannot get the full benefit of the high refractoriness of carbon; but metals, as tungsten, which are less refractory than carbon, can give a higher efficiency by being operated at higher temperature. Great differ- ences in stability, however, exist between different modifications - of carbon. * Bulletins of the National Bureau of Standards. + See “ Radiation, Light and Illumination,” by the author, p 70. {See “ Radiation, Light and IJlumination,” p. 77. § See “ Radiation, Light and Illumination,” p. 79. 122 ILLUMINATING ENGINEERING 7. The Production of the Carbon-Filament Lamp. Base Carbon and Treated Carbon, and their Stability The first commercial carbon-filament incandescent lamps were made of carbonized bamboo fiber. Very soon this was replaced by the squirted filament, which could be produced more uniformly. A solution of cellulose in zine chloride (or cupric ammon), or of nitro-cellulose in glacial acetic acid, is squirted through a fine hole into a hardening solution: methyl alcohol with zinc-chloride solution, diluted acid with cupric-ammon solution, water with nitro-cellulose. The filament is then washed, put into the desired shape (in the case of nitro-cellulose, after reduction to cellulose) and dried. It then consists of a structureless cellulose, in appear- ance very similar to horn. This is now carbonized in a gas furnace at high temperature, and constitutes what is now known as a “ base filament,” because it is mainly used as a base on which to deposit a better form of carbon. The base carbon is not very stable at high temperature, and early lamps made of it, therefore, had only a relatively low efficiency. It has a high resistance and a high negative-temperature coefficient, as shown by its characteristic in Figs. 1 and 2. Somewhat later a considerable improvement in efficiency resulted from the introduction of the “ treated filament.” The base filament is electrically heated in an atmosphere of hydro- carbon vapor (gasolene) in a vacuum, and by the dissociation of the vapor a shell of a different modification of carbon is deposited on the base. This shell carbon has a far greater stability at high temperature, thereby allowing the operation of the lamp at higher temperature and thus higher efficiency. It is of lower resistance, and in the treated filament lamp most of the current thus flows in the shell; less in the inner core or base of the filament. The temperature coefficient of the shell carbon is still negative, but decreases with increasing temperature, and finally begins to rise, so that the compound structure of the treated filament gives a characteristic as shown in Fig. 2. &. Metallized Carbon, its Resistance and Temperature Coefficient, and the Gem Lamp A few years ago a further advance was made by discovering a form of carbon of still much higher stability, the metallized carbon used in the so-called “gem lamp.” The shell carbon (but not ELEcTRIC ILLUMINANTS 123 the base carbon) converts at the highest temperature of the electric furnace into a modification of carbon of nearly metallic character ; it has a very low resistance, lower than some metals, and a positive- temperature coefficient, like metals, though lower than that of pure metals, as shown by the characteristic of the carbon filament with metallized shell, in Figs. 1 and 2. In the production of the gem lamp the base filament is heated in the electric furnace to expel all impurities, then treated in gasolene vapor, and thereby a layer of shell carbon deposited on it, and then is once more heated in the electric furnace. The filaments are then sealed in glass bulbs with platinum leading-in wires and exhausted. It gives an efficiency of about 3.3 watts per candle-power. Apparently, the electric resistance and its temperature coefficient are indications of the stability of carbon at high temperature; the lower the cold resistance and the higher its temperature co- efficient the more stable is the carbon at high temperature, and the higher efficiencies can thus be reached. 9. Metal-Filament Incandescent Lamps. Osmium Lamp, Tantalum Lamp, Tungsten Lamp. Their Efficiencies In recent years metal-filament incandescent lamps have been developed, and are rapidly replacing the carbon-filament lamps by their higher efficiency. First, the osmium-filament lamp was developed, giving an effi- ciency of about 1.9 watts per candle-power. Its filament was made by some squirting process, similar to the carbon filament. It found a limited use only, since osmium is a very rare metal, exist- ing in very limited quantities, and was soon replaced by the tanta- lum filament. Tantalum is a ductile metal, and the tantalum lamp is made by winding drawn tantalum wire on a glass frame. The tantalum lamp gives an efficiency of about 2.6 watts per candle-power, hence lower than the osmium lamp but higher than the gem lamp. Tantalum, while a rare metal, exists in fairly large quantities, and the tantalum lamp appeared very promising until the development of the more efficient tungsten lamp of 1.5 to 1.7 watts per candle-power. The tantalum lamp was the first incandescent lamp made of drawn metal, and showed the features of a much better life with direct current than with alternating current; with alternating cur- 124 ILLUMINATING ENGINEERING rent the drawn filament loses its ductility and gradually offsets, that is, breaks up into numerous short lengths, which are welded together. 10. The Manufacture of the Tungsten Lamp The highest efficiencies of incandescent lamps have been realized by the tungsten filament. Tungsten, or wolfram, is a fairly com- mon metal; is extremely refractory, more than osmium or tantalum, but less than carbon, but fairly difficult to produce in such purity as necessary as filament.* Several methods of manufacture of tungsten filaments have been devised and are still in commercial development, though many millions of tungsten lamps have been made. One series of processes consists of squirting the metal as powder, or in the colloidal state, with some binder, and then burn- ing out the binder by electric heating in a suitable gas; another by squirting a filament of tungsten oxide with some reducing ma- terial, reduce by heat, and then eliminate the excess of reducing material and of oxide by electrically heating in a suitable gas at reduced pressure. A third process consists of squirting or drawing a wire of some tungsten alloy, and by electrically heating evaporate the alloying metal and sinter the tungsten, and, finally, methods have been found to draw the pure tungsten metal into wire of sufficiently small size for use in filaments. All these methods except the last give a filament which is not ductile, but brittle, like the osmium and carbon filament, and, therefore, due to its ex- treme thinness, is very fragile. 11. Thinness and Length of Metal Filaments. Fragility All these metals have a much lower resistance than the base carbon, which constitutes the main part of the carbon filament, and since they are more efficient, that is, at the same supply voltage require less current for the same light flux, they must be of ex- treme thinness and considerable length. Therefore, in these lamps a number of squirted filaments are used in series, or with drawn wire a considerable length of wire wound zigzag on a frame. This difficulty does not exist with the metallized carbon filament ; * For instance, a contamination by 0.3 per cent of carbon would rep- resent an impurity of 10 per cent tungsten carbide Wo,C. ELEctrRIc ILLUMINANTS 125 while the metallized carbon also has a very low resistance, it is used only as a thin shell on the base carbon, which practically does not carry any current, in the gem lamp, while the metal filaments are solid conductors in which the whole cross-section conducts. 12. Hfficiencies of the Different Incandescent Lamps. Conven- tional Rating in Horizontal Candle-Power. Relation of Effi- . ciency to Useful Infe The approximate efficiencies, or rather specific consumptions, of the different types of incandescent lamps are: Base carbon filament (not used any more).......... 5 watts per c. p. Serre ET OLE OST ALIA TTLETI G2 ewe ncaa. 6 6-0: cd 0 0:9 0 < eles aueie ele “ Metallized carbon (gem filament)..... Uy RST Ie a.0 TCP PT TMMNUPL TIS te iota cls, ecu cin os reese vce eneeaseye 2.6 eee IP Ree ts, ce + sss ces se dase es wesc 1.9 Pare pee TIMBERS TINE, Ses oc arslels wieks sidtiw eds ces sees Sees 1b etor 1.7 * Light flux is measured in lumens, and light efficiency thus in lumens per watt, specific consumption in watts per lumen. Usually instead of the lumen as measure of the ight output of an illumi- nant the mean spherical candle-power is used, which is rik times Tv as much, and the efficiency then given in mean spherical candles per watt, the specific consumption in watts per mean spherical candle. By convention, incandescent lamps are usually rated in mean horizontal candles, and their specific consumption expressed by giving the watts per mean horizontal candles and the spherical reduction factor: Thus, above lamps are commercially rated at: Treated carbon filament...3.1 watts per mean horizontal candle-power Poy ty pp eee a re 2.6 watts per mean horizontal candle-power Vemtalum Wamp eee os 3k 2.0 watts per mean horizontal candle-power OBMHUIM JAM Do kic aie. 1.5 watts per mean horizontal candle-power PRR OTLCTULIATND: (5 oie dey ss 1.15 to 1.83 watts per mean horizontal candle- power At the spherical reduction factor 0.78, this gives above values. In comparison with other illuminants, obviously, the horizontal candle-power has no meaning, but the total flux of light, that 1s, the mean spherical candle-power, has to be used. * See “ Radiation, Light and Illumination,” p. 179. 126 ILLUMINATING ENGINEERING When considering efficiency, however, the useful life of the lamp must also be considered. Obviously, higher or lower efficiencies _ may be reached by operating the same lamp at higher or at lower voltage. When speaking of the efficiency of a carbon-filament lamp it is understood, by general convention, that the lamp is operated at such a voltage as to give a useful life of 500 hours. As useful life is understood the time during which the lamp, on constant-voltage supply, decreases by 20 per cent in candle-power.* With metal filaments no such convention has yet been generally established, but due to the higher efficiency and higher cost of the lamp probably a useful life of 1000 hours or more will be economical. Efficiency tests of incandescent iat therefore are meaningless if not accompanied by life tests at that efficiency. 18. Relation of the Efficiency of the Incandescent Lamp to the Size of the Unit or the Power Consumption. Limitation by Sup- ply Voltage at Small Units, by Size of the Lamp Globe at Large Units. Wide Range of Umts with Fairly Uniform Efficuency Characteristic of the incandescent lamp is, that its efficiency is (theoretically) independent of the unit of light; filaments of large diameter and great length, consuming large power and giving a large unit of light, give the same efficiency when operating at the same temperature as filaments of small diameter and short length, that is, filaments which consume small power and give small units of hight, and operating at the same temperature, should have the same life. Thus incandescent lamps give a wide range of sizes of illuminants of nearly the same efficiency. A limitation of the possible size of incandescent light units appears with small sizes in the voltage of the system of electric power-supply. At the same supply voltage—110 or 220—a smaller light unit requires a filament of smaller diameter, and finally a point is reached where the small diameter makes the filament so delicate that either the life of the lamp would be materially short- * See “ Radiation, Light and Illumination,” p. 79. + See “General Lectures on Electrical Engineering,’ by the author, p. 209. ELEctTRIC ILLUMINANTS 127 ened, or a lower operating temperature, that is, lower efficiency, must be allowed. Thus, with the carbon-filament lamp on 110- volts supply, 50 watts (or 16 horizontal candle-power with the treated filament, 20 horizontal candle-power with the gem fila- ment), are the smallest units at which full efficiency can be reached. Carbon-filament lamps of less than 50 watts for 110-volt circuits, therefore must be made for lower efficiency, and the efficiency low- ered the more the smaller the unit is. Obviously, for a 55-volt circuit, an 8-candle-power lamp could be made of the same effi- ciency as the 16-candle-power lamp on the 110-volt circuit, and _ the 220-volt, 16-candle-power lamp cannot be built any more for the same efficiency as the 110-volt lamp, other things being equal. The same applies still more to metal-filament lamps, as in these the filaments are thinner and longer than in carbon-filament lamps of the same voltage and candle-power. Thus in the tungsten lamps higher efficiencies are given to the larger units. For low-voltage lamps, obviously, this limitation of minimum size, by the mechanical structure of the filament, does not exist, and lamps of 1- or 2-watts consumption, or even less, at 4- to 10- volts supply, can be made of the same efficiency as the 50-watt lamp. With increasing size of the unit, a practical limitation is also reached; the useful life of the carbon-filament lamp is limited largely by the blackening of the globe by carbon deposits, and to give equal blackening the surface of the lamp globe should be proportional to the power consumed in the lamp. This, however, gives for large units impracticably large globes, and the use of smaller globes leads to a shorter life. This limitation exists less with metal-filament lamps. In these it seems that the life is not so much limited by the gradual black- ening of the globe as by impairment of the vacuum, and for equal performance only the volume of the globe and not the surface, as with the carbon filament, should increase proportional to the power consumption. This makes metal-filament lamp units of several hundred watts feasible, while carbon-filament lamps of such power. consumption are impracticable. The gem lamp, due to the metallic properties of the filament, stands intermediate between the treated carbon filament and the metal filament in this respect, and lamp units of 250 watts have been fairly successful. bes ILLUMINATING ENGINEERING 14. Inferiority of the Incandescent Lamp in Efficiency to the Flame . Arc and Luminous Arc. Superiority in Small Units. Main Field of Application of Incandescent Lamps and Nernst Lamps in Small Units where no Other Efficient Electric Il- luminant Haists The incandescent lamp thus gives units of light, of practically the same efficiency, from a fraction of a candle-power to several hundred candle-powers, covering a wider range than any other electric illuminant. However, the efficiency of light production is of lower magnitude than that of some other electric illuminants; even in the most efficient incandescent lamp, the tungsten lamp, the specific con- sumption of 1.5 to 1.7 watts per candle is of far higher magnitude than the specific consumption reached in some flame arcs and luminous arcs, of half a watt or less per candle-power. Thus, in efficiency, the incandescent lamp cannot compete with the flame are or the luminous arc, and is therefore excluded from economical use in those cases where these ares can be used, but must find its field of application in those cases where the more efficient illuminants cannot be used, and especially is this the case with smaller units of light, since the efficiency of the are rapidly decreases with decreasing power consumption, while that of the incandescent lamp remains the same, and the incandescent lamp (including the Nernst lamp) is therefore the only one available for smaller units of light, of 100 candle-power or less. GASEOUS CONDUCTORS 15. Difference between Disruptive- or. Geissler-Tube Conduction and Continuous or Arc Conduction Two forms of conduction of gases or vapors exist: disruptive- or Geissler-tube conduction, and continuous or are conduction. The distinction is, that in the former the gas which fills the space is the conductor; in the latter conduction takes place by a moving stream of electrode vapor. Gas or vapor conduction is accom- panied by luminescence of the conductor, and thus can be used for light production. In Geissler-tube conduction the light gives the spectrum of the gas which fills the space between the electrodes ; in are conduction the spectrum is that of the electrode material.* * See “ Radiation, Light and Illumination,” p. 98. ELECTRIC ILLUMINANTS 129 The conductor may be at atmospheric pressure, as in the carbon arcs, flame arcs and most luminous ares; or in a vacuum, as in the Geissler tube or the vacuum are (of which the only industrially important exponent is the mercury arc). GEISSLER-TUBE CONDUCTION 16. Electrical Characteristics of Geissler-Tube Conduction: Total Voltage, Terminal Drop and Stream Voltage as Function of Gas Pressure Very little is known on the electrical characteristics of Geissler- tube conduction. The only commercial illuminant of this class is the Moore tube. 717 Hg PLESSULE, fr ie ca Pa Sided les ips ofc || Se Save ARS GPa Fig. 4.—Volt-Pressure Characteristic of Geissler Tube. It seems that, at constant temperature and constant gas pressure, the voltage consumed by the Geissler tube is approximately constant de di characteristic of the Geissler tube thus would be a straight horizon- tal line. As result hereof, a Geissler tube cannot be operated on constant-supply voltage, but requires a steadying resistance or re- and independent of the current, that is, =0. The volt-ampere actance to fulfil the conditions of stability, 2 >0. The reactance of the step-up transformer is used for this purpose in the Moore tube. 130 ILLUMINATING ENGINEERING The voltage consumed by the Geissler tube consists of a potential drop at the terminals, the “terminal drop,” and a voltage con- sumed in the luminous stream, the “ stream voltage,’ which latter is proportional to the length of the tube. Both greatly depend on the gas pressure, and vary with varying gas pressure in opposite directions: with increasing gas pressure the terminal drop de- creases and the stream voltage increases, and the total voltage consumed by the tube thus gives a minimum at some definite gas pressure. This pressure of minimum total voltage depends on the length of the tube, and the longer the tube is the lower is the gas pressure of minimum total voltage. 2 ae i powe tnt tl Pressure, fr. Vo cH SS ozaw Fie. 5.—Volt-Pressure Characteristic of Geissler Tube. In Fig. 4 is shown the voltage-pressure characteristic, at constant current of 0.1 and of 0.05 ampere, of a Geissler tube of 1.3 cm. diameter and 200 cm. length, using air as conductor; and in Fig. 5 the characteristic of the same tube with mercury vapor as con- ductor.* Figs. 4 and 5 also show the two component voltages, the terminal drop and the stream voltage. As abscissae are used the logarithms of the gas pressure, as measured by McLeod gauge at the moment of taking current and voltage readings. *It is interesting to note, that total voltage, terminal drop and stream voltage in the Geissler tube using mercury vapor as conductor, are nearly the same as with air, and entirely different from the terminal drop and the stream voltage of the vacuum mercury are. The spectrum is the same, the mercury spectrum. ELECTRIC ILLUMINANTS yh i With increasing pressure the discharge finally stops, due to the limited supply voltage; with decreasing pressure, finally the gas density becomes so low that a tendency to are conduction appears, and the beginning of arc formation usually destroys the tube. 17. Performance, Lfficiency and Color of Light. The Moore Tube As seen, the values of terminal drop are very high, and as this voltage gives no equivalent of light, efficiency requires the use of such a long tube as to make the terminal drop a small part of the total voltage. In consequence hereof, the Moore tube is a very large unit of light and does not allow economical subdivision. It requires high-voltage alternating current, which is usually pro- duced by a step-up transformer attached to the terminals of the tube. Intermittent direct current may equally well be used, but continuous direct current is not suitable, as the Geissler-tube con- duction rapidly changes to arc conduction, and as the latter re- quires much lower voltage, leads to short-circuit. In the Geissler tube the terminals disintegrate and the gas pressure falls fairly rapidly, possibly by absorption of the gas by disintegrated electrode material. As commercial illuminant, the Geissler tube therefore requires means of feeding gas intermittently into the tube. This is done in the Moore tube by an automatic valve. As far as known, the most efficient Geissler-tube conductor is nitrogen. It gives a reddish-yellow light, of an efficiency which in very long tubes reaches values of 2.5 watts per candle-power, that is, about the same as the tantalum lamp, but of lower magni- tude than the flame arc and the luminous arcs. Carbon dioxide CO, is also used as conductor. It gives a white light, but a lower efficiency. Mercury vapor gives it green light, but also at low efficiency. The great advantage of the Moore tube is its low intrinsic bril- liancy, and in the CO, tube its white color. ARC CONDUCTION 18. Nature of the Arc Conductor. The Arc as Unidirectional Con- ductor. Rectification by the Arc. The Alternating-Current Arc. Constant-Pressure and Varying-Pressure Ares. In the electric arc the current is carried across the space between the electrodes or arc terminals by a stream of electrode vapor which 132 ILLUMINATING ENGINEERING issues from a spot on the negative terminal, the so-called negative spot, as a high-velocity blast (probably of a velocity of several thousand feet per second). If the negative terminal is fluid the negative spot causes a depression, which is in a more or less rapid motion, depending on the fluidity. Before are conduction can take place the vapor stream has to be produced, that is, an are has to be started. This is done by bringing the electrodes into contact and then separating them, or by a high-voltage spark or a Geissler discharge, or by the vapor stream of another arc, or by heating the space between the electrodes, for instance, by an incandescent filament.* The are stream is conducting only in the direction of its motion, that is, any body which is reached by the are stream is conductively connected with it, if electro-positive regards to it, but is not in conductive connection if negative or isolated. The are thus is a unidirectional conductor, and as such has found an extensive use for the rectification of alternating current.f Since the arc is a unidirectional conductor, it usually cannot exist with alternating current, since at the end of every half wave the vapor stream extinguishes, and at the beginning of the next half wave a new vapor stream in opposite direction has to be started. An alternating-current are exists only if the conditions are such that at every half wave a new arc starts. ‘This is the case if the voltage in the circuit is sufficiently high to send a dis- ruptive spark across the gap at every half wave, or if the arc temperature is so high as to start the are, as is the case with the carbon are. In their industrial application we may distinguish between con- stant-pressure arcs and varying-pressure arcs, that is, arcs in an enclosed space, usually a vacuum, in which the gas or vapor pres- sure varies with the current, etc. ‘The only industrially used are of the latter class is the mercury are. * See “ Radiation, Light and Illumination,” p. 106. + On the arc as unidirectional conductor, see “‘ Radiation, Light and Illumination,” p. 111. On the electric characteristics of the mercury arc rectifier, see “Theory and Calculation of Transient Electrical “Phenomena and Oscillations,’ by the author, p. 249. ~See “Radiation, Light and [lumination,” p. 115. ELECTRIC ILLUMINANTS 133 CONSTANT-PRESSURE ARCS 19. Volt-Amperes and Volt-Length Characteristics of the Are, de di aa. JSR SSS Sees eee ‘J SS BES See eee | S@E Sea Ree “SE SSSan a ee ee Fig. 6. Characteristic of the arc as conductor is, that the voltage de- creases with increase of current, that ig 2¢ <0 over the entire di range. ‘The volt-ampere characteristics of the are therefore are curves of fhe shape shown in Fig. 6 for the magnetite arc, for the 134 ILLUMINATING ENGINEERING arc lengths of 0.5, 1.5 and 2.5cm. With increasing current the are voltage decreases and approaches a finite limiting value, which with the magnetite arc is about 30 volts (about 36 volts with the carbon arc, 13 volts with the mercury arc, ete.). Inversely, with decreasing current the voltage increases, and tends towards infinity, eee A et Ga ee | or rather probably the voltage required by the electrostatic spark, that is, by Geissler-tube conduction across the are gap. At constant current, with increasing are length, the are voltage increases very nearly proportional to the are length, and the volt- length characteristics of the are thus are practically straight lines, as shown in Fig. 7 for the magnetite arc of 2, 4, 8 and 16 amperes.* * See “‘ Radiation, Light and Illumination,” p. 137. ELEcTRIc ILLUMINANTS 135 20. Dependence of the Arc Voltage on Two Independent Variables, Current and Arc Length, Instability of the Arc on Constant- Voltage Supply. Necessity of Steadying Resistance or Re- actance. The Stability Curve of the Arc The are as conductor in industrial illuminants thus differs from the solid conductors discussed in the preceding by two main char- acteristics : a. In the solid conductors the relation between e and i is fixed, that is, e is determined by i, and inversely. In the arc, however, two independent variables exist, the current or voltage and the arc length. That is, e is a function of i as well as of 1 which can be expressed with fairly good approximation (except for very small currents, for which the voltage is higher than given by the equa- tion) by the formula: e(1+38) ML. where e,, c and 6 are constants, depending on the material of the electrodes, and more particularly on the negative electrode. Least close is the agreement with above formula in the carbon arc, Which in many other properties shows an exceptional character as result of the physical properties of carbon.* b. In the are it always is oe SES ENG <0, while in the incandescent-lamp filaments it is 2 >0, Herefrom follows: An arc is unstable and cannot be operated on constant-voltage supply, but with constant voltage at the arc terminals a slight momentary increase of the arc resistance, by requiring a higher voltage, decreases the current and thereby still further increases the required voltage and the arc goes out. Or, a slight momentary decrease of the are resistance increases the current, thus lowers the arc voltage, thereby, at constant-supply voltage, increases the cur- rent and still further lowers the are voltage, etc., and the are short-circuits. The arc, however, is stable on constant-current supply. The are thus is essentially a constant-current phenomenon, its operation more steady on constant-current circuits, and additional apparatus is required for its operation on constant-potential cir- * See “ Radiation, Light and Illumination,” p. 140. 136 ILLUMINATING ENGINEERING cuits. That is, a resistance or reactance (with alternating arcs) must be inserted in series sufficiently large so that for the total voltage consumed by the are with its steadying resistance S2 >0. Thus, while in Fig. 8 the lower curve is the volt-ampere char- StaAbiliy —CNAr ACCEL IS UE LS crm L engtl aE Fia. 8. acteristic of a 1.5 cm. magnetite arc, to operate such an arc on a constant-potential supply a much higher voltage is required: the supply voltage must be greater than that given by the upper curve in Fig. 8 to give stable operation, and the more so the greater the required stability. This curve thus is called the “ stability curve” of the are.* * See “ Radiation, Light and Illumination,” p. 142. ELEctTrRIic ILLUMINANTS Loy 21. Instability of Parallel Operation of Arcs Without Steadying Resistances. Instability Due to Non-Inductive Resistance Shunt. Hatinction by Shunted Capacity. The Arc as In- terrupter. The Singing Arc From the characteristic of the areoe <0 also follows: Several arcs cannot be operated in parallel except by giving each of them a steadying resistance or reactance as large as would be required for its operation on constant-potential circuit. With- out this all the arcs go out but one. | Shunting the arc by a non-inductive resistance decreases its stability, and with decreasing resistance a definite value is reached at which the arc becomes unstable, that is, goes out. The stability of an arc thus can be measured by the current which can be shunted around it by a non-inductive resistance. 5 A condenser in shunt to the are makes it unstable and interrupts it; a momentary increase of arc resistance, and thereby increase of arc voltage, increases the current shunted momentarily by the condenser, thereby decreases the are current, and still further in- creases the are voltage and shunts still more current into the con- denser, etc. Even a small condenser in shunt to the are thus puts it out. If the supply voltage is sufficiently high to restart the are, after it is put out by a shunted condenser, the arc with shunted condenser then acts as an interrupter, causing rapid successive interruptions of the circuit with fairly constant frequency. The lower the stability of the arc the more sudden are the interruptions, and low-temperature arcs, as the mercury arc, thus give inter- ruptions of extreme suddenness. Inversely, if the capacity is very small and the gas filling the space around the are stream of low dielectric strength, as hydrogen or light hydrocarbons, the are may start again, through the residual arc vapor, before completely extinguished, and the arc current becomes pulsating, the so-called “singing arc.” 22. Stream Voltage and Terminal Drop of the Arc. Heating of the Terminals by the Terminal Drop. The Carbon Arc as Incandescent Radiator. Relation between the Efficiency of the Carbon Arc and the Size and the LIfe of the Terminals Voltage, and therefore power, is consumed in the are stream and at the arc terminals. The power consumed in the are stream is 138 ILLUMINATING ENGINEERING converted, more or less directly, into radiation, and if a large part of this radiation is in the visible range, as is the case with titanium, calcium and mercury vapor as conductors, the are stream may be used as illuminant. If very little of the radiation is in the visible range—as is the case with carbon vapor as conductor—the arc stream does not contribute appreciably to the light given by the lamp. The power consumed at the electrodes is partly converted into the latent heat of evaporation and the kinetic energy of the moving vapor stream (which is the are conductor) largely into heat, especially at the positive terminal. If the arc terminals then are sufficiently small to reduce the heat conduction away from them, and of sufficiently refractory material to reach very high temperature, they may be used as radiators in giving light. The radiation then is due to incandescence or temperature radiation. The latter is the case with the plain carbon arc lamp. When using pure carbon as arc-lamp electrodes the arc stream gives very little light, and that of a useiess, violet color. Considerable heat is, however, produced at the positive electrode, and if this is not too large its tip reaches a very high temperature: the boiling point of carbon, and then gives light by temperature radiation, practically — black-body radiation. The plain carbon arc therefore gives light by incandescence, just like the carbon-filament incandescent lamp, and the are stream in the former is merely the heater which raises the temperature of the radiator, the positive-electrode tip, to a high temperature, and the much higher radiation efficiency and white color of the carbon arc, compared with the carbon filament, is due to the higher temperature of the former. Nevertheless, while the radiation efficiency of the carbon arc is the highest which can be reached by black-body radiation, it is very much lower than the efficiencies available by luminescence of the are stream. Of the heat produced at the positive terminal of the carbon are. only a part becomes useful as incandescent radiation; the rest is conducted away through the electrode, carried away by air currents, etc. The lower this loss, that is, the smaller the electrodes, the higher is therefore the efficiency, and with very large electrodes the heat conduction becomes so large that the electrode tips do not reach any more the temperature of efficient radiation, and the efficiency vanishes. The efficiency of the carbon are lamp thus depends on the size of the electrodes, and increases with decreasing ELEcTRIc ILLUMINANTS 139 size. However, with decreasing size, the consumption of the elec- trodes by combustion increases, and thus requires more frequent trimming of the lamp, that is, higher cost of maintenance. 23. The Open Carbon Arc or Short-Burnming Arc Lamp. The Enclosed Carbon Arc or Long-Burning Lamp. Its Infervority in Efficiency The first carbon are lamps were operated with high current: ‘on 9.6 amperes constant direct-current circuits, with electrodes, which were fairly small relative to the current, and therefore gave fairly good efficiencies: about 1 watt per candle-power. However, under these conditions, the rate of consumption of the electrodes was very rapid, and electrodes of the greatest length, which could conveniently be used in a lamp, lasted only a few hours. As result thereof, twin carbon lamps were designed, and were in extensive use. The high cost of operation, due to the required daily trim- ming, of these so-called “ open arc lamps” or “ short-burning are lamps” led to the development of the enclosed carbon are lamp. In this type of lamp the arc is enclosed in a small, nearly air-tight glass globe, and the rate of consumption of the electrodes thereby greatly reduced and a longer life of electrodes secured. As the retarded combustion of the electrodes resulted in their assuming a more flattened shape, the are length had to be increased to limit the obstruction of the light issuing from the positive electrode by the shadow of the negative electrode. The higher arc voltage re- sulting herefrom required a decrease of current to retain the same power consumption, and while the open arc operated at 40 to 45 volts on 9.6 amperes circuits, the enclosed arc lamp consumes 70 to %5 volts on 6.6 or 7.5 amperes circuits. As the same size of electrodes was retained, or the size even increased, to get.a long life, while the current and thereby the luminous area of the elec- trodes was reduced, the heat losses by conduction and convection were greater in the enclosed arc, and the efficiency therefore lower than in the open arc. Nevertheless, the advantage of lower main- tenance cost resulting from the less frequent trimming, weekly with the enclosed arc lamp against daily with the open arc lamp, has led to the entire abandonment of the latter, and while open arcs have survived in a few cities they have practically ceased as an article of manufacture. 140 ILLUMINATING ENGINEERING 24. Uneconomical Operation of Continuous-Current Series Arc Circuits. The Series Alternating Enclosed Are Lamp. Its Very Low Efficiency In regard to the electrical-power supply, the enclosed arc lamp is inferior to the open are lamp, since with the former the higher voltage and lower current gives, with the same maximum Voltage of the constant-current circuit, a smaller unit, and with direct current an arc machine was required for each circuit. This was such an economical disadvantage that the direct-current series enclosed carbon are lamp is used to a limited extent only in such places where efficiency of light production is essential, and the illuminant, which is most universally used for street lighting, is the constant-current alternating enclosed carbon are lamp. With this lamp, operating from constant-current transformers, the small size of the individual arc circuit is not such a serious handicap. The economic disadvantage of numerous small machine units, which handicapped the series direct-current are lamp, has been eliminated by the development of the constant-current mercury arc rectifier system, which permits operation of constant-direct current are circuits from constant-current transformers. This de- velopment, however, was too late to help the direct-current carbon arc, but, coming after the development of the luminous are, it led to the rapid introduction of the latter in place of the carbon arc. The efficiency of the alternating-current carbon are lamp, how- ever, is much lower than that of the direct-current lamp: in the alternating-current lamp the losses of heat through the electrodes are more than doubled: while the heat loss by conduction and con- vection is continuous, heat is produced at either electrode mainly during that half wave of current where the electrode is positive, and then only during that part of this half wave where the current is high. Thus, while the alternating-current carbon are lamp gives light from both electrodes, its efficiency of light production is much lower, and with the standard series enclosed alternating-current arc lamp at,70 to 75 volts per lamp, on 6.6 and 7.5 amperes con- stant alternating-current circuits, the specific consumption is up to 2.5 to 3 watts per candle-power, and even higher, that is, the efficiency has dropped down below that reached with modern in- candescent lamps. In spite of its very low efficiency, the small amount of attention required by it, and the convenience of operation from alternating- EvEctric ILLUMINANTS 141 current supply circuits, through constant-current transformers in street lighting, has led to the almost universal adoption of the alternating-current enclosed carbon are lamp, and probably more lamps of this type are used in street lighting than of all other types together. 25. Replacement of the Enclosed Alternating Carbon Arc by the Magnetite Arc Lamp in Street Lighting, by the Intensified Arc or the Tungsten Incandescent Lamp in Indoor Inghting. The Intensified Arc Lamp However, with the development of high-efficiency incandescent lamps, the position of the standard enclosed alternating carbon are lamp became untenable, and while it is still being used in enormous numbers it is being rapidly replaced by the magnetite arc lamp in street lighting, and by the intensified are lamp and the tungsten incandescent lamp in mdoor lighting, and the manufacture of the enclosed alternating carbon arc lamp has greatly decreased. While thus the enclosed carbon are lamp is rapidly disappearing from the streets, before the luminous arc, for indoor lighting, where the luminous arc and the flame arc are handicapped by being too large units of light, and by producing smoke and gases, and the tungsten lamp is the only competitor, the enclosed carbon are lamp is retaining its field as the “intensified are lamp.” Since the efficiency of the carbon are lamp increases with decreasing size of carbons, by the use of very small carbons in an enclosed type of lamp, a very good efficiency, about 1 candle-power per watt, is reached in the so-called “intensified arc lamp” on direct current as well as on alternating current. The life of the electrodes of the intensified arc lamp is shorter than that of the enclosed arc lamp of old, but as this lamp is mainly used indoors, where usually the daily operation is only a few hours, the life is sufficient to reduce the frequency of trimming satisfactorily, and the higher efficiency and white color of light gives to the intensified arc an advantage over the tungsten Jamp in those cases where large units of light are permissible. 26. The Luminous Arc and the Flame Arc. Their Characteristic Differences, Advantages and Disadvantages. The Magnetite Are The carbon arc is an illuminant using a solid radiator and pro- ducing light by incandescent radiation, like the incandescent lamps. 142 ILLUMINATING ENGINEERING -In all other arcs luminescence plays an essential part, and all or most of the light is given by the arc flame as vapor conductor. These luminescent arcs can be divided into two classes: the luminous arcs and the flame arcs.* In the luminous arcs the lumi- nescent material is introduced into the are stream by electro-con- duction from the negative, that is, is used as are conductor. Typical arcs of this class are the so-called magnetite are and the mercury are. The latter, as vacuum arc, will be discussed later. In the flame arcs the luminescent material is introduced into the arc stream by heat evaporation, either from the positive as the hotter terminal, or from both terminals. The characteristic difference resulting herefrom is, that in the luminous are the temperature of the electrode has no direct relation to the efficiency, and the electrodes thus can be maintained at such low temperature as to consume very slowly. The luminous arc thus lends itself to the production of long-burning arc lamps, that is, lamps requiring very infrequent trimming, and the size of the electrodes is usually made such as to give a life of 100 to 200 hours as the longest time which it is advisable to allow a lamp to burn without cleaning the globe, — and other attention. The positive electrode of the luminous arc is entirely immaterial, and usually made of some metal of high heat conductivity so as not to consume appreciably, that is, of a life of some thousand hours. At the same time the number of materials which can be used in the luminous are is much more limited, the difficulties of design so as to get steady operation, greater than with the flame arc, and no successful luminous are has yet been commercially developed for alternating-current circuits, but the luminous are has been developed for direct-current circuits in the so-called “ magnetite arc lamp,” also occasionally called “ metallic-oxide arc lamp” and “ferro-titanium are lamp.” In this the negative electrode is a mixture of the oxides of iron, titanium and chromium (magnetite, illmenite, rutile, chromite), usually enclosed by a thin iron shell. The positive electrode is a permanent part of the lamp. The magnetite arc lamps are operated on constant direct-current eircuits of 4 amperes and of 6.6 amperes, with about 75 volts per lamp, usually from constant-current transformers through mercury are rectifiers. * See “ Radiation, Light and Illumination,” p. 123. Ewiectric ILLUMINANTS 143 27. The Flame Carbon Arc. Relation between Size of Electrode and Efficiency. The Short-Burning and the Long-Burning Flame Carbon Arc. The Yellow Color of the Flame Carbon Arc. Titanium, Calcium and Mercury as the Three Most Eficuent Arc-Stream Radiators In the flame arcs the luminescent material is introduced into .the are stream largely by heat evaporation, a high temperature of the positive electrode thus is essential, and, to some extent, similar relations exist between the size and therefore temperature of the electrodes and the efficiency. Carbon is always used as the main electrode material, since carbon gives the hottest arc, and also the steadiest arc, and the inherent steadiness of the carbon are has made the development of the flame carbon arc lamp less difficult and therefore more rapid than that of the luminous are, and made it possible to operate such arcs on alternating-current circuits as well as on direct-current circuits. Since, however, carbon rapidly consumes, and the size of the electrodes cannot be materially increased without loss of efficiency, the flame carbon arc lamp is essentially a short-burning are lamp, requiring daily trimming. This has in this country excluded its use “for general street illumination, and restricted it largely to decorative lighting. To make the flame carbon arc long burning requires enclosing it similar as with the enclosed plain carbon arc to reduce the access of air. Since, however, by the consumption of the electrodes the luminescent materials contained therein escape as a smoke, means are required to deposit this smoke, by a circulating system, at some place where it does not obstruct the light by deposition on the globe. A number of such long-burning flame lamps have been designed, but none of them has yet found an extended in- dustrial introduction, probably largely due to conditions outside of the lamp mechanism: the yellow color of the light, the large unit of light, the expense of the electrodes, lack of steadiness, etc. - The only materials which thus far are used in flame carbon arcs as luminescent matter are calcium compounds, as fluorides, borates, phosphates, tungstates, etc. They give a very high efficiency, but a yellow light. White-flame carbons have not yet been introduced of an efficiency comparable with that of the more efficient yellow- flame carbons. | | 144 ILLUMINATING ENGINEERING To some extent the flame carbon arc stands intermediate between the luminous are and the plain carbon are: the plain carbon arc gives light only by incandescence of the electrode terminals, the luminous arc only by luminescence of the arc stream, and the flame carbon are gives most of its light by luminescence of the arc stream, but also some light by incandescence of the positive carbon terminal. ) It is interesting to note, that thus far only three materials have been found which in the are give very high efficiencies of light production, reaching in large units values of 3 to 4 candles per watt; titanium, calclum and mercury. The first gives a white light, and is used in the magnetite arc; the second gives a yellow light, and is used in the flame carbon are; and the third is re- stricted to the vacuum arc. , 28. The Mechanism of the Arc Lamp: Starting Device, Feeding Device, Steadying Device, Shunt Protective Device, Damping Device. Series Lamp, Shunt Lamp, Differential Lamp Due to the nature of the arc, as discussed above, all are lamps require an operating mechanism. Since the arc does not start spontaneously, a starting device is required. ‘l'his consists of a mechanism which brings the electrodes together, thereby closes the circuit between them, and then sepa- rates them and so starts an are. Since, in supplying the vapor conductor of the are stream, the electrodes consume, more or less rapidly, a feeding device is necessary, that is, a mechanism which gradually moves the elec- trodes together so as to maintain the proper length of the are stream. In constant-potential or multiple lamps a steadying device is necessary since, as seen, the are is unstable on constant potential. This consists of a resistance in direct current, of a reactance in alternating-current are lamps, which is connected in series to the arc, and usually made adjustable so as to accommodate the lamp to the different supply voltages met in electric-supply systems. In constant-current or series lamps a shunt protective device is necessary to close the circuit around the arc in case the circuit in the lamp opens by breakage or consumption of the electrodes. This usually consists of a shunt resistance, connected across the lamp terminals by a potential magnet. ELECTRIC ILLUMINANTS 145 In addition thereto dashpots or other retarding devices are nec- essary to slow down the motion of the operating mechanism so as to draw the arc sufficiently slowly not to break, and to guard against over-reaching of the feeding mechanism. _ The operating mechanism is actuated by electromagnets or solenoids, frequently in combination with weights, and rarely springs, as the latter have usually proved unreliable in continuous operation. If only series magnets are used the lamp is called a series lamp; if only shunt magnets are used it is called a shunt lamp; if series and shunt magnets are used, a differential lamp. The series lamp regulates for constant current in the lamp, thus is not applicable where several lamps are connected in series; the shunt magnet regulates for constant voltage, irrespective of the current, and the differential lamp regulates for constant relation of current and voltage. The latter type is most commonly used. The different forms of arc-lamp mechanisms which are in in- dustrial use cannot be described here, but may be studied from the publications of the various arc-lamp manufacturers, which give detailed information, or by inspection of the exhibit of typical are lamps shown here,* and only some general principles can be discussed, which may enable a judgment of the correctness of individual operating mechanisms. 29. The Effective Resistance of the Arc. Relation between Arc Length and Efficiency. The Short-Carbon Arc and the Long Luminous and Flame Arcs The effective resistance of the arc is not constant, but continu- ously and often rapidly varies or pulsates somewhat. The arc conductor is a vapor stream of a temperature very much higher than the surrounding air, and thus, even when well screened, more or less affected by air currents, drafts, etc. In the plain carbon are lamp, in which the heated terminals are the radiator, and the voltage consumed by the are stream is wasted, the arc length is ~ made as short as possible, without obstructing the light by the shadow of the electrodes, and the fluctuations of the are resistance therefore are moderate. In the flame arcs and luminous arcs, however, in which the light is given by the arc stream, and the * Also see “ Radiation, Light and Illumination,” p. 151. 146 ILLUMINATING ENGINEERING potential drop at the terminals represents largely wasted power, efficiency requires a long are stream, and this is more sensitive to air currents, thus the fluctuations of the are resistance are greater, especially when very small currents are used, as necessary in smaller units of light. | The problem in arc-lamp design thus is to devise an operating mechanism which regulates as closely as possible for constant production of light by the arc lamp, and at the same time permits the use and economical operation of the are lamp on existing dis- tribution systems. 30. Regulation of the Arc Lamp for Constant Inght Flux: the Floating System of Control of the Carbon Arc and tts Ad- vantages. Fixed Arc Length Required by the Luminous Are. Its Difficulties in Constant-Potential Lamps. The Compro- mise Control of the Flame Carbon Lamp In the plain carbon arc the light production depends on the current, but not on the are length, provided the latter is sufficient to minimize the shadow of the electrodes. Regulation for constant light flux, therefore, is closest by control for constancy of current. Thus the series magnet, which varies the are length to maintain constant current, is most satisfactory in constant-potential lamps, while in constant-current lamps the controlling mechanism merely has to maintain the are length sufficient for reducing the electrode shadows, and not too long to give too much waste of power. As the are length has no direct effect on the light, a floating system of control thus can be used, and is always used, as being easiest to operate. That is, one or both carbons are held floating by the counteracting forces of shunt and series magnet, or of series magnet and weight, and continuously move in adjusting the arc length to the fluctuations of are resistance. The voltage at the terminals of such a constant-current arc lamp thus shows very small fluctuations. Entirely different, however, are the conditions in the luminous arc. In this the light flux is proportional to the current and the are length, and any fluctuation of the are length, by a floating system of control, would give a corresponding fluctuation of light flux, and is therefore objectionable. A fluctuation of are resistance is accompanied by a change of luminosity, such that an increase of arc resistance and therefore of arc voltage at constant are length usually gives a decrease of luminosity, and thereby of light flux; ELECTRIC ILLUMINANTS 147 and regulation for constant light flux therefore would require an increase of arc length at an increase of are voltage caused by an increased arc resistance. The floating system of control, by short- ening the arc at an increase of arc voltage, thus in this case controls in the wrong direction and accentuates fluctuations of light, and the nearest approach to proper regulation of light flux is given by maintaining constant arc length. Jn luminous are lamps there- fore always, as far as it is possible, a control for fixed are length is used. That is, the arc terminals are locked in position at a fixed. distance, and at intervals, depending on the rate of consumption, _ this distance is adjusted by resetting the arc. This fixed arc-length control gives a curve of terminal voltage, which fluctuates con- siderably, following the fluctuations of the are resistance. In con- stant-current circuits this is not objectionable, as the voltage fluc- tuations of the numerous lamps in series with each other superpose to a constant total voltage. In multiple or constant-potential lamps, however, the fluctuations of arc voltage may interfere with the operation, and thus either a very large inductance has to be used in series to the arc, to steady the current, or regulation for con- stant light flux more or less sacrificed by the use of a floating system of control, and as the result, the multiple-luminous arc lamp is less steady than the series arc lamp. In flame arc lamps, usually larger currents and thus longer arcs are employed, and a sluggish floating mechanism, if limited to work over a moderate range only, is less objectionable, but never- theless the light flux of the lamp is less steady than in the plain carbon lamp, and one of the main objections of the flame arc is its inferiority in steadiness of the light flux. $1. Classification of Arc Lamps. The Most Important Forms of Are Lamps - In classifying the different types of arc lamps we have: By the nature of the light production: the plain carbon arc, the flame carbon are and the luminous arc, the latter including the - mercury arc as vacuum arc. By the life of the electrodes: the short-burning arc and the long- burning are. The former giving a life of electrodes of from 8 to 20 hours, depending on the current and the size of electrodes, the latter a life of 50 to 250 hours, or even much more, as with the mercury arc. 148 ILLUMINATING ENGINEERING By the protection of the arc against the access of air: the open arc and the enclosed arc. By the nature of the supply circufts: the constant-potential or multiple arc lamp and the constant-current or series arc lamp. By the arrangement of the electrodes: the vertical arc and the horizontal are. In the former the electrodes are arranged vertically above each other, and the maximum light flux thus issues in the horizontal direction, except in the direct-current plain carbon arc, » in which the maximum light flux is downwards from the upper positive electrode as radiator. In the horizontal are the electrodes are converging downwards, and the maximum light flux thus is in the downward direction. The most important forms of are lamps thus are: The open plain carbon arc. A short-burning arc, anieh has survived in a few cities on 9.6 amperes series circuits. The enclosed plain carbon arc. Long burning, for multiple and for series circuits, on alternating and on direct current. The ma- jority of the arc lamps now in use are series alternating enclosed carbon arcs, on 6.6 amperes and on 7.5 amperes series circuits. This type of arc is, however, rapidly disappearing, due to its low efficiency. The intensified arc. It is an enclosed plain carbon arc, medium long burning, gaining its efficiency by the small size of the elec- trodes. It is mainly used for indoor lighting of high efficiency and white color, on constant-potential direct- and alternating-current circuit. The yellow-flame arc. Usually an open and short-burning arc, with converging carbons for downward distribution of light, used mainly for outdoor decorative lighting, and to some extent for second-class interior lighting. Its disadvantage is the yellow color of the light. The magnetite arc, mainly used on 4 amperes and 6.6 amperes direct-current series circuits, for street light, where it is taking the place of the series enclosed carbor arc. It is an open, long-burning are. The mercury arc or vacuum arc, mainly used for indoor lighting of high efficiency and steadiness. Its disadvantage is the green color of the light. ELECTRIC ILLUMINANTS 149 32. Increase of the Efficiency of the Arc with Increasing Size of the Light Unit. Relation between the Efficiency of the Arc Lamp and the Current, Arc Length and Power, at Constant Are Length, Constant Current and Constant Power. The Conditions of Maximum Efficiency Unlike the incandescent lamp, in which the efficiency of hght production remains practically constant over a wide range of units of light, the efficiency of the arc lamp increases with increasing power consumption and thus increasing size of unit of light, but wi ce ae ; J00 7 10 - Saeed oharonterites of Paras PL | | rhestenatite me |_| | pe RR BERS | Brak) | orpors [pal asi, (pela ANE ee | Sp ee Tay ay Dalal a ee Bee fe ee ieee Fie. 9. falls off with decreasing size of the hght unit, and the arc lamp thus is essentially a large unit of light, but for small units does not have the efficiency to compete with the modern incandescent lamps, while inversely for large units it reaches efficiencies of higher magnitude than possible with incandescent lamps. The relation of the efficiency of light production by the arc to the power consumption can, with fair approximation, be calculated, © especially for the luminous arc. For instance, in the series direct-current magnetite arc, the ap- proximate equation of the arc voltage is 123 (1+.05 (1) 150 ILLUMINATING ENGINEERING where the are length | is given in inches, and the approximate ex- pression of the light flux ®, in mean spherical candle-power, is: ®=150h (2) (assuming, as approximately the case, the light flux as proportional to the are length and the current). For constant arc length | then follows, from equations (1) and (2), for different values of current i, the power consumption p=el and the efficiency y. Curves, for the arc length 1=.7 inches, are given in. Fig.-9, ae ieee oF AMM Gi Cae Fic. 10. For constant current, i=4 amperes, curves of the power con- sumption and of the efficiency for different are lengths are given in Fig. 10. As seen, with increasing current at constant arc length, and with increasing arc length at constant current, the efficiency in- creases, but the power consumption also increases. For constant power consumption, p=el, then follow, from equa- tions (1) and (2), values of arc length, are voltage and efficiency. They are plotted, for 300 watts and 500 watts power consumption in the arc, in Fig. 11 as function of the current. As seen, with Evectric ILLUMINANTS 151 increasing current at constant power consumption, the efficiency increases to a maximum—which is higher with the 500-watt arc than with the 300-watt arc—and then decreases again. Determining then the condition of maximum efficiency, as func- reams see yy i SS eee oe eS SS Eee A bid edi td pecaeeett i Se (7 i a RA ees 2 MLE DER PS Ts Si | PROSITE NES SSE NG SSR ee KS = RIA Baer are Fia. 11. tion of power consumption in the arc, gives the curves shown in Fig. 12. As seen, to operate at maximum efficiency, with increasing power consumption the current in the arc and the arc length has to be increased, while the arc voltage remains nearly constant. The efficiency rises rapidly with increasing power consumption. 6 152 ILLUMINATING ENGINEERING 38. Comparison of the Arc Lamp and the Incandescent Lamp As seen from Fig. 12, the efficiency of the tungsten incandescent lamp, of approximately 0.66 candle-power per watt, is reached at 70 watts power consumption. Ze an | CL Lo Fic. 12. Considering, however, that the efficiency is not the only factor in the cost, but that the cost of attention, trimming, etc., also en- ters, furthermore, that at the lower consumption some efficiency would have to be sacrificed to steadiness by increasing the current beyond, and therefore reducing the are length below that corre- sponding to maximum efficiency, the dividing line between tungsten ELEctTRIc ILLUMINANTS 153 incandescent lamp and magnetite arc lamp for use in street lighting probably lies at about 100 to 150 watts power consumption, depend- ing on the individual conditions; below this the tungsten lamp above the magnetite arc is more efficient, other things being equal. Similar relations exist with other types of ares: with the flame carbon arcs, approximately the same relations would exist—except that the numerical values of efficiency are proportionally changed— provided that the size of the flame carbons is changed proportional to the current. If the same size of flame carbons is retained, the efficiency falls off more rapidly with the decrease of current, and _ increases more rapidly with its increase, due to the change of the rate of evaporation.. However, in economical comparison with the tungsten lamp, the very much higher cost of trimming, with the short-burning flame lamp, would probably shift the dividing line of economical use, between the tungsten lamp and the arc lamp, to higher values of power, while more efficient long-burning lumi- nous arcs would shift it to lower values of power. VACUUM ARCS 84. The Low-Pressure Mercury Arc in the Glass Tube. The High- Pressure Mercury Arc in the Quartz Tube. Thetwr Charac- teristics The only industrially used vacuum arcs are the mercury arcs: the low-pressure mercury arc, operated in a glass tube, and the high-pressure mercury arc, operated in a quartz tube. In the mercury are the terminal drop is constant, and about 13 volts, while the stream voltage is proportional to the are length and independent—within a certain range—of the current, but depends upon the diameter of the arc tube, and on the vapor pres- sure ; it increases with decreasing tube diameter and with increasing vapor pressure, so that in an arc tube of about 2 cm. diameter and a high vacuum it is as low as 0.5 volts per centimeter, and rises to 8 to 10 volts per centimeter in a tube of 1 cm. diameter at a mer- - cury-vapor pressure about equal to atmospheric pressure. The mercury are is a luminous arc and stands at the one end of a series, of which the carbon arc stands at the other end; while the latter is the hottest arc the former is the coldest, and in the low- pressure mercury arc in a glass tube the temperature of the arc stream is only about 200° to 250° C. 154 ILLUMINATING ENGINEERING Like all arcs, it requires a starting mechanism; the feeding is done by condensing the mercury vapor in a condensing chamber, and returning it to the negative electrode by gravity. A valuable characteristic of the mercury arc is, that it can be built of very good efficiency in smaller units than any other arc: as low as 80 to 100 watts. ) In the high vacuum of the mercury arc in the glass tube the arc length is very great at moderate voltages, and mercury arc tubes of over 3 feet length are operated on 110-volt circuits; in the quartz-tube arc, due to the high vapor pressure, the are length is short and comparable with that of other arcs of the same voltage ; an are length of 8 inches requires a 220-volt supply. Like all arcs, the mercury are requires a steadying resistance on constant-potential supply circuits. The light of the mercury are has the advantage of great steadi- ness and high efficiency, but the disadvantage of a green color, which is almost entirely deficient in red rays, and therefore greatly distorts colors. SENSITIVITY TO VARIATIONS OF THE ELECTRIC-POWER SUPPLY 85. Comparison of the Various Forms of Incandescent Lamps and Arc Lamps Regarding Their Sensitivity to Variation of the EHlectric-Power Supply: The various forms of electric illuminants must find their place in existing electric distribution systems, either constant-potential or constant current. No electric circuit, however, maintains abso- lutely constant-potential respectively constant current, but fluctua- tions of greater or lesser extent occur, and it thus is of importance to know the sensitivity of the illuminants to variations of the sup- ply circuit. Since the limit of sensitivity of the human eye for changes of light flux is not much below 2 per cent, a sudden change of light flux of 5 per cent is not seriously objectionable, and a grad- ual change even of 20 per cent is hardly appreciable. The per- missible range of sudden and of gradual variation of the electric- supply system, and inversely, in a system of given regulation, the degree of satisfactoriness of an illuminant would then be deter- mined by the ratio of the change of light flux to the change of the electric supply causing it. In the following are given a number of approximate values of the ELECTRIC ILLUMINANTS 155 percentage change of light flux of various electric illuminants, resulting from a change of the electric-supply voltage, current or power by 1 per cent. In the calculation of the incandescent lamp values, the curves of Fig. 2 have been used; the arc-lamp values are calculated from the characteristic curves of the arc, equations (1) and (2). They depend to a greater or less extent on arc length, per cent of steady- ing resistance, etc., and thus can be approximate only. APPROXIMATE VARIATION OF CANDLE-POWER, IN PER CENT For 1 per cent variation of— Power Voltage Current Incandescent lamps: Peemecmcarpon filament..........%.3...% 2.8 5.6 5.6 PO TIMER ERTL OCR creole as oI Bieta Cac ale wig'S mies 2.5 4,45 Dar AIM BteNMIAINENt. . oo... ck ew awe ees 2.33 3.75 6.25 Constant current arcs—75 volts per lamp: - Magnetite arc lamp ........ pote ote aaa As 1.42 ahr 1.0 Flame carbon arc, differential control... 1.7 3.4 3.4 Flame carbon arc, shunt control....... 1.55 +5, 1.55 Constant potential arcs—110-volt supply, 33 per cent steadying resistance: PAOPGUTYVOOTC 15 0:0.» A, Roe 5 erg 75 3.0 1.0 Magnetite arc (constant are length).... 88 {Qe 1.0 Flame carbon arc, differential control.. a ley f 3.4 3.4 Flame carbon arc, shunt control....... 1.17 4.7 1.55 Flame carbon arc, series control....... 2.65 2.65 Incandescent lamps in general are much more sensitive to changes of supply than arc lamps, that is, require a closer regula- tion of the electric supply. Especially the arcs with constant fixed are length, as the mag- netite arc and the mercury are, are very little sensitive to changes of current, while the arc lamp with floating-feed and differential control is most sensitive to current changes, though less so than the incandescent lamp. Inversely, on constant-potential supply, the constant-pressure . are with fixed arc length shows the greatest sensitivity to voltage variations. This depends on the amount of steadying resistance, and decreases with increasing steadying resistance, while with less than 33 per cent steadying resistance the sensitivity increases so that the are soon becories inoperative. The least.sensitivity on multiple circuit is afforded by series control. 156 ILLUMINATING ENGINEERING It thus would follow, that the incandescent lamps with high- positive temperature coefficient have an advantage on constant- potential supply, but a corresponding disadvantage on constant- current supply. On constant-current circuits the are lamps with fixed arc length, as the magnetite and mercury, would be most con- stant in their light production, and next thereto the lamps with shunt control, while inversely on constant-potential circuits these two operating mechanisms are most sensitive to voltage variations. ace) GAS AND OIL ILLUMINANTS By Arex. C. HUMPHREYS CONTENTS Introduction. Scope of lecture. Brief reference to the special character of the illuminants con- sidered. Petroleum and by-products—kerosene. Illuminants considered. Pintsch gas. Brief history. Present extent of use. How made. Externally heated retorts—low pressure. Internally heated generators, low pressure and high press- ure. Special characteristics. How employed. Lighting of railroad cars. Lighting of buoys, beacons, lightships, etc. Special appliances—especially pressure regulators, car lamps and buoy lanterns. Pintsch system provides for scientific distribution of light. Carburetted-air gas. Brief history. Present extent of use. Produced from certain hydrocarbons. Special characteristics. How employed. Isolated plants. Town plants. Special appliances. Acetylene. Brief history. Present extent of use. Carbide of calcium—CaC,. How produced from CaC,. Special characteristics. Liquefaction. Special precautions. 158 ILLUMINATING ENGINEERING How employed. Isolated plants. Town plants. Portable lamps and lanterns. Special appliances. Introduction Those who unselfishly have taken the initiative in arranging for this course of lectures on the science and art of illuminating engi- neering, sparing neither time, thought nor effort, should be exempt from all unfriendly criticism. Then it should be understood that in 36 lectures, treating of 19 divisions of the subject, not more can be done, certainly with regard to some of the divisions and sub- divisions, than point the way to those who desire to devote them- selves seriously to the study and practice of illuminating engi- neering. This lecture is one of two which are expected to cover “ Gas and Oil Illuminants.” To Professor Whitaker has been assigned the open flame and the incandescent mantle, and to me Pintsch gas, carburetted-air gas and acetylene. It must be apparent that the hour and a half allotted to each lecture is entirely inadequate for a comprehensive consideration of the three systems named. It should be understood that this lecture, notwithstanding the sub-title of Part V, is not intended to cover coal gas, water gas or natural gas, which are the gas illuminants most generally dis- tributed and which, especially if taken together, furnish more artificial illumination than electric light together with the three illuminants here to be considered. As we proceed it will be seen that Pintsch gas, carburetted-air gas and acetylene do not compete with coal gas, water gas or natural gas, but are employed where these are not commercially available or obtainable, or where a special character of service is. required. Of these three sources of artificial illumination, two, namely, Pintsch gas and air gas, are made from oil. Pintsch gas is pro- duced by the destructive distillation of petroleum oil. It is not to be understood that the manufacture of oil gas is confined to this. process. Oil gas has been employed to a considerable extent in the United States and Europe for the illumination of small towns, factories, etc. Oil gas was so employed before it was applied in GAS AND OIL ILLUMINANTS 159 compressed form to car lighting, and patents for oil-gas manu- facture were granted in the early part of the last century. In some few cases compressed oil gas has been employed for the lighting of small towns, the compressed gas being delivered in cylinders instead of through mains laid in the thoroughfares ; these undertakings were short-lived. In Scotland, prior to the production of petroleum in large quantities, a high candle-power gas was made from oil distilled from rich shales. By far the most extensive use of oil in the making of illumi- nating gas has been in the manufacture of carburetted water gas. Although the title of Division V includes oil as an illuminant, neither Professor Whitaker nor I are expected to consider it as a direct source of illumination. When we realize that refined kerosene oil is used throughout the whole civilized world, com- peting with all other sources of artificial illumination covered in these lectures and relied upon where these are not to be found, this well serves to illustrate the fact that the 36 lectures cannot be made to cover, even superficially, the whole field of artificial illumination. In this connection, let me refer you to “ Petroleum and Its Products,” by Sir Boverton Redwood, 2d Edition, 1906, two vol- umes, published by Charles Griffen & Company, London. This work is most valuable in itself, and also for the extensive bibli- ography annexed. Redwood gives an interesting and instructive history of the petroleum industry, beginning with a reference to an account writ- ten by Herodotus, 450 B.C., of a well producing “ asphalt, salt and oil.” Petroleum is now being produced in all parts of the world, and in many places in large quantities. Vast quantities have been discovered recently in Mexico, this oil being unusually rich in asphalt. The production of oil from coal and shale is of interest, especially as much of scientific and practical value was learned in the course of the evolution of the process and apparatus employed. I presume that other of the lectures included in this. course will give some account of the several by-products from the dis- tillation of petroleum which have been and still are employed in manufacturing water gas and enriching coal gas, and of the commercial utilization of these and other by-products of kerosene 160 ILLUMINATING ENGINEERING manufacture which has enabled the great oil companies, especially the Standard, to produce kerosene at a minimum cost. The internal combustion engine, particularly as used in motor cars and motor boats, has, within the last few years, developed an extensive and rapidly growing market for the more volatile of the distillates which, together with the so-called gas oil, were almost a drug on-the market 25 years ago. Some idea of the magnitude and growth of the production of kerosene oil is found in the records for 1906 and 1909. In the former year the total production of kerosene is estimated by the Standard Oil Company to have been 48,000,000 barrels or 2,016,- 000,000 gallons; and, in 1909, 53,000,000 barrels or 2,226,000,000 gallons, an increase in 3 years of more than 10 per cent. Pintsch Gas Pintsch gas is so named after Julius Pintsch, of Germany, the founder of the great firm of that name. Pintsch gas is made by the destructive distillation of petroleum or other mineral oil in retorts (cast iron or clay) externally and continuously heated, or in generators filled with fire-brick checker- work, internally and intermittently heated. The product is in great measure a fixed gas, principally methane (CH,) and heavy hydrocarbons with a very small volume of hydrogen. The oil gas as so made, unlike water gas, is not diluted. The Pintsch system was originally developed for the lighting of, railway passenger cars. In the early days of railroading some trains were not run after dark, and in many cases where the trains were run through the night hours it was not considered necessary to furnish artificial illumination. The illuminants first employed were candles and oil lamps. In 1866 experiments were begun in Germany in the lighting of railway carriages with coal gas. It happened that in the United States the Reading Railroad also began to light some of its cars with coal gas in the same year. By reason of the limited space available on saattdaet cars for the storage of the illuminant, city gas was found to be too bulky, » and this suggested that the gas should be of comparatively high candle-power and be compressed into a greatly reduced volume. This led Pintsch to turn his attention to gas made from coal oil and petroleum. GAS AND OIL ILLUMINANTS TOL As compared with coal gas a double advantage was secured by the substitution of compressed oil gas for railroad lighting and similar service, for the oil gas, in addition to an initial illumi- nating power three or four times higher than that of coal gas, suffers a loss in illuminating power due to compression of only one-third to one-half of that of coal gas. This loss in compressing Pintsch gas to 10 atmospheres is only about 10 per cent. The advantages of compressed oil gas so markedly apparent in its application to the hghting of railway passenger cars were in even greater degree found to be applicable to the lighting of buoys, beacons, stake lights and lightships. In the late seventies Pintsch turned his serious attention to the development of a system to satisfy the varying demands of lighthouse authorities and met with prompt success. For the storage of compressed gas at the works Pintsch developed a process of welding by which were produced storage cylinders of large capacity free from seams or rivets. These seamless cylinders are now manufactured to a maximum size of 8 feet in diameter by 33 feet in length. For lighthouse work welded buoys were made of the several required shapes, the body of the buoy serving as a holder for the compressed gas. Difficult as was the welding of the storage cylinders, the welding of the buoy bodies was far more difficult. The application of this welding system to the manu- facture of buoys was particularly useful, because by eliminating riveted joints there was obtained the necessary strength and ca- pacity with the minimum of weight, and consequently the maxi- mum of buoyancy. | Pintsch also devised ’a wind- and wave-proof lantern which demonstrated its ability to maintain a steady and constant light under the severest weather conditions. In the use of compressed gas for car lighting, and still more for lighthouse service, it was necessary to develop a pressure regulator capable of receiving the gas at a pressure of from 150 pounds to. 1 pound per square inch, and delivering it constantly to the burner supply pipe at such a reduced pressure as might be required for the most efficient operation of the particular burner employed. To meet this requirement Pintsch invented a regulator which, prac- tically without change, has met successfully all the requirements of nearly 40 years of the most varied and exacting service. 162 ILLUMINATING ENGINEERING As far as I know, and I had a very personal experience with this regulator from the latter part of the year 1881 to the end of 1884, no gas, compressed or uncompressed, is supplied to the point of ignition under more uniform pressure than the gas supplied by the Pintsch system. J lay particular stress on this point because I know that questions have frequently been raised as to the com- plete reliability of such an instrument for constant and accurate regulation within narrow limits of outlet pressure. I will describe briefly a couple of tests which occurred under my own eye about the year 1883. The first was a test by the representatives of the United States Lighthouse Board of a Pintsch regulator and buoy lantern in competition with similar appliances of a rival system. The claim was made for the latter system that operating under 600 pounds pressure a decided advantage was secured by reason of the longer supply of light thus obtained from the one filling of the gas reservoir. Although the Pintsch goy- ernor was only tested and guaranteed for a pressure of 150 pounds, to meet the claims of the competitor, the Pintsch Company’s rep- resentatives offered to subject this governor to the 600 pounds pressure. Upon examination it was found that the storage holder of the rival concern was charged only to 300 pounds instead of 600 pounds as claimed. U-water gauges were connected to the pipes connecting the governor outlets to the lanterns. The inlet pressures to both governors were first adjusted at 1 pound, and the corresponding outlet pressures as indicated by the U gauges were accurately observed and marked. By a quick movement of the hand the full pressure of 300 pounds was admitted to the inlet of each of the governors. In the case of the Pintsch governor the fluctuation of the governed pressure, as indicated by the U gauge, was found to be less than one-tenth of an inch of water and the flames were not affected; whereas in the other case the water was blown out of the U gauge and struck the ceiling of the room in which the test was being made, and the light was extinguished. In this test the lanterns were also subjected to conditions repre- senting a hurricane, the wind effect being obtained by the use of an air blower and the washing of the waves by. water delivered from a 2-inch hose under heavy pressure against all parts of the lanterns. The Pintsch lantern remained lighted while the other was extinguished. GAS AND OIL ILLUMINANTS 163 The other case also served to show the reliability of the governor and the buoy lantern under extraordinarily severe conditions. Fol- lowing a heavy storm it was reported that one of the buoys recently anchored in New York Harbor had been extinguished. With the Lighthouse Board’s district inspector, I made a personal investi- gation. When we arrived at the buoy, from the tender it appeared that the light was extinguished. Determined that there should be no question as to the accuracy of the record I climbed into the cage surrounding the lantern of the buoy. Opening the lantern I found that the set-screw which regulates the size of the flames had been screwed down hard so that the amount of gas leaking by was only sufficient to produce flames practically non-luminous, with the result, even after the lantern was opened, that those on the lighthouse tender could not see the flames. That the record should not depend upon my word I demonstrated, by lighting a piece of paper at the flames, that the light was not extinguished. The delicacy of action of the governor and the efficiency of the lantern can be understood when I say that the flames were so small that after lighting the paper I game tiehed them by fanning them with a single motion of my hand. While the use of pressure regulators in connection with the dis- tribution of city gas introduces unnecessary complications, in the case of such special service as that which the Pintsch system has to perform, which necessarily demands special appliances designed and constructed to operate with mathematical accuracy, no addi- tional complication is introduced provided the regulator is com- pletely dependable. Given a gas delivered at a pressure well above that required for maximum efficiency with any illuminating burner, an important economic advantage is secured by the use of a gov- ernor which can be relied upon to reduce this excessive pressure to any desired point. This is well illustrated in the application of the Pintsch system to mantle lighting, as later to be explained. Between the years 1870 and 1880 the Pintsch system of lighting was introduced to a very considerable extent on the Prussian State lines. i Pintsch’s first United States parents were taken out between the years 1870 and 1880. In the year 1880 the Pintsch system was brought to the United States, being first applied in hghting the sound steamers of the Stonington Line and the cars of the connecting line of the New 164 ILLUMINATING HNGINEERING York, Providence and Boston Railroad, now part of the New Haven system. The Pintsch plant for supplying the boats and cars was located at Stonington, Conn. . The next railroad to adopt the light was the Erie, the works for making and compressing the gas being built in the railroad’s yards in Jersey City. Shortly thereafter a similar plant was built at -Weehawken for the West Shore Railroad, and practically all of its passenger cars then being built were equipped for the new hght. At first the policy of the United States Pintsch Company was to induce each railroad adopting the system to own and operate its own gas works, one or more. This would have led to unneces- sary multiplication of gas works throughout the country. The policy was persisted in for a number of years, and in this is to be found the reason why the system made but little progress in the United States during the first years of the American company’s existence. It was not until a new element came into control of the United States Pintsch Company that this policy was aban- doned and more rapid progress made, the company undertaking the building of gas works and the supply of compressed oil gas to the railroads adopting the system. While now some of the railroads own and operate plants built for them by the company, the Pintsch Company owns and operates works of its own through- out the United States, Canada and Mexico, in many cases sup- plying several roads from the same plant. In a number of cities Pintsch gas is manufactured and distributed to the railroads by the local gas company operating in partnership with the Pintsch Company and the railroads served. The Pintsch system is in use practically throughout the civilized world. Up to date about 180,000 cars in all are equipped for Pintsch light. Up to April 30, 1909, there were in service in the following coun- tries, namely, Great Britain, Germany, Holland, Belgium, France, Portugal, Denmark, Russia, Tunis, Sweden, Austria, Italy, United States, Brazil, Argentine Republic, Uruguay, Egypt, India, South Africa, Canada, Australia, New Zealand, Algiers, Spain, Japan and China, buoys, 1947; beacons and stake lights, 485; lightships, 96; these being supplied from 77 charging stations. A later return, covering the lighthouse service for the United States and Canada, shows that on August 10, 1910, the number / GAS AND O1L ILLUMINANTS 165 of buoys in service in these two countries was 461, an increase of 30 in the 15 months. Up to June 1, 1910, there were in the United States, Canada and Mexico 93 Pintsch gas works, supplying compressed gas to 360 railway stations. In the same territory, up to January 1, 1910, the number of cars equipped for the Pintsch system was 35,137. ) During the last few years the Pintsch system has been further developed to secure the additional advantages to be obtained through the use of incandescent mantle burners. Up to date there are mantle lamps installed in railway cars as follows: France, about 95,000; Great Britain, about 61,000; other European countries, about 152,000; United States, Canada and Mexico, about 80,000; total, about 388,000. These figures represent mantle-lamp equip- ment for about 55,400 cars. Pintsch gas, as has been stated, is obtained by the destructive distillation of oil. In the early days of the system oil produced by the distillation of coal or shale was used. Of late years crude petroleum oil and its distillates have been employed, market con- ditions controlling the choice. The crude oil can be satisfactorily employed and was at one time largely used. To-day market con- ditions generally lead to the use of a distillate. At first, and until recent years, the gas was manufactured only in cast-iron retorts externally heated. Much of the gas is still so made. ‘Two retorts are set in each “bench” or furnace, the two retorts being so connected at their back ends that the gas passes from one to the other. The oil is introduced at the front of the upper retort and falls upon a removable sheet-iron tray which col- lects most of the carbonized oil. The gas and vapor produced in the upper retort pass down to the back of the lower retort, and so through to the front of the bench, passing by a decension pipe to the hydraulic main located below the floor of the house. Issuing from the hydraulic main the gas and vapor pass through a dry scrubber, condenser, purifiers and station meter, and are collected in the low-pressure storage holder. From the storage holder the gas is drawn by a compressor, compressed into one or more of the welded cylinders before described, and is then ready for dis- tribution through the high-pressure pipes to the cars or transport holders. All necessary precautions are taken to trap the liquid hydrocarbon thrown down by the process of compression, the object 166 ILLUMINATING ENGINEERING being to obtain a thoroughly dry gas, which result is secured to a remarkable degree. The early German practice limited the compression between 8 and 10 atmospheres. The more recent practice, especially in the United States, is between 12 and 14 atmospheres. Particularly in connection with the larger plants, clay retorts, as used in coal-gas manufacture, came into use. This change, by reason of the porosity of the clay retorts, has made necessary the employment of exhausters to draw the gas from the retorts and push it on through the other parts of the plant to the storage holder. When the gas is distilled in clay retorts the distillation is com- pleted in a single retort, the oil being introduced through a wrought-iron pipe carried through the front of the retort, extending nearly its entire length and open at the end. The oil, gas and vapor issue from the open end of the pipe and return through the retort to the front. The gas and vapor issue from the front of the retort and pass by an ascension pipe to the hydraulic main located on the top of the bench, and from there, as before described, to the storage holder. Some years ago experiments were indents to determine if greater economy could be secured by distilling the oil in generators internally fired. This is necessarily an intermittent process and so is markedly differentiated from the continuous retort process. The generator consists of a steel shell 6 feet in diameter and about 12 feet in height. It is lined with fire-brick and the interior is divided into two compartments, a smaller lower compartment _ which serves as a combustion chamber, and a larger upper com- partment which is filled with fire-brick checker-work nearly up to the top of the shell; this upper chamber terminates in a cone, upon the top of which is a stack valve. The tar, obtained as a by-product from the distillation, is used as fuel. This is injected into the combustion chamber below the checker-work by means of a liquid-fuel burner. A mechanical blower produces the necessary forced draft. As soon as the generator has been “ blown ” to its proper working temperature the tar fuel, steam and air are shut off and the stack valve is closed. Gas oil under pressure is then injected through three oil nozzles located in the top of the generator and the finely divided oil is thrown upon the checker brick. The oil vapor so Gas AND OIL ILLUMINANTS 167 formed passes down through the heated checker bricks and is so decomposed, the gas produced finally issuing from the generator through the take-off pipe located in the side of the combustion chamber. The cycle is divided into a heating period (“blow”) of about 5 minutes, and a See period (+ 7un ~~) tof from. 6 -to-8 minutes. The rate of flow of oil is regulated by the so-called trowel test which the gas maker applies at short intervals. This test con- sists in permitting a fine jet of the hot gas to impinge upon the polished blade of a mason’s trowel, the figure made upon the trowel by the condensed tar indicating to the practiced eye the amount of condensable vapor in the gas. With care in operation the gas is obtained of quite uniform quality in spite of the gradually de- creasing temperature of the generator. About 1500 feet of the gas are made per “ run.” The gas after leaving the generator is dry scrubbed and cooled, and is then collected in a “ relief” holder. From the holder it is drawn by the compressor through the purifiers and station meter, and then compressed into the high-pressure storage holders at a pressure of about 14 atmospheres. It is found that by this method of intermittent distillation in internally fired generators a gas can be obtained about 10 per cent higher in candle-power than by the retort process, with the at- tendant advantages of largely reduced floor space, reduced cost of construction, and lower manufacturing cost due to economy in fuel, labor and repairs. In order to simplify the apparatus and reduce the investment at stations where the output is small, a still later development is the generation of the gas under the pressure required for delivery. (See Fig. 1.) To withstand this heavy pressure, the generator shell is con- structed of heavy steel plates. ‘The shell is divided as follows: At the bottom, a combustion chamber; above, a chamber filled with. fire-brick checker-work ; above this, a space for the oil sprays; and above this, another chamber filled with checker-work. The “blow ” and “run” occur as in the low-pressure generator. In order, however, to check the rapid decomposition of the oil, which would otherwise occur when operating under heavy pressure, steam is injected with the oil into the generator. The steam so 168 ILLUMINATING ENGINEERING Ne FG: Y, ] Z it Y Y Y , ss Z.. Uf SG SS Wwe EWC yy 5 Al uw £ 4 io? i 5 ‘\ < Nee <; 4 t V HD) P ' lj 1 i = LecrS: | ——a Li AH ---4 = = TAH ett wo he ! ay wr t | i ray 1) eet a eit Parti Res: YY 1 ih i | if , ‘ | | | it 1 A \ f) it i! il \ SS Sa a —— — mil 48) PA | a m N NECTION Y ————— cee ee A Y YL Tepe Qnaw ZL, We € % sich} ome PLAN st une ———— mac Fic. 1.—Pintsch Gas High-Pressure Generator Plant. GAS AND O1L ILLUMINANTS 4 STURTEVANT EXHAUST HEAS ORAM To FILTER TR OOLING JALKETO24¢ RBA, FROM RELIEF ORE OGRE FILTER TANK if 4-7 es [COOLING JACKET Tess th 5 esse ey iD 4 i ey vidi : ‘ H ; ‘ 1 2 Ur NvT CouPune i, 2% ry Busine SEX HV CROSS / 2 CaMV Y PIPE AUXILIARY PLUG AT OUTLET OF LAST COOLING JACKET — = SECTION L-M =— i. M4 0n To BURNERS. 2"SAFETY VAWE DISCHARGE "STEAM TO BURNERS 9) oy ] | iT | | TI } CHECK VALVE % 44 STEAM TD GOTTON OF GLMERATOR MAIN ee hs ROI O AIL. AIA AVI LENT MINTO DIS II I NN aS SOM INS IE ALLL REIS ONTO YSIS LISI EN NOON IOLA LS ELLE VME Soe a RS, a bases Bae. 3 ———== SECTION AB === LSS 9 Fic. la.—Pintsch Gas High-Pressure Generator Plant. 169 170 ILLUMINATING ENGINEERING used acts as a carrier and protector for the oil vapor and gas, and does not react with the carbon of the oil to produce water gas, the temperature of the generator being too low for this reaction. The steam enters the generator at the top, being superheated in passing down through the upper checker-work. Coming to the SG Y Y IZ L ] a Y —SECTION-N-0 — SUANERS 4 eunce Fig. 1b.—Pintsch Gas High-Pressure Generator Plant. intermediate chamber it meets and mingles with the finely divided oil, and then steam and oil vapor pass down through the second checker-work wherein the oil vapor is decomposed. The gas and superheated steam finally leave the bottom of the generator through the take-off pipe in the side of the combustion chamber. The gas Gas AND O1L ILLUMINANTS bal and highly superheated steam are then dry scrubbed and cooled, and the gas, tar and water are charged into the first storeholder under a pressure of about 14 atmospheres. Passing from the first storeholder the gas is purified under pressure and is then stored in other high-pressure storeholders. Before the next “blow” the gas and oil vapor which remain in the generator under pressure are displaced by means of steam at sufficient pressure, being thus forced through the scrubbing and cooling devices: and into the storeholders. _ This high-pressure plant is more simple and compact because the low-pressure gas holder and compressing apparatus are not required. Three of these high-pressure generator installations have been put into operation, and one of these has been operating satisfac- torily for 2 years; three more are now in process of construction. In both low- and high-pressure systems the generators are oper- ated at a temperature of about 1200° F. The average of analyses of 25 samples of compressed Pintsch gas was as follows, and furnishes a representative indication of its composition : NR EA Eee ee cages w suone oo sigtore''s «evn 8 60% Heavy illuminants: Benzene C,H, ..... ae POD VEC NC dO allen ep) ks cusdicioap ih od of diets Ole Salart 35 Ethylene C,H,, ete. Ob erect: OE NR RT ars ais a ary ate ve: 5 nee NN rr es Ca cea hs he te o athe ters 4.5 100.0 Specific gravity .80 to .85. Ignition temperature, determined by Milton L. Hersey, chemist and chief engineer of tests of Canadian Pacific Railway, made at McGill University 1562° F. or 850° C. Explosive limit between about 4 per cent and i0 per cent of the gas. The horizontal candle-power of the compressed gas, tested in open. flat-flame burner sufficiently small to avoid smoking and calculated to the 5 feet per hour consumption, is about 40. By reason of the necessarily small rate of consumption this does not furnish a re- liable indication of the candle-power. The spherical illuminating power of the lamps, naked flame and mantle, as later to be stated, are the values to be considered for purposes of comparison. 172 ILLUMINATING ENGINEERING Most of the Pintsch gas is used for the lighting of railroad cars. While a relatively small amount is used in lighting buoys, beacons, etc., the service performed is one of commanding importance. In the early days steamers and ferry boats were satisfactorily lighted by this system. Many of the ferry boats plying in New York Harbor were at one time lighted by coal gas, uncompressed or com- pressed. In some cases these methods were superseded by the Pintsch system. The advance in the art of electric lighting, coupled with the special adaptability of electric lighting to the illumina- tion of vessels equipped for steam power, led naturally to the re- placement of compressed gas by the electric light. 1 N i LMM ———T.O BE SCREWED IN es TH D LEAD AND ——-- >_> — € ’ REO LEA Fig. 2.—Pintsch Gas Regulator. The Pintsch regulator deserves more than a passing notice. (See Fig. 2.) The essential parts of the regulator are a needle valve of special form and a large diaphragm made of leather so treated as to be gas proof and extremely flexible. The diaphragm is sub- jected only to the reduced or regulated pressure and controls the movement of the valve through a lever of such proportions that the pressure of the valve against its seat is 11 times the total pressure against the diaphragm. A pair of springs acting on the lever through a knife edge oppose the pull of the diaphragm and can be regulated so as to give the required outlet pressure. The needle valve, so controlled, is relied upon to exclude the high pressure from the interior of the regulator, no auxiliary valve being em- ployed for that purpose when the lamps are shut off. For the illumination of railroad cars many forms of naked-flame lamps have been employed. These have all been designed to meet ~ GAS AND OIL ILLUMINANTS 173 the exacting requirements necessarily involved in the lighting of cars running at varying speeds, subject to abrupt stops, so ven- tilated that the lamps are required to resist strong air draughts, and under the care of trainmen who cannot be relied upon to give the lamps expert attention. As this is one of a number of lectures on illuminating engi- neering it is in order that I should call particular attention to the fact that the engineers of the Pintsch Companies here and abroad have recognized constantly that they were required to solve their problems from the standpoint of the engineer of il- lumination. Not only has the effort been to secure the greatest amount of hght from a minimum of material and at a minimum cost, but the effort has been to distribute this light so as best to serve the travelling public. It has always been recognized that an important element in the problem was to secure ‘an effect which would be pleasant and restful to the eye. All the problems in- volved have been under discussion and subject to experimentation constantly. It was recognized that the first step was to obtain a steady flame, free from flicker, and that this must be secured through the design of a draught-proof lamp and a pressure regu- lator at once sensitive and reliable. I know that some hold that illuminating engineering was not the subject of scientific study by gas engineers until the electric light engineers led the way. I am inclined to think that some of our electric light associates in the I]luminating Engineering Society are of this number. Many facts in regard to gas engineer- ing practice could be cited against this proposition. In addition to the record made by the Pintsch engineers, let me refer to one example, which is notable in this connection. Some few years ago, at a meeting of a committee of our Society, I learned that the electrical engineers present were of the opinion that a notable advance in the science of illumination was made when rooms were first illuminated by light reflected from sources hidden from the eye, and that this advance was to be credited to the electric light _ engineers. I then described the lighting of the Liverpool Phil- harmonic Hall by naked gas flames placed so as to be hidden from view by the plaster cornice, the light being reflected down into the hall from the curved surface of the ceiling. This installation was made 50 years before I first saw it, which was over 10 years ago. | I trust I may be pardoned for this little digression, and especially by my electric light associates. 174 ILLUMINATING ENGINEERING Figure 3 shows a flat-flame four-burner railroad car lamp. It is here to be borne in mind that the methods of hanging and the design of the body of the lamp have been varied to meet practical conditions and the demands, sometimes artistic and sometimes not, of the railroads’ managers. In this lamp the air supply to the burners passes through the upper portion of the body and so into the cylinder enclosing the four chimneys, down into the lower portion of the lamp and so into the globe, where it reaches the flames. The products’ of combustion go up past the central re- £ at —. 268 Fie. 3.—Four-Burner Flat-Flame Railroad Car Lamp flector, and so on up through the chimneys, some of the sensible heat of the products of combustion being transferred to the in- coming air. | The four burners togéther consume about 314 feet of gas an hour, and give 30 to 35 mean hemispherical (lower) candle-power. Of recent years the Pintsch Companies have devoted much at- tention to the application of incandescent mantles to car lighting and buoy lighting. Experiments with vertical mantles were not successful, by reason of frequent breakages. After the trial of many devices to reduce the effect of shock the engineers of the United States Company solved the problem by means of a strong inverted mantle rigidly fixed to the burner. To secure increased GAS AND OIL ILLUMINANTS 175 strength these mantles are made heavier than the ordinary mantle, and to compensate for the loss in illuminating power due to this increase in mass the gas is supplied to the burners at a pressure of 2 pounds. This advantage is secured by the use of a compressed gas controlled by a reliable governor. It is a rather remarkable fact that the lamps are not provided with means of adjustment. The gas orifices and air inlets are drilled to standard sizes, and, Fig. 4.—Single Mantle Car Lamp. having passed the calibration tests, the lamps are erected .as turned out from the factory. These mantle burners consume 2 feet of gas an hour and give - (the mantles alone) 90 to 100 horizontal candle-power without the aid of reflectors. As arranged in the car lamp, they give a mean hemispherical candle-power of 90 to 100. Comparing with the flat-flame lamps already described, the lighting effect is about 4 to 1, and with the same gas storage capacity the length of period between fillings is practically increased 60 per cent. 176 ILLUMINATING ENGINEERING These inverted mantles as now used have established a satis- factory life record. Some little time ago a careful observation was made of their service on 25 steam railway cars engaged in New - York suburban traffic. These cars were equipped with 125 lamps. The cars were handled in the regular way by the trainmen, who were not informed that the lamps were under special observation. The Pintsch employees, however, renewed all broken mantles so that an accurate record of the mantles used might be obtained. The result of this test for the 125 lamps was an average mantle GAS TANK PRESSURE REGULATOR NO 254 FILLING VALVE NO ©344 Fic. 5.—Car Equipment for Pintsch Lighting. life of 376 days. This shows a notable improvement even over the old inverted mantle as first made. The construction of the lamp is shown in Fig. 4. The regu- lated gas at 2 pounds pressure is admitted through fitting No. 3146, and passes down to a strainer of peculiar construction placed in the vertical channel. The gas issuing therefrom is met by the air pulled in at the sides by the gas, and the gas and air mixture then passes down unobstructed to the burner, which consists of a metal dise accurately drilled with seven orifices. Fig. 5 shows car equipment for Pintsch lighting; Fig. 6 is an interior view of a railway coach lighted with mantle lamps, and Fig. 7 is an illumination diagram for such a coach. I cannot conclude this section of my lecture without describing, at least briefly, the Pintsch buoy, a very beautiful example of GAS AND OIL ILLUMINANTS barge specialized engineering akin to illuminating engineering. (See Fig. 8.) The buoy body is a seamless welded-steel shell designed and constructed to withstand the high pressure of the gas stored therein, and to afford ample buoyancy for the support of the anchor chain, lantern and other parts. The buoy bodies are made in Fic. 6.—Interior View of Coach with Mantle Lamps. different shapes to meet varying conditions as to depth of water, anchorage, tideways, etc. A suitable tower surrounded by a cage supports and protects the lantern and carries a platform to afford a footing for the attendant when lighting or adjusting the flames. The lantern is designed and constructed to protect the light from 178 ILLUMINATING ENGINEERING rain, waves and wind under the severest possible conditions to be found close to the surface of the sea. The base of the lantern forms the case for the pressure governor. In the original lantern the burner was placed inside a Fresnel dioptric fixed-light lens which, by bending the light rays, confined them approximately between two horizontal planes, thus increasing as wn Ww > | LAMP No.3508. BOWL FILE 272 X SONILUS 31S —— rar) o eS tial EXTREMEVARIATION — _2-15. __ _ __- BD heaige nt CARNo-. / = 1 oe a ll | ag, | KIND OF LIGHT = PINTSCH MANTLE No.3508 __. s ie | | NoOFLAMPS.. — 2 gee eee RTT | pube s-ce No.OF BURNERS — 1c et cee HN i 5 10 = GLASSWARE-GROUND BOWL —OPAL TOP Pry Se uzes | GAS PER HOUR: = 2559:04 2 es HIGH WS PRESSURE ______. @ POUNOS___ __ _ DAS UC Gr TEMPERATURE 222 ee tee 4 | TTT | esa FREEGASPERHOUR ___— 9.96 NL ate AVERAGE FOOT CANDLES #03 __ _ __ TAN HHHHh 7-15 16 aes MAX.FOOT CANDLES _ __ 3-40 _ __ ___ hi ii 191 ap) MIN. 2233: aie coh sc See 2 9 1@) ° A Zeer S55 Jo VAR\ATION(ABOVE MEAN) _©72-5 __ __ : / 13 20] > 92 (BELOW 9? J2SS4-2 2a ce eBid Fe No.0F STATIONS. =. ae ee 156 138 CUBICFEET GAS PER HOUR FOR : [3 24] |: Sa 1FT.CANDLE ILLUMINATION “+90 _ _ 224 340 D 25 26 240 3.05) 27 28 194 218 29 30 184 220 SIIANYD LOS Ni NOLLWNIWATTI i" = - i" EE ——| a to} 1S MEAN HEMISPHERICAL G.P ° 86.2 Ss ———— ——— -_———4 ——— —— re SONILLIS MOGNIM —--o = CANDLE POWER — 0 DIAGRAM OF LAMP — NoOoWs Fig. 7.—Illumination Diagram for Coach with Mantle Lamps. the power and range of the light. Some of the lanterns thus equipped are still in use. In order to give the light a specific char- acteristic and at the same time reduce the gas consumption and so increase the interval between gas chargings, a further improvement was made by the addition of a flashing mechanism. This is a simple and reliable device which controls the flow of gas to the burner so that the gas is ignited and extinguished at intervals, the GAs AND OIL ILLUMINANTS 179 lengths of which are predetermined to meet the particular condi- tions of each case. This automatic mechanism is enclosed in a chamber located immediately above the governor, and is actuated by the gas flowing through this chamber on its way from the governor to the flash-light burner, which is ignited by a pilot light burning continuously and receiving its gas supply direct from the governor. \ | \ eee cees ee ee eeeee see ereeesl Fig. 8.—Pintsch Buoy. The relative periodicity of light and darkness can be varied by the adjustment of the mechanism to meet varying requirements. - The standard adjustment gives periods of equal lengths, usually 5 seconds or 10 seconds each. If desired the periods can be made non-uniform. The latest form of this mechanism provides for the buoy being used either as a fixed or flash light, as required for any location; all the buoys as now built and supplied are so equipped. Nearly 180 ILLUMINATING ENGINEERING all the buoys now in use are equipped with the flash-light mechan- ism, and most of these are of the convertible type. As the fixed-light lens permits the rays to radiate horizontally through 360 degrees, to still further increase the power and range of the buoy lights a “ bull’s-eye” or flash lens can be employed instead of the flashing mechanism just described. If desired, a series of these lenses can be grouped in a circle around the light source. That the light may be visible at all points in the horizon the bull’s-eve lens, or series of lenses, must be revolved. This is effected by a motor driven by the gas flowing to the burner. This lens arrangement delivers a light at least 20 times as powerful as that from the fixed-light lens. An additional advantage is that the characteristic of the buoy light can be further determined by the design and the relative positions of the lenses of the series. There are comparatively few of the revolving lenses in service. Until recently flat-flame burners were used exclusively in the Pintsch buoys, but mantle burners are now displacing the flat flames. The older lanterns are being remodeled for mantle burners, and all new lanterns are of this type. (See Fig. 9.) As compared with the flat flame the mantle burner gives a candle-power three times as great, and its intrinsic brilliancy is ten times as great, resulting in greatly increased power for the same consumption of gas. The flat-flame burners are made for different rates of consumption, while the mantle burners are made for one rate only. Bells operating either above or below the surface of ne water and actuated by the flow of gas supplying the burner are in some cases attached to these buoys. With one gas charge these buoys will run from 55 to 528 days; the size of the buoy body, whether flat-flame or mantle burner, whether fixed or flash light, and if flat flame, the size of burners, determining the number of days. Stationary beacons and light ships are also ‘eantDee for and operated with Pintsch gas. Gas under a pressure of 100 atmospheres is now being used ex- tensively for this marine work. For beacons and light ships it is burned direct from the cylinders in which the gas is conveyed. In the case of buoys the high-pressure cylinders obviate the neces- sity for large storage holders and compressors on the supply tender, GAs AND O1L ILLUMINANTS 18] m-Outer Cap Lantern Glass H. «, Lers—} hi Hantle RY ohelete A Mo. 5664 flashing Chamber Seale 671" Fie. 9.—Pintsch Buoy Lantern with Mantle Burner. 182 ILLUMINATING ENGINEERING the buoys being charged direct up to 10 atmospheres from the 100- atmosphere cylinders. It is found that about 133 volumes of the gas can be stored under a pressure of 100 atmospheres, and that little or no additional loss in candle-power is suffered in carrying the compression from 14 to 100 atmospheres. There is an additional deposit of liquid hydro- carbon, as indicated by the increased storage volume, but if the outlet pipe is sealed in this liquid the liquid revaporizes, and at the reduced pressure of 14 atmospheres and below it is carried through the appliances to the burner practically as a dry gas. Let me conclude by pointing out two features of the Pintsch system of great practical advantage to its patrons. In connection with the filling of the cars it is important that the amount of gas delivered to each car should be readily ascertainable for record. It is even more important that the attendant should be able to tell by inspection at any time how many hours of lighting are provided for by the gas in the cylinder. Both of these re- quirements are met by making the cylinders of standard sizes, the cubical contents in feet being marked and recorded. A high-pres- sure gauge showing the pressure in atmospheres is attached at each car-filling valve. The simple calculation of multiplying the gauge reading by the capacity of the cylinder gives the available volume of gas contained. Another important feature is that throughout the territory cov- ered by the United States Pintsch Company all parts of machinery and all fittings are interchangeable. The design of the smallest and apparently most insignificant part has been carefully con- sidered. The engineers have from the first recognized that they were offering to perform a special service involving many diffi- culties. As a result, a system has been developed that provides for the supplying of Pintsch gas to any railroad car equipped with Pintsch standardized appliances, no matter how far that car may be from its home territory, provided it is within reach of any one of the 93 gas works or any one of the 360 Pintsch gas-supplied railway stations located in the United States, Canada or Mexico. Carburetted-Air Gas Carburetted-air gas consists of atmospheric air to which hydro- carbon vapor has been added, the proportions of air and vapor vary- ing with the process employed. Gas AND OIL ILLUMINANTS 183 The application of carburetted-air gas as an illuminating and heating agent to meet certain special conditions has been an in- dustry for about 40 years. As a source of energy in the internal combustion engine its use has been of late greatly increased and extended. Carburetted-air gas machines can be grouped in two classes, those operated without heat and those operated with heat. Those of the former group have been more generally employed, especially where the principal service has been lighting. In operating with cold air it is necessary to use refined highly volatile gasoline; but if steam or other heat source is employed to assist evaporation, the somewhat less volatile and less expensive naphthas are used. Carburetted-air gas differs fundamentally from coal gas, water gas or oil gas through the fact that whereas in the process of mixing the liquid hydrocarbon is vaporized it is not changed chemically, while in the case of the other three gases the manufacturing process to which the coal or oil is subjected converts the hydrocarbon into fixed gases in major proportion and certain vapors in minor proportion. In the distillation of crude petroleum, as the temperature of the still rises, the several distillates are driven off successively accord- ing to the following approximate classification : Readings of Corresponding He ainctse Specific Gravity Trade classification 90° and above 0.6363 and below Rhigolene & cymogene 90° to 80° 0.6363 to 0.6667 Gasoline 80° to 70° 0.6667 to 0.7000 Light naphtha i tO our 0.7000 to 0.7368 Heavy naphtha Following these distillates come the kerosenes, lubricating oils, gas oil, solid hydrocarbons, tars and solid carbons or hydrocarbons. While refined gasoline of 90° B. (sp. gr., .6363) is obtainable in this country, the price and the extra difficulty in holding it against evaporation have operated to prevent the development of a wide market for this grade. , Refined gasoline lighter than 86° B. (sp. gr., .6481) 1s not gen- erally obtainable in this country. This distillate consists mainly of hexane (C,H,,) and pentane (C,;H,,), with some still lighter and some heavier hydrocarbons. It should evaporate under condi- tions of use without giving off at first an excess volume of light vapors or leaving unvaporized heavy residues. A distillate capable 184 ILLUMINATING ENGINEERING of meeting these conditions can be obtained only by repeated dis- tillations in the refinery to isolate in the gasoline those closely related hydrocarbons which will evaporate in approximately the same volumes under the same conditions. The refining process must also provide for the removal of all traces of tar which other- wise would deposit in the smaller pipes, gum the floats and clog the burners. For the making of air gas the more general practice has been to use a gasoline of about 84° B. (sp. gr., .6542). While this distillate leaves unvaporized a little residue, the amount is small, and as a rule does not have to be pumped out oftener than every 6 to 12 months. It is interesting to note that the residue is about 63° B. (sp. gr., .7254). The nomenclature which developed to identify the distillates of petroleum in many cases is based only upon a commercial or industrial suggestion. As the names given to several of these distillates have been the occasion for considerable confusion, a few words of explanation may not be out of place. When these lighter distillates from petroleum were first obtained uses for them in the arts were still to be found. In manufacturing kerosene, for which there was a ready market, the refiners were embarrassed to find storage for these distillates produced as by- products, and for which there was little or no market. At that time benzene—a hydrocarbon having the chemical formula C,H,, obtained principally ‘from the distillations of coal-tar—possessed a considerable value in the industries as a solvent for fats and greases and an enricher for gas. It soon became clear that some of the lighter distillates of petroleum could be used as a substitute in part for benzene, and thus a commercial reason was furnished for designating these distillates by the name benzine. In the same way other distillates of coal-tar, known as light and heavy naphthas, had their names pre-empted for other petroleum distillates. As the — nomenclature thus developed fails to meet the requirements of a technical terminology the result naturally has been a most em- barrassing confusion in technical and industrial literature. As an example, there are uses for benzene and coal-tar naphthas for which the petroleum distillates cannot be substituted; hence the need to be sure whether the substance under consideration is benzine or benzene in the first case, or naphtha or petroleum “ naphtha” in the second case. Another feature of commercial practice which has led to confusion is that of designating the specific gravity of petroleum distillates by the Baumé hydrometer readings, even to GAS AND OIL ILLUMINANTS 185 the extent in some cases of calling that reading the specific gravity. This is all the more unfortunate for the reason that in the upper part of the scale as the Baumé reading increases the distillate is of a lighter specific gravity, and in the lower part of the scale as the Baumé reading decreases the distillate is of a heavier specific gravity, the Baumé reading of 70° indicating a specific gravity of .70. An additional complication arises from the fact that the Baumé scale for liquids lighter than water is calculated on more than one formula, and therefore the tables used in converting Baumé degrees to specific gravity do not always agree. The values here given are . 140 130+ Baumé reading which is the American standard. Another formula more often fol- 146.3 146.3-+ Baumé reading” the tables are frequently given without the formula and the unwary may be deceived. Some authorities are careful to state in the title of the table, “ American Standard.” In the majority of books of reference the tables do not go above 80° B., and in some the tables are even more limited. Jor these reasons for American prac- tice. it is convenient to remember the formula sp. gr. equals 140 130+ Baumé reading ° The volume of gasoline vapor that can be carried by a given quantity of air depends upon the temperature, the pressure remain- ing constant. The ability of air to take up and hold in suspension gasoline vapors increases very rapidly with the increase in tempera- ture. Professor Leslie says in this connection that while the temperature itself advances uniformly in arithmetical progression the increased dissolving power thus communicated to the air ad- vances with the accelerating rapidity of a geometrical progression. While experiments that have been made to test this theory have . not agreed in confirming its truth, they suggest that it may be at least approximately true. Sir Boverton Redwood states with regard to 86° B. (sp. gr., .6481) gasoline that 100 volumes of air at 32° F. will retain 10.7 per cent of vapor, (9.7 per cent of the mixture). 7 calculated on the formula sp. gr. equals lowed in English books, is Unfortunately, 186 ILLUMINATING ENGINEERING 100 volumes of air at 50° F. will retain 17.5 per cent of vapor, (14.9 per cent of the mixture). 100 volumes of air at 68° F. will retain 27 per cent of vapor, (21.3 per cent of the mixture). In this connection Redwood goes on to say that “air charged with 735 grains of gasoline per cubic foot has been found to pos- sess an illuminating power of 16.5 candles when consumed at the rate of 314 cubic feet an hour in a 15-hole Argand burner.” If we assume the gasoline vapor to have a specific gravity of 3., it follows that the mixture has 3114 per cent of gasoline vapor by volume. | Redwood goes on further to describe a series of experiments, which he carried on with the assistance of Mr. Blunderstone, to determine “the manner in which crude petroleum and certain volatile petroleum-distillates evaporate when subjected to a current of dry air. ... In these experiments, dry air was caused to bubble slowly through the liquid in a series of graduated tubes maintained at a constant temperature. ... A set of determinations being made at temperatures of 40°, 60°, 80° and 100° F.” At 60° three determinations were made with gasoline of a sp. gr. of .639, 44.7 c. c. of the liquid being used. In the first, 0.9 liter of air was passed through the six tubes; in the second, 2.15 liters, and in the third, 3.55 liters. The first gave a total evaporation of .66 volume of liquid to 100 volumes of air; the second gave .59 and the third .51 volume. It is thus seen that the relatively small amount of air took up the largest amount of gasoline. The result of the first test, if calculated, shows that the mixture contained 53 per cent by volume of the gasoline vapor—certainly an extraordinary result. The probabilities are, at least in this last series of experiments, that the small quan- tity of air slowly bubbling through the liquid in six small streams resulted in a selective evaporation. If so, this does not truly repre- sent the result from a liquid of .639 sp. gr. Certainly, we are not warranted in believing that any such percentages of gasoline can be carried in air-gas practice as are indicated in the two cases last quoted. ; The limits between which gasoline vapor and air form an ex- plosive mixture are 2 per cent of vapor with 98 per cent of air and 5 per cent of vapor with 95 per cent of air by volume. This fact furnishes a reason for dividing carburetted-air gas into two classes: GAS AND OIL ILLUMINANTS 187 First, that in which the proportion of gasoline vapor to air is less than 2 per cent; and, second, that in which the proportion of gaso- line vapor to air is more than 5 per cent. The former presents some very interesting features. A carburet- ted-air gas containing 114 per cent of gasoline vapor is low in heating value, is non-explosive, is non-asphyxiating, and yet, when used with a Welsbach mantle, furnishes a satisfactory light. It would appear that such a gas has much to recommend it. This class of air gas has been adopted in England to a considerable ex- tent for lighting country estates, audience halls, summer hotels, and the like. As yet it has received little recognition in this coun- try. A company is now presenting its claims for recognition. The specific gravity of the vapor of gasoline, as now generally used for air gas, is about 3. The calorific value of gasoline is variously quoted. In this con- nection it is to be remembered that “ gasoline” is not a substance of constant chemical composition. Furthermore, the statements do not always show whether the value quoted is gross or net heating value. The United States Geological Survey gives 19,200 B. t. u. per pound as the net value of gasoline of .71 to .73 specific gravity. Bulletin No. 191 of the United States Department of Agriculture, on the authority of Lucke & Woodward, gives 21,120 gross, 19,660 net, B. t. u. per pound. Redwood, in discussing vapor tensions, says: “ Salleron & Urbain give also the following as the determined vapor- pressures (vapor-tensions) of petroleum products of various densities.” He then goes on to say that the values given are “ founded on a belief not in all cases correct.” This table, so rather guardedly quoted by Redwood, gives as the vapor tension of distillate of sp. gr. .65 (B. 85.38), 2110 mm. of water. This can be accepted at least as approximately correct, and would then show that air would be saturated when 20.42 per cent by volume of gasoline was present. In this country the use of carburetted air has been confined for many years to machines that produce a mixture containing over 5 per cent of gasoline vapor, and it has been the practice to use 514 to 61% gallons of gasoline to 1000 feet of the mixture, the con- tent of gasoline vapor then showing a wide margin of safety above the 5 per cent explosive limit. A 514-gallon gas burned in an Argand burner, gives from 15 to 16 candie-power, it contains about 188 ILLUMINATING ENGINEERING 1314 per cent gasoline vapor, and its specific gravity is about 1.26. The specific gravity of the mixture is important; for being heavier than air, in case of leak, not possessing the tendency to rise, it is less rapidly dissipated by the ordinary means of ventilation. This necessitates increased precautions against explosion and asphyxia- tion. Such a gas cannot be subjected to 4 temperature below 43° F. without depositing gasoline in the pipes; therefore, it must be protected against cold either by wrapping the pipes or by ex- ternal heat. This gas will have a calorific value of about 570 B. t. u. per foot, and therefore can be employed to advantage for lighting (especially by mantles) and heating. Four principal systems, the first substituting hydrogen for air, are used in the application of gasoline vapor to gas making, and these are as follows: 1. Although not an air-gas system, it may be convenient to men- tion here, by reason of similarity of method, the process of forcing manufactured hydrogen gas over or through gasoline by which the hydrogen, which has no illuminating value of its own, becomes saturated with the rich hydrocarbon vapors. This mixture has a high heating value ; and especially when used with the incandescent mantle, a high illuminating value. This system is seldom found in general practice and is principally used in metallurgical labo- ratories. 2. The employment of devices by means of which a current of air is forced over or through a body of gasoline or some porous or fibrous material saturated or impregnated with gasoline, by which means the air becomes carburetted with the hydrocarbon vapors to such an extent that the mixture can be used advan- tageously for illuminating and heating purposes. This method is called the cold-air process, and is the one most used in small private installations and town plants. Fig. 10 shows such an installation. It consists of a blower “ A,” carbureter “LL” and mixer “MM.” The blower, operated by sus- pended weights, as shown in the drawing, or water power, takes in air and forces part through the carbureter and part into the mixer. Fig. 11 shows a sectional view of a box-type carbureter, the kind generally used in plants of moderate size. It is a flat, rectangular box made of sheet metal, having partitions running longitudinally and parallel to each other through the box, but leaving a connect- ES ——— GAS AND OIL ILLUMINANTS Ton i), ANN | e i : ; \ m as i} = heel \\\ oN PANS ie \ \ ® ioe tp af \ \ h } i] B \ hh \ enw Z \ | | HVS q Hii ; Z pe Sl] y it , yi) | re } | ! ie BEANS AA Z A ALN nm he IY) ENS KY AY S A) is y KY AY] KY /] Wy \ \ \ A. ve , nr \ \ \\ NNN MH \ \ “\ . w IS ii, Wy HH My i, Hy Wy] 7 Mi i, 189 190 ILLUMINATING ENGINEERING ing opening between each two adjacent compartments sequentially at alternate ends. In these compartments are hung or stretched, as shown, strips of Canton flannel. There is an opening for filling, an inlet for air from the blower at one end, and at the other end an outlet for the carburetted air. The carbureter is about 15 inches deep but is filled with gasoline to a depth of only 6 inches. It is buried in the ground. The air entering through the top at one end o Vent es CREE: NBM SER UR Pe 44 EAN AN Gt X aN re ear ane ee ener oo Mes \ / , 4 lif i Ais oo ee ee RZe4 / Wadd? 1 1 my bony po me Canton Flanre/ Fig. 11.—Carbureter, 50-Light Air Gas Machine. traverses all the passages, flowing through the flannel which, by capillarity, is kept wetted with gasoline; the carburetted air then passing on to the mixer. The box. must be of sufficient size to per- mit a very slow movement of the air and the recovery from the surrounding earth of the heat rendered latent by the evaporation of the gasoline. As stated before, commercially refined gasoline is a mixture of several hydrocarbons, though largely composed of hexane and 7 Ce arburretted Arr Outlet », Gas AND OIL ILLUMINANTS 191 pentane. Under the conditions of slow evaporation here presented, there is a selective evaporation, the lower boiling fractions going off in large volumes first, gradually decreasing in volume as the gravity of the remaining gasoline increases, until finally a mini- mum permissible candle-power is reached, when the carbureter must be recharged. The cycle is then repeated. To minimize this fluctuation in candle-power and heating value, a tank containing a considerable supply of gasoline is sometimes connected to the carbureter with a ball and float valve, by which the height of the gasoline in the carbureter is replenished as fast as evaporated. It is claimed that this is an unnecessary refinement when a separate mixer is employed. When air is brought so intimately in contact with highly volatile gasoline the quantity of gasoline vapor that passes off with the air may be considerably in excess of that required to saturate the air at the final temperature. The gas from the carbureter is, there- fore, not then in condition to use; it is too rich and unstable as to condensibility. As has been shown, and perhaps explained, Red- wood is authority for the apparently contradictory statement that while air will require only 22 per cent of gasoline vapor to saturate at 60° F., yet when the air is bubbled slowly through a series of six tubes containing gasoline of the same gravity at the same temperature, the mixture of vapor and air passing off consisted of more than 50 per cent vapor. The carburetted air from the carbureter is passed into the mixer (Fig. 10), The mixer consists of a small holder rising and falling above the water in an enclosing metal cylinder. The holder has trips which open and close cocks at its lowest and highest points, thereby operating automatically by the flow of the gas. There is a test light and an adjusting cock for regulating the pro- portion of air to be mixed with the highly carburetted air from the carbureter, and a valve which is designed to control within certain limits the proportions of air from the blower and carburet- ted air from the carbureter. This is known generally as the cold-air process; under proper’ and reasonable supervision it affords a safe and practical means of illumination and heating. When installed so as to comply with the underwriters’ requirements it involves no increase in insurance rates. While designed and intended only for a mixture above the explosive limits it could be mechanically adapted to yield a mixture below the explosive limits. 192 ILLUMINATING ENGINEERING 3. To convert gasoline into a vapor by the application of ex- ternal heat and then by suitable mechanical means to mix the gas or vapor so formed with any desired proportion of air. This process has been applied in a number of types of air-gas machines. Generally, the heating device is in the form of a coil through which the gasoline passes and which is heated by a burner. Machines of this class are simpler as to number and complexity of parts, but the direct application of flames to a coil containing gasoline has not been considered safe by most insurance companies, and their use is therefore restricted. 4. The fourth method consists of inducing a current of air into a small tube by a jet of steam and at the same time allowing sufficient gasoline or naphtha to enter to condense the steam. and combine with the air. The latent heat of the steam in this process is intended to compensate for the refrigerating action of the gaso- line or naphtha in passing to the state of vapor. With both the third and fourth methods petroleum naphtha of a considerably lower gravity may be used, say 72° to 68° B. (sp. gr., .6931 to .7071) ; while with the cold-air process gasoline not heavier than 82° B. (sp. gr., .6604) can be used without the neces- sity of pumping the residue from the carbureter oftener than once in 6 months. The fourth method, one of the earlier inventions of Hiram Maxim, is probably best for a large output of gas. Fig. 12 shows one of these machines with a sectional view of the steam injector for air and naphtha. Steam at about 60 pounds gauge pressure, controlled by a regulator, is supplied to chamber “ A,” from which it issues at high velocity through injector nozzle “lL” into tube “Gq,” drawing in air from “C” by the injector action. At the other end of tube “G” a secondary injector action takes place, naphtha entering by the adjustable valve “D.” The latent heat of the steam vaporizes the naphtha and by doing so the steam itself becomes condensed. The naphtha vapor and air unite and pass into the gas holder, while the condensed steam is trapped away. The operation of this machine is entirely automatic. When work- ing close to its capacity very little of the gas remains in the holder, but when the consumption of gas is reduced to a minimum the holder fills with gas, and by means of a system of trips and levers the process is interrupted by the closing of the steam noz- zle; when the holder descends the operation is reversed, the steam GAS AND OIL ILLUMINANTS 193 nozzle is opened and the making of gas continues as before. By regulating the adjustable air and naphtha valves any desired mix- ture of vapor and air can be obtained, and in larger quantities than with any of the cold-air processes. The simplicity of carburetted-air processes is evident; no puri- fying of the delivered gas is required, and all the heat of the liquid fuel is directly transferred to the air and vapor mixture. The burners used for securing illumination through the agency of carburetted air are the ordinary flat-flame lava tip, and the various forms, both upright and inverted, of mantle burners. Where no mixer is installed and the gas is consumed directly from the carbureter the lava-tip burner has a small set-screw, by which the gas can be adjusted in its flow so as to prevent heavy and smoky flames. The specific gravity of the gas being much greater than that “of coal or water gas, it requires a larger opening in the check for the same quantity of gas to flow through, and in some cases larger openings for the air through the Bunsen are required. When a well-designed mixer is installed with the machine, as it 194 ILLUMINATING ENGINEERING always should be, there is no inconvenient fluctuation in the candle- power of the light from the mantle burner. When burning a mixture containing less than 2 per cent gaso- line—below the range of explosibility—the Bunsen burner on the Welsbach burner is omitted entirely, as the gas contains sufficient air for a non-luminous flame. The extent to which carburetted-air gas is used for lghting cannot be determined accurately from available statistics. It occu- pies a field similar to acetylene—that of isolated plants and plants for the general supply of small towns and villages. From many of the plants, especially those operated by municipalities, no answers are received to applications for information; in many other cases the answers are vague and ambiguous. Brown’s Gas Directory shows that in the United States there are 124 town — plants. It is claimed that, including the smaller plants, there are twice this number. A fair estimate of the amount of gas made and distributed by the 124 town plants is not less than 166,000,000 cubic feet a year. The gas is used for street lighting as well as for domestic consumption. In some cases the gas is distributed through a considerable mileage of mains. ‘The prices charged vary from $1.25 to $2.50 per 1000 feet. One of the largest com- panies reports a total annual sale of 35,000,000 cubic feet sold through 126 meters and 44 public lamps and distributed through 814 miles of mains. All things considered, perhaps the field in which carburetted- air gas can demonstrate its greatest economic efficiency is in that of factories using various special heating devices of comparatively small individual capacity. The plant being installed primarily for this special heating, it can also be employed economically for lighting. Acetylene Acetylene is one of the group of hydrocarbons covered by the general formula C,,H,,, its own formula being C,H,; that is, its one molecule contains two atoms each of carbon and hydrogen. This gas has long been known to the chemists; and even as pro-" duced synthetically, by uniting the elements in the compound, the record goes back to 1836, though the reaction was not then fully understood. In 1862 Woehler announced the discovery of the GAS AND OIL ILLUMINANTS 195 production of acetylene from calcium carbide made by heating to a very high temperature a mixture of charcoal with an alloy of zinc and calcium. Acetylene was known by chemists, and gas engineers also, as one of the heavy illuminants analytically pro- duced in small percentages during the destructive distillation of coal in the making of coal gas and in the generation of water gas, and its high value as an enricher was understood. Acetylene polymerizes at about 600° C. (1112° F.), that is, at elevated temperatures it is converted into other hydrocarbons hav- ing the same percentage composition, but containing more atoms of carbon and hydrogen in their molecules. Acetylene readily polymerizes to benzene, C,H,. This change is indicated by the equation 3C,H,=C,H,. Benzene, like acetylene, contains by weight almost exactly 92.3 per cent carbon and 7.7 per cent hydro- gen, but its molecule contains six atoms of each element instead of 2, as in the case of acetylene. It will be seen later that this instability of acetylene, together with its other characteristics, has a most important bearing upon its treatment and application and the precautions to be taken against accidents. In 1892 Thomas M. Willson, an electrical engineer, while ex- perimenting on the production of metallic calcium, employing therefor an electric furnace of high voltage in which was a mix- ture of lime and coal-tar, obtained a mass which he accidentally discovered contained calcium carbide, and which gave off acetylene when immersed in water. Willson was the first to demonstrate that acetylene could be obtained from calcium carbide in sufficient quantities and at a cost that would secure it a place in the in- dustrial arts. This discovery of Willson’s undoubtedly increased and intensified the interest in electro-chemical research and in synthetic chemistry, which two fields of research hold out much of promise for the bene- fit of mankind. It has also served to strengthen the theory or sur- mise that metallic carbides exist in the earth’s interior, and are the origin of petroleum and natural gas. Calcium carbide is com-. posed of one part of calcium and two parts of carbon, as shown by the formula CaC,. It is a hard, crystalline substance, dark gray in color, specific gravity about 2.22. One cubic foot of compact carbide therefore weighs about 138 pounds. The two highly refractory substances, lime and carbon, are forced to combine under the action of excessively high tempera- 196 ILLUMINATING ENGINEERING tures, as most readily obtained in the electric furnace. The re- action is shown by the equation C20 SRO 3c | CaC, x CO (Quicklime) (Carbon) ~ (Calcium Carbide) (Carbon Monoxide) which shows that 56 pounds of lime combine with 36 pounds of carbon to form 64 pounds of calcium carbide and 28 pounds of carbon monoxide. Roughly, then, for the making of a long ton of the carbide, there is required a short ton (2000 pounds) of lime and 1275 pounds of carbon. In the manufacture of the carbide the purity of the raw material is of prime importance. Those forms of carboniferous material in which there is a low percentage of fixed carbon are to be avoided as the rapid evolution of gaseous products therefrom is likely to lead to explosions. The calcium carbonates, such as limestone, marble, etc., from which the lime or calcium oxide is prepared, must be low in con- tent of magnesia, alumina, silica, sulphur and phosphorus. The ordinary limekiln cannot be used because of the impurities that ‘would be introduced therefrom. As it takes about 100 pounds of carbonate of lime to yield 56 pounds of the oxide, those impurities not driven off with the carbonic acid would be nearly doubled. These necessary precautions led to the general practice of cal- cining the carbonate at the carbide factory. After mixing the lime and carbon in proper proportions they are fused by a powerful electric current. Resistance and are furnaces are both used. ‘The furnace must be operated under uniform heating. For the generation of the heavy currents required re- course may now be had to more or less remote water powers if other- wise desirable, as railroad transportation of the carbide is no longer hampered by onerous restrictions. The carbide is neces- sarily packed in tightly sealed cans to protect from moisture. While a generation has not yet elapsed since the first introduc- tion of acetylene to the commercial world the files of the patent offices contain such a multiplicity of applications, granted and rejected, that it would be futile at this time to touch on this branch of the subject. Many of these applications show that the inventors neither understood the principles involved nor the progress of the art, an ignorance frequently accompanying much so-called invention. Oe GAS AND O1L ILLUMINANTS 197 The production of carbide in Europe in 1908 is approximated as follows: Tons mveden and Norway <=. cies mye. so %u. 35,000 PELAUNOG cece ch ansls ERNE waiters er cate Fore 26,000 PoP ETC na eee Pet Erg oo he sk 30,000 UL Uae ho Sh aes et ae a ot Ea SS ERS Ce 31,000 RMA Mette ae cree nee aha! get cha wh Uae RE 20,000 Rata R Cote g Wa aos os alc laces u's ofiphess Tite hence 40,000 PP OLCOICT dee sac Bi duck eke ks ete s Ue 10,000 MarR tress crete, «eek Ra exe's © arena Te 192,000 Practically all of this carbide was used for the production of acetylene. Coming now to the manufacture of acetylene, it is to be regretted that more complete and accurate data cannot be had as to its use as an illuminant, and especially in the United States. Brown’s Directory of Gas Companies records 184 acetylene town plants in operation the first of this year. hese works report a total output of 18,500,000 cubic feet. A paper read before the Iiluminating Engineering Society in 1909 is authority for the statement that there were at that time 290 towns lighted with acetylene. It can — be understood readily that the record in Brown’s Directory, de- pending for its facts as it does upon answers to question sheets, may be quite incomplete by reason of the indifference of those in control, and especially so in case of the municipal plants. In addition to the acetylene so distributed, the total is con- siderably increased by that used in private houses, contractors’ plants, car lighting and portable lamps, particularly automobile search-lights. The rate charged for acetylene by the town companies seems to run from 11% to 2 cents per cubic foot, or $15 to $20 per 1000 eubie feet. Under efficient management, as to installation and operation, these rates are said to afford a fair return on the in- vestment. To comprehend the precautions to be taken in the use of calcium. carbide and acetylene, there must be borne in mind the difference between exothermic and endothermic reactions. Exothermic compounds are those whose formation from ele- mentary substances is attended with liberation of heat, and whose decomposition into simpler compounds or elementary substances is attended with absorption of heat. 198 ILLUMINATING ENGINEERING Endothermic compounds are those whose formation from ele- mentary substances is attended with absorption of heat, and whose decomposition into other compounds or get te substances is attended with liberation of heat. These latter compounds are not very numerous, they are more or less unstable, and some of them are resolved into their elements with explosive force. Acetylene 1s an endothermic compound. Acetylene is obtained from calcium carbide through a double decomposition. “The first step is shown by the equation CaC, a HO (Calcium carbide) (Water) Si G,Ho) CaO 3 ™ (Acetylene) (Calcium oxide or lime): (1) But the quicklime, CaO, in the presence of an excess of water, will be found in the form of slaked lime, or calcium hydroxide, Ca(OH)., as shown by the equation CaO0+H,O=Ca(OH),. (2) As these reactions in the presence of sufficient water may occur simultaneously, the double reaction can be shown by the equation CaC, +2H,0—C,H, + Ca(OH),. (3) This is an exothermic reaction because the quantity of heat lb- erated exceeds the quantity of heat absorbed. There is some little question as to the heat of formation of calcium carbide, authori- ties varying from —0.65 calories (large) to +3.9. But these differences of opinion do not affect the question as to whether the reaction as a whole results in absorption or liberation of heat; it only affects in minor degree the quantity of heat liberated. The heat of formation of Ca(OH), (exothermic substance) is +160.1 large calories; the heat of formation of water (exothermic substance) is +69, and hence for decomposition is —69; taking heat of formation of calcium carbide as +3.9, for decomposition it is —3.9. The heat of formation of acetylene is —58.1. As the formation of Ca(OH), is obtained by the decomposition of the water and the carbide and the formation of the acetylene, we have heat liberated in the formation of the Ca(OH), 160.1, and the heat absorbed as follows: GAS AND O1L ILLUMINANTS 199 Formation of acetylene — 58.1 Endothermic substance. Decomposition of water — 69. Hxothermie. Decomposition of carbide — 3.9 Exothermic. Total —131.0. Deducting the 131 absorbed, from the 160.1 set free, we have as a net result 29.1 large calories liberated. While this reaction as a whole is exothermic, acetylene as a substance is seen to be decidedly endothermic, and so is ready to liberate large quantities of heat whenever the conditions for de- composition obtain. While this reaction may be modified it should be pointed out that the reaction where there is no excess of water, as indicated in equation (1), produces in practice results which are quite dif- ferent from those obtained where there is excess of water, as indi- cated in equation (3). In the acetylene generators of the most modern and usual pat- tern, some of the surplus water is evaporated by the heat liberated, and some of this water vapor, even at low temperatures, is carried away with the escaping gas. If the heat liberated during the de- composition of the carbide is not otherwise absorbed, it is sufficient in amount to vaporize almost exactly three parts by weight of water for every four parts of carbide attacked. But if this quan- tity of heat were expended upon some substance, such as acetylene or calcium carbide, which, unlike water, cannot absorb an extra amount by changing its physical state, as from liquid to gas, the heat thus generated during the decomposition of the carbide would be in evidence to a far greater extent. For reasons that can be indicated only within the time allowed me, it is essential for good working that the temperature of both the acetylene and the carbide shall be prevented from rising to any considerable extent. Experiments were conducted by Caro and by Lewes to determine the temperature of the carbide due to decomposition. Caro’s ex- periments showed a maximum temperature of 280° C. (536° F.). Lewes’ experiments gave a maximum temperature of 807° C.. (1480° F.). The temperature attained is in part dependent upon the time elapsed in the reaction, for the longer the time the greater the opportunity for the escape of heat liberated. The divergence in the results obtained by Caro and Lewes is explained by the difference in the design of the generators and the speed at which they were operated. In Lewes’ generator little or no provision was 200 ILLUMINATING ENGINEERING made against overheating, and it is not to be supposed that such temperatures as were observed by Lewes are found in a commer- cial generator. But his determination is important as showing the danger to be avoided, for the temperature he found is considerably above that at which acetylene decomposes into its elements in the absence of air, namely, 780° C. or 1436° F. Excessively high tem- peratures in the generator must be avoided, because whenever the temperature in the immediate neighborhood of a mass of calcium carbide which is evolving acetylene under the attack of water rises materially above the boiling point of water, one or more of three objectionable effects is produced; namely, upon the gas generated, upon the carbide decomposed,.or upon the general chemical re- action then taking place. Time does not permit a full discussion of the questions here involved, but a few hints may be given. Lewes points out that not only does acetylene decompose at 780° C., but it begins to polymerize at 600° C. (1112° F.). Sup- pose acetylene polymerizes into benzene, the burner adapted to the efficient utilization of the former will not be so adapted for ben- zene. Furthermore, under certain conditions, the benzene liquefies and deposits with water vapor in the pipes. An additional trouble from polymerization occurs when the temperature rises above the point at which benzene is formed, for then other hydrocarbons may be formed having a higher proportion of carbon than is present in acetylene and benzene, setting free non-luminous hydrogen, and thus reducing the illuminating value of the gaseous mixture. In certain experiments by Lewes the loss in candle-power was found to be a reduction from 240 to 126. Another effect of heat upon acetylene has already been indicated. Being an endothermic sub- stance it gives out heat upon decomposing. It decomposes at 780° C. when free from air, a spark, or shock, or pressure of 30 pounds or more being sufficient to effect the change. This change raises the temperature and so increases the pressure of the disasso- ciated hydrogen, and may cause the containing vessel to explode. If air is present, as it may be through bad design of apparatus or incompetent attendance, the acetylene can be ignited at 480° C. (896° F.). Under certain conditions 25 per cent of air and 75 per cent of acetylene are explosive. The extreme limits of explosibility of acetylene mixed with air are variously stated. Clowes gives the extremely wide range of explosibility from 3 per cent to 82 per cent of acetylene. Le GAS AND OIL ILLUMINANTS 2()] Chatelier gives 2.9 per cent to 64 per cent. Hitner made exhaustive tests with several gases, in each case the mixture being saturated with aqueous vapor, thus reducing the limits of explosibility. For acetylene he gives from 3.35 to 52.30 per cent. Teclu, experi- menting with a dry mixture, determined the limits as 1.53 to 59 per cent. These results naturally are changed if the mixture con- tains other gases besides acetylene and air, but enough has been said to show that acetylene cannot be handled carelessly. This is emphasized by Hitner’s experiments, comparable but not giving extreme limits, which gave as the limits for coal gas 7.90 to 19.10 per cent, or a range of only 11.20 per cent against acetylene range of 48.95 per cent, as shown above. In the generator the effect of heat on the carbide itself may be troublesome. If part of the gas polymerizes part may so be re- solved into tar, which coats the carbide still unattacked and so protects it more or less from further attack, thus reducing the output and leaving the residue with a content of acetylene, which may later occasion trouble during or after removal. - The effect of accumulating heat in the generator itself has to be guarded against. For example, at a temperature as low as 200° C. (392° F.), if the ordinary solder were used in the joints it would be melted and the vessel become unsafe. This serves to point to the fact that the materials used and the minor details of construction in a generator may be such as to condemn a design generally commendable. Having indicated most superficially some of the conditions to be considered in the design and construction of acetylene genera- tors, with the aid of diagrams taken from Leeds and Butterfield’s work entitled “ Acetylene, Its Generation and Use,” I shall show in a general way how these conditions are met, but without at- tempting to discuss the relative advantages and disadvantages of the several types. Acetylene generators may be roughly classified as follows: 1st. Carbide to water. (a) Non-automatic. (b) Automatic. 2d. Water to carbide. (a) Non-automatic. (b) Automatic. 202 ILLUMINATING ENGINEERING In general, the type having the widest limits of safety is that in which a small quantity of carbide is introduced into a considerable body of water, the acetylene as it bubbles through the water passing directly out and into a holder. If this holder has ample capacity for the maximum night’s demand, it can be filled with gas during the day and the generator locked for the night. This non-auto- matic form may be criticized on the ground of first cost. Ce2he Cale wi Wie. 18: Fie. 14, Fic. 13.—Acetylene Generator. Non-Automatic. Carbide to Water Type. Fic. 14.—Acetylene Generator. Automatic. Carbide to Water Type. If the introduction of carbide is controlled by an automatic device which admits carbide automatically as the acetylene is con- sumed, a smaller generator and holder can be employed. Figs. 13, 14 and 15 show types of carbide to water generators. Fig. 13 represents the non-automatic type. The carbide is fed by hand through the chute A into the generator B. The generator is filled with water above the opening of the chute to prevent the gas from escaping through the chute. Grids D and E catch and support the lumps of carbide, permitting the acetylene to be com- GAS AND OIL ILLUMINANTS 203 pletely liberated before permitting the mass to mix with the sludge of slaked lime in the bottom of the tank. The carbide cannot be used in small lumps, as then the generation of acetylene would be sufficiently active to blow the seal and allow the gas to escape through the chute. Fig. 14 shows an automatic generator of the first class. The carbide is held in a hopper which is supported by holder bell I, which rises and falls according to the volume of acetylene con- tained. The hopper is closed at the bottom by a valve G, from ~ ‘ Fic. 15. Fig. 16. Fia. 15.—Acetylene Generator. Automatic Dipping. Carbide to Water Type. Fic. 16.—Acetylene Generator. Water to Carbide Type. Water Inlet at Top. which depends a rod H. As acetylene is withdrawn from the bell the bell falls until the rod strikes the bottom of the tank, the valve is thus forced open permitting more carbide to fall into the water, more acetylene is released, the bell again rises until the valve seat and valve engage, when the supply of carbide is again stopped. Fig. 15 shows a dipping generator. ‘The carbide is held in a perforated vessel which hangs from the inside of the crown of the 204 ILLUMINATING ENGINEERING holder bell. As the acetylene is consumed the bell falls until the carbide dips in the water, when acetylene is again liberated. Figs. 16, 17 and 18 show types of water to carbide generators. Fig. 16 shows a generator in which the carbide is contained in a series of pans, P, P1, P2 and P3, a small quantity in each pan. Water is admitted at the bottom through pipe M. As each pan is flooded the acetylene rises to the top of the tank and passes out fi2 0 C2 He A SS en ean ee Fiq. 17.—Acetylene Generator. Water to Carbide Type. Water Inlet at Top. at R. The gas passing out is charged with water vapor, and this water acting upon the carbide in the upper pans produces “ after generation,” which is an objectionable feature. Fig. 17 shows a better type. The carbide is contained in pans as in the previous case. Here the water is admitted at the top of the tank and first acts on the carbide in the top pan. The gas passes off without coming in contact with the carbide in the other pans. As the first pan is flooded the water overflows through the pipe S to the second pan. This is repeated until the carbide in the last pan is attacked. The aeetylene escapes from the pipe at the top of the tank, as shown. i ie - Gas AND OIL ILLUMINANTS 205 Fig. 18 shows a generator not to be commended. The carbide is contained in the tank T. Water enters at the top in drops or a fine stream. This type produces “after generation” and dan- gerous overheating. Generally speaking, in the water to carbide generators the gen- erator is opened to the air while being charged with fresh carbide; this is a decided disadvantage, for, as already shown, acetylene should be guarded from mixing with air on account of its wide range of explosibility. Fig. 18.—Acetylene Generator. Water to Carbide Type. Crude Form. What I have said fails to show the great variety of apparatus actually employed or the manner in which the several types merge into each other. I have not attempted to show the complete acety- lene installation, including the parts for generation and governing. It should be pointed out that it is necessary either to use a pure carbide or provide means for purifying the acetylene, as otherwise compounds of phosphorus, silicon, ammonia and sulphur might be present rendering the gas objectionable on the score of spon- taneous inflammability or non-hygienic qualities. Leeds and But- terfield’s work give the rules and regulations adopted by govern- ments and insurance companies for the construction and installa- tion of acetylene plants. The carbide is sold in several sizes. For generators the size varies from 314 inches by 2 inches down to 14 inch by 1/12 inch. For lamps, from 1 inch by 1% inch down to dust. The rate of 206 ILLUMINATING ENGINEERING evolution is inversely proportional to the size of the lump. Lumps coated with dust may give irregularity in operation. Acetylene liquefies at 0° C. and about 211% atmospheres pres- sure. It is then most unstable, spontaneous disassociation with explosive force being due to occur on the application of a spark or when shocked. After quite a number of disastrous accidents it is now generally understood that liquid acetylene is too dangerous to use. As before mentioned, the gas is liable to explode if heated to 780° C. or if held under a pressure of 2 atmospheres absolute, or above. Acetylene is readily soluble in many liquids, and this property is utilized to bring the acetylene into small compass. Acetone, at ordinary temperature and atmospheric pressure, will dissolve about 25 volumes of acetylene, and at 12 atmospheres will dissolve about 300 volumes. Acetone is an exothermic substance with a composi- tion shown by the formula C,H,O, and hence combustible, and within certain limits of pressure its presence tends to decrease the severity of explosion. At 20 atmospheres pressure the acetone adds to the danger from explosion. Acetylene dissolved in acetone car- ried up to a pressure of 10 atmospheres is safely employed, but there are practical objections to its use in this liquid form. ‘To overcome these objections the cylinders are filled with some porous material which does not react on the acetone. A material is used which has a porosity of 80 per cent, that is, when the vessel is apparently full of the material about 20 per cent only of the space is really occupied. 'The portable cylinders for this service cannot be filled with acetone, for the reason that ample space must be left for expansion as the liquid takes up the gas. A cylinder having a normal capacity of 100 volumes will have say 20 volumes taken up by the porous filling, and can safely be charged with 40 volumes of acetone. This 40 volumes of acetone dissolves 40x 25=1000 volumes of acetylene; and by compression to 10 atmospheres this is increased to 10,000 volumes. In this form acetylene is sold under various trade names and used for automobile head lights and similar service where limited storage capacity is of decided moment. ; Acetylene, under favoring conditions including moisture, will combine with copper to form acetylide of copper, an explosive compound. As acetylene is now generally produced and used these conditions are not apt to obtain, so the danger from this source is = Pee ee ee, ee ee —- GAs AND O1L ILLUMINANTS — 20% now not regarded seriously. Copper alloys and compounds should not be employed in the construction of parts of plant exposed to the gas or in the process. Straight acetylene, burned in an open-flame burner of a char- acter and size best adapted to give the highest illuminating value, the burner being so placed as to carry to the photometer disc the strongest horizontal rays, the bar readings being calculated pro rata to a consumption of 5 feet an hour, gives a candle-power of from 240 to 250. The general practice of selecting the burner and rate of con- sumption so as to develop best efficiency of the gas instead of being confined to one type of burner and a rated consumption of 5 feet an hour, has received the approval of the Gas Referees of London acting under Parliamentary powers. The specific gravity of acetylene is .9056, usually taken as .91. For self-luminous flames, lava-tip burners are employed, the gas issuing either from a slot or two holes, both producing flat flames. With the latter form the flat flame is produced by the impinging of the two currents of gas against each other, the plane of the flame being produced at right angle to the plane of the two holes. The burners are made in many different forms in the effort to overcome difficulties due to the richness of the gas and its instability. The richness of the gas made it necessary to employ small burners or to make extra provision for injecting air into the body of the flame by the action of the issuing gas. This was best accomplished by some form of two-jet burner, which dragged in the air at a point between the jets and below the flame. To better accomplish this result burners were devised with two tips so as to separate farther the two jets of gas. Further, to assist in the in- jection of air, acetylene is burned at a pressure far in excess of that employed with coal gas. Its high specific gravity also calls for additional pressure. The design of acetylene burners well il- lustrates that burners must be designed to supply such a quantity of air to the flame as will produce a maximum incandescence. If - one of these burners were used with coal gas, so much air would be dragged in that the carbon particles of this thinner gas would be consumed with little or no preliminary incandescence. The comparatively high efficiency of the acetylene flame is due not alone to the high carbon content; an important factor is the high flame temperature, which is in part the result of liberation 208 | ILLUMINATING ENGINEERING | of heat at time of disassociation of this endothermic gas. Mahler gives the flame temperature at 0° C. and 760 mm. as 2350° C. or 4642° F. Le Chatelier gives 2100° C. to 2400° C. Acetylene is also employed with incandescent mantles, resulting in a considerable increase in candle-power, this gain according to different authorities being from 160 to 200 per cent. For certain special applications a still larger gain has been secured. ‘There are decided difficulties to be overcome and advantages to be aban- doned in using acetylene for incandescent lighting, and the high efficiency and the whiteness of the self-luminous flame make it less necessary or desirable to overcome these difficulties. Acetylene is also employed for illumination in the form of car- buretted acetylene or carburylene, and in this form it is more ad- vantageously apphed to incandescent lighting, but time does not permit a discussion of this branch of the subject. In connection with illuminating engineering, the color of the acetylene flame is of great importance. A comparison with sun- light and other light sources will be given in another of these lectures. 7 Acetylene can also be used for heating. Its calorific value per foot is 363 large calories, or 1440 B.t.u., which is about two and one-half times that of city gas. The comparison is not favorable to acetylene, however, when relative costs are considered. Within the limits of a single lecture, inordinately long, it is true, I have, according to instructions, endeavored to cover three sources of illumination. Many lectures could be devoted advan- tageously to each of these. Acetylene alone could not be covered completely in many lectures. BIBLIOGRAPHY PINTScH GAS King’s Treatise on the Manufacture of Gas. Volume III. The Comparative Merits of Various Systems of Car Lighting: A. M. Wellington, W. B. D. Penniman, Charles Whiting Baker. Engineer: ing News Publishing Company, New York, 1892. Engineering Chemistry: Thomas B. Stillman. The Chemical Publish- ing Co., Easton, Pa., 1910. Car Lighting: R. M. Dixon. Stevens Institute Indicator, Vol. XXV, No, 1). Jan., 1908: Lighting of Railway Cars: Geo. E. Hulse. Transactions of the Illumi- nating Engineering Soc., Vol. V, No. 1, January, 1910. GAS AND OIL ILLUMINANTS 209 Car Lighting: L. R. Pomeroy. Proceedings Canadian Railway Club, Vol. IX, No. 2, February, 1910. Leuchtfeuer und Nebelsignal: E. Klebert. Journal fur Gasbeleuchtung und Wasserversorgung, May, 1909. Oelgasaustalt mit Generatorbetrieb: Fritz Landsberg. Zeitschrift des Vereines Deutscher Ingenieure, Nr. 37, Band 52, September, 1909. Oelgasherstellung in Generatoren und Gasfermversorgung in Hoch- druckleitung: Fritz Landsberg. Glaser’s Annual, August 1, 1910. Lighting of Passenger Cars: Max Buettner. Published by Springer, Berlin, 1901. Petroleum and its Products: ‘Vol. II, Sir Boverton Redwood. Published. by Charles Griffin & Co., Ltd., London, England, 1906. Brief descrip- tion under oil gas. AIR GAS Petroleum and its Products: 2 Vols. Sir Boverton Redwood. Pub- lished by Charles Griffin & Co., Ltd., London, England, 1906. This work contains a very full bibliography. Petrol Air-Gas: Henry O’Connor. Published by Crosby Lockwood & Son, London, England, 1909. ACETYLENE Acetylene: The Principles of Its Generation and Use by F. H. Leeds and W. J. Atkinson Butterfield. Published by Charles Griffin & Co., Ltd., London, England, 1910. Calcium Carbide and Acetylene by Geo. Gilbert Pond. Bulletin of the Department of Chemistry of the Pennsylvania State College, 1909. This work contains a full bibliography. on as vor AUER VON WELSBACH V (2) INCANDESCENT GAS MANTLES By M. C. WHITAKER CONTENTS INTRODUCTION ~ Heat sources: chemical, electrical. Combustion. Substance: gas, wood, coal, etc. Supporter of combustion: oxygen, air. | Kindling temperature: electric spark, lighted match, etc. Chemistry of combustion. Marsh gas + oxygen — water vapor + carbon. Carbon + oxygen = carbon dioxide. Open tip combustion. Bunsen burner combustion. INCANDESCENT GAS ILLUMINATION Principles involved. History: Hare, Drummond and Claymond lights, Siemens-Lungren lamp, Auer von Welsbach lamp. Bunsen burner: history, construction and chemistry of operation. Adaptations for use with incandescent mantles. Upright and inverted. Single, cluster and arc. Inside and outside. Upright burner construction. Bunsen tube. Check for gas; plate, needle, multiple hole, check; air adjustment; gauzes; gallery. Inverted burner construction. Types: vertical, horizontal and goose-neck burners; velocity, gravity and buoyant action in downward flow of mixture. Checks for gas; air adjustment; means for overcoming flash-backs; crown for glassware. GAS MANTLES Process of manufacture: history, knitting, washing, saturating, incin- erating, shaping, collodionizing, trimming and inspecting, packing and shipping. Physical structures of mantles. Basic fibers: cotton, ramie, artificial silk. Threads, weaves, stitches, etc. a1? ILLUMINATING ENGINEERING Chemicals and sources. Lighting principles; thorium and cerium. Thorium; source (monazite, thorianite); manufacture, market, use. Collodion; composition, manufacture, use. Types of mantles: upright and inverted, railroad train, sizes, pressure, rag, acetylene, kerosene, etc. Quality and service characteristics as determined by process of manu- facture. Cotton: shrinkage, depreciation in candle-power; color value; physical strength. ' Ramie: ditto, etc. Artificial silk: ditto, etc. Introduction Assuming that the illuminating power of a gas flame is derived from the heating of solid particles to incandescence, the practice of _ gas illumination divides itself into two general principles: First. Where the solid incandescent material is supplied by the decomposition of the gas in the process of combustion. (Open-tip flame. ) Second. Where the gas is completely consumed in a Bunsen burner for the production of the maximum amount of heat and a permanent incandescent material is supplied as a part of the apparatus. (Incandescent gas system.) The first steps toward the improvement of the efficiency of gas for lighting was made on the first of these principles by pre- heating the gas before it reached the point of combustion in the so-called regenerative burner of the Siemens-Lungren or Gordon- Mitchell type (Fig. 1). There are some of these regenerative lamps in use at the present time. The regenerative burner was the most effective ever produced by following the first principle - mentioned above, and gave the most efficient results up to the in- troduction of the incandescent mantle system, which is based on the second principle. Professor Robert Hare (Philadelphia Chemical Society, 1802) first fully described a form of “ incandescent” gas light, which is the basic principle now utilized in this industry. At a meeting of the Philadelphia Chemical Society, held in December, 1801, he showed experiments and described this in- candescent lime light as follows: “The cock of the pipe communicating with the hydrogen gas was then turned until as much was emitted from the orifice of the cylinder as when lighted formed a flame smaller in size than that of a candle. Le ne en, a INCANDESCENT Gas MANTLES 213 Under this flame was placed the body to be acted on, supported either by charcoal, or by some more solid, and incombustible substance. The cock retaining the oxygen gas was then turned until the light and heat appeared to have attained the greatest intensity. When this took place, the eyes could scarcely sustain the one, nor could the most refractory substances resist the other.” Fig. 1.—Regenerative Lamp. Fie. 2—Drummond Calcium Light. Henry Drummond, in 1826, made use of the incandescent lime light, similar to that suggested by Professor Hare, for signaling. Drummond’s application of this principle of producing an illumi- nation of high intensity was adopted generally, and he is usually eredited with the invention. The lime light is sometimes called the “ Drummond light” (Fig. 2). ere, At the Crystal Palace Exposition in Paris in 1883 a lamp of the inverted type was shown in which the illumination was produced by a platinum basket suspended in a blast flame. The life of the basket was limited to 50 or 60 hours. Various other lamps for the application of the principle of sup- plying the incandescing material were suggested, such as cones 214 ILLUMINATING ENGINEERING made from platinum wires covered with a refractory coating, per- forated baskets, grids placed above the flame of the fish-tail burner, ete. The greatest step in the development of a commercial incan- descent gas light was made by Dr. Carl Auer von Welsbach. In 1886, Dr. Auer, while a student in the laboratory. of Professor Robert Bunsen, in Heidelberg, discovered that the ash formed by saturating a cotton fabric in a solution of erbium salts and burning out the organic matter would take the shape of the original fibers, and would adhere to form a mesh of considerable strength. This finely divided ash fabric, when suspended in the flame of a Bunsen burner, became intensely luminous. Erbium, however, produces green light. Nevertheless, the principle of forming an attenuated but closely adhering ash was established by Dr. Auer in these © experiments, and he immediately proceeded to develop this idea with a view to producing a commercially desirable light by heating oxide webs which he called “ stockings” or mantles. His early mantles were made from a mixture of lanthanum and zirconium oxides. The light given by this mixture was not sat- isfactory, and the investigation was continued until he discovered the wonderful luminescence obtained with a mantle made from the rare oxides of thorium and cerium. Incandescent Burners The earlier burners constructed to use Auer’s invention were de- signed for use with the lanthanum-zirconium mantle, which did not give the high candle-power given by the present mantle. These burners were consequently very large and clumsy and hore a very remote resemblance to the modern types. Modern Types The present practice in incandescent burner construction should be divided, for clear discussion, into— Furst. Individual upright burners. Second. Individual inverted burners. Third. Gas arc lamps (upright burners). Fourth. Gas are lamps (inverted burners). Fifth. amps for special application (pressure oil lamps, rail- way coach lamps, kerosene lamps, etc.). INCANDESCENT Gas MANTLES 215 Upright Burners The functional parts of the upright incandescent burner may be divided into (Fig. 3): (a) Bunsen tube. (b) Bunsen base. (c) Gas-adjustment means. (d) Air-adjustment means. (e) Mixing chamber. (f) Gallery to support chimneys, glassware, reflectors, etc. Mixing chamber. Gallery. Bunsen tube. Gas adjustment. Air adjustment. Bunsen base. Fig. 38.—Upright Burner Cut to Show Interior Construction. The Bunsen tube is carefully designed to meet a wide range of gas conditions, such as fluctuations in pressure, gravity, etc., and still produce a mixture which has entrained the proper quantity. of air to produce complete combustion at the gauze line. The dimeusions of this tube have’ been carefully determined in ex- perience, and are comparatively uniform in all styles of standard burners. The Bunsen base is usually turned from solid brass bar and threaded internally to fit the average run of 1£-inch gas nipples 216 ILLUMINATING ENGINEERING rather than any standard thread. This base is also adapted to carry the gas-adjusting device and to form an assembly base for the entire lamp. A gas adjustment is an essential feature of the standard burner used in this country. Some foreign burners, and many of the early burners in this country, had a fixed gas orifice, but the variation in density and pressure of the gas in different localities have com- pelled the modern gas burner to include some means for acreage the gas flow. There are several prevailing types of gas checks, some of which fulfil the function of regulating the flow of gas, but fall far short of meeting other essential requirements. The efficiency of burners of this type is largely dependent upon the velocity of the gas jet, and its consequent ability to entrain the amount of air necessary to produce complete combustion. Any construction which tends to cut down this jet velocity seriously affects the efficiency and proper operation of the burner unless the initial gas pressure is high enough to produce a proper jet velocity in spite of the design of the check. Low and variable pressures are common conditions and, as a consequence, must be provided for in all designs intended for general sale and use. A single round hole through a thin plate offers the minimum amount of resistance to the flow of the gas stream and, as a con- sequence, gives the maximum jet velocity in the Bunsen tube. An iris diaphragm, similar to the device used in a camera, has been suggested as the ideal way to construct an adjustable single-hole check, but the cost of construction and the mechanical difficulties involved in making it gas-tight prevent its general adoption. Among the adjustable checks in general use the preferred types seem to be included in the following general designs: First. The Mason check, which is a series of round holes in superimposed plates, one of which may be rotated upon the other in such a way as to bring more or fewer holes into action, depending upon the direction of rotation. While the number of small holes offers somewhat more friction to the flow of the gas than the ideal single hole, it is thought that this device, which is capable of economical and reliable mechanical construction gives the most efficient results over the widest range of conditions. Second. The annular-orifice check is produced by inserting a needle in a single round hole and providing a mechanical construc- INCANDESCENT GAS MANTLES aa tion which permits the needle to be drawn in or out in relation to a stationary hole, or a stationary needle with a cap-orifice arranged to be raised and lowered. Obviously, the annular orifice, which may give satisfactory results with favorable conditions, will offer unfavorable resistance to the flow of the gas on lower pressures and thereby affect the mixture. Fig. 4.—Upright Burner. Adjustment of the air supply is usually automatically taken care of by the regulation of the gas flow when the composition and other conditions are normal. Certain gases require some extra provision for air adjustment, and most upright burners are now so constructed as to permit of this equipment, if necessary. The mixing chamber is the enlarged portion at the top of the Bunsen tube, and exercises an important function in producing . a more intimate mixture of gas and air, and also serves as a mounting for the mantle. The function of the gallery is obviously for supporting the chimney, globe, reflector or other equipment. _ : Modern burner design is carried out on the best scientific lines with a view to producing a burner satisfactory for all gas condi- 8 ILLUMINATING ENGINEERING 218 Adjustable gas checks, automatically mixing air supply, tions. properly proportioned Bunsen tubes and mixing chambers, a shapely exterior construction with the finest material and workmanship, make the modern burner a very effective and artistic appliance (Fig. 4). SY \ \ \ N oP OG, Be Maite : ee stig : Crown for holding glassware. Refractory burner tip. Fie, 10.—Inverted Burner Cut to Show Interior Construction. of the inverted mixing tube it is seen that this ascending tendency is thereby greatly increased. The method used for overcoming the ascending tendency of the mixture is to project it downward with sufficient velocity to carry it to the point of combustion without regard to the specific gravity. The only force available for projecting the mixture downward is that obtained from the velocity of the gas at the check orifice. When it is considered that in many cases the initial gas pressure INCANDESCENT GAS MANTLES 225 is very low, thereby greatly reducing the available force, and also that a certain portion of this force must be given to entraining the air for the mixture, it is obvious that great importance attaches to this function of the inverted burner. To meet the conditions of varying composition and pressure, or Fie. 11.—Gas Arc Lamp. Upright for Inside Lighting. uniformly low pressure in the gas supply, a construction is re-- quired embodying all the features of a highly efficient projector for gases. This requires an adjustable check which will give the greatest jet velocity to the gas as it is admitted to the Bunsen; air ports properly placed to give the most efficient entraining capacity; a “raceway” of correct diameter and length to give the mixed gases the velocity necessary to carry them through the mixing chamber and to the point of combustion. 226 ILLUMINATING ENGINEERING An analysis of the large variety of inverted burners on the market, in the light of these facts and principles, will show a number which do not conform to any specifications except cheapness. Rapid progress is being made, however, and standardization will ultimately be reached on a combination basis of efficiency, relia- bility, convenience, durability, pleasing appearance—all with a fair and reasonable cost. Fic. 12.—Gas Arc Lamp. Upright for Inside Lighting. Gas Are Lamps and Clusters Following the introduction of the upright burner, high candle- power unit requirements were met by forming a cluster of indi- vidual burners, with separate gas cocks and chimneys, gathered under a common reflector. These groups of burners were next simplified by the introduction of a cluster of burners controlled by a single gas cock and surrounded by a single globe to replace the individual chimneys. This design of lamp was called a gas arc lamp, and it met with success on account of its simplicity of construction and easy maintenance. The principal aims in the development of the gas arc lamp have been to produce a unit (Figs. 11 and 12): INCANDESCENT GAS MANTLES Gee First. With a concentrated source of light. Second. With high efficiency. Third. Simplicity of operation. Fourth. Minimum cost of maintenance. Fifth. Individual gas adjustment for each burner. No principles differing from those encountered in the individual Fie. 13.—Gas Are for Outside Lighting. burner were involved in the development of this upright are lamp, although some perplexing conditions were met with. It was found that in order to approximate the efficiency of the individual burner, the are would have to be constructed with a “stack ” to induce more active combustion at the burner heads. These stacks are made from fused enamel on steel, or from brass . in various finishes. Mechanical devices have been evolved for con- venient methods for renewing and replacing mantles, removing and cleaning glassware, and innumerable other methods of simplifying and economizing maintenance and up-keep. Upright ares have been successfully developed for use outside in places exposed to the action of wind and rain (Fig. 13). 228 ILLUMINATING ENGINEERING Inverted Gas Arcs Arcs of the inverted type for both inside (Figs. 14 and 15) and outside (Figs. 16 and 17) lighting are just coming into use, and are being rapidly improved and developed with every prospect of great success. Fig. 14.—Inverted Gas Are for Inside Lighting. Two different methods of construction are utilized in the most prominent types of inverted arc lamps. One in which an indi- vidual Bunsen is provided for each mantle (Fig. 14), and the other where a single common Bunsen leads into a manifold head from which outlets are provided for each mantle (Fig. 15). Both of these types are now appearing in various sections, and experience alone will demonstrate the wisdom of the design. Incandescent Mantles The incandescent gas mantle was invented by Dr. Carl Auer von Welsbach in 1885 and 1886. INCANDESCENT GAS MANTLES 229 The basis of Dr. Auer’s invention is the refractory hood or mantle made from an attenuated mixture of the oxide of thorium with a small percentage of cerium oxide. The cerium, which is present in quantities varying from 1% to 2 per cent, is not an acci- dental impurity as has been inferred, but is an essential constituent exerting, by very small variations in amount, a marked effect upon the candle-power and quality of the light. The candle-power-cerium Fic. 15.—Inverted Gas Arc for Inside Lighting. relation is best illustrated by the curve shown in Fig. 18, in which the candle-power is plotted vertically and the per cent of cerium horizontally. It will be noted that the maximum candle-power is: obtained with 1 per cent of cerium, and that a small amount of cerium more or less than 1 per cent causes the candle-power to fall off very rapidly. This peculiar result may be attributed to the existence at the 1-per-cent point of a solid solution or a definite compound which possesses a higher emissivity than either the thorium alone or the cerium alone. 230 ILLUMINATING ENGINEERING The manufacture of incandescent gas mantles is a most inter- esting and complicated chemical process, and by a peculiar coinci- dence resembles in the delicacy of the hand work involved the close attention to details and the technical supervision required in the manufacture of the incandescent electric lamps. A brief outline of the materials and processes involved in the mantle manufacture may be of interest. Fig. 16. The first step consists in knitting a tubular fabrie of open mesh from threads of some combustible organic substance which, after being properly saturated with the thorium solution, may be con- veniently burned out, leaving the ash in a more or less adherent mass reproducing the physical form of the original fiber. The selection and preparation of the original fiber is therefore a matter of vital importance. Imperfect fibers or threads, mineral impuri- ties, irregular knitting, etc., all directly affect the quality of the mantle. The present practice is to use threads made from natural cotton fiber, natural ramie fiber or artificial silk fiber. INCANDESCENT GAS MANTLES 931 Fic. 17.—Inverted Arc Lamp for Inside Lighting. 232 ILLUMINATING ENGINEERING The cotton thread must be made of a high grade, long staple, Sea Island fiber, uniform in size and free from knots or flaws. The tensile strength of the resulting mantle fiber depends largely upon the length and physical characteristics of the basic fiber. Further- more, if any knots, flaws, thin places, etc., exist in the threads they are reproduced in the mantle. Ramie is a natural vegetable fiber made from a substance known as “China grass.” The commercial supply of ramie is obtained almost entirely from China, India and Italy. In its crude form the ramie fiber contains large amounts of resins and mineral matter, and its purification is a very difficult and complicated chemical process. FREER EEE ZEBS Vf SA ee ee Pu NN ee ee fat | | ONE ae ‘at ree PE a EEREREREESSST UU pe ee GEE Fia. 18. Ramie fibers are long compared with cotton and possess greater tensile strength and would naturally be expected to make a stronger mantle. While mantles made from a ramie base do not shrink as badly as mantles made from cotton their tensile strength is some- what disappointing, especially after being used for a time. 3 Artificial silk, as the name implies, is an artificial fiber. It is made by dissolving cellulose in some suitable solvent to form a thick viscous solution, squirting this syrup through very fine dies, by great pressure, into some fixing bath. The resultant continuous filaments are then twisted into a thread. This thread may be knitted into mantle fabric and subjected to a special process of treatment for the production of a remarkably improved product. Mantles made from artificial fibers show improved physical strength, no tendency to shrink, no change in quality of light, INCANDESCENT GAS MANTLES 233 and a remarkably small candle-power depreciation, even after several thousand hours of continuous burning. Saturating is a comparatively simple process, where the thor- oughly dried fabric is placed in a suitable vessel and covered with the lighting fluid. As soon as it is thoroughly saturated, the ex- cess of fluid is drawn off and the fabric is put through an equal- izing machine piece by piece, in order to bring each mantle to a uniform degree of saturation. In the highest grades of mantles the amount of lighting fluid used is based upon a careful consideration of the amount of oxide required to produce a mantle of the highest physical and candle- power life. The lighting fluid is composed of a solution of approximately 99 per cent nitrate of thorium and 1 per cent nitrate of cerium in distilled water. This solution is usually of about 3 parts by weight of water to 1 part by weight of mixed nitrates. While the formula varies somewhat with different manufacturers, the limits are not wide. The commercial source of the nitrates of thorium and cerium is from a mineral known as monazite. This mineral occurs in commercial quantities only in North and South Carolina and in Brazil. The Carolinas’ monazite is found as a sand in the stream beds of the old mountainous districts, while in Brazil it occurs as a beach sand. | Monazite sand is mined on the principle involved in placer mining for gold. The gravel and associated minerals are shoveled onto screens and worked through into sluice boxes, where the min- erals of lower specific gravity are carried away by the water cur- rents, while the heavy monazite remains behind. This crude con- : centrate, carrying from 20 to 40 per cent monazite, is shipped to central plants, where it is further concentrated by the use of Wilfley tables and magnetic concentrators. The final product, as it is delivered to the manufacturer of lighting fluid, contains about 90 per cent of monazite of the following average composition: PHGsonOric WMnNyY Aides; & cise ysin's.d ine < eas 28% Det aHE OS 10Gt. . . 8 cn padetem eae ck 30 PEI ORIG o's oie sie ns eine ci wale se 14 Neodymium and praseodymium ....... 16 RNIN 408 1008 4s. So Se ea ee 5 PeEM UT OX LGR! . Wa tS. Ga caddie eae 2 Iron oxide, calcium oxide, etc.......... 5 Matt ihen hom x cik wig Dare em CaM ad OMe ae es 100% 234 ILLUMINATING ENGINEERING The manufacture of nitrate of thorium from monazite sand is a very difficult and complicated chemical process. It requires from 4 to 6 months to recover the small percentage of thorium and render it sufficiently pure to be used in the manufacture of lighting fluid. The by-products from this process have great scientific and chemical interest but no commercial value, and the thorium must stand the entire expense. The refined thorium nitrate must be chemically pure—free from all traces of mineral impurity and the other constituents of the monazite sand. The saturated fabric is now fixed for suspension by using as- bestos thread to form a loop, then shaped up preparatory to burn- ing out the organic material and converting the nitrates into oxides. The burning-out process is accomplished by igniting the fabric’ with a torch and waiting until the organic matter slowly oxidizes. After the fabric is completely consumed the ash of thorium and cerium oxides hangs in a soft, shapeless, flabby condition, and pre- sents a very remote resemblance to a mantle. When Dr. Auer first explained his idea for making a mantle to Professor Bunsen that famous teacher replied: “ It is extremely doubtful if the ash can be made to hold together.” This opinion was based upon Professor Bunsen’s knowledge of the general char- acteristics of metallic oxides, but the oxides with which Dr. Auer was working were notable exceptions. The incandescent gas light- ing industry depends upon this remarkable exception. After the organic matter is completely burned out in the process just described, the soft, flabby ash is carefully adjusted over a blow-pipe. The operator of this device controls levers which raise and lower the mantle, and which adjust the gas and the air supply to the blow-pipes. In some cases the gas is used under a pressure of several pounds to produce the intense flame required, but in either event the adjustment of the flame and the control of the position of the mantle is entirely in the hands of the operator. Under the influence of this intense blast flame the flabby ash, left when fhe organic fabric was burned out, is blown (by the proper control of the flame) into the required shape, and is changed from its soft, pliable state into a hard, resilient form. This opera- tion requires greater skill and experience than any other work con- nected with mantle manufacture. Coating. The object of this process is to form a protecting elastic skin over the ash to carry it while the mantle is going INCANDESCENT GAS MANTLES 235 through the inspecting, trimming, packing, transportation and in- stallation stages. This coating, or collodion, as it is usually called, is made from soluble cotton. Soluble cotton is made by the so-called nitrating process in which the loose cellular fiber is treated with a mixture of sulphuric and nitric acids, and a product is formed closely allied to gun-cotton. This nitrated cotton, after being thoroughly washed and dried, is dissolved in some of the numerous solvents such as alcohol- ether, acetone, etc., and a thick, viscous liquid is produced. The collodion is placed in suitable vessels, over which the mantles are suspended and into which they are dipped, then transferred to hoods to dry. The mantles are then inspected and packed to meet the great variety of needs of the established markets. It is estimated that the American market consumes 60,000,000 mantles per year, most of which are standard-sized upright and inverted mantles. Large quantities of mantles are also produced for railroad-coach lighting with Pintsch gas, kerosene lamps, gaso- line systems and high-pressure oil lamps. In the limited allotment of time for this subject, this review must necessarily be brief and superficial, but I have attempted to make it clear to you that the development, growth and future of the incandescent gas-lighting industry is a matter of immense scientific and economic interest. Core e ree ee ey er ye 7 VI THE GENERATION AND DISTRIBUTION OF ELECTRIC- ITY WITH SPECIAL REFERENCE TO LIGHTING By Joun B. WHITEHEAD CONTENTS PRINCIPLES AND DESIGN 1. Interior illumination. a. Systems of power supply: generating plants; constant potential; direct current, 2- and 3-wire; alternating current, 2- and 3-wire; alternating current, high voltage single and polyphase; trans: formers; isolated power plants. b. Systems of distribution: 2-, 3- and 5-wire parallel distribution, for incandescent glower, vapor and arc lighting; series parallel distribution; low voltage incandescent lamps on direct and alternating current circuits. c. Design of electrical system: Choice of system; regulation of sup- ply system; voltage drop in direct and alternating circuits; permissible voltage variation; size of feeders; diversity factor; number and sizes of branches. 2. Exterior and street illumination. a. Systems of power supply: Constant potential and constant cur- rent, high and low voltage, direct and alternating; constant- current generator; constant-current regulators and rectifiers. b. Systems of distribution: Parallel and series parallel constant potential, for arcs and incandescents. Constant-current series systems for arcs and incandescents. Alternating current to direct current systems. ; c. Design of electrical system: Choice of system. Constant voltage and constant current regulation. Size of feeders. Power loss in series circuits; underground and overhead systems. 3. Meters. a. Types of meter. b. Accuracy, calibration and inspection of meters. THe INSTALLATION OF ELECTRIC LIGHTING SYSTEMS 1. Interior illumination. a. Type of installation. 'Two- and three-wire. Exposed and con- cealed wiring. Conduit systems and outlet boxes. b. Control. Service connections. Distributing centers. Switches. Protective devices. Subdivision of total copper. c. Relative costs. 238 ILLUMINATING ENGINEERING d. Fire and insurance control. Ground connections. e. Specifications, drawings and contracts for work of installation, including materials. f. Tests. 2. Exterior illumination. a. Type of installation, arc or incandescent, parallel or series. Over- head or underground systems. Insulation. b. Control. Automatic cut-outs. Protective devices, lighting arresters. c. Municipal restrictions. Underground construction and cables. 2. Cost of operation. a. Cost of electric power. b. Systems of rates of sale of power; flat rates; maximum demand; two-rate systems. ce. Contracts for purchase of power. Principles and Design Electricity for lighting may be taken from any type of gen- erator. The earliest types of generator were developed to meet the requirements of lighting apparatus. With the introduction of other applications of electricity generators have been designed with characteristics to meet particular purposes, but it is probable that every operating generator furnishes more or less current for lighting. In modern installations, in which a large portion of the total capacity is consumed in lighting, the generators are designed with special reference to the regulation required by lighting ser- vice. Such generators are of various types, the extremes being the smallest continuous-current dynamo of the isolated plant for a single building, and the modern high-power (20,000 kw.) alter- nator of the city central station. | The proper circuit conditions for electric lighting are either constant potential or constant current. The general problem of central-station design to meet these conditions involves a knowl- edge of the various sources of energy, types of prime movers, gen- erators, control and regulating apparatus, and is distinctly within the province of the present-day electrical engineer. The electrical phase of the problem of the illuminating engineer will only in extremely rare instances contain the questions of prime movers, generators and station design. In general his concern, certainly in interior illumination, need go no further back than the avail- able service mains. At this point he need only recognize the type of service, know what regulation he may demand, and be able to GENERATION AND DISTRIBUTION OF ELECTRICITY 239 draft a service contract for his client. From this point inward he must be able to design the distributing system electrically and mechanically, with due regard to fire hazard and conformity to local regulations. He must be able to draft a specification and prepare drawings for an installation which shall amply secure for his client a completed and tested lighting system for a definite price. ‘The exterior problem requires a somewhat wider knowl- edge of the principles of distribution, but will rarely, if ever, ap- proach the station nearer than, say, a constant-current regulator. In brief, the illuminating engineer can generally assume that the electrical engineer will furnish him with constant pressure or con- stant current. The electrical problem of the former is to know the limits of this constancy, and to be able to design, install and test the proper distributing system. Should the illuminating engi- neer ever desire to extend his knowledge to the engineering of generating equipment, many excellent treatises on the subject are readily available, and it does not appear desirable, in the short space allotted here to the electrical problem of the illuminating engineer, to devote more than occasional mention to a kindred topic of wide extent and well treated in the literature of the subject. 1. Intertor Illumination (a) Systems of Power Supply. The commonest class of public power supply for interior lighting is at constant potential. In the hearts of cities it is usually in the form of continuous current supplied by an underground three-wire interconnected network of mains. This network is fed, over underground feeders con- nected to the mains at various points, from rotary converters or motor generators in one or more substations. The general plan of such a network is indicated in Fig. 1. These machines are operated by alternating current which is generated at voltages up to 15,000, or even higher, in central stations at some distance from the substation centers of distribution. The voltage of these networks is 220 to 240 between two so-called “ outside ” wires, and ~ 110 to 120 volts between either outside wire and a third or “neutral” wire which is usually kept.at the potential of the earth, or “ grounded” by connecting to an underground system of water pipes, or by other methods. Most interior lighting devices are designed for voltages in the neighborhood of 110, and the aggre- gate load is divided as uniformly as possible between the two sides 240 ILLUMINATING ENGINEERING of the three-wire network. In this way the two halves of the load are connected in series, and the distribution for 110-volt service is accomplished at 220 volts, with great saving in the amount of copper, since, at a given loss and distance, the amount of copper necessary varies inversely as the square of the voltage. The use of the neutral conductor, however, reduces the amount of this theoretical saving. The neutral conductor is made necessary by the facts that the component parts of the load on the two sides of the system are often separated by some distance, and especially that the two sides of the system are never exactly equally loaded. a ee Pee Ael, Main. Fig. 1. Fig. 2. Fic. 1.—Direct-Current Underground Network. Fig. 2.—Outlying Alternating-Current Distribution. The excess current of the more heavily loaded side flows back to the substation over the neutral conductors of the mains and feeders. This conductor therefore only carries the difference in the current of the two sides of the circuit, and in a large system with average balance of load between the two sides of from 2 to 5 per cent, its cross-section may be considerably less, say one-half that of the outer wires. This system therefore requires a genera- tor connection at a point midway between the potentials of the outer terminals. 'This may be accomplished by operating two generators in series and connecting the neutral to their junction. By the use of various auxiliary devices single machines may be constructed for supplying three-wire service. ._ GENERATION AND DISTRIBUTION OF ELECTRICITY 241 The cross-section of the main conductors of such a network may aggregate several million circular mils, divided into lead-covered cables of 1,000,000 or 2,000,000 c.m. each. The feeder cables are usually somewhat smaller, with neutral one-half the section of the outside conductors. These feeders are provided with a small insulated strand leading back to the station, which serves to indicate in the station the potential at the network. The voltage drop in the feeders varies from time to time and may be as great as 10 per cent. In locations at sonie distance from the central station or sub- /IOV me eee 3 | S/o V : S1ov : Slo VW Fig. 8. Fig. 4. Worke2 Vv Fie. 3.—Alternating-Current Secondary Network. Fic. 4.—Two-Phase Three- and Four-Wire Systems. station power is transmitted as high-voltage alternating current, and the voltage lowered by transformers which feed into the con- sumers’ circuits. For the extreme outlying districts with widely scattered consumers, each is often fed from a single small trans- former located at the property line, and supplying power over two wires only. In intermediate regions where the consumption is fairly dense several consumers may be fed from the same trans-. former, as indicated in Fig. 2. For still denser regions, beyond the reach of the continuous-current network, a secondary alternating- current network fed by several transformers at different points 1s _ sometimes formed (Fig. 3). In each of these cases the three-wire system is commonly used with 220 to 240 volts: on the outer wires, and the neutral connected to the middle point of the transformer 242 ILLUMINATING ENGINEERING secondaries. Both the primary and secondary circuits in this class of supply are usually carried overhead, though not invariably. The modern large central station generates at 25 cycles, three- phase. This frequency is the best for transmission and for trans- formation to mechanical power. It is not, however, well adapted to either arc or incandescent lighting, although there are many instances in which it is used for the latter. Economy of trans- mission copper and the superiority of the polyphase motor for power service result in the general use of three-phase instead of single-phase primary circuits. For lighting from such systems motor generators are often used for changing from 25 to 60 cycles, the latter being the standard frequency for alternating-current lighting. Hiab. Fa. 6. Fic. 5.—Three-Phase Three-Wire System. Fic. 6.—Three-Phase Four-Wire System. The 60-cycle generator for city lighting operates usually at some voltage between 2200 and 2600. Since there is always a market for power also, it is commonly of two- or three-phase type. Secondary lighting circuits at 220 to 240 volts are obtained from the polyphase primaries by transformers connected in various ar- rangements. If the service is for lighting only, single-phase sec- ondaries only are needed, and single transformers for the separate loads are connected to the various phases, and in such manner that the aggregate load is as nearly as possible divided evenly among the several phases. In some instances, however, there is a power load requiring small motors which cannot be operated at the high primary voltage. These moderate-size motors are also . most satisfactory in the polyphase type. The secondary distrib- uting system must therefore be polyphase, and this is accomplished GENERATION AND DISTRIBUTION OF ELECTRICITY 243 by various transformer combinations, resulting in three-, four- and even five-wire secondary systems. Figs. 4, 5, 6 and 7 show several of these combinations. Lighting circuits may be taken from any one of the branches of such a symmetrical system. This results, however, in placing both lamps and motors on the same transformer. Since the alternating-current motor often takes a starting current several times as great as its normal running cur- rent, the starting of the motors frequently results in a momentary fluctuation of voltage which is noticeable at the lamp. For the most satisfactory results the lighting and power loads should be on separate transformers, as the greater part of the voltage dis- turbance occurs in the secondary distributing circuit and in the transformer itself. : : //OV tig tenn Fie. 8. Fic. 7.—Two-Phase Five-Wire System. ' Wie. 8.—Two-Wire Distribution. — . 8 NE An important type of supply system is the so-called isolated plant of a single large building or factory. These plants are either steam-, gas- or water-driven, and generate current of the class and voltage required at the lamp. Thus many of the earliest plants are equipped with 110-volt, two-wire continuous-current compound generators. Those of more modern design, however, have 220-volt three-wire generators, as the extent of the distributing system is. usually sufficient to demand the resulting economy in copper. This type of plant for lighting alone constitutes as reliable a source of supply as can be obtained. Properly chosen, the generating plant will give as constant voltage regulation as may be desired, and satisfactory performance of the lamp will then depend only on the design of the distributing system. Usually, however, these 244. ILLUMINATING HNGINEERING plants must also furnish power. Little trouble is caused if the motors are of moderate size and the power load fairly constant. The elevator or other similar motor, however, with its large starting current will usually cause serious voltage fluctuations unless special provision is made for its fluctuating load. The most approved equipment for this purpose is the storage battery with “ booster ” generator; the battery automatically charges at values of load under the average and discharges when the elevator motors re- quire their greatest currents. This equipment also serves to equal- ize the demand on the generators between the light and heavy portions of the daily load curve, the battery charging during the morning hours and discharging as the lighting peak comes on. HOV 22ZO0V SioVv S1OV R2O0V SLOV Fig. 9.—Three-Wire Distribution. (b) Systems of Connection. Except in rare instances all in- terior electric lighting is obtained from lamps designed for constant voltage. The range of this voltage between 110 and 130 volts | is that within which the incandescent lamp can be most satis- factorily constructed. This has probably been the most important influence in fixing this practically standard value for the voltage of low-tension distributing circuits. The various other types of lamp for interior service have, therefore, naturally developed with conformity to this voltage, or to double its value, as obtained from the outer wires of the three-wire distributing system. Incandescent lamps, therefore, for interior illumination may be fed from the simplest type of two-wire distribution, shown in Fig. 8, or they may be connected between either outer wire and the neutral of a three-wire system, as in Fig. 9, or they may be GENERATION AND DISTRIBUTION OF ELECTRICITY 245 connected across any branch of a secondary polyphase lighting and power network, as already described. The usual voltage in these cases is between 110 and 130. Incandescent lamps for operation on 220 volts are obtainable, and are sometimes used on a 440-volt three-wire system to secure the benefits of the higher voltage for distribution. These lamps are inefficient and less rugged than those of lower voltage, and this system has not been generally adopted. Obviously the incandescent lamp may be supplied from either alternating or continuous-current circuits. Several exceptions to this statement must be noted, however. The life of the tantalum lamp, for reasons not yet understood, is shortened when used on alternating circuits; the amount of this shortening is about 50 per cent when operated at 60 cycles. In many instances it is possible to detect a flicker in lamps operated from 25-cycle circuits ; this is most noticeable in lamps of low candle-power and high voltage in which the filament is necessarily of small diameter. Nernst lamps operate on 110- and 220-volt constant-potential alternating circuits. A glower adapted to continuous current has been developed but has not met with success. Such lamps, there- fore, are adapted to the several types of alternating-distributing systems only. The mercury vapor lamp is best adapted to constant-potential continuous-current systems, but is also manufactured for alter- nating service. It may be constructed for a wide range of voltage, but is commonly manufactured for 110- and 220-volt circuits. Interior illumination of stores, factories, etc., by means of arc lamps is quite common, and in such instances the lamps are oper- ated from constant-potential circuits. Although the are lamp in its best form is a constant-current device, constant-current cir- cuits are usually of a voltage too high for introduction into build- ings. Multiple or constant-potential arc lamps have, therefore, been developed, and it is now possible to secure an arc lamp suit- able for any type of available supply system. Thus single are lamps may be supplied from either 110-volt side or from the 220-volt outer wires of either a continuous or an alternating three-wire distributing system. Lamps for 110 volts continuous current may be operated singly or two, four and five in series from 110-, 220-, 440-, 550- (railway) volt circuits. Lamps may be operated singly, by means of compensators or transformers from alternating circuits of any voltage or frequency. 246 ILLUMINATING ENGINEERING Incandescent lamps are frequently connected several in series, where the available voltage is higher than that of the lamps. The most familiar instance of this method of connection is found in the cars and buildings of the street-railway system operating at 550 volts. The introduction of the efficient metallic filament has led to an extension of this method of connection, as applied to low- voltage, low candle-power incandescent lamps operating from 110- volt circuits. This method of connection has arisen from the desire for a lamp of lower rating and more durable construction | than the 25-watt, 110-volt tungsten. Standard-base tungsten lamps may now be had for any voltage below 130, and lamps of 1.25-watt consumption in 10-, 15- and 20-watt sizes and at voltages from 10 volts upward are standard with manufacturers. The obvious objection to this series parallel method of connection is the fact that the failure of one lamp cuts out the others in series with it. These lamps are especially hardy, however, owing to their short, stout filaments, and when once in place in rigid sockets the plan is well adapted to long passageways and other areas requiring four or more units of low intensity without inde- pendent control. Four 28-volt, 10-watt lamps in series on a 115- volt circuit is a very satisfactory instance of this type of connection. Ten 10- or 12-volt, 5-watt lamps in series are sometimes used for sign lighting, but the arrangement is not satisfactory owing to the result consequent upon the failure of one lamp. Multiple operation and independent control of low-voltage lamps on existing multiple wiring is possible on alternating circuits by the use of transformers and “economy coils” or auto-trans- formers. With the use of the latter it is possible to operate the lamps in series, and the failure of one lamp will not affect the others. (c) Design of Electrical System. ‘The designer of interior il- lumination will rarely if ever find it necessary to extend the system of electrical conductors beyond the property line. In cities, for ex- ample, the source of supply will be either an underground continu- ous-current three-wire network with connections from a nearby manhole available at the building line, or an overhead secondary alternating-current line at a greater or less distance, or in many of the larger problems the power supply will be in or very near the building itself in the form of an isolated plant. Considering, first, the source of supply, the careful engineer GENERATION AND DISTRIBUTION OF ELECTRICITY 247 will consider (a) its capacity, (b) its reliability, (c) its voltage regulation, and (d) its distance and the class of current, i. e., whether continuous or alternating current, and if the latter, its frequency and voltage. The capacity of the source of supply, in- cluding the transmission conductors up to the point from which the new lighting load is to be taken, must be sufficient to ensure satisfactory and continuous operation of all the loads upon it. Moreover, the application or removal of any individual load should be without disturbing effect on any of the others. The questions of capacity and reliability are not apt to arise in connection with an underground continuous-current network, or with an individual isolated plant constructed especially for the system under design. Also, in the commoner instances of alternating-current secondary- distributing systems, since the transformers are the property of the supply company, the question of capacity will be taken care of by them. The question of reliability in such systems assumes importance when the transformers are at the end of long feeders, particularly if the latter pass through open country for any dis- tance. Suburban lighting from the best class of supply company is often subject to interruption from line troubles due to wind, snow and sleet, and lightning. For large installations, where even a short interruption is to be avoided, these considerations may be sufficient to justify an isolated plant. Generally, however, occa- sional brief interruptions in localities where this class of service is the only one available can be tolerated, and the engineer need only satisfy himself that the overhead lines are of approved con- struction and protected by lightning arresters of design and loca- tion dictated by the best present-day knowledge of this imperfectly understood portion of the problem. A committee of the National Electric Light Association is now engaged in an effort to standard- ize the methods of installing the various types of distributing system. At this time definite recommendations have covered sec- ondary-distributing systems only, and are contained in a report to the Association at its convention in May, 1910. ‘The work of this committee when completed will furnish an excellent reference for all questions of overhead lighting wiring. Should the engineer find it necessary to specify and install his own transformers, the questions as to the methods of installing them, together with their fuse blocks, are considered at length in the report mentioned above. The transformer capacity and subdivision, in its relation 248 ILLUMINATING ENGINEERING to the installation, depend on the time distribution and concen- tration of the connected load. ‘These two elements are usually combined in the “ diversity factor,” or the ratio of the sum of the maximum demands of the several consumers to the maximum demand which actually results from their combined service. For transformers in residence lighting this factor is about 3, in com- mercial lighting from 1.6 to 1.1. Speaking generally, transformers may be operated for an hour or two at 50 per cent over their rated capacity, and for short intervals at 75 per cent or 100 per cent. On account of the short distances to which low-voltage alternating current may be trans- mitted, transformers on poles rarely exceed 15 kw. in capacity, and 30 kw. is about the limit in size for transformers for lighting only. The voltage regulation of the supply system, next to constancy of service, is the most important factor for satisfactory lighting. Too often the engineer has to be content in this particular with what he can get. In the present state of the art it is rarely pos- sible to secure from a supply company any statement or guarantee as to the limits of fluctuation of its voltage. Probably the most constant voltage obtainable is that in the best type of isolated continuous-current plant, as found in a few modern office buildings with special provision for motor loads. In this case the feeders are all short, and the regulation approximates the practical con- stancy obtainable in compound generators.. Often, however, the isolated plant has too little capacity, and carries both motor and lamp loads without special regulating apparatus. In such cases the regulation is very poor. The underground 220-volt, three-wire continuous-current net- work of the best type of city plant yields excellent regulation. Such a system comprises a close network of mains, often compris- ing several 1,000,000 circular-mils cables. The voltage in this network is maintained constant by connecting it at various points with feeders from the station. Potential wires, as already men- tioned, are also run to the station and indicate the voltage through- out the network. The voltage on the feeders is varied according to the needs by connection to several sets of bus-bars of different voltages, operated from separate machines, or through boosters and other regulating devices. The method is indicated in Fig. 10. The load changes of such a system, owing to its size, are quite . A q : ; 5 j GENERATION AND DISTRIBUTION OF ELECTRICITY 249 uniform, so that voltage adjustment at any point of the network is simple. In such a system a daily constancy within 1 or 2 volts is obtainable. Alternating-current secondary-distributing systems do not, as a usual thing, afford as satisfactory voltage regulation as the con- tinuous-current system. The drop in the primary wires is rarely a disturbing factor, since this is compensated for in the station, and that in the transformer may be less than 2 per cent on non- inductive incandescent-lamp load. A serious drop due to induc- tive reactance, however, occurs in the low-voltage secondary cir- cuits, and limits their length to comparatively short distances. For this reason secondary networks, commensurate in size with those of the continuous-current system, are not used. In such . iain oer 111 {| 1] Fig. 10.—Station Connections Direct-Current Feeders. - an alternating-current network a transformer fed from a separate pair of primary wires constitutes a feeder corresponding to that of the continuous-current network, and since alternating-voltage regulation is simpler, the station apparatus of this system is less elaborate and, therefore, cheaper. ‘The transformers must be close together, however, owing to the drop in the secondary circuits, and this condition is greatly aggravated in the fairly common event of one transformer getting into trouble. These facts are sufficient to have restricted the alternating network to compara- tively limited areas. When several transformers are connected to the same primary circuit, station control compensates for the variable drop of changing load; obviously that this arrangement be satisfactory to all consumers, they should all have approximately the same type of load variation. It will be thus seen that the voltage regulation of alternating sources of supply may be good 250 ILLUMINATING ENGINEERING or bad depending on the type of control at the station, the number of consumers on a line, the particular way in which these con- sumers vary their demand, etc. If the lighting circuits are also used for motors, it is still more difficult to secure good regulation. In the better classes of service momentary variations of 1 or 2 volts in 110 should not be cause for complaint. As the load goes on the voltage is raised at the station either automatically or by hand, and this may cause an extreme daily variation of 3 or 4 volts. Departing from the best class of service, it is possible to find almost any degree of poor regulation in lighting circuits. In these days, however, a total daily variation greater than 5 per cent should not be tolerated from a company professing to give first-class service. With the voltage variation of the supply system given, the engi- neer must design his distributing system so as to add as little voltage variation as possible, and so keep the voltage at the lamp as nearly constant as the source of supply will permit. The prin- ciples involved in this design are simple, and the problem is usually the very indefinite one of a decision as to what additional drop to allow in order to secure a low cost of the distributing system. With continuous current the application of Ohm’s law in one of its several forms will determine the size of conductor for the chosen voltage drop. ‘Temperature variation of resistance, however, must be duly considered. If many calculations are to be made it is usually worth while to make use of tables giving relations between current, voltage drop, distance, ete., such as may be found in Hering’s Wiring Computer and other like works. In. most cases, however, it will be more satisfactory to make calcula- tion using resistance tables with temperature factors clearly given. The loss or drop in voltage in alternating-current circuits is due to resistance and reactance. The resistance may usually be that given by any wire table with temperature correction. ‘The reactance drop is caused by the electromotive force induced in the circuit by its own alternating magnetic field. This electromotive force is therefore proportional to the current, and to the frequency, and to the self-inductance, which depends on the length, the sepa- ration and the size of the conductors. The mathematical expres- sion for the reactance in ohms is 27NL, and for the reactance volts 27NLi, N being the frequency, L the self-inductance and i the current. The resistance and reactance volts are both propor-_ GENERATION AND DISTRIBUTION OF ELECTRICITY 251 tional to the current, but differ in phase by one-quarter of a period so that the total drop in volts is the square root of the sum of the squares of the resistance and reactance volts. While - the resistance decreases rapidly with increasing size of wire the reactance decreases very slightly, consequently there is in alter- nating-current distribution an early limit to the improvement in voltage regulation by increase in the size of conductor. It is for this reason that low-tension alternating circuits must be short. The resistance and reactance at 60 cycles per mile of a circuit of two No. 5 wires, 24 inches apart, in ohms, are 3.24 and 1.4; for No. 00 the values are .8 and 1.24; it is seen that for sizes in this neighborhood little is gained by increasing the size of wire. Com- plete tables of resistance, reactance and impedance volts for vari- ous sizes of wire, separation, frequency, are now readily available, so that calculations may be quickly made. Attention to the re- actance drop is especially necessary in designing overhead service connections with space separation, and must not be lost sight of even in interior wiring where the two sides of the circuit are close together inside one conduit. For example, two No. 0 wires in a 2-inch conduit may easily have an average interaxial separa- tion of 1 inch; the reactance per 1000 feet is about .1 ohm or, one-half as great as the resistance; the impedance is therefore .224 or 25 per cent greater than the resistance. Secondary-distributing networks must therefore have trans- formers connected at fairly frequent intervals. A common method is to run three-phase primaries, supplying three or four city blocks from one phase through three transformers with their secondaries connected to a common three-wire main. The next three blocks go on the next phase, etc., preserving the balance as far as possible. Speaking broadly high-class secondary distributing or service cir- cuits should not exceed 400 to 600 feet in length, or between transformers. In calculating the wiring for any installation two types of volt- age drop must be considered, viz., that due to the gradual daily increase of the total load, and that due to the sudden cutting in or out of a portion of the total load. The former occurs gradually and principally in the mains from the supply system, and in the “risers” and distributing feeders. If the maximum load on all branches is definitely known, the voltage drop due to this cause may, of course, be kept within any limits by proper choice of con- 252 ILLUMINATING ENGINEERING ductors. A wide range of variation of this kind is very objection- able. If the lamps are chosen for the high voltage, their luminous efficiency is impaired as the load goes on; if for the low voltage the life of the lamps used at light loads is shortened. As this type of variation is gradual it is not noticeable, and too little at- tention is given it in design. The second type of voltage variation is necessarily less in amount than the first, and is principally ob- jectionable in causing a momentary fluctuation of light from other burning lamps. This disturbance is reduced by designing so that the smaller part of the total permissible drop takes place in the mains and principal distributing feeders, and by increasing the number of branch feeders. A change of 1 per cent in the voltage on a tungsten lamp causes a variation of 4 per cent in its candle- power. Fluctuations of this nature, therefore, are to be par- ticularly guarded against in those cases where there is frequent cutting in or out of large numbers of lights. It is difficult and scarcely necessary to fix an absolute limit to the permissible voltage variation on an incandescent lamp. Sat- isfactory illumination is given by the 120-volt tungsten lamp over a range of 4 volts or more than 3 per cent; in fact, a given lamp is now rated for 3 voltages covering this range. The important consequences of this variation are the effects on the efficiency and life of the lamp, rather than on the illumination. Speaking gen- erally, with a supply system constant to within 1 or 2 per cent, very satisfactory service will be given if the maximum voltage drop inside the service connection be limited to 3 per cent. Of this the smaller part should be in the service wires and larger branches. A greater drop than this may be allowed when the greater proportion of the lamps are operated together, and so cause approximately a fixed drop in the service wires. With the entire load connected as one unit, i. e., with no independent opera- tion of single lamps, any amount of drop in the service connection may be allowed, by a proper choice of lamp. The calculation of the size of service wires, feeders and branches to meet the require- ments of voltage is thus a simple matter of distances as soon as the location of the individual outlets and sizes of lamps are fixed. The usual installation begins at the service wires, which may be either overhead or underground; these are generally 220-volt, three-wire, carried directly to a center of distribution, which may be of any degree of elaboration. A simple iron box containing GENERATION AND DIsTRIBUTION oF ELECTRICITY 200 a main switch and fused branch cut-outs suffices for a small resi- dence. Tor large installations a switchboard having panels for the main connection and individual feeders, as found in the largest buildings, may be required. From this center feeders run to distributing centers in various portions of the building. From these distributing centers sub-feeders are often taken to smaller local centers, though, more commonly, so-called branch circuits lead directly to the lamp outlets. The number of feeders and sub-feeders is regulated by the height and the floor area of the building. For great heights individual feeders for one or more floors may be necessary. Generally, however, several floors may be fed from one riser. For large areas, sub-feeders from the distributing to local centers may often be used to advantage. The three-wire system, is carried to the centers where branch circuits are connected. Probably the most important factor in determin- ing the number of feeders is the permissible length of branch circuit. The “ National Electrical Code” limits the lamp capacity of a single branch circuit to 660 watts. This figure was chosen as representing twelve 55-watt carbon lamps. Under this rule it is now possible to install twenty-six 25-watt tungsten lamps, although such a plan is not advisable. Further, no wire smaller than a No. 12 B. & 8. should be used for the branch circuits. At 115 volts, 660 watts represent about 5.5 amperes, and the re- sistance of No. 12 wire is 1.62 ohms per 1000 feet. An average length of 50 feet of this circuit would therefore cause a drop of 1 volt. With good regulation of supply system and ample copper in service wires and feeders, branch circuits may sometimes have a length of 100 feet, but this should be the maximum of conserva- tive practice. Exceptional cases may be met by increasing the size of the branch circuit. A radius between 50 and 100 feet, therefore, marks the area to be fed from one center or feeder con- nection. In small buildings, such as residences, therefore, no feeders are required, all branch circuits starting from a suitable distributing board where the service wires enter. In larger build-_ ings the density of the load on various floors will determine whether more than one floor may be fed from one feeder. The low consumption of tungsten lamps will usually permit two or three floors to a feeder or a riser, with 10 or 12 branch circuits to a floor. In such a case it is advisable to place a distributing board on each floor, and not extend the branch circuits from a center on one floor to outlets on floors above and below. 254 ILLUMINATING ENGINEERING With all feeders brought back to the service connection, which should be located as near the mean center of load as possible, it is a simple matter to calculate the voltage variation on any lamp with all lamps burning. With a fixed limit of variation, this condition will usually call for larger feeders-and service wires than necessary. A study of the particular problem only can determine the probable maximum number of lights to be operated at one time. For residences this number will rarely exceed one-third to one-half of the total, while in office buildings, churches, theaters, etc., the total connected load may often be in operation at one time. It is only in exceptional cases that the cost of copper in the feeders is a sufficiently large proportion of the total cost to warrant the reduction of their size. No great increase in cost will generally result from designing service wires and feeders to the end that the operation of the maximum connected load will only cause the permissible voltage variation on the lamp most un- favorably located. 2. Exterior and Street Illumination (a) Systems of Supply. Exterior illumination may be taken from any available source of supply. The use of constant-poten- tial continuous-current service is limited to loads concentrated within a small area, owing to the fact that the distributing losses mount very rapidly for any considerable distance. Instances of this type of supply are electric signs from 110- to 220-volt mains, multiple are lamps in front of buildings or stores, and street arches supplied from 550-volt railway circuits, the lamps being connected in series-parallel. Constant-potential alternating current at 2200, 4400 or 6600 volts is probably the most common type of exterior supply circuit, and it may be utilized in various ways for exterior lighting. It may be simply transformed to low-voltage, constant-potential ser- vice or to high-voltage, constant-alternating current for series are and incandescent circuits, or to high-voltage continuous current by means of the mercury rectifier. The last mentioned is perhaps the most satisfactory of all methods of are lighting. For many years constant-continuous current, series arc circuits were supplied from Thomson-Houston and Brush constant-current generators. Many instances of the latter type of installation are still in operation, and these machines operate with as high voltage 1 ON ns Ot Pe a eee ee cea = GENERATION AND DISTRIBUTION OF ELECTRICITY 255 as 13,000 with currents of 5 to 10 amperes supplying upwards of 220 lamps. These excellent machines, after a highly honorable record, are now being rapidly supplanted by constant-potential to constant-current transformers fed from 2200 volts constant-poten- tial alternating circuits and supplying on the secondary side con- stant-alternating current. These transformers are equipped with one stationary coil and a movable coil which automatically shifts its distance from the fixed coil to meet the demands of the load. Fic. 11.—Constant-Current Transformer. In a transformer under load there is a repulsive force between the two coils. In ordinary constant-potential transformers this force is held in check by the close-fitting iron of the magnetic circuit. In the constant-current transformer this force is allowed. to act, free motion of the secondary away from the primary being allowed by providing a greater opening in the magnetic circuit than is required by the cross-section of the coils. But a separation of the two coils, due to a rise in current, is accompanied by a fall in the secondary voltage, since a portion of the magnetic field set up by the primary leaks across the gap between the coils and so 256 ILLUMINATING ENGINEERING does not pass through the secondary. The tendency to a rise in current is thus checked by a fall in voltage. By means of suitable counter-balancing of the weight of the movable coil, and by other auxiliary devices, the transformer regulates very closely for con- stant current, and arc circuits may be taken directly from their secondaries. Fig. 11 shows a picture of this transformer. More satisfactory, however, is the series continuous current are circuit, which may be-had by combining with the constant-current transformer a mercury-are rectifier. ‘The combination gives excellent constant A C Supply Regulating Transformer Mercury Rectifier Starting Transformer D C Circuit . Fig. 12.—Direct-Current Series Arc Rectifier. continuous current regulation. The method of connection is il- lustrated in Fig. 12, and the apparatus provides a very reliable means of transformation between constant alternating-potential and constant continuous current. These equipments are available for any voltage between 220 and 13,000, and for any standard of frequency. ‘They may be had in sizes supplying as many as 75 lamps. (b) Systems of Distribution. Arc lamps may be operated from any available source. Their operation on low-voltage, constant- potential circuits is less satisfactory than on a constant-current circuit. ‘The alternating-current multiple lamp is the most un- satisfactory of all, but its use is often justifiable in outlying dis- GENERATION AND DISTRIBUTION OF ELECTRICITY aod tricts with widely scattered lights. The constant-current series method of connecting arc lamps is the most common of all, and the series circuits may be either alternating or continuous current with preference for the latter. These circuits cover wide expanses of territory, and since the connection from lamp to lamp is by one conductor only the distributing system is simple and may be looped in various directions. Exterior lighting by incandescent lamps may also be adapted to any class of service. For condensed loads, such as signs, it is possible to use the multiple connection from low-voltage circuits using standard lamps. Low-power, low-voltage lamps must be con- nected two or more in series on continuous-current circuits; on alternating circuits the use of small transformers or economy coils will avoid the undesirable series connection. Street lighting is sometimes accomplished by the series-parallel connection of in- candescent lamps on railway circuits or other available constant- potential lines, but the most acceptable system for distributed and uniform lighting by incandescent lamps is the series connection of a number of these lamps across constant-potential high-voltage alternating circuits, or in constant-current circuits, either alter- nating or continuous. On constant-potential high-voltage service the lamps are shunted by small reactance coils, so that the circuit is continuous, and the voltage consumed by reactance if an indi- vidual lamp should fail. Tungsten lamps for this system are to be had with ratings of 1.75 to 4 amperes, and from 8 to 40 volts, so that it is possible to operate 260 such lamps in series on 2200- volt circuits. It is claimed for the system that operation is still satisfactory with 20 per cent of the lamps broken or out. The series connection of tungsten lamps may also be operated at constant-alternating current by use of the constant-current trans- former already described. By this method upwards of seven hun- dred 30-watt, 3.5 or 6.6 amperes, lamps may be operated in series. In this system each lamp is equipped with an insulating film which withstands the lamp voltage but breaks down if the lamp fails, thus preserving the continuity of the circuit. The transformer ad- justs automatically for the lowered voltage. (c) Design of the Electric System. Constant-potential regula- tion is obviously much less important in. outside than in inside lighting. Incandescent lamps employed in this class of service are comparatively few, and the objections to voltage fluctuations are 258 ILLUMINATING ENGINEERING practically limited to the effect on the life of the lamps. The arc lamp is essentially a constant-current device and is not seriously affected by slight voltage variations. For the short connections usual in the use of constant-potential are lamps no special caleula- tion is necessary for the wiring beyond providing ample current- carrying capacity. Series arc lamps take from 4 to 914 amperes, according to the type. The commonest types are the 4-ampere continuous luminous lamp and the 6.6-ampere alternating or con- tinuous enclosed lamps. The regulation of the Brush generator, of the constant-current transformer, and of the mercury rectifier are all extremely close; it follows, therefore, that the design of the distributing system for exterior illumination will very rarely involve any serious problems of voltage regulation. The series circuits themselves and the resistance in lamps consume a large part of the applied voltage, and the constant-current regulating devices adjust automatically to a wide range of resistance. The series circuits of large cities carry 50, 75 and 100 lamps at volt- ages from 4000 to 8000. The distance of the separation of lamps varies, but averages from 200 to 300 feet. ‘The voltage drop in the conductor itself is usually between 5 and 10 per cent, and wires in the neighborhood of No. 8 B. & S. are used. The low- tensile strength of smaller wires renders their use inadvisable. It is not uncommon to find a circuit of this kind comprising 10 miles of single No. 8 wire and seventy-five 4-ampere lamps. Series incandescent lighting from constant-potential high-volt- age circuits is accomplished with lamps taking from 1.5 to 4 amperes. For voltages above 550, the circuit should be insulated from the main line by a transformer. In series incandescent cir- cuits fed from constant-current transformers the lamps may be had for currents between 1.75 and 10 amperes. The common size of wire for this class of service is from No. 10 B. & 8. up. The regulators are rated in terms of the aggregate kilowatt capacity of total connected lamps. This rating includes an allowance of 5 per cent ohmic and 10 per cent reactive drop in the series circuit. | The insulation of overhead conductors should be of the best rubber core and braided class of manufactured product. The underground conductor may be either fiber-, paper- or rubber-in- sulated stranded conductor, and in every case is surrounded by lead. These cables should withstand the test prescribed for all GENERATION AND DISTRIBUTION OF ELECTRICITY 259 high-voltage apparatus, namely, they should be subjected to double the maximum voltage for a period of 1 minute. 8. Metering The subject of metering is a highly important one in the com- plete discussion of the entire electric-lighting system. Meters are usually owned, inspected, tested and read by the company supplying power. The illuminating engineer will rarely be called upon to do more than provide proper spacing and accommodation for meters. Almost invariably the present-day meter measures watt hours. For continuous-current service the best meters are essentially the same as the original Thomson watt-hour meter. This consists of a continuous-current shunt motor containing no iron. The line current flows in the field circuit and the line voltage is applied to the rotating armature with the insertion of a very high re- sistance. This permanent shunt connection across the circuit, therefore, takes current at all times. While the current of an individual meter is extremely small, nevertheless, the aggregate of the meters of a large system results in quite an appreciable fraction of the total load on the station. The retarding force on the arma- ture of this meter is a copper disc rotating between the poles of several permanent magnets. The shaft of the armature is equipped with a small pinion which engages a train of gears connected with dials constituting the recording mechanism. For alternating cur- rents the induction-watt meter has many advantages over the Thomson type, although the latter may be adapted to alternating- current service. Induction meters operate on the induction-motor principle, series and shunt coils with different phase character- istics, giving the two components of the rotating magnetic field. A light aluminum disc constitutes the rotating element or arma- ture. By their principle they read true power, and are independent of phase difference between current and electromotive force. Alternating-current meters are, in general, more permanent and | reliable than those for continuous currents, in that they have no commutator nor brushes. The present-day meter, as furnished by the best manufacturers, has been brought to a high degree of perfection, and may be relied on to a very close figure of accuracy. No meter, however, will maintain its calibration indefinitely, and those in service should be tested and inspected regularly. This 260 ILLUMINATING ENGINEERING is generally carried out by the supply company, which in most cases owns the meter. In some instances a meter rental is charged for the purpose of covering not only the original cost of the meter but for defraying this regular charge for inspection and repair. Questions sometimes arise between customers and supply com- panies as to the accuracy of meter readings, and public service com- — missions have in many places provided regulations by which a consumer may demand a test and calibration of his meter at any time by the payment of a small fee. The usual method of testing meters is that of comparing them with portable standard meters. It is, of course, necessary that these portable meters should be compared with permanent standard instruments in the laboratory at sufficiently frequent intervals. The methods of charging for power for lighting as based on meter readings will be referred to later in these lectures. The general subject of meters has been exhaustively covered by the reports of the committee on meters of the National Electric Light Association for 1909 and 1910. Tre INSTALLATION OF ELEctrRic LIGHTING SYSTEMS 1. Interior Illumination (a) Type of Installation. The engineering questions arising in connection with the installation of a system of electrical con- ductors for distributing electric power for lighting are compara- tively simple. Such distribution is accomplished at moderate volt- ages for which the space requirements are not great. The usual problem is that of running a more or less elaborate system of two- or three-wire circuits inside a building. The objects which must be had prominently in view are those of safety, reliability, per- manence and unobtrusive appearance. ‘The system must operate without danger of fire or to life, The possibility of fire arises in the results following short-circuits and grounds in the system. The danger to life is not generally present in continuous-current service but arises in alternating-current distributing systems fed from transformers supplied by high-potential primary circuits. It is obvious that satisfactory operation will require that at all times the system will perform its functions of not only distributing power, but in permitting its ready control and the prompt elimi- nation of all abnormal conditions likely to cause interruptions. i i a GENERATION AND DISTRIBUTION OF ELECTRICITY 261 The life of the installation depends largely on the materials and quality of labor entering into its construction. In this regard possible exceptions may enter in the installation of systems which are to have intentionally a short existence. Generally speaking, however, the material and workmanship of electric-lighting in- stallations should be of the best obtainable, and in accordance with the latest recommendations of engineering bodies. The distrib- uting system for residences, hotels and dwellings, generally, as well as in all buildings where agreeable and attractive appearance is required, should be as unobtrusive as possible. This considera- tion in the instances mentioned leads to the entire concealment of electric wiring. In factories and other buildings where no particular attention is required as to appearance, the conductors and supports are often installed exposed. This method is a per- fectly satisfactory one, if due attention is paid to the location of the conductors in such places as will render them free from mechanical injury. Exposed wiring presents the general advan- tage of accessibility and convenience of inspection. Concealed wiring, on the other hand, is almost invariably free from the danger of mechanical injury. Decision as to which general method should be followed will depend on the particular conditions of the problem. The methods of installing electric wiring are rigidly controlled by the National Board of Fire Underwriters, and the regulations governing this class of work are published by that body in a pam- phlet known as “The National Electrical Code.” In addition to these rules there is published a list of manufactured material which has been subjected to laboratory test, and which is known briefly as “approved ” material. In many cities there is a further list of requirements which apply to particular local conditions., _ Four classes of interior wiring are usually permitted. They are known as “ open-work,” “ moulding,” “ concealed-knob-and-tube ” and “ metal-conduit ” installations. In open work the wires are run entirely exposed and supported on porcelain insulators and | knobs; they pass through all walls, joist, partitions, etc., in por- celain tubes. The space requirements in the way of separation of wires from each other, and from walls and their relation to other circuits, etc., are rigidly specified. This type of installation is entirely satisfactory where its appearance can be tolerated, and is the simplest and cheapest to install. The principal precaution 262 ILLUMINATING ENGINEERING to be taken is against mechanical injury. Moulding and knob and tube work have been developed as methods for installing wiring in buildings originally constructed without any idea of future elec- tric service. They represent the most unreliable and unsatisfactory types of wiring installation. In the case of moulding the wires are run behind either wood or metal strips which are laid on the ceilings and walls of interiors. In knob and tube work the wires are concealed by “ fishing”? them from point to point behind the plastering and under the floors of buildings without disturbance to these surfaces. This method is highly undesirable, and even when most carefully installed during the progress of building in- troduces great danger of fire. Both moulding and knob and tube work are make-shifts, and should never be installed by a careful engineer unless absolutely unavoidable. The complete enclosure of the entire wiring system up to the lamp or fixture outlet in metal conduit represents the best present- day method, and one which bids fair to form the ultimate standard of construction. In this system the entire wiring is completely surrounded by metal. The materials are to be had in the form of rigid or flexible metal conduit. The rigid conduit consists of iron pipe of various sizes, and usually in 10-foot lengths. Elbows, bushings and other fittings are also supplied for each size. This conduit is usually made as soft as possible to permit easy bending for adaptation to building peculiarities. It is either galvanized or covered inside and out with some protective enamel which is valuable in protecting the metal of the conduit rather than as insulation to the conductors enclosed. Flexible conduit com- prises the several varieties of the familiar tubing made in spiral form from cut steel. This conduit is best adapted to locations where straight runs are few, and where there is difficulty of access to wiring compartments. With either system of conduit construc- tion iron boxes are used for all classes of outlets. The conduit leads to these boxes and is mechanically and electrically connected to them by means of washers and nuts.. These boxes form con- venient points for pulling the wires into the conduit after the latter is installed, and also for making connections for branch circuits. This type of installation is readily installed in new buildings, whether they be frame, brick, concrete or other class of construction. Old buildings may generally be equipped with electric wiring in flexible-steel conduit with permanent damage GENERATION AND DISTRIBUTION OF ELECTRICITY 263 to plastering only. In the case of concrete buildings the outlet boxes for lamps, switches, plug cut-outs, etc., must be located and firmly attached to the forms with complete conduit interconnection before the concrete is poured. The entire conduit system should form a complete metallic system which should be grounded. In this condition the installation provides practically absolute safety from mechanical injury, and when supplemented by proper cut- outs and fuse apparatus, from fires originating in short-cireuits or grounded wires. The only objection to this type of installation which has arisen is the condensation of moisture inside of the conduits. This has been known to take place to such an extent as to result in the rotting of the insulation of the wires due to their permanent immersion in water. This objection may be largely obviated by running the conduit so that there are no pockets in the system, and so that they have a pitch or slope towards some outlet. It is customary to run three-wire mains, feeders and duplex branches in one pipe. It is not permitted, however, to run more than one set in a single pipe. Reliance, therefore, is placed entirely on the insulating covering of the wires without space sepa- ration, and on the suppression of any arc or spark between con- ductors or between conductors and ground by the walls of the conduit. ‘'T'wo-wire service is now limited to the smallest instal- lations, the maximum number of outlets permitted by supply com- panies on two-wire service varying somewhat, but generally not exceeding 25. It is permissible to run the wires of either two- or _ three-wire service in a single pipe. The magnetic influence of the iron-protective covering in the case of alternating-current circuits has never arisen as a prohibitive factor. The running of a single Wire carrying alternating current in an iron pipe is prohibited by the large increase of the impedance of the circuit and by the heat- ing of the conduit due to hysteresis and eddy currents. A series of tests have been made by the author to determine whether two- and three-wire circuits in an iron pipe could result in any appre- ciable increase of the impedance of the circuit. Two No. 6B. &S8._ wires were separated the maximum distance permitted by the inte- rior diameter of a 114-inch conduit, being rigidly held in position by strapping to opposite sides of a strip of wood. At 60 cycles, and for currents between 40 and 80 amperes, there was an average increase in the impedance of the circuit over the value when the circuit was in air and not surrounded by conduit of 214 per cent. 264 ILLUMINATING ENGINEERING It is obvious, therefore, that in the moderate lengths usually met with in interior illumination, this introduces no disturbing factor. The lighting of interiors by arc lamps fed from series circuits . is to be avoided. As already mentioned, these circuits operate at high voltage, and special precautions must be taken in insulating any such circuit within a building. In most localities the intro- duction of such circuits into buildings is prohibited. Multiple-connected are lamps are frequently used for the ighting of stores, factories, sheds, etc., and they are supplied by low- voltage distributing mains. In such circumstances due considera- tion must be given to the regulation of these circuits if incan- descent lamps are also to be operated from them. The are lamp takes from 4 to 9 amperes, and when this is the only type of lamp on the circuit the carrying capacity is often the determining factor rather than any question of regulation. The National Electrical Code prescribes the maximum values of current which it is per- mitted to carry on various sizes of wire. Each lamp or series of lamps, in case several are operated in series, must be provided with a fused cut-out. The general description and rules covering incandescent wiring, as already described, apply also to multiple are circuits, but the underwriters’ requirements prescribe certain additional regulations, which are duly set forth in the publications mentioned above. (b) Control. It is obvious that the entire system of an interior installation should be under control. We may define “control” as the possibility of individual and separate operation of all lamps, and the prompt cutting out of any portion of the system which may develop trouble. Thus every lamp or group of lamps should be operated by an accessible switch, and every branch circuit should also be equipped with apparatus permitting its easy separation from the remainder of the system. Individual distributing centers or the feeders supplying them should be equipped with switches. In addition to these essentials for manual operation, the whole system must be protected by fuses or automatic circuit-interrupting devices. It is highly essential that the main distributing center, the service connections, and all subsidiary centers should be in well-illuminated and readily accessible locations. In the denser sections of a distributing system, the service wires will usually be brought in from underground. Connection to a residence is usually made from a manhole permitting access to GENERATION AND DISTRIBUTION OF ELECTRICITY 265 the underground network. The manhole is an essential part of a system of underground ducts. The building connection is usually made from these manholes by small conduit connection, this con- duit being made either of fiber, treated wood, terra cotta or any of the many types offered by the market. These conduits are brought through the building line underground, and the service wires brought above the surface by a continuation of the conduit or in iron pipe. ‘These conduits should drain back to the manhole, that is, away from the house, and after the wires are drawn in the conduit opening should be stopped so as to prevent gases from flowing into the building. In the outlying districts where the distribution is overhead various methods are used for bringing the service wires inside buildings. In many instances this is done by putting suitable bushings through the walls near the roof of the house. The best practice, however, takes the service wires from the transformer into an iron pipe some distance above ground level, the pipe leading below ground into the basement as already described. This pipe - connection should be provided at the top with a rain-proof bushing, and is particularly desirable in localities where there is a possi- bility of future underground service. The report of the committee on overhead construction of the National Electric Light Associa- tion, 1910, describes in detail various methods of making service connections. Interior-lighting systems, whether supplied from isolated plants or from public-service companies, should be equipped with a main switch controlling the entire system. Also each feeder should be equipped with a switch. The next subdivision at the distributing centers should provide either a switch or enclosed fuse for each two-wire branch. The main switch of the system, and the indi- vidual feeder switches, should each be equipped with fuses or sup- plemented by some form of automatic circuit-interrupting device. It is sometimes desirable to have a switch at the distributing center, although this is not necessary if the feeder furnishing this . center is so equipped. Branch circuits must be equipped with fuses, but not necessarily with switches. The underwriters’ re- quirements limit the capacity of a single circuit from a distributing center to 660 watts. This figure was probably originally based on the demand of twelve 55-watt carbon lamps. And, in general, branch circuits in the past have been limited to 10 or 12 outlets. 10 266 ILLUMINATING HNGINEERING It is now possible to run many more outlets to a branch circuit by the use of low-power tungsten lamps. The branch circuits for incandescent lighting are usually protected by fuses of 10-ampere capacity. These fuses are either of Edison “screw-plug” or of “ cartridge ” type, with present tendency to a return to the former. As already stated, the feeders must be protected by fuses, and for this purpose the “cartridge” fuse is best. In many large instal- lations the feeders are protected by circuit breakers located on switchboards of more or less elaborate design. ‘The requirements of theaters lead to especially detailed switching and regulating de- vices. Fuses are manufactured up to 500- and 600-ampere ca- pacity, but circuit breakers are preferable above the former figure on account of the cost of the fuses and of the time required for their operation. Flexible cable must be used in all conduit instal- lations, and may be had to accommodate practically any current. In the larger installations feeders frequently have a cross-section of 500,000 circular mils, and in extreme instances are even of greater size. The subdivision in these cases of the total capacity — required is highly advisable on the score of convenience of instal- lation. The installation of conduit of diameter larger than 2 inches will usually involve difficulties unless special provision is made in the design of the building. Two-inch conduit will accom- modate three No. 00 wires; 3- and 4-inch conduit has been used, but 2 inches marks the limit for convenient installation. The neutral wire is made of full size in all interior wiring, so that when for any reason one side of the circuit is interrupted the neutral will provide full carrying capacity for the return current. (c) Cost of Interior Wiring. Since the prices of labor and ma- terial differ in different localities and at different times, it is dificult to state even approximately what the cost of distributing systems for lighting should be. In large cities, however, these variations are not very wide, and it is possible to state the limits within which the cost, expressed in terms of the usual contractor’s price per outlet, should lie. The figures given below apply to interlor wiring of all classes, from the small residence up to the large hotel or office building. They cover the portion of the work from the main source of supply, assumed to be at the building line. In case the building is lighted from its own plant these figures will apply to the portion of the installation lying between GENERATION AND DISTRIBUTION OF ELECTRICITY 267 the lamp and the plant switchboard. No lamps, fixtures or re- flectors are included in these prices: Exposed wiring, $1.50 to $1.60 per outlet. Wire in wooden moulding, $2.00 to $2.50 per outlet. Concealed knob and tube wiring, $2.50 to $3.00 per outlet, with $1.00 added per switch outlet. Wiring in iron conduit and in new buildings, $4.50 to $5.00 per outlet. | Wiring in iron conduits in concrete buildings, $5.00 to $6.00 per outlet. In the above, switches and base-board plugs are considered as outlets when the iron box is included. If the switch and plate is also to be furnished, approximately $1.00 per outlet of this nature should be added. For the larger installations in modern buildings the price of $7.00 per outlet, including all wiring and feeders up to the lighting fixture, has been found to be a fairly close figure. For that portion of the wiring which may be necessary beyond. the building line, as, for instance, the service connection and transformers, in those regions where alternating service is sup- plied, it is hardly possible to state even approximate figures of what the prices will be. The cost of wire follows that of copper more or less closely, and transformers vary somewhat in price. Lighting transformers suitable for erection on poles and for 60- eycle operation may be had in any capacity between 6/10 kw. and 50 kw. As adapted to 1100 or 2200 primary circuits, and trans- forming to 110 or 220 two- or three-wire secondary, their price varies from $27.00 per kilowatt for the 1-kw. size to between $7.00 and $8.00 per kilowatt for sizes in the neighborhood of 40 kw. and 50 kw. The prices are somewhat higher for higher primary volt- ages, and ‘transformers adapted to location in subways are from 10 to 12 per cent more expensive than the usual out-of-door type. Transformers for 25 cycles cost from 40 to 50 per cent more than those for 60 cycles. (d) Fire and Insurance Control. The National Board of Fire Underwriters, and in most places municipal regulations, require strict supervision of the installation of electric wiring. It is usually required that the electrical contractor shall secure a permit for any new work or repairs to electric wiring in buildings. In many eases the fire underwriters are satisfied with the municipal super- 268 ILLUMINATING ENGINEERING vision and make no independent demands of their own. This is especially the case where the city adopts the National Electrical Code for its own regulations. Presumably this permit for wiring is followed up by an inspection of the work after completion, by a city official. Too often, however, this inspection is of the most perfunctory character. The inspector will almost invariably be content with a visual inspection of the installation. From the nature of the troubles and imperfections that are likely to arise from a system of wiring, electrical tests are the only ones which can yield complete evidence as to the state and the character of the work. Insurance and city authorities therefore would do well to require a thorough testing of every installation before approval and acceptance. Since there is at present no municipal regulation which ensures tests of this nature, the designing engineer should be careful to incorporate in his specification clauses requiring the complete testing by the contractor. This method of accomplishing the testing should be easily available to the city, which in yielding a permit could stipulate that before acceptance proper tests should be made in the presence of the city official. It has been already mentioned that the entire system of metal conduit of an interior installation should be grounded. Grounding means connecting as definitely and permanently as possible to the earth, thus maintaining the grounded portion at the potential of the earth. The neutral of underground direct-current systems is almost invariably grounded. Interior-wiring systems should, in the writer’s opinion, be always grounded. Ground connections may be readily made by connecting between the grounding point of the circuit and the metal pipes of the city water supply. Such connec- tions should be soldered and of fairly large size of wire. To en- sure a ground independent of water or gas pipes an iron pipe may be driven 5 or 6 feet into solid soil, the damper the soi¥ the better, and the ground connection soldered to this pipe. The conditions will be improved by using several pipes and by removing the earth from around the top of the pipe to a depth and diameter of about 1 foot each, and then filling this hole with salt. There has been a wide discussion as to the advisability of ground- ing alternating-current secondary circuits. ‘These circuits are usually three-wire, and the ground connection should obviously be taken from the neutral. The great advantage of grounding the neutral is in the fact that should. the primary voltage reach the GENERATION AND DISTRIBUTION OF ELECTRICITY 269 secondary wiring by the failure of a transformer or by the crossing of the respective lines, the high-voltage circuit thus brought into connection with the low-voltage wiring would be grounded and thus prevent arcing and danger to life. In many instances, also, electrostatic charges may be induced in the secondary wiring by disturbances in the primary circuit. This may result in serious shock to persons handling the secondary circuits if these circuits are not grounded. . The supposed objection to grounding such circuits is that it places the potential of one side of the three-wire system between the bare contacts on lamps and other devices and the ground, thus offering the possibility that persons receive shocks. The National Electric Light Association recommends that the grounding of sec- ondary circuits be limited to those on which the voltage of one side does not exceed 150. This means that no shock of a higher value than that stated could be received by anyone touching an unin- sulated portion of the circuit. The reasons for not grounding cir- cuits of higher potential do not appear to be good. There can be no question that the grounding of the circuit offers great pro- tection from any trouble that may arise from the primary circuit. This is undoubtedly the most likely and the most serious source from which trouble may come. The danger of shock to persons is hardly greater when the system is grounded than when it is not, and in those systems in which the voltage is carried to values dan- gerous to life it would appear desirable to provide the safeguards in other ways, such as complete insulation of all live contacts, or by other methods usual in high-voltage circuits. (e) Specifications and Contracts. In preparing specifications and making contracts for an installation it is highly desirable that each should be as complete and explicit as it is possible to make them. The specifications should always be accompanied by draw- ings. Of the numerous clauses for the protection of the client which should be inserted, none perhaps is more important than that applying to the charges for alterations or extensions of the. work, as set down in the specification. In competitive bidding on work of this nature a contractor will often look to his charges for extras and alterations for the best part of his profit. The engineer should therefore endeavor to describe on the drawings or by explicit statement every outlet of installation. General clauses should be inserted which shall protect the client during the process 270 ILLUMINATING ENGINEERING of the work from damage to persons and property, and relieve him from all responsibility until the installation is ready to be turned over complete. In large installations the contractor should be required to place insurance on completed portions of the work and to give bond for its completion within the date stipulated in the contract. The specifications should cover carefully the sizes of all mains, feeders and branches, together with the conduit in which they are placed. Full details should be given of all switches, distributing boards, panels, etc. The trade names of manufactured articles which will be accepted should also be given, and the gen- eral statement made that no material not approved by the Board of Fire Underwriters may be used. The drawings should show the accurate location of all outlets, service connections, distributing centers and the run of all feeders. It is highly desirable that the engineer and architect should have early consultation so that the latter may know what space will be required by the engineer. ‘Too often the architect’s plans are completed before the engineer sees them. The architect, as a general thing, has a very limited knowl- edge of the requirements of an electric-wiring installation, and it is usually assumed that the illuminating engineer requires no space at all for his circuits. This consultation is especially advisable for buildings of reinforced concrete where it is inadvisable to pass conduit through reinforced beams. The drawings should also indicate the type of fixture, lamp, reflector, mounting height, etc. ‘The National Electrical Con- tractors’ Association has published a set of symbols which are in general use for indicating the nature and location of distributing ~ centers and the various types of outlet, ete. A standard set of symbols of this nature applying to the different methods of mount- ing lighting units and describing their character would be very useful. : The wiring for lighting systems is often installed on what is known as the time and material basis. This means that the con- tractor charges the cost of material used and the hours of labor required to the owner, with a certain percentage added. ‘This is rarely, if ever, a satisfactory method to the owner. To ensure a reasonable charge it requires a constant inspection of material and labor time. It will usually be possible to secure competitive bids, and then require the contractor to give the owner the benefit of any saving under the contracted figure which results from keeping } i . GENERATION AND DISTRIBUTION OF ELECTRICITY 271 a record on the time and material basis. In such a case the con- tractor furnishes the engineer with a statement of material and labor time at regular intervals. (f) Tests. Satisfactory performance in wiring installations de- pends primarily on regulation and on the nature of the material and workmanship. The regulation will depend largely on the sizes of conductor specified by the engineer, and a test of regulation will only check up the methods which have been employed in making joints and contacts. A full-load test, however, should be invariably applied to the system before its acceptance. Every switch should be operated and each lamp socket and base-board plug tested. Insulation tests are rarely applied to interior-wiring systems. It is advisable, however, to apply at least double the normal operating voltage to the completed system. A stipulation to this effect should be included in the specification. The con- tract should contain a clause requiring the contractor to carry out the tests in the presence of the engineer and the details of this test should be given. 2. Hzxterior Illumination (a) The commonest form of outside-lighting circuit is that of the series incandescent or arc system. ‘These circuits are usually run overhead, except in the more densely populated portions of the city. No special comment, therefore, seems needed as to the instal- lation beyond the regulations set down by the National Electrical Code. These circuits are of moderate voltage (from 2000 to 8000), and may therefore be handled by a variety of approved grades of | manufactured wire, insulators, ete. Series circuits are controlled, as a whole, from a generating station or substation, the entire protective apparatus being installed there. Special precautions may be necessary in some places for the protection of low-voltage lighting circuits and of telephone and telegraph wires. This class of service is more satisfactory when run in underground conduits, and this is usually required by the authorities in the centers of. large cities. The cities usually own the conduit system and rent space to the supply companies. The single conductor of the are or incandescent circuit is insulated with rubber or paper and the whole covered with lead. The manholes of the duct system are usually from 400 to 600 feet apart, and individual lamps are fed through branch conduits between the manhole and the base of the 272 ILLUMINATING ENGINEERING pole. The cables then rise inside the iron pole to the lamp. Since there is little or no difference in potential between the two sides of such a loop from a manhole to a lamp, a duplex conductor may safely be used for this portion of the circuit. The lamp itself, however, should be insulated from its support, since it may receive the full potential of the circuit. Grounds on this class of circuit are very dangerous. The lead sheathing of underground cables usually affords sufficient protection between mains of different classes of service; thus are circuits are frequently run in the same duct with the low-potential multiple-distribution mains. Instances have been known in which trouble has arisen by reason of this proximity, but a rental charge on the part of a city of 5 cents per duct foot per annum is usually sufficient to cause the supply company to put as many conductors as possible in one duct. Hx- cellent data as to the construction of conduits, their cost, etc., may be found in the Standard Hand-Book for Electrical Engineers. 3. Cost of Operation There is probably no phase of the general problem of electric lighting which attracts more public discussion than that of its cost. Public-service corporations, particularly if they have a monopoly of the consuming market, are naturally the objects of public suspicion. This is especially true of companies selling elec- tricity for lighting, and the explanation is to be found in the great discrepancy always existing between the admitted cost of electrical energy at the station bus-bars and the price at which it is sold to the consumer. The latter figure is often ten or more times as great as the former, and consequently is often the object of unin- formed public clamor. The reasons for the difference will be better understood after a discussion of some of the factors entering into the actual cost of generating and delivering electric power. (a) Cost of Electric Power. The commonest basis of estimating the cost of electric power is the summation of all expenditure nec- essary to deliver the power at the station feeder bus-bars ready for distribution. This total cost divided by the total energy generated gives the unit cost, i. e., the cost per kilowatt hour. This apparently simple method, however, will rarely yield the same figure for two different months, or weeks, or even days in the year, for the total cost of electric power is not directly proportional to the amount generated. GENERATION AND DISTRIBUTION OF ELECTRICITY 273 The total cost may be divided into two classes: (1) fixed charges and (2) operating expenses. In the item fied charges are in- cluded all expenditures necessary whether or not the plant gen- erates power. Thus in this class fall the items of interest, taxes, insurance, depreciation and obsolescence. They represent the ag- gregate cost of having an up-to-date power station ready to deliver power. By depreciation is meant the outlay necessary to keep all generating equipment in repair, and to replace efficient apparatus worn out in service. By obsolescence is meant the cost of pur- chasing apparatus and equipment to replace that which has been rendered obsolete and inefficient by improvements and increased knowledge of the art. Interest and taxes expressed in per cent of the cost of the plant will not vary with the type of plant; insur- ance is often eliminated entirely in modern plants of fire-proof construction; depreciation and obsolescence vary widely with the type and size of plant, being greatest for reciprocating steam plants and least for water-power plants. The aggregate of fixed charges, in per cent of the cost of the plant, varies from 9 to 17 per cent in modern plants of size required to furnish city lighting service. The lower figure is reached only in the best type of water-power plant, and the upper refers to reciprocating steam engines oper- ating under poor conditions. The cost of the power plant varies from $80 per kilowatt of installed capacity, in the case of steam turbines, to $100 or $125 for reciprocating steam engines, and to $200 or more for water-power plants. Large gas-engine plants cost about $135 per kilowatt of installed capacity. The second class of expense in the production of power is called the operating expense, and it includes all items, such as fuel, oil, attendance, etc., which are approximately proportional to the amount of power generated. The proportionality between total operating expenses and amount of power generated is not exact, since the efficiency of steam and electrical apparatus is not the same for all values of the load upon them. With proper sub- division of the total capacity into smaller units, however, it is - usually possible to operate with machines loaded to more than 50 per cent of their rated capacity, and in such conditions the oper- ating expenses per kilowatt hour are approximately uniform at all times. Average values of operating expenses in large stations are .3 cent per kilowatt hour for gas-engine plants, .4 to .5 cent for steam-turbine, and .6 cent for reciprocating-engine plants. 274 ILLUMINATING ENGINEERING It is obvious that since the fixed charges are constant and the operating expenses proportional to the amount of power generated, the cost per kilowatt hour will be least when the station is gen- erating its greatest output. The minimum possible cost would be ' reached if the station could operate continuously at its maximum capacity. In such a case, at 12 per cent fixed charges, an up-to-date steam-turbine plant could generate power at the feeder terminals at approximately .5 cent per kilowatt hour. Unfortunately, how- ever, the maximum load on the usual central station lasts a very short time, the load curve having a sharp peak in the late afternoon and early evening hours. The value of the maximum power output shown by this peak determines the capacity required at the central station. Consequently, at periods of light load, as for instance, during the morning hours, fixed charges must be paid on more generating equipment than are required to handle the load. This variation of the load throughout the day, in its effect on the cost of power, is described in terms of a quantity known as the “load factor,” which is the ratio of the average daily, monthly or yearly load to the maximum loads occurring in the corresponding inter- vals. The daily load factor then is a quantity less than 1, and represents the proportion of the maximum daily power output which may be multiplied by 24 in order to arrive at the total num- ber of kilowatt hours generated through the day. It is therefore highly desirable to increase the average daily load, and so render the load factor as near to the value 1 as possible. The load factor corresponding to lighting service only is very low, and lighting companies make great efforts to develop a day load comprising motors of all kinds, and heating, cooking and other domestic ap- pliances. The daily load factor of a large central station, which supplements its lighting load in every way possible, is about .50; the yearly load factor about .30. At load factor .50 the average total cost of generation in a gas-engine plant is .65 cent, in a steam-turbine plant .7 cent, and in a steam-engine plant about .9 cent per kilowatt hour. ; | (b) Systems of Rates for Sale of Power. In the early days of electric lighting it was customary to charge a consumer simply in terms of the number of lamps installed without reference to the number of hours they were used. This method of charging, known as the flat-rate system, was obviously unfair to the economical user, and meters for reading the total number of kilowatt hours were Oe, a GENERATION AND DISTRIBUTION OF ELECTRICITY 275 developed as a basis for charging. This method alone, however, is obviously not equitable, since it costs the supply company more to supply a consumer during the time of peak load than at other times. Consequently, consumers are often classified on some basis representing the times of the day during which they take their maximum power, and different rates apply to the several classes. Such a classification might separate, for instance, the services to residences, to stores or factories, and to day motors. A further refinement in the methods of charging is found in the so-called two-rate systems, which aim to charge a consumer a higher rate for the power he uses during his peak hours and a lower rate for the remainder. ‘This method evidently aims to charge each con- sumer his proportionate share of the fixed and operating charges, respectively. The obvious difficulty is that of ascertaining the maximum load of each consumer. For residence lighting it is usually assumed that some proportion of the total number of lamps connected will be burned together for a definite number of hours each day. This number of kilowatt hours will then be charged for at the higher rate, and all power in excess at some lower rate. Mazimum-demand meters, which indicate the highest value of power taken during any chosen interval, have also been used as a means of arriving at the value of a consumer’s peak. This, how- ever, constitutes a separate measuring instrument for each con- sumer, and on account of the expense involved the plan has not as yet been widely adopted. The actual price at which power for Cereicen is sold varies widely in different places. In the larger cities the primary rate is rarely less than 10 cents per kilowatt hour, which may be charged, for instance, for all power up to the amount consumed by one-half the connected load if burned for 30 hours. All power in excess of this during the month would then be charged for at a less rate, say 7 or 5 cents per kilowatt hour. One reading per month of a meter indicating kilowatt hours, therefore, serves to fix the amount of the consumer’s bill. . The wide discrepancy between the prices at which power is sold and the cost of its generation have led to frequent agitation by the public of the question of regulating the rates for the sale of power by law. This type of discussion arising as well in connection with other classes of public-service corporations has led to the forma- tion in many states of public-utilities commissions, which have 276 ILLUMINATING ENGINEERING the power to investigate and regulate the conditions of manufac- , ture and sale of the respective public commodities. The figures of cost of generating power which have been given apply at the station bus-bars. The discrepancy alluded to above includes the cost to the supply company of distributing the power to the con- sumers, the cost of meters and their regular inspection, and the general office expenses. While the cost of distribution, which in- cludes the capital charges on all the distributing system, as well as its inspection and maintenance, duct rentals, etc., is usually a much larger figure than at first apparent, the several items men- tioned do not bring the actual cost of delivering the power to the consumer very near to the figure at which it is sold. The remaining difference is not all profit to the company, however, but is in part applied to paying the obligations of early lighting companies, bought up by the present one, and defunct through obsolescence or other cause. It is worth noting that a recent careful investigation by a public-utilities commission of the rates charged by a lighting company in a large city in the middle West resulted in a decision that 14 cents and 8 cents per kilowatt hour were equitable primary and secondary rates. BIBLIOGRAPHY F. Koester: Steam Electric Power Plants. Franklin and Esty: Elements of Electrical Engineering. C. W. Stone: Modern Lighting Systems. Proc. A. I. E. E., June, 1910. Sheldon and Hausmann: Dynamo Electric Machinery. C. P. Steinmetz: General Lectures on Electrical Engineering. H. G. Stott: Cost of Power. Trans. A. I. HE. E., XXVIII, p. 1479, 1909. H. B. Gear: Diversity Factor. Proc. A. I. E. E., Aug., 1910. Reports to National Electric Light Association. H. Foster: Electrical Engineers Pocket-Book. Standard Hand-Book for Electrical Engineers. a a eo VII (1) PRINCIPLES OF MANUFACTURE AND DISTRIBUTION OF GAS, WITH PARTICULAR REFERENCE TO LIGHTING By EK. G. CowpEry CONTENTS Manufacturing. General characteristics of coal gas and water gas. Effect of different constituents on the calorific value and illuminat- ‘Ing power of coal gas. Illuminants, their characteristics. Manufacture of coal gas. Open furnace heating of benches. Regenerative furnace heating of benches. Development in the retort under varying heats and conditions. Brief references to through retorts. Brief reference to vertical retorts. Brief reference to inclined retorts. Brief reference to by-product coke oven process. Purification of coal gas. Tar extraction. Cooling. Ammonia extraction. Sulphur extraction. Carburetted water gas. General statements. As made from fixed carbon, steam and oil. Development. Harris process. Tessie du Motay. Lowe process. Treatment of different oils. Paraffin base oil. Semi-paraffin base oil. Asphalt base oil. Basic claim Lowe patent. Efficiency of Lowe apparatus. Purification of water gas. Carburetted water gas made from oil and steam only. Producer gas. Metering gas at the manufacturing station. Gas holders. 278 ILLUMINATING HNGINEERING Distribution. Low pressure. District holders. Reinforcing pressure mains. High pressure for suburban or long distance distribution. Semi-high pressure or “‘ Booster ” system. Formula for flow of gas through pipes. Low pressure. High pressure. Excessively high pressure. Location of gas works. Station governors. Design of a distribution system. Drainage of mains. Pipe joints. Brief mention: services, gas meters, house piping and photometry. Calorimetry. There are three characteristic ways in which manufactured gas is used, each of which, in its own sphere, results in its extensive employment as an agent for the production of artificial light. When burned without previous mixture with air, it produces a flame of considerable intrinsic brilliancy ; when burned after previous mix- ture with air, it produces a non-luminous flame of high tempera- ture; and, thirdly, the application of its explosive action, when mixed with air and ignited in the cylinders of gas engines, places certain grades of artificial gas among the most economical agents for the production of power. I shall devote myself mainly to a description of the principles involved in the manufacture and distribution of the various gases delivered by the artificial-gas companies of the United States, but attention is purposely called to the use of producer gas for the production of power, as being an important modern means towards conservation of energy, and this phase of the subject will be briefly presented. Kinds of Gases. ‘The gases we will eonlatdee are generally classi- fied as follows: Illuminating gas is divided into two great classes, coal gas and carburetted water gas. Coal gas in turn is divided into two sub-classes, viz., that pro- duced by the distillation of gas coal in comparatively small re- torts, and that produced by the distillation of coking coal in larger ovens. MANUFACTURE AND DISTRIBUTION OF GAS 279 Carburetted water gas, on the other hand, is divided into that made from fixed carbon, steam and oil, and that made from oil and steam only. Producer gas is made by the action of steam or air, or both, upon fixed carbon. General Considerations. [rom this classification it becomes evi- dent that coal gas is produced analytically, distilled from certain kinds of coal, while water gas and producer gas are synthetically made, that is, built up from the action of several constituents upon each other in a manner to be described later. The results in each case do not widely differ, as is illustrated in the table shown as Slide 1. In this connection it is to be under- stood that the analyses shown are representative only, and not abso- lute, under all conditions. Producer gas has been omitted from this nls but will be con- sidered later on. It is to be noted that the use of water gas made from steam and oil, owing to local conditions of supply of the raw materials, is at the present time practically confined to the Pacific slope, where it is extensively used. It is particularly interesting to note how closely this gas compares in composition with coal gas, although produced from very different materials. In this country, generally, and in Europe and Great Britain, carburetted water gas is understood to be the gas produced from coal or coke, steam and hydrocarbon oils, as shown in the third column of the table. TABLE OF GENERAL CHARACTERISTICS OF COAL AND WATER GAS bt + Coal mae made yah Pic ba ae tak = g te . : . 2 > Og His a ES hoods 50 Bb vokes SE ° © ons “tnd 3 mM HH Per cent by volume. Tiltminant?’ i... . 4.75 4.8 12.8 VUE 32236" 2 4.4 0 PNA e Sas ca dv wes 2.8 1764.4 1.0868 38. JE SO eee u0-02 36.0 13.4 34.64 1009. 0.5529 5. PIVOPTOLOY os ite se es 47.04 49.7 38.9 $39.78 326.2 0.0692. 0 Carbon monoxide .. 8.04 4.1 30.9 U.21". s2odn. OS6EE ea Carbon dioxide .... 1.60 13 2.8 2.62 0 EBLgS. eG OC GGEL ik aero ea 0.39 0.7 0.6 0.16 0 1.1052 0 Bitropen iiiilemsds is 2.16 3.4 2.8 6.58 0 0.9701 0 ROLE bets ivr dorsi. 3 100.00 100.0 100.0 100.00 280 ILLUMINATING ENGINEERING Coal gas made Water gas made in rom Retorté. “vans. anciel amen aaa Specifici:sravity cn wee ees 426 ‘Dee .683 482 BU ee Pe ee are one 678. 675. 682. 680. Candlepower: oo eeene Geo eG 15.8 22. - 19.69 Cu. ft. air req’d for combustion one .cubici{oolst eet oe tan 5.65 5.63 5.74 5.81 Note.—The B. t. u. per cubic foot of “ illuminants ” varies consider- ably in different gases. In computing the amount of air required for combustion the illuminants were assumed to have a composite formula of C,H,. In discussing this table it is to be noted that each gas differs from the other only in the relative proportion of the same con- stituents. ‘To indicate this more clearly, it is seen that coal gas contains less illuminants, usually more hydrogen, considerably less carbon monoxide, and less carbon dioxide than water gas. These characteristic features exercise a considerable effect upon the candle-power, calorific value and specific gravity of the gases. For instance, a smaller amount of illuminants means lower candle- power, usually lower heat value and higher specific gravity. More methane means lower candle-power, usually higher calorific value, but it is of lesser specific gravity than the illuminants. An increased quantity of hydrogen means lower candle-power, lower heating value and very much lower specific gravity. Carbon monoxide burns with a blue flame, and in itself has only a relatively low calorific value. Carbon dioxide, being the product of the combustion of carbon, when present in gas, decreases the candle-power and heating value, but increases the specific gravity. These comparisons are general only, and give the result of the effect of any one of these constituent gases, considered from the point of view of such gas only, without consideration of the effect of other constituents at the same time. For instance, it might conceivably happen that an increase in the proportion of methane would be accompanied by such a large decrease in the percentage of carbon dioxide and nitrogen that the candle-power might actu- ally be raised. In other words, it is necessary to look at the com- position of a gas as a whole, in order to arrive at a satisfactory idea of the various enumerated properties. Dr. William B. Davidson, of Birmingham, England, in his re- cent paper entitled, “ Experiments in Carbonization on the Bir- MANUFACTURE AND DISTRIBUTION OF GAS 281 mingham Coal-Test Plant,” read before the British Institution of Gas Engineers in 1910, gives some interesting data on the effect of these various constituents on coal gas. An extract from the same appears as follows: “In this connection it is interesting to consider the effect of each of the main constituents of coal gas on both the illuminating power and the calorific value. On this subject, the information available in technical literature is both incomplete and incorrect, and I have therefore undertaken a series of laboratory experiments with the object of ascertaining the effect on candle-power of ad- mixtures of small quantities of different gaseous constituents. The effect on calorific value is already known. The approximate results are given in the following table, and apply alike to No. 2 and No. 1 argand burners used with full flame. EFFECT OF DIFFERENT CONSTITUENTS ON THE CALORIFIC VALUE AND ILLUMI- NATING PoweErR oF CoAL GAS ON A BASIS OF 540 B. T. VU. AND 16 CANDLES. Calorific Illuminating ; Constituents. Value ower Ratio. Per Cent. Per Cent. OR 8 ) AARe ee Ee — 1.0 — 3.5 1 to 3.5 decrease OPM ee SH. — 1.0 — 3.0 1 to 3.0 e. Ni vis shleaty Stwriotoaba 3 5.1648 — 1.0. — 2.6 1 to 2.6 > PCT OMM er ti. — 1.0 — 2.7 MPA Kn Poo? 9 we OED Age hein Arg ae — 0.4 — 0.5 Latoc1.0 7 18 Ry gs ae, ORG ee — 0.4 — 0.5 tO 120) Increase in calorific value SPUD GATE: Sala sett + 0.9 — 0.6 = twice the decrease in illuminating power. eS EG) SP ear a + 1.9 + 10.9 1 to 6.0 increase ENS NS ee Barer aera + 6.0 + 18.0 L to. 3,0 “5 Celitcads Fite ike ot kh + 10.5 + 125 1 to 12 Nore.—Gas saturated with naphthalene vapor at 60° F. contains only 0.0085 per cent by volume of this constituent. The increase in candle- power, due to this small amount, is only 0.16 or 1 per cent. It should be understood the per cent of illuminating power given is theoretical and true only within narrow limits. ‘ The figures for carbon dioxide, oxygen and nitrogen have been confirmed by experiments with the large test plant. It calls for remark, however, that in short trials the effect of the admission of air was not nearly so drastic as was indicated by laboratory tests. This was doubtless due mainly to the fact that the iron oxide underwent a large rise in temperature and threw off certain 282 ILLUMINATING ENGINEERING hydrocarbons—chiefly benzene—with which the water in the mate- rial had become saturated. In one instance, the admission of 3 per cent of air appeared to effect no reduction at all on the multiple. In experimenting with air it is, therefore, necessary to allow the plant to attain equilibrium before starting the test, and to prolong the trial. It will be observed that the effect of an admixture of 1 per cent | of nitrogen reduces the candle-power by about 2.6 per cent. As it is this ingredient that varies most of all in the composition of coal gas as manufactured in this country, and seeing that the effects of carbon dioxide, oxygen, carbon monoxide and benzene have all nearly the same ratio, it follows from theoretical considerations that 2 per cent reduction of illuminating power for 1 per cent reduction of calorific value the result previously indicated is ap- proximately what we should expect to find.” For purposes of gas-engine use a gas should be able to withstand a relatively high compression without undue loss or premature explosion. Methane withstands high compression without change. However, it may be stated that in general, for illuminating gas, the illuminants, ethane, methane, hydrogen and carbon monoxide are all desirable constituents, because they all add candle-power or heating value, but carbon dioxide, oxygen and nitrogen are un- desirable because of the lack of these properties. Illuminants. The illuminants play a large part in the charac- teristics of candle-power and calorific value of both coal and water gas. Some of the more important of these compounds, with their special characteristics, are given in the following table: TABLE OF ILLUMINANTS Spec. Grav. Dlum. B.T.U, Cu. Ft. Air ; Req. for Sertes Name onan, Cason ss 5 CrH», |Ethylene | C.H, 0.9676 68.5 1588.0 14.355 1 Propylene Cable 1.4514 aes 2347.2 21.533 . Butylene C,H, 1.9353 123. 3099.2 28.710 “ . Amylene CsH4 2.4191 igs 3847.2 35.888 C,H, Acetylene C.H, 0.8984 240. 1476.7 11.963 CyrHen_-. Allylene C,H, 1.3823 eee 2227.1 19.140 if Crotonylene C,H, 1.8661 eae 2975.6 26.318 C,Hon-, Benzene C,H, 2.6953 349. 3807.5 35.888 . Toluene C;H,; 3.1792 mane 4552.0 43.065 re Xylene C,H 3.6630 ah, 5294.2 50.2438 i Mesitylene C,H, 4.1468 stile 6108.0 57.420 CyHon+2 Naphthalene C,,H; 4.4230 980. 5906.8 57.420 283 MANUFACTURE AND DISTRIBUTION OF GAS “*Ya0710H HE.LaW “dalsldne Snivevdd oe wt “SIH dAaMaaNnYuosS “HASNaCGNOD ¥ Sv Ivo) ¥YalsoWHxa “Se acInSs 284 ILLUMINATING ENGINEERING NoTe.—All volumes of gases and vapors are given at 60° F. and 30” pressure. Benzene, being a liquid under ordinary conditions, was tested for candle-power by mixing its vapor with hydrogen, and a slit burner used. Naphthalene, being ordinarily a solid, was similarly mixed with coal gas. —Coal-Gas Manufacture—As Produced in Retorts The art of coal-gas manufacture is over a century old. William Murdoch, in England, between the years 1792 and 1798, was en- gaged in experimenting with different coals, and in devising appa- ratus for their distillation. In 1797-1798 lighting by coal gas was actually accomplished, for Murdoch, by means of his experi- mental plant, first lighted up his dwelling house, and a short time later a much larger building at Birmingham. From these first attempts, coal-gas manufacture has been de- veloped to the present state of the art. Fic. 2.—Simple Retort Setting. Principles of Coal-Gas Manufacture The generation of coal gas from gas coal is a process of destruc- tive distillation. The solid coal is charged into the retort, which in laboratory parlance would be called a muffle, and the retort is heated externally. Figure 2 shows a setting, which, though too primitive for modern use, exemplifies the primary principles. Jt consists of a retort set upon parallel fire-brick piers having openings through them for the passage of the heated products from the furnace, a furnace for heating, an open space around the retort to per- MANUFACTURE AND DISTRIBUTION OF GAS 285 mit its envelopment by the heated products of the fire, and a flue for the escape of the products. The retort of burnt fire-clay, 3 inches thick, cross-section oval, D shape or circular, being open at the front end only, has bolted to that end a cast-iron extension called a mouthpiece, which, projecting from the front wall of the setting, is fitted with a gas-tight door, through which opening the coal is introduced and the coke withdrawn. At the top or side of the mouthpiece is an opening to which is connected a cast-iron pipe rising vertically, the upper end dipping into a seal of water. When ~ the charge of coal is placed into the heated retort distillation im- mediately begins, vapor and gases, air and steam being given off until the pressure is sufficient to overcome the seal in the dip-pipe, when the gas begins to bubble through and continues until car- bonization (by which is meant destructive distillation of the coal) ceases. The door is then opened for the withdrawal of the coke remaining in the retort and reintroduction of fresh coal. As soon as the door is opened there is a return of pressure in the retort to normal atmospheric, the water rises in the dip-pipe thereby preventing gas, from the collecting main from all the retorts, escaping through the open door. The practical extravagance of such a setting is at once apparent. Cold air enters through a shallow fire, burns to carbonic acid and steam, and the heated products pass around the retorts, and while still highly heated escape to the chimney. When the door is open for charging fresh fuel, which is usually hot coke withdrawn from the retorts, and when clinkering the fire, cold air sweeps over the fire directly around the retort, chilling it. Again, the combustion process is the one least suitable for surrounding, with combustible gases, retorts set some distance away, averaging 4 to 5 feet. Hav- ing but a short distance to travel through the fire, the conversion of the oxygen of the air into CO, is almost instantaneous, and the total heat of the chemical combination is confined to the fire, with the result that the fuel becomes heated to a temperature well above the fusing temperature of the ash. This rapidly seals off the fire, reducing the draft through it, and the combustion rate diminishes, cooling the setting, while the retorts are surrounded only by the products of combustion, and, except for the bottoms, immediately over the fire, get only the sensible heat of the products. Water is placed in the ash-pan so that a small quantity of steam rising therefrom may pass through the fire to assist in keeping down the 286 ILLUMINATING ENGINEERING temperature of the fuel bed. This, while necessary to protect the grates, to a certain degree increases the difficulty, since the hydro- gen thus formed burns at once to water at the top of the fire, further localizing the intensity of combustion immediately above the surface of the fire. The result is, that uniform heating of the retorts is difficult and uneconomical. Thirty years ago this style © of setting was in wide-spread use. By having a large mass of fire-tile and small retorts, however, good results, as far as the quality of the gas was concerned, were obtainable. The difference between heating a setting of retorts and a boiler fire, for instance, is readily understood. In the latter case com- bustion must have progressed to near completion before the com- bustible products impinge on the comparatively cold tubes or shell and combustion is arrested. In a setting of retorts, where all parts are kept at a temperature well above the ignition point of the most dilute gaseous combustibles, it is desired that the fuel bed should be kept at a temperature just sufficient to carry on the chemical reaction for the conversion of the atmospheric oxygen into carbon monoxide, and the final combustion of that gas occurs around the retorts situated at a comparatively remote distance above it. Sahene The solution of these difficulties led to the adoption of the re- _ cuperative—sometimes called regenerative—method. Here there is a furnace below an arched chamber containing nine retorts exposed, except where supported, to the envelopment of heated products. This arched chamber and its contents of retorts is called a bench. Continuous arches so filled are called a stack of benches. The heated products of combustion on their way to the stack are led through passages made by thin fire-clay tiles; the primary air in its passage to the ash-pit, and the secondary air in its passage to the nostrils above the fire, pass around these tile flues, absorbing heat that was wasted in the former setting. Again, the fuel bed was deepened so that the oxygen on entering the fire, being first converted into CO,, passes up through more fuel and becomes re- duced to CO. We have now gaseous firing. There will be stored in the fuel bed only the heat developed by the combustion of car- bon to carbonic acid, and there will be abstracted from the fuel bed the heat absorbed by the separation of the hydrogen from oxygen of the steam, the reduction of the carbonic acid to carbon monoxide, and the increase in the sensible heat of the escaping MANUFACTURE AND DISTRIBUTION oF GAS 287 atmospheric nitrogen. The top of the furnace is covered with a heavy covering of fire-tile built with an opening for the passage of the combustible CO diluted with N to the setting above. At this point, the highly heated secondary air combines with the gases from the fire and combustion at high temperature ensues. The fire, meanwhile, being deeper, has an arrangement by which false grate bars can be driven in at clinkering time, some distance above a, aay Wire Saar e 3 © 1 z a ies j N wy; ; P fi} ? Goa 3 | aie ig eter sel 2 9 SOMALI, EEE PAB ELEC ec ee me “isu itis A 3 ee = a Mee Oe one 3. G4 e ae yy Vee Ie ae | neo , con _fhre center. Bench of Nine Retorts, with Full Depth Recuperators. Fig. 3. the fixed grates, holding up the fire while the clinker is being removed from between the false and fixed bars. There is also an arrangement by which small streams of water drip through the bottom of the fire, reducing the temperature further. This method with care, gives satisfactory results, and is in extended use to-day. A further improvement in conditions is now obtained by returning a small quantity of the products of combustion through the fire, diluting the oxygen of the air and prolonging the period of combustion until all the retorts are bathed in flame. 288 ILLUMINATING ENGINEERING Modern practice requires careful attention to bench heating. The per cent of combustible in the stack gases, the quantity of primary and secondary air are accurately read by meter and pro- portioned, and the heats of the combustion chamber and through- out the setting are noted at frequent intervals, with the result that uniform heats in the retorts at from 1700° F. to 1900° F. are maintained with an expenditure of fuel per ton of coal carbonized much less than formerly obtained. A retort, when discharged of its coke, should show a uniformly heated interior surface through- out—bright red in color. The angle at which the retorts are inclined to the horizon is a question of much importance. But before we have sufficient data to take up a discussion of this question, we must look into what goes on inside the retort. After a century of close study, it may be said, with regret, that not all of the details of the chemical reaction attending the con- version of coal into gas by the retort process are known at this time. The process is considered as occupying three stages: In the first one, a quantity (about 350 pounds) of cold, damp coal is charged into a retort 9 feet long and approximately 14 inches by 26 inches in cross-section; then there is a rapid cooling taking place on the inner surface of the retort. There is an ab- sorption of heat by the coal, due to the high thermal head existent, and the heat rendered latent by the immediate evaporation of the water and the more volatile vapors in the coal. We know that the distillation begins on that portion of the coal in contact with the sides of the retort. | When coal is‘ heated in a closed vessel at a heat of about 660° to 700° F., fusion of the coal commences and hydrocarbon vapors begin to come off. If these vapors were condensed, they would be found to be mainly paraffins and olefins. The second stage ensues in which these hydrocarbons, meeting with the higher temperatures, begin to be affected. It is believed that there is a rearrangement and loosening of the C-H and the C-C bonds, and other compounds are formed. In the third stage the heat of the interior of the retort rises still higher, the reactions, almost instantaneous in many instances, are most complex, and so far have resisted entire elucidation. The aliphatic hydrocarbons, that is, the open-chain series, paraffins and olefins, as found in gas coal and petroleum, are, on the one hand, loosening their MANUFACTURE AND DISTRIBUTION oF GAS 289 carbon bonds and splitting off the initial or simplest members of their series, while the residues unite into more complex closed- chain or aromatic compounds, such as benzene, toluene, xylene, ete. These benzol compounds, under the influence of heat, in time are decomposed with the liberation of hydrogen, carbon and the formation of still higher ring compounds. On the other hand, the free hydrogen present reacts on the aliphatic hydrocarbons. In the meanwhile, the oxygen and the nitrogen in the coal are forming other combinations, some of the nitrogen going into am- monia and some of the oxygen uniting to form phenols. A West Virginia coal would have a hydrocarbon component that is expressed as approximately C,,,H,,,O;o. This third stage is the one which does most to determine the candle-power and heating value of the gas obtained. The retort is filled to about 40 per cent of its volume with coal. After the water and first vapors are driven off, the coal continues to fuse and the evolution of gas becomes more rapid, and, passing above the coal, is exposed to the highly heated sides and top of the retort. The hydrocarbons and other vapors pass off in gradually decreas- ing proportion during the distillation period of the charge, which we are now considering as being of about 4 hours’ duration, and as the volume becomes less the energy expended on them dimin- ishes and the retort gradually increases in temperature toward the end of the period, at which time, the temperature being higher, the flow of gas slower, the effect ge Naas upon the gas is con- stantly changing. I have so far asked your attention to the consideration of that form of modern retort setting in which the charge of coal is dis- tilled in the shortest time, generally 4 hours. This design, being only a mechanical improvement upon the century-old chemical distillation of coal—an improvement looking toward economy in heating the bench and procuring more “even” heats, except so far as those bettered conditions could—did nothing to improve the chemical reactions. The distillation of coal is still conducted under very different conditions at the beginning than at the end of the period, and the gas emanating from the coal in the back of the retort is exposed to different heating conditions than that in the front. Avoiding a too technical and voluminous discussion of these changes, it will still be well for me to make a simple statement 290 ILLUMINATING ENGINEERING of the most important changes occurring in this third stage of how vapors of the paraffin and olefin series, which are those coming from the second stage, are affected by the temperatures of the retort. It is doubly important to the gas engineer, because the same reactions occur in a water-gas apparatus or in an oil-gas plant, where paraffin base oils are subject to the “ cracking-up ” process. It constitutes one of the chief sources of interest and study of the gas engineer, and a better knowledge is sure to be rewarded by more economical operation of a gas plant, a better profit and improved product. The higher members of the paraffin series and olefin series break down even at temperatures below their boiling points, under normal pressure, to lower hydrocarbons of the same series, and the paraffins to some extent are converted into the olefin series. Under con- tinued exposure to these high temperatures, the lower paraffins and olefins are converted into members of the benzene series with de- posits of free carbon; if the heat still continues there is a produc- tion of acetylene, followed at once by a breaking down into marsh gas and a large deposit of free carbon. Benzene (C,H,), the lowest member of the benzene series, at ordinary temperatures exists as a vapor. It has a high illuminating value, and, in water gas made from some oils, contributes largely to the illuminating power, though not so much to its heating value. It is clear that the “ cracking-up ” process cannot go beyond the benzene-forming period without disastrous effect on the value of the gas, and it is true, further, that the formation of the benzenes are a loss in candle-power value over what would have occurred if the olefin gases, such as ethylene, had not been broken up. In other words, if we could convert the paraffins and olefins all into members of the olefin series, gaseous at ordinary temperatures, the highest efficiency would be realized, but in the rush of gas through the retort all the reactions are taking place at once. While some of the heavy paraffins and olefins are breaking down into lighter members of the same series others are being converted into benzols, while some of the benzols are going into hydrogen and free carbon. We must, therefore, use a heat which will crack up all the heavy paraffins and olefins, remove the gas before the final general breaking down occurs, and expect some losses in the process. The difficulties that the coal-gas engineer has to meet are now MANUFACTURE AND DISTRIBUTION OF GAS ag evident. He must maintain a heat in his retorts that will secure the proper “cracking up” of the heavier rush of gas in the first hour, and he must expect, in the form of retort under discussion, that there will be, toward the end of the carbonization period, too great an exposure to the heat of the smaller volume of gas, break- ing down into free carbon and methane—a non-illuminating gas. Other designs of retort settings suggest themselves as better than the one we have so far discussed. Instead of withdrawing the coke from the same door through which the coal was charged, retorts are used in many installations which open at both ends. The coal is charged into the retort until it is nearly full, and the coke is eal RODS LPI TE: (am UQAKRAANN SOONER NOVA RSE oes Liddbdabdddde aE og q Fig. 4.—Retorts. pushed out through the other end, the operation of pushing the coke out and recharging the retort being done by machinery in one motion. By this means the gas from the coal flows through the retort more rapidly; by reason of the smaller area existing between the coal and the top and sides of the retort, the temperature of the retort is reduced and a longer time is given for the carbonization period. There is still, however, direct exposure of the gas to the radiant heat from some portions of the retort. ; Another development is in the vertical retort. Here the coal is charged into the top and the coke taken from the bottom of a vertical retort, which usually tapers to somewhat larger at the bot- tom. Here the coal is fused, filling the retort; there is no appre- ciable amount of space between the coal and the sides of the retort for the gas to be highly heated, and the gases must flow, in a large 292 ILLUMINATING ENGINEERING part at least, up through the central unfused core of the coal itself, thereby escaping the difficulty under discussion. That there is less breaking down into free carbon, marsh gas and hydrogen in the vertical-retort process than in the horizontal is apparent by the smaller percentage of free carbon extracted from the gas by the tar in the after processes. ‘The coal is raised to a greater altitude than in the horizontal retort, and when charged into the mouth at the top, which by machinery can be done with little labor, falls of its own weight out of the bottom as coke. Vertical retorts are ) G Pa OSLLILELO LT DONO IIL ES // jae = = ZZ IIIT IIT III | we Fig. 5.—Vertical Retorts. in wide use in Europe, having superseded inclined retorts, which do not appear to suit the theoretical conditions as well as the verticals. The coke oven is another attempt at the solution of the problem of getting uniform, moderate heat throughout the body of the coal and throughout the carbonization period. It is, in effect, a large “ double-end ” horizontal retort in which large quantities (6 to 8, sometimes 10 tons) of coal are exposed to carefully graduated but moderate heats for from 20 to 36 hours. What effect upon the cracking up of hydrocarbons, of tempera- ture versus heat has, can hardly be discussed by me now. What is the relative effect of long-continued exposure to moderate tempera- ture, to quick exposure to high temperatures? Some of our leading MANUFACTURE AND DISTRIBUTION OF GAS 293 developers of the chemistry of gas manufacture, notably the veteran Young, probably the most original, as he was the pioneer in this field, maintain that radiant heat has a very different effect on “ cracking ” than conducted or convected heat. CAST /ROW BOX Fig. 7.—Sketch of Purifier. Purification of Coal Gas The principal impurities in coal gas, which must be extracted before the gas is fit for commercial use, are tar, ammonia, sulphur and sometimes cyanogen. In connection with purification the sub- ject of condensation will be treated. The fundamental principle of condensation is to reduce the gas, during its passage through the works to a proper temperature, so that in its distribution through the gas mains to the consumers’ 294 ILLUMINATING ENGINEERING appliances no vapors will condense out of it. In other words, after proper condensation at the works, the gas is, generally speaking, in a permanent fixed form for the ordinary conditions of dis- tribution. The principles employed in condensing coal gas are as follows: First, gradual reduction in temperature down to about 110° F. Above this point, as much of the tar as collects in the hydraulic main and foul mains is allowed to pass off into the tar well. If coal gas at or below 110° F. is allowed to remain in contact with je Fic. 8. coal-tar a great amount of the heavy hydrocarbons in the gas are absorbed by it. By draining the tar off at proper points in the process, the benzol and other heavy vapors are retained in the gas. Some tar is always carried with the gas through the various works pipes, and serves to absorb excess naphthalene vapors. After the primary condensation down to about 110° F., a further extraction of tar takes place. . This is accomplished in various ways, such as hot washing, or scrubbing, by centrifugal force, or mechan- ically, as in a P. & A. tar extractor, where the particles of tar are projected by high velocity against metal suntare? where they are deposited and run off. : MANUFACTURE AND DISTRIBUTION OF GAS 295 The condensation principle of gradually cooling the gas is im- portant, as this prevents the sudden shocks to the gas, with at- tendant losses of valuable hydrocarbon vapors. Certain hydro- carbon vapors possess the property of apparently carrying other hydrocarbon vapors in a so-called state of suspension, up to the saturation point, which varies with the temperature. Naphthalene, Coal Gas. The subject of condensation would be incomplete without brief reference to naphthalene. Its formation is believed to be principally due to the latter-day high heats of an Vertical Atmosphere Condanser: » Vertical:Muleitubular Condenser Longitudinal Mugitubular Condenser Condensers iras.o: carbonization, and where it occurs in quantities it becomes ex- ceedingly troublesome. Recently, washing the gas with certain oils has proved very successful. In mixed coal- and water-gas- plants naphthalene is very readily handled, owing to the fact that the rich hydrocarbons in water gas absorb and carry it along. The mechanical principle employed in condensers is simply the transmission of the heat, either sensible or that freed by reason of the latent heat of condensation of vapors, through steel, usually tubes, to air or water which are used as the mediums for absorption. 296 ILLUMINATING ENGINEERING Ammonia is extracted from coal gas by the well-known principle of the power of water to absorb it. The mechanical methods of doing this are by so-called washing and scrubbing. In the earlier stages of the process it is advisable to wash or scrub the gas with crude ammoniacal liquor, which assists in removing tar, CO,, H.S and CS, from the gas. The crude liquor also extracts ammonia. Of course, the fina] traces of ammonia are eliminated by the use of fresh water. Sulphur exists in crude gas as H,S, and also organic compounds, the latter being largely CS,. Washing or scrubbing the gas with AS MoniachE LIQUOR Fie. 10.—Water-Cooked Condenser. crude ammoniacal liquor extracts a portion of these compounds, which form various chemical combinations with NH,. A recent system of treating the gas, called the Feld system, eliminates usu- ally by far the greater portion of H,S, also some organic sulphur is removed in the purifiers. In the United States iron oxide is used in the usual system of pur- ification. The H,S in the gas combines with the iron oxide to form iron sulphide. The “fouled” material, by exposure to air, revivi- fies, the oxygen of the air combining with the iron sulphide to form iron oxide, leaving the sulphur in the material in the free state. MANUFACTURE AND DISTRIBUTION OF GAS 297 The free sulphur probably does extract a certain amount of CS, from the gas, as CS, dissolves sulphur. In England the hydrated form of quicklime is employed. ‘This process removes CS, as well as H,S, but is not much used in this country on account of the expense. Carburetted Water Gas as Made from Fixed Carbon, Steam and Ou It is not the intention to present for your consideration mere history, but a brief reference to the development of carburetted water gas may not be out of place, and will probably assist in the clearer understanding of the principles underlying this process. vy e@ ) \J ) Y \. at A NN [\ \\ ch 5 A-S- 3-93. Fie. 11.—Plate No. 2—Rotary Scrubber. | The fundamental chemical principles underlying the process of making this gas from fixed carbon, steam and oil are compara- tively simple. In the first place, there is a bed of fuel, brought up to high temperature, which we may call incandescent carbon for the purposes of this lecture. Steam is admitted and passed through this fuel, and, as is well known, decomposes into its elements hydro- gen and oxygen in the presence of incandescent carbon. To give you an idea of such reactions, and the approximate minimum tem- peratures at which such decomposition takes place, whether in the presence of incandescent carbon or not, the following table is shown: ~H,O<>H+0. Min. temp. about 1000° Cent.—1200° Cent. H,O+C=CO+H. Min. temp. about 600° Cent. | From this you will note the comparatively low temperature re- quired to decompose H,O in the presence of incandescent carbon. 298 ILLUMINATING ENGINEERING The result of this reaction, which takes place in a fire-brick-lined vessel called a generator, is the formation of so-called blue or uncarburetted water gas, which consists principally of carbon mon- oxide and hydrogen, and burns with a blue practically non-lumi- nous flame, and has a calorific value of about 320 B.t. u. per cubic foot. | This blue gas then passes into a fire-brick-lined vessel filled with a checker-work of fire-brick, which has been heated to incandes- cence. A spray of hydrocarbon oil is admitted above this checker- brick, is vaporized and gasified by the heat, and mixes with the blue gas previously described. The oil furnishes the illuminants necessary for candle-power, and from the analysis submitted in the early part of this lecture, it will be seen that a good calorific value is also obtained. The candle-power and calorific value depend very largely upon the relative quantities of blue gas and the gas re- sulting from the decomposition of the oil. The mixture of blue and oil gas is subsequently subjected to a so-called “ fixing” process, by being passed through an additional amount of heated checker-brick, the effect of which is merely to render the various hydrocarbon gases more permanent under ordi- nary temperatures, probably by the reason of the decomposition or partial decomposition of some of the richer hydrocarbons into the simpler and more stable forms. Development of Water Gas The production of water gas has been attempted in three ways: First. In the earlier forms it was attempted to produce water gas by contact of steam with heated coal or coke contained in a retort externally heated, as is illustrated by the Harris patent. DESCRIPTION OF THE HARRIS PATENT A bench of three clay retorts, shown in Figure 1, was used. Re- tort A, or the decomposing retort, was provided with a perforated tile (Fig. 3). The retort was filled above the tile with anthracite coal broken to the size of an egg. Retorts B and C were filled with rich cannel coal. Figure 2 shows a cross-section of the decomposing retort. Figure 4 il- lustrates the steam drier which was placed near the base of the furnace. Figure 5 represents the steam superheater. | Steam supplied from a boiler heated by the waste gases from the bench was first passed through superheater E into retort A, 299 MANUFACTURE AND DISTRIBUTION OF GaAs LHOL3Y DSNISOcWOORG 40d “Qa UL asivyodysad « ‘OL “DIA a YSLVAHHAdNS Wv3aLSs ‘SSgg0ud Siu v H “Sy” LYOLad SNISOdWOOSG HDNOYHI NolLoas "Se Ola MSNHO Walls ey ALS 11 9 300 ILLUMINATING ENGINEERING passing through the distributing tile D into the highly heated anthracite coal. Leaving this retort the gas was conducted to the rear end of either of the lower retorts, B and C, through pipes H, and from this retort through stand-pipes K to the hydraulic main. The gas from the decomposing retort was supplied to one bitumi- nous retort until the rich hydrocarbon vapors of the charge in this retort were exhausted. | This retort was then closed off by means of cock 3 and the gases from retort A were then passed to the other, ete. Retorts B and C were charged at intervals of about 2 hours. These attempts were unsuccessful, but your attention is directed to them to illustrate the basic principles. Various patent appli- cations, from time to time, show the recurrence of this idea in different men’s minds. The reason of the failure of this process is because the chemical reaction of steam upon the fixed carbon of the incandescent coal or coke is an endothermic one, in other words, one which absorbs energy in the form of heat, and requires much more heat to maintain it, and more intimate association of the steam and coai or coke than can be obtained in this way. Second. 'The next step in the process is embodied in the ideas formulated by Tessie du Motay. In general, this process consists | in making blue-water gas intermittently in a generator and storing same in a_ holder. The apparatus consists of generator A, gas-relief holder, bench of retorts with furnace C, retorts D, hydraulic main E, and naphtha vaporizer B. The generator is filled with anthracite coal or coke, through which steam is passed, after this bed of fuel has been brought to incandescence; the resulting gas being a blue-water gas, largely CO and hydrogen, this gas being passed along to the relief holder for storage. ‘The bench of retorts having been brought to the proper heat for vaporizing, the oil gas is admitted to the front end of retorts at point “ H,” and at the same point naphtha vapor is admitted, the naphtha having been vaporized in vaporizer “ B” by means of steam coils or otherwise; the naphtha vapor and blue- water gas are each regulated at this point, “ H,” to produce the proper candle-power of gas, and passing through the retorts “ D,” coming in contact with the heated surface is sufficiently heated to be largely converted into a fixed gas, passing off at the opposite end of the retorts to the hydraulic main, afterwards treated in a 301 MANUFACTURE AND DISTRIBUTION OF GAS ‘eT: : ZId¥OdVA~ ‘SNivuvddYV “WHIdYN AVLO aya | Ne ‘SSQTIOH saASINAY Noe ses al “al 201s 302 ILLUMINATING ENGINEERING similar manner to other gases. In operating, the generator was first brought up to heat by blowing sufficient air through a bed of fuel to raise this bed of fuel to a high temperature. When the fuel was hot enough, the blast was cut off, a valve closed and steam admitted, which, on passing through the fuel, resulted in the pro- duction of blue-water gas. The endothermic action of decomposi- tion of steam in the fuel bed resulted in a rapid cooling of the fire. When the fire temperature became so low that the steam was no longer readily decomposed, the admission of the steam was dis- continued, and the blast turned on again, as before, and the cycle of operations repeated. In the meantime hydrocarbon oils were being vaporized in a sepa- rate apparatus, and these vapors, mixed with the blue-water gas, were passed through an apparatus externally heated, wherein the gas was “ fixed” or rendered permanent. The limitations of this system of gas manufacture were that the oils which could be vaporized were the refined fractions of crude oil, called naphtha, and as these oils rapidly advanced in price the limit of economical operation on a commercial scale was soon passed. The Lowe Process Third. ‘The Lowe process. This method, or modification of it, is the one in use to-day. ‘To describe its essential principles it is advisable to insert a short description of the apparatus used. A Lowe water-gas set, or its equivalent, consists of— First. A generator, or vessel built of an iron shell with a fire- brick lining, and containing a deep bed of fuel. Second. A carbureter, or vessel consisting of an iron shell lined with fire-brick, and filled with a checker-work of fire-brick. This vessel has an open chamber at the top into which the oil is sprayed. Third. A superheater, or vessel built and checkered similar to a carbureter. To explain the operation of such a set we will first assume it cold, but with a coke or anthracite fire started in the generator. By means of a blower an air blast is turned under this fire, and the carbon in the fuel bed burns partly to CO,, partly to CO. The CO,, on passing through the incandescent fuel bed, is practically wholly _ decomposed to CO, the amount depending on blast velocity, tem- perature, etc. MANUFACTURE AND DISTRIBUTION oF GAS 303 When the producer gas (for such it is) reaches the top of the generator above the fire it consists principally of N, CO and a small percentage of CO,. By means of a large fire-brick-lined connection this producer gas is conducted to the top of the carbureter. Here an additional blast opening introduces fresh air, and a portion or all of the CO in the producer gas burns to CO, in the carbureter. The resulting mixture passes out of the carbureter, and into the bottom of the superheater, where still another blast admits enough air to burn the remaining CO to CO,, in case it is desired to heat the superheater higher, but if not, no further air is admitted here. The final waste gases then pass out of the stack valve at the top of the superheater and escape into the atmosphere, or are first passed through some apparatus to abstract as much of the remain- ing sensible heat as possible. This process of blasting or blowing is continued until the entire fuel bed is highly incandescent, the checker-work in the carbureter at a high heat, and at a reduced temperature in the superheater. ‘T’he set is then ready to make gas. The blast is first shut off from all of the vessels, and the stack valve on the superheater closed, live steam is then turned into the generator below the fire. The resulting reactions are very instruc- tive. The H,O vapor is first decomposed by the incandescent car- bon to hydrogen and oxygen. This reaction is endothermic, that is, . heat is absorbed in doing this work. The hydrogen passes through the fire unchanged. The oxygen, on the other hand, immediately combines with car- bon to form CO and CO,, and every pound of carbon thus burning to CO, gives off about 14,544 B. t. u., the reaction being exothermic. The CO passes on through the fire, but the CO,, in the presence of the incandescent carbon, decomposes to CO, the reaction being endothermic. The gas appearing on the top of the fire, then, is a mixture of hydrogen and carbon monoxide, in practically equal proportions, together with a small percentage of CO, and some impurities. This mixture is the so-called blue or uncarburetted water gas, and © is merely one form of producer gas, having a calorific value of about 320 B. t. u. It will be noticed that the reactions in the generator are mostly endothermic, and, in fact, the fire is cooled very rapidly during the admission of steam, a run being generally from 5 to 10 minutes, at the end of which it is necessary to blast again. 304 ILLUMINATING ENGINEERING Coming back to the blue-water gas, so-called because it burns with a blue flame in air, we find upon leaving the top of the gen- erator that it passes into the top of the carbureter. Here it meets with a spray of oil. This is sometimes the crude oil, but more often a gas distillate, which is the fraction obtained from crude oil after distilling off the gasolines and kerosenes, and stopping before the heavier lubricating oils appear. This oil, coming into the top chamber of the carbureter, vapor- izes under the intense heat and, mixing with the blue gas, starts through the carbureter. The lower portion of the carbureter and the superheater are merely heated checker-work for rendering the gases permanent under ordinary conditions, or “ fixing” it, as it is called in operative parlance. Crude petroleum consists of a mixture of a great number of definite hydrocarbons, that is, hydrocarbons that may be designated by exact chemical formulae, but which are so almost inextricably mixed in the oil that the separation of any one of the hydrocarbons in considerable quantities requires repeated distillations under fa- vorable conditions and chemical treatment. | Crude oils are designated as paraffin base, semi-paraffin base and asphalt base, according to the general character and composition of the oil. Paraffin-base oil, as I have stated in discussing coal-gas manu- facture, is one made up almost entirely of members of the paraffin and olefin series. Paraffins from simple CH, methane to penta- tricontane C,,H,, have been isolated; methane CH,, the simplest member existing as a gas; pentatricontane (C,,H,.), as a solid, melting at 76° F. This oil is found in the northern oil districts, such as Pennsylvania and Ohio. Sem1i-paraffin-base oil contains, in addition to paraffins and ole- fins, naphthenes (C,H.,). These compounds have the same chem- ical formulae as the olefins, but have markedly different character- istics. ‘The explanation for this is in the way that the C and H atoms are united, differing in the two series, the carbon particles in the olefins existing as a simple chain, whereas the naphthene car- bon atoms are considered as being grouped as a closed ring. This class of oil is found in southern districts, like Louisiana and ~ Oklahoma. Asphalt- or naphthalene-base oils are made up largely of naph- thene and olefins, paraffins being almost entirely absent. Examples MANUFACTURE AND DISTRIBUTION OF GAS 305 of this kind are found in Texas and California. The naphthene series are much more stable than the paraffin; they do not yield paraffins or olefins in cracking under heat, but pass at once into members of the benzene series, such as benzene, toluene, xylene and higher members. These benzenes exist in the gas only as vapors, and are subject to the laws of vapors regarding saturation and precipitation; consequently, gas made from naphthene oils must be very carefully handled in the processes subsequent to generation to secure to the consumer equal candle-power at all seasons of the year. Tor additional information on the treatment of this gas I would refer you to a paper presented to the American Gas Insti- tute by W. H. Gartley in 1907. The results of gasifying the oil show that the various hydro- carbons evolved depend, as to nature and relative quantities, on time, temperature, relative quantities of oil injected, and amount of heat available from the fire-brick. The richer illuminants pre- dominate, of course, and this rich oil gas, mixing with the blue water gas, results in carburetted water gas, and which has a high candle-power and calorific value. By varying the relative quan- tities of blue gas and oil gas, and the heats, time of run, etc., the candle-power and heating value may be made high or low, as de- sired. The maximum and minimum limits would be about as follows: With no blue gas and all oil gas, the candle-power would be about 85, and the calorific value about 1300 B.t.u., or, with all blue gas, and no oil gas whatever, the candle-power would be practically zero, and the calorific value about 320B.t.u. Any intermediate condition could be attained, but in practice it is found that a gas exceeding 26 to 30 candle-power, burns with a smoky flame in ordinary burners, under usual conditions, and, further- more, the tendency of the present time seems to be towards a standard gas of an average of about 600 B.t.u. calorific value. When a water-gas set has been making gas for a certain number of minutes it becomes too cool for economical operation. ‘The oil is then shut off, next the steam, and then the stack valve is opened. Thereupon the blast is turned under the fire and the whole cycle of operations is repeated. On account of the steam striking the under side of the fire and cooling it too rapidly, it is now customary to make a so-called “down run” every third or fourth time. This simply means that the direction of flow of the steam through the fire is reversed, now 306 ILLUMINATING ENGINEERING passing downwards instead of up, the connections on the machines being so arranged as to permit of this being done. As often as the fire requires it, fresh coke or coal is put into the generator, the ashes and clinkers being taken out at the bottom. From the description given of the principles involved in the Lowe process it will be seen that it is essentially an intermittent one. In the first place the deep fuel bed is brought up to a high temperature in the most economical way, namely, by internal com- bustion in the generator, and in this way differs from the early processes first mentioned. Secondly, it differs from the second type, or that promulgated by Tessie du Motay, in making use of the heat from the generator gases to vaporize and fix the oil. These differences may be seen from the basic claim of the Lowe patents, which, in brief, are as follows: Basic Claim Lowe Patent The apparatus consists of the primary gas generator A, super- heater D, heat-restoring stack I, boiler R, the usual washer V, and scrubber Y. The gas generator A is filled with anthracite or bituminous coal, air is forced by a blower through the heat-restoring stack I and pipe L into generator A below the grate bars, having been pre- heated in passing through stack I. The products of combustion are conducted from the top of generator A through pipe F, through the superheater, which is filled with loose fire-brick above the arch, to the atmosphere through stack I, Valves E’ and H having previously been opened. The heat from the out-going gas is partially transferred to the air from the blower, which is forced around the stack tubes into pipe L. After the fuel in the generator is thoroughly incandescent and the superheater is heated, the air is cut off and the valves E and H are closed. Steam is now admitted into the top of the superheater through K’ from boiler R. The steam in passing through superheater becomes intensely hot, and is admitted to the generator below the grate bars through pipe H’. The steam in passing through the heated carbon is de- composed, liberating hydrogen and producing a proportionate quan- tity of CO,. The CO, in passing through the heated carbon is, for 307 MANUFACTURE AND DISTRIBUTION OF GAS “SN WL ADWuOlLs WoO Tee ‘c]-] “HAIWaHHadnNs ane BONY unas “MSaLVSHSBYd iSV1E #7? MHOVLS "HBHSUM “A ~ VdaNa SS300u "HS 108 AVBH a2LSWM ET. Meieore? i d 340] o1SvG ’ “HS Q10H ‘pl aans 308 ILLUMINATING ENGINEERING the most part, changed to CO, and the gas at the top of the fuel bed is H, CO and a small part of CO,. At the same time steam is admitted to the superheater, petroleum or other hydrocarbon oils are introduced in regulated quantities from tank M on to the top of the hot coals in the generator, where it is volatilized and mixes thoroughly with the gas coming through the fuel bed. These gases are then fixed by the heat before leaving the generator from which they pass to the top of the boiler R through numerous tubes, transferring some of their sensible heat to the water. All of the steam used for the gas-making process is furnished by this boiler, and the heat of the gas is the only energy used for generating the steam. Passing through the boiler the gas enters the washer V, thence through the scrubber Y into the purifiers, and finally into the holder A’. It should be stated that this apparatus never worked satisfac- torily for the reason that the oil gas was not subjected to suffi- cient heat to fix it into a permanent gas. Mr. Lowe later changed his method, although conforming to the original patent, and sub- stituted in place of the superheater for drying and superheating the steam, a superheater filled with checker-brick properly heated by internal combustion in the superheater of the producer gases formed in the generator at the time of blasting up the heats. When making gas the blue water gas from the generator, with the oil vapors generated at the top of the generator, pass through the superheater for the purpose of fixing the oil vapors; this principle being the same as that employed in all water-gas-making appa- ratus up to the present time. Returning for a moment to the original table giving composition of gases, it may be stated that the illuminants methane and ethane, result from gasifying the oil, while the carbon monoxide and hydro- gen result from the action of steam upon the incandescent fixed carbon in the generator fuel. The balance of the constituents re- sult from both sources, but to a varying extent. The subject of the efficiency of a Lowe water-gas set as a heat machine may be stated practically about 60 per cent. The subject is too lengthy to be discussed here, but anyone interested is referred to a paper by Mr. A. G. Glasgow, Proceedings American Gas Light Association, 1890, or to an abstract thereof which appears in the “ Mechanical Engineers’ Pocket-Book,” by William Kent, under the general subject of illuminating gas. 309 MANUFACTURE AND DISTRIBUTION or Gas SOMA “GT “SIA y. 310 ILLUMINATING ENGINEERING In general, we may use the following average figures to illustrate the efficiency of a Lowe water-gas set, all per thousand cubic feet gas made reduced to 60° F.: Pounds anthracite: generator fuelic. 12) eee 30 Pounds 01] admittedto* carbureter: =: {oyneen 32 Pounds steam used during run............... 30 Pounds resulting gas produced............... 46 This serves to introduce the principles of water-gas manufacture, and we will now discuss the subject of treatment of this gas after leaving the generating apparatus. Purification of Water Gas Coming to the subject of impurities, we find that tar and sulphur are the predominating ones that must be abstracted. Before treat- ing these, however, it is to be remarked that water gas is to be condensed, in a measure, similar to coal gas. Water gas, however, in modern practice, is not reduced to as low a temperature in the works as is coal gas. The principle of water-gas condensation, however, is the same as for coal gas. The heat to be abstracted consists of the sensible. heat plus the latent heat of vaporization of the various gases and vapors which compose the gas. This results in deposition of some of the heavier hydrocarbons, forming the so-called water-gas tar. In modern practice water gas is seldom condensed below 90° F., because its purification is most economical at this or somewhat higher temperatures, and also because more of the richer illumi- nants remain in the gas at the higher temperatures. A large amount of condensation takes place in the relief holder. Naphthalene is easily avoidable in water-gas practice by proper regulation of the heats. Tar is extracted from water gas by condensation, washing and scrubbing, and also by mechanical means, such as a P. & A tar extractor. With the oily water-gas tar, however, the P. & A. must be operated, between rather narrow limits of temperature, say be- tween 105° and 110° F., and under great differential pressure. Usually, after all the washing and scrubbing, there remains a mist of light tarry vapors which are exceedingly difficult to ex- tract. This is perhaps best accomplished by means of shaving scrubbers, in which light wood shavings simply absorb the mist as the gas slowly passes. MANUFACTURE AND DISTRIBUTION OF Gas 311 Sulphur exists again as H,S and organic sulphur, and is usually removed by means of iron oxide as described under coal gas. In coal gas the purification is usually carried on under lower tempera- tures than in water gas, because in coal gas the gas is previously reduced to a low enough temperature to permit the extraction of the ammonia. Carburetted Water Gas as Made from Oil and Steam Only Lowe Oil Gas. There is time here only for a brief mention of carburetted water gas as made from oil and steam only. This process is more largely used on the Pacific slope on account of the low cost of oil and the high cost of coal and coke. Jones Ore Gas Set The development of this oil-gas process is due to the efforts of Mr. Lowe, as well as largely to Mr. E. C. Jones, Chief Engineer of The San Francisco Gas & Electric Company. The principles underlying the manufacture of gas by this method are unique in a way. No standard type of apparatus has been de- veloped, but there are various forms of one-shell and two-shell types in use on the Pacific coast to-day. These shells are of iron, lined with fire-brick and checkered with fire-brick. ‘To heat up the set oil is introduced, or sprayed in with a steam spray, and burns by means of an air blast, the products of combustion passing off through a stack valve in the usual manner. 312 ILLUMINATING ENGINEERING When the set is up to heat the air blast is cut off, and the oil and steam admitted alone. An accurate adjustment of the quantity of oil to the heat is necessary for best results. | The oil gasifies under the heat of the fire-brick, and the steam is partially decomposed into its elements. Some of the heavier illuminants are decomposed, and considerable free carbon or lamp- black results. The gas produced, as will be seen from the early tables, resembles coal gas very much in its analysis. The impurities to be removed from this oil-gas process are lamp- black, tar and sulphur. The lamp-black removal, handling and treatment is a problem in itself, but it is removed from the gas by washing with copious quantities of water, and by scrubbing, and is subsequently fired under the boiler.in a wet state, or it can be used as generator fuel in an ordinary water-gas set. The tar and sulphur are removed in the customary ways. Oil gas, as made above, is treated much like ordinary water gas, except it is never passed through condensers, but is subjected to much washing and scrubbing. ‘This process of treatment at once appeals to anyone as being logical, on account of the large quantities of lamp-black made during its generation. Under conditions of best practice to-day, this process of gas manufacture requires about a total of 7 to 8 gallons of oil per 1000 cubic feet made, and there is every likelihood that this quan- tity will be materially reduced. From general figures it would seem that only about 2 gallons of oil should be necessary to supply the required amount of heat, and if we figure an average of 41% gal- lons for making the gas, it would seem as though from 6 to 61% gallons will ultimately be all that is required for this process. Re- cent results indicate that these figures may be attained. Producer: Gas Producer Gas. Producer gas is usually made by one or both processes already explained under coal- and water-gas manufacture. In some forms it consists of CO and N, produced by air being blown through a bed of incandescent fuel, the resultant gas having a calorific value of about 120 to 130 B.t.u. per cubic foot. If, in addition to air, we add steam, the resultant gas will contain H, CO and N. If steam alone is used the gas will consist of H and CO, and will have a heating value of about 320 B. t. u. Gas, as an agent for the production of light and heat, must not be understood to be restricted to artificial gas, as before outlined, MANUFACTURE AND DISTRIBUTION oF Gas AL but many other forms besides these mentioned are used, such as retorted oil gas, blast-furnace gas, acetylene, gasolene air gas, resin gas, wood gas, hydrogen-methane gas, garbage gas, ete. Producer gas is only mentioned at this time on account of its adaptation to gas-engine practice. STATION MeTER Drum. pres GW Metering Gas at Works—The Station Meter Station Meter. ‘The gas after passing through the purifiers is ready to sell, except that the amount made must be determined in order to keep the several parts of the works under control. This 314 ILLUMINATING ENGINEERING measuring is usually done by means of a large four-compartment drum which revolves in a cast-iron case filled about two-thirds full of water. The inlets and outlets of the drum compartments are so ar- ranged that when the outlet is below water the inlet is above, and the compartment fills with gas. The drum revolves something like a squirrel cage, and shortly after the inlet dips below the water the outlet comes above and the compartment discharges its contained gas. The cubical contents of the compartments being accurately known, the motion of the drum is communicated by gearing to the dial, and thus we have an apparatus which accurately measures the gas made. It is customary to make proper corrections for tem- perature and barometric pressure, and in practice we reduce the gas manufactured to a basis of ‘60° F., and 30 inches barometric height. On account of the large size of station meters various forms of proportional meters have been tried. ‘These measure only a small fraction, usually 1 per cent, of the make, and are also arranged to register the total, but so far there is really no reliable proportional meter on the market for measuring artificial gases. Recently various other methods of measuring gas have been tried. Drums have been made of the rectangular screw-thread type, rotary meters have been introduced, and the most recent is the electric gas meter. The time is too limited to attempt to explain these in detail. Gas Holders Gas holders are simply inverted cups placed in water, and so arranged that the gas enters or leaves the holder above the water through pipes arranged for the purpose. They act as storage reservoirs for gas, and thus allow the plants to manufacture uni- formly during the 24 hours, taking care of constantly varying con- sumption. ‘The only principles involved are as given, and the great questions involved in connection with gas holders, outside of their design and construction, are “ How much gas-holder ca- pacity is required as related to the maximum manufacturing ca- pacity?” and “ Where shall these holders be located—at the gas works or in other localities? ” The latter question is largely a matter of distribution methods, and the former the question of the minimum permissible holder MANUFACTURE AND DISTRIBUTION OF Gas 315 capacity any plant may have and be safe. This is a very important engineering and commercial detail. Istribution In the distribution we have a vast subject, and one in which many problems remain to be solved. Formerly gas was sent out from the works at not to exceed the maximum pressure thrown by the works holders. In such systems the delivery obtainable from a given size and length of pipe was iw aw. al aA iD eae LOD vara ar arate aaa aa J RID LI PIPL A SSC SSS Vici ece, ouTeer ~SECTION~ Fic. 18. that due to the differential head or pressure between the lowest permissible pressure at the extreme end of the pipe, say 2 inches water column, and the maximum holder pressure, which rarely ex- ceeded 5 or 6 inches. Thus the actuating pressure, or differential head, was very little, possibly less than one-tenth of 1 pound per square inch. Subsequently, as cities spread out, gas holders were erected in’ outlying localities and called district holders, and these supplied the district surrounding them, as before, by low pressure. ‘These district holders were filled with gas through separate pumping mains from the works. In the course of time these systems were found to be inadequate, and if re-enforced under the low-pressure ideas would have entailed 12 316 ILLUMINATING ENGINEERING vast construction expenditures to remedy conditions sufficiently to produce good service. To overcome bad distribution systems, especially in the larger cities, the next step in the progress of distribution methods was to erect pumping plants at the works and holders, run separate pres- sure re-enforcing pipe lines to the heavy points of consumption, and there install some device to automatically reduce the pressure to the required regular distribution pressure. In some cases pres- sure-indicating instruments were located at such points of heavy consumption, and no regulators used, the pressure and amount of gas pumped being controlled at the works and holders so that a given pressure was maintained at this point where the indicator was located. The instruments transmitted the amount of pressure back to the pumping plant, or a small separate-pressure tell-tale line was used. ‘These systems used various pumping pressure, usually not over 5 pounds per square inch. — | In the meantime still another development was taking place. Communities were growing and spreading out in all directions, and especially around the larger cities where suburban communities were being formed at some distance from the cities, and in which the houses were far apart. It was not possible to profitably supply such places with gas with the great investment required in low- pressure mains under the old system, so high pressure was devel- oped to meet this requirement. Pressures up to 50, 60 and even 80 pounds per square inch are now being used, as compared to the old system of low pressure, with a maximum of about 14 pound. Such high pressure requires reduction to say 4 or 6 inches water column before entering the piping in the consumer’s building, and this is accomplished by automatic gas regulators, a number of different types of which are now on the market. Reasons for High Pressure. In the meantime other forces were at work tending to hasten the advent of high pressure. The uses to which gas was applicable were increasing in number, it was also used more freely in hghting, heating and power work, and this resulted finally in very much larger sales of gas per capita per annum than prevailed formerly. Add to this the fact that the price of gas was gradually being reduced and another stimulus » is seen. ‘Thus vast quantities of gas were being consumed as com- pared to former years. MANUFACTURE AND DISTRIBUTION OF GAS 317 The principles underlying the development of high pressure then resolve themselves into the fact that it was necessary to provide for vastly increased demand, and also that the distances through which it was necessary to supply gas in large quantities were greatly augmented. This development was not rapid in the early days of the gas business, and, in fact, it may be said to have developed with the advent of fuel gas, the possibilities of which have only been realized within the most recent years. In fact, it may be said that the application of high pressure to artificial gas is a development of the last decade. Higher pressure permits of small pipes to transmit large quan- tities of gas. The reasons for this are that the differential head is very much greater than under low pressure, and also a given mass of gas occupies a much smaller space when compressed. The flow of gas, or any liquid through pipes, is governed by the differential head or effective driving pressure, the length of the pipes, its diameter, the condition of its interior surface, whether the line is straight or full of turns, the density of the traversing gas or fluid, and the questions of pulsations, obstructions, etc. Formulae for Pipe Conductivity. Various formulae have been devised to determine the flow of gas in pipes, but the one com- monly used for low pressure is Dr. Pole’s formula. Qae ,/th Q=quantity of gas in cubic feet per hour at atmospheric pressure. e=a factor, which may vary from 1000 to 1400, but a fair average value for which is:1250. This factor is inserted for the purpose of allowing for condition of the interior pipe sur- face, obstructions, such as tar, etc. d=diameter of pipe in inches. h=differential head, or pressure, in inches of water. s=specific gravity of gas, air being 1. l=length of pipe in yards. From this formula it appears that the capacity of a pipe to trans- mit gas under low-pressure conditions, among other factors, varies as the square root of the fifth power of the diameter. As a result of this it may be stated that when a pipe is doubled in diameter its capacity under low pressure is multiplied about 5.6 times. 318 ILLUMINATING ENGINEERING For High Pressure. The following formula covers the range of high-pressure artificial gas: Q=33.3 jf Pera) Ls Q=quantity of gas in cubic feet per hour at atmospheric pressure. d=diameter of pipe in inches. p, absolute initial pressure in pounds per square inch. p.=absolute terminal pressure in pounds per square inch. L=length of pipe in miles. s=specific gravity of gas, air being 1. For Very High-Pressure and Long Pipe Lines. ‘The formula for ordinary high-pressure work, previously given for use with artificial gas, is found to give results that are too small when applied to a higher range of pressure and long pipe lines. In particular, for natural-gas work, where pipe lines many miles in length are in use, it is found in practice that more satisfactory results are se- cured from the following formula: 2 2 Q=42a / Ps =p," iv Q=quantity of gas in cubic feet per hour at atmospheric pressure. a=a factor, which in practice is found to vary with the diameter of the pipe, and for which fairly satisfactory amounts have been determined. For instance, a=95 for a 6-inch pipe, 556 for a 12-inch, etc. See Ohio Geological Survey report. p, absolute initial pressure in pounds per square inch. p.=absolute terminal pressure in pounds per square inch. L=length of pipe in miles. This last formula is based upon a gas of 0.6 specific gravity. Where the gravity of the gas varies the quantity found is multi- plied by the square root of 0.6 divided by the gravity determined. Temperature corrections are usually neglected in natural-gas measurement. Elevation. In the olden days the question of elevation was pertinent. Gas, being lighter than air, in a confined pipe tends to exercise greater pressure at higher elevation, as compared to the atmosphere, because it weighs less than the equivalent column of air under the condition of being exposed to atmospheric pres- sure at the initial low point, as, for instance, through a gas holder. MANUFACTURE AND DISTRIBUTION OF GAS 319 When gas was distributed entirely under low pressures some points of a given city lying much below the level of the works received insufficient pressure, and other points, much above the works, re- ceived excessive pressure. Recently, however, where high pressure is used, the question of elevation causes no concern because of its comparatively slight ef- Fic. 19.—Station Governor. fect under such conditions. Under low-pressure conditions, and. with gas of about six-tenths specific gravity, the difference in pres- sure due to 100 feet elevation is about six-tenths inches water column. Station Governor. A station governor is an apparatus which automatically maintains a given outlet pressure, which must be less than the inlet pressure. This is simply produced by the effect 320 ILLUMINATING ENGINEERING of the outlet pressure on a float or a diaphragm. Some governors have been devised which increase or decrease the pressure auto- matically according to the demand. Principles of Design of a Distribution System We will first consider the principles underlying the design of a low-pressure distribution system. Under this kind of a system we are limited to the maximum pressure allowable on consumers near the plant or holders, and by the minimum pressure allowable on the outlying consumers. For purposes of illustration, assume this maximum and minimum to be 6 and 2 inches, respectively. Then the maximum differential head is 3.8 inches, allowing 0.2 inches drop in services. Next, having a complete map of the city, it is necessary to deter- mine the maximum demand per unit of area, which for purposes of illustration we may assume as 1 square mile, and having selected the center of each square mile, we proceed to run low-pressure feeders from the works, in several directions if necessary, and large enough to furnish all the gas required at peak load to each unit of area reached by such main, and under the limitations of pres- sure assumed. If we determine that the loss of pressure from the center of each unit of area, to the outside limits thereof at peak load, shall not exceed 1 inch, then the maximum drop in pres- sure in the feeders from the holder outlets must not exceed 2.8 inches to come within our assumed limits. On the basis of this assumption we are thereupon obliged to design the distribution system in each unit of area so that at peak load the maximum drop in pressure from the center, or point of supply from the feeder mains, to the farthest outlying point in each area shall not exceed 1 inch at peak load to come within our required assumed conditions. To do all this requires the knowledge of maximum demand per consumer, the probable maximum number of consumers per block and per unit of area, the length of blocks, and certain other prac- tical considerations, such as presence of electric surface-car line tracks, ete. Naturally, smaller and simpler systems for smaller cities are easier to design, but the principle of maximum permissible drop in pressure is the same. ie MANUFACTURE AND DISTRIBUTION OF Gas 321 Design for High Pressure. When we come to consider high- pressure systems the same general principles hold true. We may run high-pressure feeders to the centers of the units of area, or we may design them to carry only moderate pressure, say up to 5, 6 or 8 pounds per square inch. If such a system is adopted, it becomes necessary to install pressure-reducing devices at the points where the high-pressure feeders deliver gas into the low- pressure system. Such devices are called district regulators. == Fic. 20.—Section of Manhole on 5-lb. High-Pressure Line. Another entirely different system is to carry moderate or high pressure on the entire system of mains. In such cases it is neces- sary to install pressure-reducing devices on each pipe entering each and every consumer’s premises to reduce the main-pipe pressure, whatever it may be, to the pressure required by the consumer. Such devices are called individual gas-pressure regulators or gov- ernors. The advantage of the use of high pressure lies in the fact that much smaller distributing pipes can be used, thus saving great investment charges. The cost of compressing gas is generally a small item. 322 ILLUMINATING ENGINEERING Drainage of Mains. Artificial gas, as it leaves the works, always contains water vapor and various hydrocarbon vapors, which con- dense out of it as it passes through the distributing pipes, owing to changes of temperature and other causes. These vapors con- dense and liquefy, forming the so-called drip water. For this reason it is necessary to lay artificial gas pipes on a slight grade, and at the low points devices for collecting this drip water are installed so that it may be pumped out. Fig. 21.—High-Pressure Main, Service Meter and Drip Installation. A. %” saddle with 5/16” main top L. 1’ ell. (galvanized). M. 1’ vent from safety seal (end B. %” corporation cock with 14” protected with No. 16 wire opening. gauge). C. 3,” street tee (galvanized). N. 3%” ell. D. %” street ell (galvanized). O. Reducing ell. E. 3%,” curb cock with full gas P. Reducing ell. way. Q. 1” ell. F. %” street ell (galvanized). R. To riser. G. 34” tee (galvanized). S. Mercury seal (see schedule). H. 34” meter cock with 5/16” gas T. 1” x 3@” tee. way. U. %” long screw. J. High-pressure governor (see V. %” ell. schedule). W. %” vent from regulator. K. Cross. xX. 1” ell: MANUFACTURE AND DISTRIBUTION OF GAS Bo Materials and Joints. For low-pressure distribution, and in the larger cities it is customary to use cast-iron for the main pipes on account of its long life, resistance to corrosion and to electrolytic action. ‘The joints are almost universally of the bell and spigot type, in cast-iron mains, and the jointing material is either lead or cement, caulked or placed into the joint against an inside roll of jute packing to prevent it from entering the pipes. Such joints are not conceded to be safe at high pressure, and when wrought-iron pipe is used screw or threaded joints are used. On account of the mechanical strength of cast-iron, it is to-day the general practice to use but little pipe smaller than 4-inch cast- iron pipe for gas distribution, so that under that size wrought pipe is employed. Under 6-inch pipe the wrought is usually cheaper in first cost than cast-iron pipe. Pipes are usually much stronger than required to merely resist the internal pressure. External con- ditions, such as pressure of soil, loads, settlement, corrosion, etc., are the factors which determine the minimum permissible thickness of pipes. Special types of pipes and joints have at various times been brought forth, such as Universal, vitrified clay, and even wood has been used, but to a very small extent. Gas mains are usually laid deep enough to be under the frost line, and are kept away from car tracks and underground obstruc- structions as much as possible. Services, or the pipes leading from the mains to the consumers’ premises wherever possible, are graded into the mains. Electric surface-car lines have proved a bug-bear to underground piping systems on account of electrical current leakage setting up an electrolytic action. A portion of the return current from such car-line systems finds its way into the piping and leaves it again usually at some point near the generating or substations, or where it jumps to some other conductor. The troubles occur where the current leaves the pipes. Various remedies have been suggested and tried, such as double. systems of piping, one on each side of the car tracks, also various forms of insulated pipe covering and joints, also bonding the pipes to the rails or to the return conductors. All, so far, have proven to be more or less in the nature of palliatives and not complete remedies. The subject of electrolysis is one of great importance. As I have used more than the time allotted me, I shall not take 324. ILLUMINATING ENGINEERING up the subject of the gas meter, the instrument employed for measuring the amount of gas used by the consumer, or house piping or photometry, as I understand some of the subsequent lectures will incorporate about all there is to be said upon these subjects. I would like to say a few words regarding calorimetry. Owing to the fact that by far the greater proportion of gas sold to-day is sold as a heating agent, either through fuel appliances or through mantle burners, it seems necessary to change our system of meas- uring quality to one that will define the calorific value. This may Fig. 22. be determined in two ways, first, from the chemical analysis gas, as the heating value of its constituents are pretty well known. There has been, however, adopted for quite general use an instru- ment whose essential principle of operation is, that the products of combustion of a gas shall be passed through a vessel which is water-jacketed, and in which the radiated heat from the flame and the sensible heat from these products of combustion are absorbed by water in the jacket. The quantities of gas and water being known, the rise in temperature furnishes a measure of the amount of heat liberated by the combustion of that amount of gas. VII (2) THE MANUFACTURE AND DISTRIBUTION OF ARTI- FICIAL GAS, WITH SPECIAL REFERENCE TO LIGHTING By Water R. AppicKs Introduction The subject of this lecture, ‘“‘' The Manufacture and Distribution of Artificial Gas, with special reference to Lighting”, is so com- prehensive that it is difficult to outline the field without shghting essential features of the gas business covered by the assigned subject. The following sub-divisions are made to facilitate reference. (A) Quality of Artificial Gas. (B) Purity of Artificial Gas. (C) Uses of Artificial Gas. (D) Kinds of Artificial Gas (including Natural Gas for com- parison ). (E) How Artificial Gas is manufactured. (F) The handling, within the gas plant, of raw materials, of by- products, and of the finished product, Artificial Gas. The Retort Coal Gas Process described for illustration, with some reference to an auxiliary carburetted water gas plant useful for enriching coal gas, for utilizing the coke by-product of the Retort Coal Gas Plant, and caring for variation in the daily demand for gas. (G) Distribution of gas from Storage Holder at Plant through transfer mains to the City Distribution Holder. (H) Distribution of gas ‘from Distribution Holder through Street Main System to the gas service pipes leading to the houses. (I) Distribution of the gas from the Street Mains through gas service pipes, house service pipes, meters and governors to appli-- ances for utilizing the gas. (IK) Observations relating to the piping of modern buildings and its relation to other utilities in use. (L) Observations relating to the appliances used in burning gas. (M) Influences that govern, in the selection of a particular type of gas, in a given geographic location. (N) The future of the Artificial Gas business. 326 ILLUMINATING ENGINEERING A. Quality of Artificial Gas Gas should no longer be manufactured with special reference to lighting alone; it must still be designated by its candle power, where State laws, special and general, define quality as the candle power given by a specified quantity of gas burned through a flat flame or argand burner. The same quantity of gas burned by means of a bunsen burner as a heating flame in contact with the Welsbach mantle will give four times the light. It is quite common, in describing an artificial gas, to say that it is a 16, 18, or 20 candle power gas, meaning that when a specified quantity of gas is burned in a specified burner that it will give 16, 18, or 20 units of light when compared with the original unit of light, the candle. B. Purity of Artificial Gas It is required in many States that manufactured gas shall be free from sulphuretted hydrogen, and contain but limited quan- tities of ammonia and fixed sulphur. Such laws are quite unnec- essary for the reason that the extending use of electricity will com- pel commercial purity in gas. C. Uses of Artificial Gas Artificial gas is used for :— (la) Lighting by means of the flat flame or argand burner. (1b) Lighting by means of heat generated by the gas when burned in a Bunsen burner to a blue flame and making incandes- cent the fabric of the gas mantle. (2) Heating through the use of the Bunsen flame in gas ranges for cooking, in a multitude of industrial appliances increasing day by day, and in steam boilers. (3) Power by means of the internal combustion engine, made familiar to all by the introduction of the automobile. D. Kinds of Artificial Gas (Including Natural Gas for comparison ) Artificial Gases are known as:— (1) Water Gas, an odorless gas, containing Hydrogen and Car- bonic Oxide, giving a non-luminous flame when ignited; is no longer distributed. It must not be confused with (2) Carburetted Water Gas which is a mixture of water gas and oil gas having a distinct and pungent gas odor, and when burned gives a brillant white flame. MANUFACTURE AND DISTRIBUTION OF GAS Bat (3) Retort Coal Gas, a gas of lower specific gravity and less brilliant flame than Carburetted Water Gas. (4) Coke Oven Gas, similar in all respects to Retort Coal Gas; only 35% to 50% of the gas made is distributed, the portion distributed is usually of equal candle power to Retort Coal Gas. The remainder of the gas is burned under the ovens in place of coke. (5) Oil Gas, a heavy petroleum gas which when burned in prop- erly constructed burners gives a bright light. The California Oil Gas distributed on a large scale in California is a type of this gas. The familiar Pintsch Gas used in railroad passenger cars is a type of this gas: Blau Gas is another. Carburetted Water Gas contains from twenty-five to forty per cent of oil gas. (6) Acetylene Gas gives a brilliant white light when properly burned. It is prepared as required by adding water to calcium carbide: the lamps of automobiles are a familiar example of its use. In country districts, hamlets, villages and small towns are supplied from a central plant with this gas. (7) Carburetted Air Gas. This gas is the familiar type used in country houses and hotels; it is simply air saturated with vapors of gasolene. (8) Producer Gas contains Nitrogen and about 25 per cent com- bustible gases; when cold usually requires heating to make it ignite; is seldom distributed beyond the boundaries of a manu- facturing establishment. (9) Natural Gas, one coming from the earth usually in a dis- trict where petroleum oil is also present, and frequently under pressure of many atmospheres; it is usually sold at much less cost than artificial gas so long as the natural gas supply remains available. H. How Artificial Gas is Manufactured (1) Water Gas, sometimes called blue gas, is made by raising the temperature of a fuel bed, by means of a forced blast of air, to incandescence (the Producer Gas made usually being wasted), when, the air being shut off, steam (H,O) is passed through the fuel bed (C,), which, on decomposing yields Hydrogen and Carbonic Oxide (CO), the Carbon being supplied by the fuel. Usually hard fuel is used, either anthracite coal or coke, though bituminous coal has been used. The fuel bed is usually contained in a cylindrical shaped fire brick furnace (Fig. 1 illustrates a twin generator) which in turn is surrounded by a gas pressure tight cylindrical steel rivetted 328 ILLUMINATING ENGINEERING shell, supplied with gas tight stack valve, coaling and cleaning doors aud proper air, steam and gas connections governed by valves, all manipulated by the gas maker. ‘The cylinder containing this fuel bed is commonly called a Generator; when single it is eight to twelve feet in outside diameter and twelve to twenty feet in height. Water gas is colorless, odorless, specific gravity .550, yields on analysis (Stillman) CO, 0.14, O, 0.13, illuminants 0.0, CH, 7.65, CO 37.97, H, 49.32, N, 4.79; on burning yields only a blue, non- luminous flame and 385 B.t.u. per cubic foot. CARBURETER ji | bn tf Re. ; 8 | tok ha Ze gt ies SOY. q RIDEER 5, a 3) f f it si ¢ rs dF Hl ~€. cat rt ‘, and Ab A Aa - DOUBLE CENERATOR Fie. 1. (2) Carburetted Water Gas: The water gas constituent of this gas 1s made in an identical manner as above outlined for water gas. The oil gas constituent may be made by heating oil in ex- ternally heated retorts, but is now usually made as follows: (2) The cylinder described for making water gas is connected with sim- ilar cylinders in duplicate or triplicate, though the diameter may be slightly varied and the height is frequently increased by fifty per cent. The additional cylinders are not used for containing - fuel but are filled with many hundreds of standard fire brick placed in checker work fashion thus providing interstices between bricks for the passage of gases. The checker-brick work is raised to in- 329 AS a MANUFACTURE AND DISTRIBUTION oF G SER SEPT Dean CONDEM Serugger Sureavneater TMG 503: Ate (eb oe 330 ILLUMINATING ENGINEERING candescent heat by burning up the Producer Gas (wasted in the manufacture of water gas) made from the fuel bed of the Water Gas generator when it is being brought to incandescence by a blast of air preparatory to making water gas; all additional air required for this secondary combustion comes from the same source as for the first. When two additional cylinders are used the second is called the carbureter, because petroleum is dropped on the hot bricks in this cylinder and on vaporizing gives light-giving proper- ties to the water or blue gas flowing over hot from the Generator, Fic. 4. while the third cylinder, usually taller than the carbureter, is called the Superheater or Fixing Chamber; the function of the hot fire brick in this cylinder being the further heating of the water gas-oil gas mixture and the “ fixing ” of the oil vapor prod- ucts into fixed gas. This term fixed gas is used in a limited sense to include only usual atmospheric temperatures and pressures. (3) Carburetted Water Gas has the familiar pungent “ gas” odor; it has a specific gravity of about .660, contains normally as sold, no sulphuretted hydrogen, no ammonia and but seven grains of sulphur compounds in 100 cubic feet. It yields on analysis approximately 331 MANUFACTURE AND DISTRIBUTION OF GAS > Y ATT NAN NAAN J ty) ASI bt | Ny Now Y \ 2a , t wan Kigae AN \Y \ R2aRneny SSS NW 2 ¥ eed ZZ ZA ZZ NN Y WN ST ann onnd safes Nena Lie ea eee eta HH HHH HH a gm e SLLALLTLP., BLLLLSSLAS ASP OPP ISTLAPIIPIDIILOIDD SD PPP LLLP SPSL Y\ o Retorts on Throug . 1 Transverse Sect AY MUI = WW \\y \ Sees AN CEOOWWWUWONOOW 22 IW EE SSSR SADT EAN \ “saa ry aay \ SY oo a an a INQ NAY ANT WW RY NAN ANN KY VOY AE \ AANY WoW Ay NN Yes iW N NAS ---- NAS... NW RAN EEA A WW ae \ \\ — Ny AN \\ NY, q LLLLZ 1 Section Through Retorts. Longitudina Fic. 5.—Bench of Gas Retorts. 13 B32 ILLUMINATING ENGINEERING (Mass. State Inspector 1897) CO, 2.91, O, 0, Lluminants 14.92, Marsh Gas 25.90, CO 25.30, H, 27.87, N, 3.04. ‘Ten thousand cubic feet of gas would require in its manufacture about 400 lbs. of fuel (where waste heat boilers are not placed after the car- bureters) and 446 gallons of oil; the gas produced would be about 25 candle power and as a by-product may yield from 14 to 9/10 gallons of water gas tar. (3) Retort Coal Gas is made by distilling at about 2200°-2600° Fahrenheit as much as 1000 lbs. of bituminous gas coal in a (4) clay retort having a “D” cross section typically 16 inches by 26 inches and 9 feet to 20 feet long, either vertically, inclined or hori- zontally placed. The dimensions as well as the position may vary and the weight of charge is graduated to the retort capacity; i- variably the retorts are externally heated, (5) usually in groups of six to nine, by a single furnace but when retorts are 20 feet long, usually by two furnaces. Furnaces are usually fired without forced blast: The coke fuel is obtained hot from one of the group of retorts at the end of the distillation period, which varies from four to nine hours. About 10,000 cubic feet of gas of 16 to 18 c. p. is obtained from one gross ton of coal and there remains as by- products of manufacture, about 1000 lbs. of coke, about 12 gallons of tar, and ammonia sufficient to produce 20 to 22 pounds of sul- phate of ammonia. Retort Coal Gas in all essentials has the odor of carburetted water gas, though the manufacturer may dis- tinguish in the odor; it has a specific gravity of .400 to .450, and as distributed contains no sulphuretted hydrogen, though often 12 or more grains of sulphur compounds, 0.3 grains of ammonia, and on analysis yields approximately CO, 1.75, O, 0, Iluminants 4.88, Marsh Gas 33.90, CO 6.82, H, 46.15, N, may at times be found as high as 6.50 though 1.5% may be considered a fairer per- . centage. The heat units approximate 600. (4) (6) Coke Oven Coal Gas is manufactured by charging several tons of bituminous gas coal in the top of an elongated “D” oven 26” wide, 72” deep, and 30 feet long, and distilling it normally at a lower temperature than in the case of Retort Coal Gas but for periods varying from 24 hours to 36 hours. The heat for distillation is obtained by burning the poorer quality of -gas which comes off after the first 10 to 12 hours and, after removing the ammonia and tar, is supplied to the exterior of the coke oven through pipes at low pressures; air for combustion is in some sys- tems heated in regenerators by the waste combustion gases from the MANUFACTURE AND DISTRIBUTION OF GAS 320 ovens and is supphed to the ovens under moderate fan pressures 01 by the natural draft of tall stacks. This process is really not a gas making process but a coke making process, 1n which gas is but a by- product. 314 gross tons of coal produces 5200 lbs. of Coke similar to Bee Hive Coke and as by-products, 10,000 cubic feet of gas Un y oe ce a | Al N 6). MNGi Ses HE uah nant Wr BY NESS Wg 4 a INS Z LW Yes KZ, yoy, oS La oO VG DS \ Iw NTN 2K KCK GY AY \: eats NY VF \: NX (ee \V J or | NS NG SEG \V; eRhanZ N | N Ve 5nG y d SIRES, Longitudinal Sections. HERD © o 0 Ob tf Lt Jk Teakzic LA LA NS WTA OOS “Wiis “a ‘ZZ ee SSSI SS ST SAR MSS ’ | : Y n Aa Ata Wr Gree SIDELELILEETLOLELEEEEETEEEEE EE —e — So cee SS Shhh bbb Dh hha Daas | | Section Through Regenerator. Elevation. Transverse Sections. Fic. 6.-—Early Type of Otto-Hoffman By-Product Coke-Oven. of 17 to 19 candle power, 30 gallons of tar, and ammonia suffi- cient to manufacture 73 lbs. of sulphate of ammonia. The by- product gas available for distribution has a specific gravity and heat unit value quite similar to retort oven coal gas and yields on analysis approximately CO, 0.1, O, 0.1, Illuminants 5.55, Marsh Gas 38.90, CO 6.57 (may reach 8.00) H, 42.1, N, 6.65, and when made with 334 ILLUMINATING ENGINEERING sulphurous coals, contains as impurities, after purification with lime for carbonic acid, feul lime for fixed sulphur compounds and oxide of iron for sulphuretted hydrogen, normally 18 or more grains of sulphur compounds and 0.2 grains of ammonia. (5) Ow Gas may be made in iron retorts of similar pattern to the clay retorts used in Retort Coal Gas but they are smaller in cross section and usually not exceeding 9 feet in length: latterly clay retorts have been used. The external heating is effected by means of the best available fuel. As in Carburetted Water Gas the usual by-product is tar. Oil Gas burned in a special burner has a candle power of 60 to 100, specific gravity about that of air, and heat units of 1200 or over. (7) In California (see paper by K. C. Jones, American Gas Institute 1909, p. 410) Oil Gas is manu- factured on a large scale and by the use of specially designed appa- ratus, in which oil is used for fuel to heat up checker brick work in chambers quite similar to the carbureter and superheater of the carburetted water gas apparatus, as well as to make the gas. The character of the oil gas here made is distinct from oil gas made in retorts and for a comprehensive description the student is re- ferred to the able paper above referred to. The only residual, lamp black, is used in place of coal to manufacture water gas . which is mixed with the oil gas. The low labor charge per thousand cubic feet made is an argument for the use of this type of gas ' where crude oil is very cheap. The analysis of the distributed gas is given as CO, 3.63, Illuminants 9.70, O, 0.34, CO 10.24, H, 36.54, CH, 33.16, N, 6.39, Candle Power 21.88, B. t. u. 710.7 and specific gravity .523. (6) Acetylene is made by adding water to Calcium Carbide (which has previously been made in the Willson (8) or similar Electric Furnace from lime and coke). When burned in special burners the resulting gas gives an intensely brilliant white lght of about 250 candle power, has a specific gravity of .910 and a heat unit value of 756 B. t. u. (7) Carburetted Air Gas (9) is made by forcing air through a carbureter in such a manner that it will pick up 10 to 17 per cent of gasolene vapor. It must be burned in special argand or mantle burners. Its heat unit value has been given as 815 B. t. u. (8) Producer Gas is made in the Generator in the fuel heating period of Water Gas and Carburetted Water Gas manufacture. (10) It is likewise made by exhausting air or air and steam through any incandescent bed of fuel, or by means of a jet of steam below 330 MANUFACTURE AND DISTRIBUTION OF GAS O:x. Gas Ser. Jones” eerie Sy Seino RIN Fig. +s. ILLUMINATING ENGINEERING 306 Fia. 9. At DORON SI ONT LL RE: tt tee AER eee OTE TAA Ca ta EEE oss (alien eelaciap nimnonemsdaapacasatien pili AE lata sens ee Fiag. 10. MANUFACTURE AND DISTRIBUTION OF Gas Aro ae the ash pit injecting air and steam vapor through the fuel bed. This gas has a specific gravity of about .812 and heat units of 135-165 B.t.u.. Containing about 75% N, for maximum efficiency it should always be burned in its hot state as it emerges from the generator, as in the case of Carburetted Water Gas manufacture. (9) Natural Gas has a specific gravity of .520 and heat units 1124. mraivers-CO. 0.0, 0, 1.3, Illuminants 0.5, CH, 95.2, CO 1.0, H, 2.0, N, 0.0. It issues from the earth in some localities at a pressure of from 300 to 400 lbs. per square inch. Its high heat units and low price per thousand cubic feet make it, for any purpose, a com- petitor that artificial gas cannot compete with on equal terms. Natural Gas is here mentioned to accentuate this fact and to give a fairly complete view of the commercial field occupied by gas. F. Handling, Etc., Within the Gas Plant The only raw material required to manufacture simple coal gas by the Retort Process (or the Coke Oven Process) is a coking bituminous gas coal. In general, a first-class bituminous gas coal should contain at least 36% volatile matter, no more than 34 of one per cent of sulphur, and should be received in the condition that a 34” mesh screen at the mines would leave the larger portion of the run of mine coal. Natural conditions, handling, and cost of such a coal largely modify these general specifications. Gas Coal to-day is mined (lla) by Electric Mining Machines, is transported (11b) by pit wagons to the mine coal tipples (11c) and dumped (11d) into hoppers with screens, and if a gas plant is favorably located cars loaded (11le) with screened coal at the mines may be run into the Gas Works coal storage shed, or even into the retort houses and there unloaded into the retort house coal bins. In other cases coal cars may go to tide water and the coal be discharged into (12) large capacity ocean going steamers that will deliver the coal alongside the gas plant wharf several hundred miles distant, or the coal cars may be carried hundreds of miles and then discharge into harbor lighters of about 1000 or more. tons capacity which deliver the coal to gas plants five to forty miles distant. In the latter case the coal contained in the rail- road cars from the mines may be dumped bodily or through chutes into the lighters without any hand labor. (13a-13b.) The Astoria (14a) coal gas plant will serve as an illustration of retort coal gas manufacture: On arrival at this gas plant (14b) automatic grab O vA — cc — eS Z end ie) a = o Z = H a Z = = D | = — Fic. 11b. 339 MANUFACTURE AND DISTRIBUTION OF GAS Fic. 11d. 340 ILLUMINATING ENGINEERING buckets picking up two gross tons of coal at a trip deliver the coal, through the instrumentality of an electrically driven traveling crane, to either 50 ton railroad cars, that may be sent direct to the retort houses, or to temporary coal storage pile at a rate as great as 250 tons per hour per crane. An electrically driven storage bridge 600 feet long (15) with a 7 gross ton automatic bucket transfers at the rate of 300 tons per hour, the coal from the temporary storage to the storage yard, or the unloading crane first mentioned may reclaim the coal from the temporary storage and place it in 50 ton cars for its journey to the Fig. ile. retort house. The storage bridge at appropriate times transfers coal in storage to the same 50 ton cars, or when conveniently and hap- pily located, may deliver the coal directly to the track hoppers in front of the retort house. Ordinarily a 40 ton steam locomotive places two 50 ton cars con- taining different grades of coal side by side on two parallel sur- face railroad tracks at one end of the retort house; beneath the tracks is a hopper into which the cars are unloaded simultaneously at varying speeds. Usually one car contains a very sulphurous while the other contains a less sulphurous coal, and thus a uniform mix- ture of coals is obtained. The track hopper contains a chain scraper conveyor which moves the coal at the rate of 125 gross tons per hour ae MANUFACTURE AND DISTRIBUTION OF GAS 341 AA Wand V7 Nae PRR M, Fig. 12. Fig. 13a. 342 ILLUMINATING ENGINEERING up an inclined plane dropping it at the end into coal crushers, which discharge the coal uniformly crushed into vertical elevators which | raise the coal to the roof of the retort house where the coal falls on to longitudinal conveyors, which in turn distribute the coal into longitudinal coal bins in the inclined retort house, and, with the aid of cross conveyors store it in large bins convenient for charging machines in the case of the horizontal retort house. In the inclined house (16) the coal drops by gravity into measur- ing hoppers which are manipulated by hand and the coal thus directed to its final resting place by gravity into a “D” retort Higs 13b: normally 16” x 26” x 20 feet long. In the horizontal house the coal drops into a charging machine electrically controlled (17) which is run on rails opposite to and below the level of all retort lids; this machine measures all charges and charges the retorts by means of large scoops driven into the gas retort, on releasing its charge of coal uniformly distributed in the retort the scoop is withdrawn. | While the charge remains in the retort which is heated on its exterior by the combustion of hot coke drawn from a previous charge, gas is being continually driven off through a seven inch as- cension pipe as will be presently outlined. After a distillation period that may vary from 4 to even 8 or 9 hours, the mouthpieces are 343 MANUFACTURE AND DISTRIBUTION OF GAS ‘SPT “OIA 344 ILLUMINATING ENGINEERING ¥ 4 mo ge hE hater PEIN TAO > % > ere nine ae a on one nee, , 5s Scan Fig, bos 345 F GAS O TION i — = — ae Higs. 56 5 | ate gee h ca RE eR ATING ENGINEERING MIN Lung 346 ICE SR. ua. 19. MANUFACTURE AND DISTRIBUTION OF GAS 347 Hig Zo. | ae | ees Sena eames, \ » “wer Fig. 21. 14 348 ILLUMINATING ENGINEERING Fig. 22. 349 MANUFACTURE AND DISTRIBUTION OF GAS ‘$6 “OI IN inate 14* 350 ILLUMINATING ENGINEERING slacked off, fired and opened, and the residue of the coal being deprived of its volatile matter and now called coke, is either, in the case of an inclined retort, allowed, by gravity, to fall into a con- veyor in front, or in the case of a horizontal retort, is pushed by an electrically controlled machine (18) somewhat similar in ap- pearance to the charger, on to an electrically driven longitudmal hot coke conveyor running below the mouths of all retorts. Some of this hot coke may be deflected into the bench furnaces for heat- Bigs oa: ing the retorts externally, but the larger proportion proceeds along the house, meeting sprays of quenching water in its travel, and drops at the end of its journey into transfer bucket conveyors which convey it horizontally and vertically into a coke storage bin. (19) By gravity, coke is delivered from the storage bin (20) to 30 ton cars on a grade railroad and by means of 40 ton locomotives delivered over a track hopper (21) at the wharf. The coke falls to an electrically driven belt which delivers the coke (22) at a speed of 200 net tons per hour to a barge alongside. Up to this time all material has been handled by electrically driven mechan- MANUFACTURE AND DISTRIBUTION OF GAS 351 ism, except in the case of the steam locomotive and the hand manipulated measuring hoppers in the inclined retort house. The barge is towed to the coke distributing points and by means of a belt conveyor within the barge located just over the keel, of a bucket elevator (23), and athwartship or cross belt conveyor in the bow (all driven by a single kerosene internal combustion engine) is delivered at the rate of 60 tons an hour on to an electrically driven inclined belt conveyor located on the wharf which (24) de- posits the coke on a coke platform. From the platform it is deliy- ered by gravity (25) over coke screens to teams or motor trucks which in turn deliver it into the sidewalk chutes of commercial buildings, apartment house steam plants or other users of coke. Only here, beyond the jurisdiction of the manufacturer of gas, is any hand labor applied since the coal left the pick of the miners in the mine from which it came. An exception to this statement would exist where coke has to be carried in baskets from the team on the street to the storage bins of the user. A convenient auxiliary to Retort Coal Gas manufacture is a Car- buretted Water Gas Plant. The fuel used to make the water gas is coke, and this should be delivered hot direct from the coal gas retorts but when necessary quenched coke is taken from the coke storage bins for use in the water gas generators in adjoining gen- erator house. Detail explanation is omitted for want of time, the explanation of the manufacture of carburetted Water Gas hereto- fore made El and 2 being deemed sufficient. As previously pointed out 1000 Ibs. in coke from each 2240 lbs. of bituminous gas coal received at the coal wharf must be disposed of as a by-product in Retort Coal Gas manufacture; the great value of this primary by-product must be at once apparent. While the coal lay in its hot bed in the retort the 36% volatile matter was seeking an outlet (26) via the ascension pipe before spoken of. ‘The length of time the charge remains under distilla- tion depends upon the degree and uniformity of heat, the character of the coal and the distribution of the charge in the retort, as well as the conductive qualities of the retort, for all have their influence on the resulting products. The heating of a charge of coal distills the volatile matter and causes a gas pressure within the retort; it is not desirable to have too great a pressure accumulate because of loss of gas through the porous sides of the clay retorts; the gas outlet of a retort or ascension pipe terminates in a metal chamber, 352 ILLUMINATING ENGINEERING Fiq. 27. MANUFACTURE AND DISTRIBUTION oF Gas 353 called a hydraulic main located above the retort bench; the ascen- sion pipes are sealed in water originally but later by accumulations of hot tar and ammoniacal liquor, products formed from a portion of the 36% volatile matter in the coal that become liquid at the temperature of the gas on passing the water seal. To prevent ex- cessive pressure within the retorts a gas pump called an exhauster Fie. 28. is installed in a house (27) beyond the retort house and the ex-. hauster is run at a variable speed, by the aid of automatic governors, so that all the gas as driven off in the retorts is at once drawn away from the hydraulic main undey a partial vacuum sufficient to over- come the water seal in the hydraulic main and to prevent but a very slight pressure in the retort. Forty years ago cast iron retorts were in use in cecal gas benches nates as g i a sneer Hp j Cea ee % Silty MANUFACTURE AND DISTRIBUTION or GAS 399 Higa 356 ILLUMINATING ENGINEERING and then no exhauster was thought necessary as gas could not penetrate in excessive quantities the cast iron retorts. In the Pintsch Oil Gas process cast iron retorts may still be used, but so far as I am aware, no coal gas works to-day employs their use. Frequently gas in traveling from the retort house to the exhauster house is cooled by atmospheric influences either in the pipes lead- ing to the exhauster house or by specially designed apparatus. The Fig. 32. gas temperature at the inlet of the exhausters closely approximates 120° Fahrenheit. On passing through the exhauster outlet the gas immediately is under pressure, for the exhauster is then forcing the gas to the storage holder against the storage holder pressure, which varies, depending upon its height, as will be explained later; additional pressure is produced by backpressure in overcoming the resistance of the gas travel through apparatus on the way to the holder as MANUFACTURE AND DISTRIBUTION OF Gas 357 well as by the skin friction of the main gas pipes of the system. Should the exhausters all stop simultaneously a safety gas blow out governor would allow the gas egress to the open air above the Ex- hauster house roof, thus preventing excessive accumulation of gas pressure between the exhausters and the retorts. Raw gas from the exhausters passes first through (28) mechan- ical tar extractors having plates with small openings that break up the gas volume in small streams and by friction disengages tar from these gas streams; the raw gas next passes through horizontal rotary scrubbers (29) where hydrocarbon liquids extract the naph- thalene in the gas. It is now believed that these washers should be placed next in order to the condensers later spoken of; from the naphthalene scrubbers the gas passes through a liquid solution of sulphate of iron in the (30) cyanogen washers which deprive the gas of any cyanogen contained. The lquid on saturation is sent to settling tanks, then to filter presses which form in a pressed cake a raw product called cyanogen sludge (31) which is shipped to the chemical factories; residue liquor from the filter presses is put through drying processes and converted into dry sulphate of ammonia, which is bagged and placed on the market for sale. After this purifying process the gas passes through the cast iron tubes of surface condensers: (32) the tubes are surrounded by salt water, where available, and the water current is arranged so that the stream of warm water leaving the condenser meets the warm gas entering the apparatus. On leaving the condensers the gas passes through water in am- monia washers (33) quite similar in their design to the Cyanogen and Naphthalene Washers, and the gas having been freed of all tar, cyanogen and naphthalene, now surrenders its last trace of am- monia. The tar from the hydraulic mains, the main pipe connections, exhausters, tar extractors and condensers is led into underground tar wells from whence it is pumped into shipping tanks near the wharf, from whence the chemical contractors take it to make . the tar into pitch, dead oil, and various coal tar compounds. The ammonia from the ammonia washers is sent to underground ammonia tanks, and together with ammoniacal liquor recovered from the hydraulic mains and other connections and apparatus where tar is present, is all transferred to ammoniacal liquor tanks near the wharf, from which the chemical contractors remove it and ILLUMINATING ENGINEERING 358 Fig. 34. MANUFACTURE AND DISTRIBUTION OF GAS 359 obtain therefrom anhydrous ammonia, sulphate of ammonia and other ammonia products. The gas leaving the ammonia scrubbers next passes into the puri- fying boxes now usually a dry process of purification. Boxes (34) 40 feet square and 8 feet deep are uniformly spread with oxide of iron, usually deposited on white pine shavings supple- mented by iron borings. The layers vary in thickness in practice, being in some cases upwards of 42 inches thick. The gas is here deprived of sulphur which is in the form of sulphuretted hydrogen. Some fixed forms of sulphur are undoubtedly taken up from time to time in the journey of the gas from the hydraulic main to the outlet of the purifying house and unless a very sulphurous coal must be used, no hme purification is found necessary to meet a 20 grain legal provision. Where it is found necessary to use the latter it is not an extravagant statement to make that the increased cost of purifi- cation (more particularly in the case of Coke Oven Gas) may be ten times the cost of ordinary oxide purification. It has been found that in order to eliminate fixed sulphur compounds that all carbonic acid must first be removed from gas in one set of boxes then lime fouled from sulphuretted hydrogen will attack the fixed sulphur compounds in a second set of boxes, and finally a third set of oxide boxes must be used to remove any sulphuretted hydro- gen that may be present. These three independent processes must be carried on in the purifying house, where but one is required when using fairly low sulphur coal. One of the three processes (the second in order) is exceedingly disagreeable to the employees of the gas company and to the neighbors as well. So little value is now attached to the requirements for fixed sulphur compounds that England, having passed through the regulating by law stage, now no longer demands any specified freedom of fixed sulphur in gas; New York only very lately passed laws respecting sulphur, merely imitating the laws of other places without reference to any necessity. Massachusetts in this respect is also moderating its position as regards sulphur in illuminating gas. Having passed the purifying house the gas now goes through 16 foot station meters, (35a-35b) in which the measuring drums | run in water; gas measurements are made as near 60° Fahrenheit as atmospheric conditions permit but the measurements are cor- rected to 60° Fahrenheit and 30 inches barometer in any event. Here I might state that unaccounted for gas, not leakage as fre- ILLUMINATING ENGINEERING 360 Fie. 35a. Baoan Fig. 35b. 361 CTURE AND DISTRIBUTION OF GAS A MANUF t f Gee ee a sspeye pales HIG sais 362 ILLUMINATING ENGINEERING quently asserted, is ascertained by taking the sum of the readings of the station meters and subtracting therefrom the sum of the readings of all the consumers’ meters, the remainder is unaccounted for gas, which includes actual loss of gas by leakage, loss of volume represented by difference of temperature at which the meters in | AKAZNZNIZNIZNILN al | i P