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ELEMENTARY ELECTRO-TECHKICAL SERIES 
 
 ELECTRIC HEATING 
 
 BY 
 Edwix J. Housto:n^, Ph. D., (Princeton) 
 
 AND 
 
 A. E. Kennelly, Sc. D. 
 
 Second Edition, Enlarged 
 
 NEW YORK 
 McGRAW PUBLISHING COMPANY 
 
 1906 
 
LIBRARY of CONGRESS 
 Two Copies Received 
 
 NOV 5 1906 
 
 s, Cepyrtfht Entry 
 OLASS A. XXc, No. 
 
 thVss 
 
 Copyright, 1906, by the 
 
 McGRAW PUBLISHING COMPANY 
 
 New York 
 
\ PREFACE 
 
 In preparing this volume on Electric 
 Heating, as one of a series entitled 
 The Elementary Electro- Techiical Series, 
 the authors believe they are meeting a 
 demand, that exists on the part of the gen- 
 eral public, for reliable information re- 
 specting such matters in electricity as 
 can be readily understood by those not 
 especially trained in electro -technics. 
 
 The subject of electric heating is to- 
 day attracting no little attention. The 
 wonderful growth in electric street rail- 
 ways, coupled with the readiness with 
 w^hich the current can be applied to 
 the heating of the cars, together with 
 the marked efficiency of the electric air 
 heater as an apparatus for transforming 
 electric energy into heat energy, have, 
 during the last decade, caused a develop- 
 
IV PREFACE 
 
 ment in electric car heating. But the 
 growth of electric heating has by no 
 means been limited to this particular 
 field. The development of electric cook- 
 ing apparatus has naturally attended the 
 extensive distribution of electricity for 
 lighting and power, and electric cooking 
 is. now taking its place with electric light- 
 ing as an adjunct to the modern house. 
 
 In the direction of the employment of 
 powerful electric currents for heating 
 effects, processes for electric welding, and 
 the electrical shaping and forging of met- 
 als, are coming into commercial use, and 
 applications are daily being made of the 
 power of electricity in electric furnaces, 
 either where the heating effect alone is 
 employed, or where both heating and 
 electrolytic effects are utilized. 
 
CONTENTS. 
 
 CHAPTER 
 
 
 
 PAGE 
 
 I. 
 
 Introductory, . 
 
 '. 
 
 •7 
 
 II. 
 
 Elementary Principles, 
 
 . 
 
 30 
 
 III. 
 
 Electrical Heating of Bare 
 
 
 
 Conductors, 
 
 . 
 
 37 
 
 IV. 
 
 Electrical Heating of Covered 
 
 
 
 Conductors, 
 
 . 
 
 69 
 
 V. 
 
 Fuse Wires, .... 
 
 . 
 
 87 
 
 VI. 
 
 Electric Heaters, 
 
 . 
 
 117 
 
 VII. 
 
 Electric Cooking, 
 
 . 
 
 151 
 
 VIII. 
 
 Electric Welding, 
 
 . 
 
 181 
 
 IX. 
 
 Electric Furnaces, 
 
 . 
 
 233 
 
 X. 
 
 Miscellaneous Applications 
 
 OF 
 
 
 
 Electric Heating, . 
 
 
 255 
 
 XI. 
 
 The Electrical Thawing 
 
 OF 
 
 
 
 Frozen Water in Pipes, 
 
 . 
 
 271 
 
 
 Index, ..... 
 
 • 
 
 279 
 
ELECTRIC HEATING. 
 
 CHAPTER I. 
 
 INTRODUCTORY. 
 
 Zoroaster, the fourxder of fire worship, 
 because of the many advantages mankind 
 derived from fire, bade his followers wor- 
 ship the sun as its prime and sustaining 
 cause. Although the idolatrous doctrine 
 of the old Persian is now entirely dis- 
 credited by civilized races, yet the truth 
 of the belief that found in the sun the 
 source of all the thermal phenomena of 
 the earth, still remains unchallenged. It 
 
8 ELECTRIC HEATING. 
 
 can be shown, from a scientific point 
 of view, that in reality, there is not one 
 of the many ways in which man can 
 produce heat on the earth, that cannot 
 trace its prime cause to the sun. 
 
 Take, for example, one of the common- 
 est methods of obtaining heat; namely, 
 by the burning of a mass of coal. Here it 
 is, at first sight, by no means evident, that 
 the heat of the glowing mass was derived 
 from the sun. In accordance with mod- 
 ern scientific belief, heat is no longer re- 
 garded as a kind of matter, but as a con- 
 dition of matter. A hot body differs 
 from a cold body in that the very small 
 particles or molecules, of which it is com- 
 posed, are in a state of rapid to-and-fro 
 motions or oscillations. When a hot 
 body grows hotter, the only effect pro- 
 duced, unless the body is melted or evap- 
 
INTKODUCTORY. 9 
 
 orated, is to increase the violence of these 
 molecular oscillations. Could we de- 
 prive a body of all its heat its oscillations 
 would entirely cease. In order to pro- 
 duce molecular or heat oscillations, en- 
 ergy must be expended on the body ; that 
 is, work must be done on its molecules. 
 In other words, a hot body is a mass of 
 matter plus a certain quantity of molec- 
 ular energy. When a hot body cools, it 
 throws off or dissipates a certain quantity 
 of its molecular energy, and, when the 
 heat thus thrown off is absorbed or taken 
 in by another body, the latter thereby 
 acquires an additional store of energy. 
 When a pound of coal is burnt in air, the 
 heat produced results from the mutual 
 attractions existing between the mole- 
 cules of the carbon and the molecules of 
 the oxygen in the air; or, from what is 
 ordinarily called their chemical affinity. 
 
10 ELECTRIC HEATING. 
 
 Unburnt coal and air possess, jointly, a 
 store of chemical energy, having the 
 power or potency of doing work, but 
 actually doing no work; while coal and air 
 after burning, no longer possess this store 
 of chemical energy, but have acquired in 
 its place a stock of oscillation or heat en- 
 ergy; i. e,, energy of oscillation. 
 
 Could the burning be effected in a heat - 
 tight space, this oscillation or heat energy 
 would be entirely confined to the interior 
 of the chamber, but as no bodies are per- 
 fect non-conductors of heat, such a heat- 
 tight si)ace cannot be obtained, and some, 
 at least, of the oscillation energy will be 
 communicated to surrounding bodies. 
 
 A steam engine is a machine for pro- 
 ducing mechanical energy at the expense 
 of molecular oscillation energy. If we 
 suppose that a pound of coal could be 
 
INTKODUCTORY. 11 
 
 burned in connection with a theoretically 
 perfect steam engine, with the necessary 
 quantity of air, all the molecular oscilla- 
 tion energy developed by the combustion 
 could be utilized by the engine, which 
 would do an amount of work exactly 
 equal to the amount of original chemical 
 energy residing in the coal and air. It is 
 known, as the result of calculation, that 
 such an engine would be capable of doing 
 an amount of work represented by the 
 lifting of one pound through a height of 
 about 2000 miles. When, therefore, a 
 pound of coal is burnt with air, an amount 
 of oscillation energy is developed, equal 
 to that which would be obtained by the 
 falling of that pound of coal from a height 
 of about 2000 miles. Owing to a variety 
 of circumstances, however, the best steam 
 engines are only capable of yielding about 
 15 per cent, of this work. 
 
12 ELECTBIC HEATING. 
 
 The store of energy existing in a pound 
 of coal was obtained from the sun's radia- 
 tion during the geological past. That is 
 to say, during the Carboniferous Age, the 
 carbon of the coal originally existed in 
 the earth's atmosphere combined with 
 oxygen as gaseous carbon dioxide. For 
 the formation of every pound of coal ex- 
 isting in the earth's crust a definite 
 quantity of carbonic acid gas was dissoci- 
 ated, or separated into carbon and oxy- 
 gen, by means of the energy of the sun's 
 rays absorbed by the vegetation of the 
 Carboniferous Era. In other words, the 
 leaves of the carboniferous flora absorbed 
 gaseous carbon dioxide from the atmos- 
 phere, and, in the delicate laboratories of 
 the leaf, by means of the energy absorbed 
 directly from the sun's rays, a dissocia- 
 tion occurred between the carbon and the 
 oxygen. The ability, therefore, of the 
 
INTRODUCTORY. 13 
 
 carbon to again recombine with oxygen in 
 the form of gaseous carbon dioxide has 
 been a result of energy expended on the 
 plant and lodged in the carbon of its 
 woody fibre. A lump of coal, therefore, 
 is in reality a store -house of the solar heat 
 of an early geological era. 
 
 Viewed in this light, a lump of coal can 
 be regarded as not unlike a w^eight raised, 
 say from the ground through a certain 
 height. Suppose, for example, a pound 
 weight be attached to a string passing over 
 a pulley and raised to a height of 20 feet 
 from the ground, and that, while in this 
 position, the string of the pulley be fixed. 
 Evidently, work has been expended in 
 raising the pound weight, and, as a result 
 of this work, the weight is placed in a 
 position in which it can, at any time the 
 string is released, fall back again to the 
 ground J and in so doing restore the 
 
14 ELECTKIC HEATING. 
 
 amount of work originally expended in 
 lifting it. In the same way, a pound of 
 coal has, by the work of the sun, been 
 placed in a condition in which it can 
 combine with the oxygen of the air, and 
 burn. In so doing it must give out an 
 amount of heat equal to that representing 
 the sun's work upon it, amounting, as 
 we have seen, measured in units of the 
 earth's gravitational work, to an elevation 
 of about 2000 miles. 
 
 But it was not only during the geo- 
 logical past that the solar energy was 
 thus husbanded in the earth's crust. 
 The sun's energy is to-day being similarly 
 stored in all vegetable foods, and it is 
 on this store that animals draw for their 
 muscular and nervous energy. That is to 
 say, all vegetable products represent 
 chemical stores of solar energy. An 
 animal is capable of releasing this energy 
 
INTRODUCTORY. 15 
 
 in its muscles by the actual combustion 
 of these chemical substances, after their 
 proper assimilation in its body. Muscu- 
 lar activity, therefore, is but another in- 
 stance of energy primarily obtained from 
 the sun's radiation. The earth's animals 
 are, therefore, in this sense truly children 
 of the sun, since they thus indirectly de- 
 rive their activity from that luminary. 
 
 Not only can the heat and consequent 
 mechanical motion, which it is possible to 
 obtain by the burning of a mass of coal, 
 or by the assimilation and consequent 
 oxidation of a certain (luantity of food by 
 an animal, be traced indirectly to the sun, 
 but the same can also be shown to be true 
 for all the other sources of mechanical en- 
 ergy with which we are acquainted on the 
 earth. Take, for example, the energy de- 
 livered to a windmill from moving air, or 
 
16 ELECTRIC HEATING. 
 
 to a water-wheel from flowing water. In 
 the case of a windmill, the sun's heat, 
 acting upon the air, sets up convection 
 currents, or winds, whereby the work ex- 
 pended by the sun in heating the air is 
 liberated in mass motion. In the case of 
 a water-wheel, where a stream of water 
 flowing from a higher to a lower level is 
 caused to impart its energy to the wheel, 
 the water, in reality, occupies a position 
 corresponding to a raised weight, and is 
 able to do work because, like the water, it 
 is at the higher level. To what source of 
 energy does it owe this ability to do work? 
 Manifestly to the heat of the sun, where- 
 by the water was raised as vapor and sub- 
 sequently fell as rain on the slopes of the 
 higher level from which it is now flowing 
 to a lower level. 
 
 The molecules of a hot body are moving 
 
INTRODUCTORY. 17 
 
 to-and-fro at varying velocities. Some are 
 moving faster than others; for, during their 
 to-and-fro motions, they frequently col- 
 lide, some molecules being thereby accel- 
 erated and others retarded. The average 
 molecule, of a given mass possessing a 
 given amount of heat, may, however, be 
 assumed to possess on the whole, a cer- 
 tain average velocity of motion. It is 
 clear, therefore, that if we could trans- 
 form the molecular oscillations of a heated 
 body into a motion of the whole mass, the 
 body would move with a uniform velocity 
 which would be its average molecular ve- 
 locity, in the sense just described. This 
 conception is valuable as affording a meas- 
 ure of the amount of heat possessed by a 
 body. Similarly, when work is done upon 
 a body, whereby it acquires, or is capable 
 of acquiring, a certain velocity of motion, 
 this motion can be represented by an agi- 
 
18 ELECTBIC HEATING. 
 
 tation of the molecules in the quiescent 
 mass of the body, the average molecular 
 velocity corresponding to the velocity of 
 the mass. Clearly, therefore, heat repre- 
 sents mechanical work, and mechanical 
 work represents heat. Or, in other words, 
 a certain quantity of mechanical work is 
 capable of being expressed as a definite 
 quantity of heat, or a certain amount of 
 heat is capable of being expressed as a 
 definite quantity of mechanical work, 
 even though, in all cases, we may not, 
 at present, possess the means whereby 
 the actual conversion of one into the other 
 can be effected. 
 
 For this reason a given quantity of heat 
 can only be made to produce a certain 
 quantity of mechanical work correspond- 
 ing thereto, even though the means of 
 conversion were so perfect that no loss 
 should take place during the process. And 
 
INTEODUCTOEY. 19 
 
 similarly, a given quantity of work can 
 only be capable of developing a fixed quan- 
 tity of heat, no matter how perfect the 
 mechanism of conversion may be. 
 
 Heat developed by electricity forms no 
 exception to the preceding principles. 
 As we shall see, a given quantity of elec- 
 trical energy is capable of producing a 
 fixed quantity of heat, no matter how 
 such heat is developed. The limit to im- 
 provement in electrical heating apparatus, 
 as in any other machinery, being such 
 as will insure the least loss of energy 
 during the process of conversion. As a 
 matter of fact, electrical energy can 
 always be completely converted into 
 heat, although, unfortunately, the con- 
 verse is not, at present, true, and heat 
 energy cannot, therefore, be completely 
 converted into electrical energy, but 
 
20 ELECTKIC HEATING. 
 
 only a comparatively small fraction can 
 be so converted. 
 
 It is a fundamental doctrine of modern 
 science that energy is never annihilated. 
 It apparently disappears in one form, only 
 to reappear in another form. Thus, heat 
 energy, or molecular motion, when disap- 
 pearing as such, reappears in some other 
 form; say, for example, as mass motion, 
 or mechanical energy. Mechanical energy 
 may in its turn disappear as such, to pro- 
 duce chemical, thermal, electromagnetic, 
 or some other form of energy. In all 
 cases, definite quantitative relations exist 
 between the amounts of energy ex- 
 changed, but in every process of conver- 
 sion a tendency exists whereby some of 
 the energy assumes the form of molecu- 
 lar motion or heat, in which it is often 
 impossible to again utilize or farther 
 transform it. 
 
CHAPTER II. 
 
 ELEMENTARY PRINCIPLES. 
 
 During the building of a brick wall, a 
 certain amount of work is done in raising 
 the bricks from their position on the 
 ground to their position in the wall. The 
 amount of this work is definite, and is 
 measured by the amount of force re- 
 quired to raise the bricks directly against 
 the gravitational pull of the earth, multi- 
 plied by the vertical distance through 
 which they are raised. 
 
 Care must be taken not to confuse the 
 ideas of force and work. Force may be 
 defined, in general, to be that which 
 causes a body to move, or to tend to 
 move. Work is never done by a force un- 
 
22 ELECTKIC HEATING. 
 
 less it actually produces a motion in the 
 body on which it is acting. For example, 
 when a brick rests on a wall, or on the 
 ground, it is exerting a force vertically 
 downward in virtue of the earth's gravita- 
 tional pull; that is to say, it is pressing 
 downward against the earth, with a force 
 equal to its weight, approximately six 
 pounds' weight, but this force is not doing 
 work since it is not producing a motion of 
 the brick. Work had to be done on the 
 brick when it was raised from the ground 
 to its position on the wall; that is, a mus- 
 cular force, equal to that of six pounds' 
 weight, had to be exerted, in order to over- 
 come the earth's gravitational attraction 
 on the brick and this force had to be con- 
 tinuously exerted while the brick was 
 being raised through the vertical distance 
 existing between the ground and its posi- 
 tion in the wall. Moreover, if the brick 
 
•ELEMENTARY PRINCIPLES. 23 
 
 be permitted to fall from the wall to the 
 ground, work will be done by the brick in 
 falling, which could be usefully employed, 
 as, for example, in winding a clock, and 
 the amount of this work could be repre- 
 sented, as before, by the weight of the 
 brick multiplied by the distance through 
 which it falls. This amount of work 
 must be equal to that which was expended 
 in lifting the brick. 
 
 In order to measure accurately the 
 amount of mechanical work done on a 
 body in raising it through a given vertical 
 distance, or the amount of work done hy a 
 body in falling, reference is had to certain 
 units of loork. A convenient unit of 
 work, much employed in engineering, in 
 the United States and in England, is called 
 the foot-pound, and is equal to the work 
 done when a force equal to a pound's 
 
24 ELECTKIC HEATING. 
 
 weight acts through a distance of one foot. 
 
 Suppose a uniform brick wall con- 
 taining 1000 bricks, each weighing, say six 
 pounds, has its top six feet from the 
 ground. The total weight of the wall 
 would be 6000 pounds, and the average 
 distance through which the bricks would 
 have to be raised, in building the wall, 
 would be three feet, so that the amount 
 of work necessarily expended in the build- 
 ing of the wall, would be that required 
 to raise its weight through its average 
 height, or 6000 x 3 - 18,000 foot-pounds. 
 
 The foot-pound is not employed as a 
 unit of work in countries outside of the 
 United States and Great Britain, nor gen- 
 erally in scientific writings anywhere. A 
 unit frequently employed is called the 
 joule, and is commonly used as the unit 
 
ELEMENTARY PRINCIPLES. 25 
 
 of ^York performed by an electric current; 
 for, as ^ye shall see, electric currents are 
 capable of doing work. The value of the 
 joule may, however, be conveniently ex- 
 pressed as being approximately equal to 
 0.738 foot-pound; or to the work done in 
 raising a pound through nearly nine 
 inches. Thus, the amount of work ex- 
 pended in the building of the brick wall 
 just referred to, was 18,000 foot-pounds, 
 or approximately 24,000 joules. 
 
 The brick wall referred to in the pre- 
 ceding paragraph might be erected by 
 the workmen in a day, or in six days, but, 
 when built, the amount of work done 
 would be the same; namely, 24,400 joules. 
 Regarding its erection from the standpoint 
 of each workman, the rate at which each 
 m^n would have to expend his energy in 
 doing the work would be very different in 
 
26 ELECTEIC HEATING. 
 
 the t^YO cases, since, if he does in one 
 day that which he would otherwise do in 
 six days, he would clearly expend his en- 
 ergy at an average rate six times greater 
 in the former case. The rate at which 
 work is done is called activity, so that the 
 average activity of the workman would be 
 six times greater, if the wall is built in one 
 day, than if it be built in six days. 
 ^ A unit of activity is the foot-pound- 
 per-second. As generally employed in 
 England and America, the practical unit 
 of activity is the average activity of a cer- 
 tain horse assumed as a standard. This 
 unit of activity is called the horse-power, j 
 and is an activity of 550 foot-pounds-per- 
 second. The unit of electrical activity 
 generally used all over the world and 
 which may, therefore, be called the inter- 
 national unit of activity is the joide-per- 
 second, or the ivatt, and is equal to 0.738 
 
ELEMENTAKY PRINCIPLES. 27 
 
 foot-pound-per-second, or 1 -746th of a 
 horse-power, so that 746 watts are equal 
 to one horse-power. 
 
 The engines of an Atlantic liner may 
 develop steadily about 30,000 H. P. in 
 driving its propeller. This represents an 
 activity of 30,000 x 550 = 16,500,000 
 foot-pounds, or 8250 short-tons, lifted one 
 foot-per- second, or one short ton lifted 
 8250 feet-per- second; or, expressed in 
 watts, or joules-per-second, 22,374,000. 
 
 A laborer digging a trench will usually 
 average an activity of only 50 watts, or 36.9 
 foot-pounds-per-second, during his work, 
 so that the average activity of a labor- 
 ing man may be taken as about l-15th of 
 a horse-power. A man frequently works, 
 however, at an activity much greater than 
 this, say at an activity of 100 watts, or 
 about l-8th horse-power, while for short 
 periods, say for half a minute, he can sus- 
 
28 " ELECTKIC HEATING. 
 
 tain an activity of, perhaps, 500 watts, or 
 even 746 watts, or one horse-power. 
 
 As we have abeady seen, a definite and 
 fixed relation is maintained between the 
 amount of heat or oscillation energy 
 present in a unit quantity of matter, say 
 a pound of water, and the amount of en- 
 ergy which must be expended on this 
 matter in order to heat it to a given tem- 
 perature. The amount of heat energy in 
 an indefinite quantity of a body, such as 
 water, cannot be determined from its 
 temperature alone; we require, beside 
 this, to know its mass. If we know its 
 weight in pounds, and its temperature in 
 degrees; i.e., the pound-degrees, we can 
 determine the quantity of heat energy 
 existing in the mass. In other words, 
 the pound' degree may be taken as a heat 
 unit, and, since this represents a definite 
 
ELEMENTAKY PRINCIPLES. 29 
 
 amount of work, this heat unit may have 
 its value expressed either in joules or in 
 foot-pounds. The British heat unit, some- 
 times called the British thermal unit, or 
 the B, T. v., is the amount of heat re- 
 quired to raise a pound of water one de- 
 gree Fahrenheit, from 59"^ to 60° F. and is 
 taken as 778 foot-pounds, or 1055 joules. 
 The heat unit most frequently employed 
 in countries other than the United States 
 and Great Britain, is the amount of heat 
 required to raise one gramme of water 
 P C. This heat is called the tvater- 
 gramme-degree-centigrade, the lesser ca- 
 lorie, or the therm. Expressed in foot- 
 pounds, one lesser calorie is equal to 4.18 
 joules, or 3.087 foot-pounds. 
 
 The amount of work expended in heat- 
 ing a cubic foot of water, of approximate- 
 ly 62 J pounds weight, from 50° F. to the 
 boiling point of 212° F., or through a tem- 
 
30 ELECTRIC HEATING. 
 
 perature of 162"^ F. , is approximately 62^ x 
 162 - 1013 B. T. U. = 1,069,000 joules. 
 
 A reservoir filled with water possesses 
 a certain store of energy, or capacity for 
 doing work, dependent both on the 
 amount of water it contains and on the 
 distance through which the water is per- 
 mitted to flow in escaping from the reser- 
 voir. In accordance with what has al- 
 ready been stated, the amount of this 
 work can be represented by the weight of 
 the water in pounds, multiplied by the 
 distance in feet through which the water 
 falls. Thus, consider a reservoir holding, 
 say 100,000 cubic feet of water, at a mean 
 elevation of 10 feet above a pump which 
 fills it. The weight of the water would 
 be approximately 6,250,000 pounds, and 
 the amount of work required to be ex- 
 pended by the pump in lifting it 10 feet 
 
ELEMENTARY PRINCIPLES. 31 
 
 would be approximately 62,500,000 foot- 
 pounds, or 84,750,000 joules. If, now, this 
 water be permitted to escape to the pump 
 level, in so doing it will expend just this 
 amount of work. If the distance through 
 which the water fell were twice as great; 
 i.e., if the pump level were 10 feet lower 
 down, then half the quantity falling 
 through this double distance would do the 
 same amount of work, and, of course, to 
 fill the reservoir through such a distance 
 would necessitate the expenditure of twice 
 as much work as in the former case. 
 
 Although electricity is not to be con- 
 sidered as a liquid, yet many of the laws 
 which relate to its flow are similar to the 
 laws controlling liquid flow. For exam- 
 ple, in order to obtain a flow of water, a 
 difference of pressure must exist, gener- 
 ally in the form of a difference of water 
 
32 • ELECTBIC HEATING. 
 
 level, and the direction of the current of 
 water is from the higher to the lower pres- 
 sure, or from the higher to the lower level. 
 So, too, in order to obtain a flow of elec- 
 tricity, a difference of electrical pressure 
 or level must exist, or, as it is commonly 
 called, an electromotive force, and the di- 
 rection of the electric current is assumed 
 to be from the higher to the lower pres- 
 sure, or from the higher to the lower elec- 
 tric level. Just as in the case of the 
 water flow, the quantity of water is repre- 
 sented by some unit quantity, such as a 
 pound, so in the case of the electric cur- 
 rent, the quantity of electricity is repre- 
 sented by a unit of electric quantity called 
 a coidomb; and, as in the case of the water, 
 the difference of level is represented by 
 some such unit as a foot, so in the case of 
 the electric flow, the difference of electric 
 pressure or level, is represented by a unit 
 
ELEMENTARY PRINCIPLES. 33 
 
 called the volt. Moreover, as the amount 
 of work done by a given quantity of wa- 
 ter in flowing, is equal to the quantity of 
 water represented, say, in pounds, multi- 
 plied by the distance through which it 
 moves in feet, the work being expressed 
 in foot-pounds, so the amount of work 
 done in an electric circuit, by the electric 
 current in flowing, is equal to the quanti- 
 ty of electricity in coulombs, multiplied 
 by the pressure, or the difference of elec- 
 tric level through which it flows, in volts. 
 The work being expressed in coulomb- 
 volts, or joules, a joule being equal to one 
 coulomb-volt. In point of fact the name 
 joule, for a unit of work, was first em- 
 ployed as the name of the coulomb-volt, 
 the unit of electric work. 
 
 When a flow of 100 coulombs of electric- 
 ity passes through a circuit under a pres= 
 
34 
 
 ELECTEIC HEATING. 
 
 sure of 50 volts, the amount of work ex- 
 pended by the electric current will be 100 
 X 50 == 5000 joules = 3690 foot-pounds; 
 one coulomb of electricity passing under 
 a pressure, or through a difFerence of. elec- 
 tric level, of 100 volts, 'will expend the 
 same amount of work; i. e., 100 joules, as 
 100 coulombs passing under a pressure of 
 one volt. An electric source, such as a 
 dynamo, or a voltaic battery, is a device 
 for producing an electromotive force ; that 
 is, a difference of electric level or electric 
 pressure in a circuit, just as a pump is a 
 device for producing a difference of water 
 level as in forcing water into a reservoir. 
 
 The activity of a reservoir, when dis- 
 charging water, depends upon the quan- 
 tity of water escaping per second; and, as 
 in the case of all activity, may be ex- 
 pressed in foot-pounds-per-second, or in 
 
ELEMENTAKY PKINCIPLES. 35 
 
 watts. So in an electric circuit, the ac- 
 tivity depends upon the flow of electricity 
 per second through a given diffference of 
 electric level, or electromotive force, 
 (abbreviated E. M. F. ) and is also ex- 
 pressed in joules-per-second, or in watts. 
 Thus, when 100 coulombs pass through 
 an electric circuit under a pressure of 50 
 volts, a total work of 5000 joules will be 
 done, and if this work be expended in one 
 second, the activity during that time will 
 be 5000 watts. If the same total flow 
 take place steadily in 50 seconds, the 
 flow-per-second would be 2 coulombs, 
 and the activity, 50 x 2 = 100 volt-cou- 
 lombs-per-second, or 100 watts. 
 
 An electric flow may be expressed in 
 coulombs-per-second; ^. e,, in amperes. 
 Since an ampere is a rate of flow of one 
 coulomb-per-second, electric activity can 
 
36 ELECTRIC HEATING. 
 
 be expressed in volt'Coidombs-per-second, or 
 in volt-amperes; i. e., in watts. A circuit in 
 which 10 amperes is flowing under a pres- 
 sure of 100 volts, is having electric energy 
 expended in it at the rate of 100 x 10 
 volt- amperes, or 1000 watts, or 1 kilowatt. 
 A kilowatt is the unit commonly employed 
 in the rating of electrical machinery, 
 since the watt is too small a unit for con- 
 venience. One kilowatt, abbreviated K W. , 
 is equal to 1.34 H. P., or, approximately^ 
 U ILP. 
 
CHAPTER III. 
 
 ELECTRICAL HEATING OF BARE CONDUCTORS. 
 
 The quantity of water which escapes 
 from a reservoir in a given time depends 
 not only on the pressure at the outlet, but 
 also on the diameter and length of the 
 outlet pipe. So, too, when an electric cur- 
 rent flows through a conducting circuit, 
 the quantity of electricity which passes 
 per second; ^. ^.,the coulombs-per-second, 
 or the amperes, depends not only on the 
 pressure, or the E. M. F., but also on 
 the length and dimensions of the con- 
 ductor, as well as on the material of 
 which the conductor is composed, and on 
 its physical condition, such as hardness, 
 temperature, etc. In the case of the water 
 pipe, the length and diameter of the pipe, 
 
38 ELECTRIC HEATING. 
 
 the nature of its walls, and the number 
 of its bends, will determine a certain hy- 
 draulic resistance, which will permit the 
 flow of water under a given head or pres- 
 sure through it, and determine the 
 amount which will escape from the reser- 
 voir in a given time. In the same man- 
 ner, in an electric circuit, the length and 
 cross -section of the conducting wire, or 
 circuit, taken in connection with its nat- 
 ure and physical conditions, will deter- 
 mine a certain electric resistance, which 
 will permit the flow of electricity through 
 it, under a given pressure or E. M. F., 
 and determine the amount of current 
 which will flow through the circuit in 
 any given case. 
 
 The law which determines the current 
 strength in amperes, which will pass 
 through any circuit under the influence 
 
HEATING OF BAEE CONDUCTORS. 39 
 
 of a given E. M. F. and against a given 
 resistance in a circuit, was discovered by 
 Dr. Ohm, of Berlin, and is known as 
 Ohns law. This law may be stated as 
 follows: The current strength in any 
 circuit is equal to the E. M. F. acting on 
 that circuit, expressed in volts, divided 
 by the resistance of that circuit, expressed 
 in units of electrical resistance called 
 ohms; or concisely. Ohm's law may be ex- 
 pressed as follows: 
 
 The amperes in any circuit equal the volts 
 divided by the ohms. . 
 
 For example, if a storage cell, with an 
 E. M. F. of two volts, be connected to a 
 circuit whose resistance, including that of 
 the cell, is 10 ohms, the current strength 
 passing through the circuit will be yV = i 
 ampere; and, since one ampere is one cou- 
 lomb per second, there would be flowing 
 in such a circuit one -fifth of a coulomb 
 
40 ELECTRIC HEATING. 
 
 per second. The work done in the cir- 
 cuit will be equal to the pressure of two 
 volts multiplied by the total number of 
 coulombs that pass in any given time. 
 For example, in ten minutes, or in 600 
 seconds, the total number of coulombs 
 that will have passed through the circuit 
 will be 600 x i = 120 coulombs, and the 
 work expended by the storage cell in the 
 circuit will be 2 x 120 = 240 volt-cou- 
 lomb, or joules, = 177 foot-pounds. We 
 also know that the activity in this circuit 
 will be the product of the volts and the 
 amperes, or 2 volts x ^ ampere =: f watt 
 2 r= joule-per-second =^ 0.295 foot-pound- 
 per- second. 
 
 During the flow of water through a pipe 
 there will be produced a certain back pres- 
 sure, or counter-hydraulic pressure, tending 
 to check the flow of water through the pipe, 
 
HEATING OF BARE CONDUCTORS. 41 
 
 In the same way, during the flow of an 
 electric current through' a conductor, 
 there will be produced a hack electric 
 pressure, or counter E. M. F., equal in all 
 cases to the E. M. F. impressed upon the 
 conductor. In fact, the current strength 
 through the conductor adjusts itself in 
 accordance with Ohm's law, in such a 
 manner that the counter E. M. F. shall 
 just be equal to the impressed E. M. F. ; 
 i.e., the E. M. F. acting on the circuit. 
 The counter E. M. F. in volts, is equal to 
 the product of the carrent strength in 
 amperes, by the resistance of the conduct- 
 or in ohms. Thus, the 10 -ohm circuit 
 above referred to, carrying a current of one 
 fifth of an ampere, develops a counter E. 
 M. F. of 10 X i = 2 volts, which is just 
 equal to the impressed E. M. F. of the 
 cell. The product of the current strength 
 and the counter E. M. F. is the activity 
 
42 
 
 ELECTEIC HEATING. 
 
 expended in the circuit, just as the prod- 
 uct of the current strensith and the E. 
 
 8 VOLTS 
 
 1 OHM 
 
 2 OHMS 
 GERMAN SILVE8 
 
 
 TOTAL ACTIVITY OF 
 BATTERY 8 WATTS 
 
 8 VOLTS 'lOHM 
 
 8 VOLTS 
 1 AMPERES 
 1 VOLT DROP 
 1 WATT ACTIVITY 
 
 Fig. 1. —Distribution of C. E. M. F. in a Circuit. 
 
 M. F. is the work expended by the 
 E. M. F. 
 
 If, for example, as in Fig. 1, four storage 
 cells, each of 2 volts E. M. F. and I ohm 
 
HEATING OF BARE CONDUCTORS. 43 
 
 resistance, be connected in series with an 
 external circuit composed of two parts; 
 viz., of a resistance of 5 ohms of copper 
 wire, and of a resistance of 2 ohms of 
 German silver wire, the total resistance 
 of the circuit wall be 8 ohms, and the cur- 
 rent strength f = 1 ampere. The back 
 pressure, or drop, in the German silver 
 wire will be 2 x 1 =2 volts. The back 
 pressure, or drop, in the copper wire, will 
 be 5 X 1 = 5 volts, and the activity ex- 
 pended in each will be 2 volts x 1 am- 
 pere = 2 watts in the German silver and 5 
 volts X 1 ampere = 5 watts in the copper. 
 
 A counter E. M. F. may be produced 
 not only by the back pressure of a cur- 
 rent passing through a resistance, but al- 
 so by the presence of certain devices 
 placed in the circuit and operated by the 
 current, such, for example, as electric mo- 
 
44 
 
 ELECTKIC HEATING. 
 
 tors, or electrolytic cells. For example, 
 if the circuit represented in Fig. 2 have 
 
 .^^J^ 
 
 -^ 
 
 
 
 
 r 
 
 h 
 
 7 
 
 2 VOLTS 
 C.E.M.F. 
 
 
 
 
 
 
 
 
 
 2 OHMS 
 
 
 .1 •, 
 
 \ ff 
 
 1=^ 
 
 ^ A\ /x 
 
 r 
 
 TOTAL PRESSURE AT 
 MOTOR TERMINALS 
 aH VOLTS 
 
 
 
 
 
 
 
 
 
 
 
 8 V0L1 
 
 ■3 
 
 1 OH 
 
 M 
 
 
 
 
 
 .^^:o^^ 
 
 TOTAL ACTIVITY OF 
 BATTERY 6 WATTS 
 
 8 VOLTS 1 OHM 
 
 ^AMPERE 
 
 ^ VOLT DROP 
 
 ^6 WATT ACTIVITY 
 
 2 OHMS 
 lK VOLTS DROP 
 
 Fig. 2.— Distribution of C. E. M. F. in A Circuit. 
 
 its German silver wire of 2 ohms resist- 
 ance, replaced by a small electromagnetic 
 
HEATING OF BAKE CONDUCTOKS. 45 
 
 motor of 2 ohms resistance, and two volts 
 counter E. M. F., this E. M. F. being de- 
 veloped by the rotation of its armature, 
 then the current strength through the 
 circuit will be 8 volts — 2 volts = 6 volts 
 effective E. M. F. divided by 8 ohms re- 
 sistance = 1 = 1 ampere. The drop in the 
 resistance of the motor would be 2 x | = 
 H volts, and the total C. E. M. F. of the 
 motor 2 + U = 3| volts. The total work 
 expended in the circuit by the storage cell 
 will be 8 X f = 6 watts, and the total ac- 
 tivity absorbed by the motor will be 3^ x 
 I = 2f watts. Of this activity that part 
 will be expended in heat which is de- 
 veloped in the resistance of the wire; 
 namely, H x |r= 1^ watts, and the remain- 
 ing, or U watts, = 2 X I = li watts will, 
 disregarding certain losses which occur 
 in the revolving parts, be expended me- 
 chanically by the armature, 
 
46 ELECTKIC HEATING. ^ 
 
 It will be noticed, in the above case, that 
 the activity in the circuit, which is the 
 product of current strength and counter 
 E. M. F. due to resistance, is expended in 
 heating the conductor, while the activity 
 which is the product of current strength 
 .and counter E. M. F., due to what is 
 called magnetic induction, is work ex- 
 pended magnetically. This may be 
 taken as a general law ; for, whenever a 
 counter E. M. F. in a circuit is due to 
 thermo-electric, chemical, or magnetic ef- 
 fects, the activity of the current on that 
 C. E. M. F. is expended thermo- electric- 
 ally, chemically, or magnetically; but 
 when the C. E. M. F. is merely that due 
 to the drop of pressure in the conductor, 
 the activity in this drop is expended as 
 thermal activity. 
 
 Consequently, when an electric source, - 
 
HEATING OF BARE CONDUCTORS. 47 
 
 such as a dynamo -electric machine, is 
 connected to a circuit, the counter E. M. 
 F. of the external circuit must be equal 
 to the pressure or E. M. F. of the dynamo 
 at its terminals. The greater the propor- 
 tion of this counter E. M. F. due to mag- 
 netic induction, or to chemical effect, the 
 greater will be the activity expended in 
 the circuit as magnetic, or as chemical 
 activity, while the remainder, due to 
 drop in pressure, or the resistance of 
 the circuit, will be expended thermally 
 in heating the conductor. When, there- 
 fore, a motor is connected to the terminals 
 of a dynamo, the efficiency of the motor 
 will increase with the proportion of 
 the counter E. M. F. due to the rotation 
 of the armature; whereas, if instead of 
 obtaining mechanical work from the 
 motor we wish to produce as much heat 
 as possible in the circuit, we cause the 
 
48 ELECTRIC HEATING. 
 
 motor to come to rest, so that all the 
 electrical activity will be expended in the 
 drop of pressure which will then con- 
 stitute the entire counter E. M. F. 
 
 The resistance of any wire depends 
 wj^oii its resistivity, (or the resistance of a 
 cabic centimetre measured between op- 
 posed faces) its length, and its area of 
 cross -section (1 in. = 2 .54 centimetres. 
 1 sq. in. = 6.4516 square centimetres. 1 
 cu. in.= 16.387 cubic centimetres.) 
 
 The following is a table of resistivities 
 of the more important metals expressed 
 in microhms, or millionths of an ohm, for 
 a temperature of 0^ C, the freezing point 
 of water: 
 
 Table of Resistivities. 
 
 Subrftance. Resistivity. 
 
 Silver, annealed, . . . 1.500 microhms. 
 Silver, hard drawn, .1.53 " 
 
HEATING OF BAKE CONDUCTORS. 49 
 
 Copper, annealed, 
 (Matthiessen's 
 standard) .... 1.594 microhms. 
 
 Copper, hard drawn, 1.629 
 
 Iron, annealed, . . . 9.687 
 
 Nickel, annealed, . 12.420 
 
 Mercury, liquid, . . 94.84 
 
 German silver, about 20.9 
 
 The reference to a standard temperature 
 is necessary, in a table of resistivities, be- 
 cause the resistivity usually varies ap- 
 preciably v^ith variations in the tem- 
 perature. Thus, the resistivity of pure 
 soft copper is given as 1.594 microhms at 
 0^ C. and this means that the resistance 
 between any such pair of opposed faces 
 as a and 6, in a block of this copper 
 one centimetre cube, as represented at 
 A, in Fig. 3, would have a resistance 
 of 1.594 microhms, or 3-^|^5_9^__ ohms. 
 
50 
 
 ELECTRIC HEATING. 
 
 If a wire having a cross-section of 1 sq. 
 cm. as a\ at B in Fig 3, have a length of 5 
 cms., then the resistance between the 
 terminal faces a' and &\ will be 5 times 
 as great as between the terminal faces of 
 the cube at ^, in the same figure, or 5 x 
 
 ^ 
 
 \ a: 
 
 Fig. 3.— Diagram Representing Relation Between Re- 
 sistivity AND Resistance. 
 
 1.945 = 7.97 microhms. Again, if the wire 
 were 5 centimetres long, and had a cross - 
 section of three square centimetres, as 
 shown at C, in Fig. 3, then each centime- 
 tre length of such wire would have one- 
 third the resistance of the unit cube, or 
 
HEATING OF BARE CONDUCTOBS. 51 
 
 i^5_9_4 = 0.533 microhm, and the total re- 
 sistance between the terminal faces a^ 
 and b\ would be 0.533 x 5 = 2.657 mi- 
 crohms. In all cases, therefore, with a 
 wire of uniform material, temperature 
 and resistivity, it is only necessary to 
 multiply the resistivity by the length in 
 cms. and divide by the cross -sectional 
 area of the wire in square centimetres, to 
 obtain the total resistance of the wire. 
 
 While the preceding is a fundamental 
 relation, yet, in practice, it is not always 
 necessary to determine the cross -section 
 of the wire in square centimetres, and its 
 length in centimetres, in order to com- 
 pute its resistance. In English-speaking 
 countries it is customary to express the 
 diameter of a wire in thousandths of an 
 inch, or in mils, one mil being the one- 
 thousandth of an inch. If we square the 
 
52 ELECTKIC HEATING. 
 
 number of mils in the diameter of a wire 
 we obtain the number of what is called 
 circular mils in the wire. Thus, if a wire 
 have a diameter of one -tenth of an inch 
 1= 100 mils, the number of circular mils 
 in the cross -section of this wire will be 
 100 X 100 = 10,000 circular mils. A wire 
 one inch in diameter would have a cross - 
 section of one million circular mils. 
 
 The resistance of a pure standard copper 
 wire one foot long, and one circular mil 
 in cross-section, is 10.35 ohms, at 20^ C, 
 that is to say, a wire one -thousandth of 
 an inch in diameter and one foot loi-^, 
 would have this resistance. The re- 
 sistance-per-foot in any pure copper wire 
 will be this resistance, divided by the 
 number of circular mils in its cross -sec- 
 tion. For example, the wire above re- 
 ferred to as having 10,000 circular mils 
 in its area of cross-section would have 
 
HEATING OF BARE CONDUCTORS. 53 
 
 a resistance per-foot of yV^iiVo = 0.001035 
 ohm-per-foot at 20"^ C. The resistance of 
 such a wire per mile would be 5280 x 
 0.001035 = 5.465 ohms. 
 
 While the use of cn^cular mils Is very 
 convenient for ^^ires whose length is ex- 
 pressed in feet, when tables or data con- 
 cerning the resistance of a circular-mil- 
 foot have been prepared, yet it is desira- 
 ble to retain also the fundamental con- 
 ception of the resistance as dependent 
 upon resistivity and dimensions for the 
 cases which may occur that are not 
 dealt with in tables. For example, a re- 
 sistance of 100 metres (10,000 cms.) of pure 
 soft copper wire at O^C. having a cross- 
 section of 0.05 square centimetre would 
 be— i--^H.?^4----- microhms = 318,800 mi- 
 crohms = 0.3188 ohm. 
 
64 ELECTKIC HEATING. 
 
 The resistivity of a metal is always re- 
 duced by the process of softening or an- 
 nealing it, although the reduction in the 
 resistivity, due to annealing, may only 
 amount to one or two per cent. The re- 
 sistivity depends very greatly, however, 
 upon the physical nature and purity of 
 the material. A very small percentage of 
 certain impurities in a copper wire, such, 
 for example, as phosphorus or sulphur, 
 will greatly increase its resistivity, and 
 even the presence of gases occluded or 
 absorbed by the substance of the wire is 
 said to appreciably increase its resistivity. 
 The purity with which copper wires can 
 be commercially obtained, at the present 
 time, is such that their resistivity is, per- 
 haps, only one per cent, greater than that 
 of the so-called pure, standard, soft-cop- 
 per wire, while it sometimes happens that 
 wires are obtained commercially whose 
 
HEATING OF BARE CONDUCTORS. 55 
 
 resistivity is actually less than that of 
 this standard. 
 
 In dealing with wires of other metals 
 than copper, such as lead, iron and Ger- 
 man silver, the tabular resistivities can- 
 not, as a rule, be relied upon to limits 
 closer than say five per cent., and where a 
 degree of accuracy greater than this is re- 
 quired, measurements of the resistivity of 
 such wires, at a given temperature, are 
 necessary. This can be done by carefully 
 measuring the resistance of a given length 
 of wire when its cross-section is known or 
 can be carefully observed. The resistiv- 
 ity in ohms, at the temperature of the 
 measurement, will then be the resistance 
 multiplied by the cross- sectional area of 
 the wire in square centimetres divided 
 by the length of the wire in centimetres. 
 
56 ELECTKIC HEATING. 
 
 The effect of temperature on all pure 
 metallic conductors is to increase the re- 
 sistivity. Nearly all alloys also increase 
 in their resistivity with increase in tem- 
 perature, though less rapidly than their 
 pure component metals. A few specially 
 prepared alloys, such as platinoid, have a 
 very small increase of resistivity with 
 temperature, and are, therefore, in special 
 request for the manufacture of permanent 
 resistance coils, whose resistances are to 
 remain as nearly constant as possible; 
 while one or two alloys have been pre- 
 pared whose resistivities are either not 
 effected by temperature, or have a slight 
 positive or negative coefficient; ^. e. , a 
 slight increase or decrease in resistivity 
 with temperature, at different points of 
 the thermometric scale. Carbon di- 
 minishes in resistivity about 0.5 per cent, 
 per degree centigrade, reckoned from its 
 
HEATING OF BARE CONDUCTORS. 57 
 
 resistivity at zero centigrade. Pure 
 metals, or metals containing only a very 
 small percentage of impurity, usually in- 
 crease about 0.4 per cent, in their resistiv- 
 ity, per degree centigrade, above that 
 which they possess at zero centigrade. 
 For example, taking the resistivity of cop- 
 per as 1.594 microhms at O^C, its resis- 
 tivity at 20^ C. will be increased by 20 
 X 0.4=8 per cent., so that its resistivity at 
 this temperature will be 1.594 x |^|-== 
 1.721 microhms, approximately. At the 
 boiling point of water, or 100^ C, its re- 
 sistivity will have become increased by 
 approximately 100 x 0.4 — 40 per cent., 
 and its resistivity will be i'-^f^^i-^ o z= 2.232 
 microhms. 
 
 When the resistivity of a wire is 
 known, either by actual measurement at 
 the temperature of observation, or from 
 
58 ELECTRIC HEATING. 
 
 its tabular resistivity at O^C. referred 
 as above to the actual temperature, the 
 amount of heat which will be developed 
 in it in a given time, by a given current 
 strength, becomes known, except in so 
 far as its temperature elevation under the 
 heating influence may be undetermined. 
 For example, if a copper wire were insu- 
 lated by a thin coating of some non-con- 
 ducting varnish and placed in ice-water 
 at 0^ C, the resistivity of the wire might 
 be 1.6 microhms, and a circular -mil -foot 
 of this wire would have a resistance of 
 9.625 ohms. If the diameter of the wire 
 were 0.01'"; ^. e. , No. 30 of the American 
 wire gauge (A.W.G.) having a cross-sec- 
 tion of 100.5 circular mils, the resistance 
 of 10 feet of such wire would be -^W.^-- 
 =0.9577 ohms at 0^ C. If a current of two 
 amperes be sent steadily through this 
 length of wire, the drop in the wire would 
 
HEATING OF BAKE CONDUCTORS. 59 
 
 be 2 X 0.9577=1.9154 volts, and the activ- 
 ity expended thermally in the wire would 
 be 2 X 1.9154=^3.831 watts, or joules-per- 
 second = 2.827 foot-pounds-per-second. 
 The heat which would be expended in the 
 wire would fail to appreciably raise its 
 temperature, since it would readily pass 
 through the insulating varnish into the 
 ice-water, and, if we assume that abun- 
 dant ice is present, the temperature of 
 the water would not be raised until all the 
 ice was melted. The work done by the 
 electric source in supplying the current 
 through this wire would, therefore, be 
 expended in melting the ice. 
 
 If, however, the same length of wire be 
 suspended in air, and the same current 
 strength, of say 2 amperes, passes stead- 
 ily through it as before, then, although 
 some of the heat would be carried off by 
 
60 ELECTEIC HEATING. 
 
 the air, yet the resistance offered by the 
 air to the escape of the heat from the wire 
 would be much greater than that offered 
 by the varnish and water in the preceding 
 case, so that the temperature of the wire 
 would be raised. This would increase 
 the resistivity of the wire at the rate of, 
 approximately, 0.4 per cent, per degree 
 centigrade of temperature elevation, so 
 that both the resistance and the thermal 
 activity of the wire would rise. 
 
 Suppose, for example, that the air sur- 
 rounding the wire is at a temperature of 
 20^ C. and that the current through the 
 wire raises its temperature 10° C. above 
 the surrounding air, or to 30° C. Then 
 the resistivity of the wire before the 
 current passed through it, would be 
 1.6 X ^§1=1.728 microhms, and after 
 the current has passed through it steadily 
 1.6 X ill = 1.792 microhms, so that the 
 
HEATING OF BAKE CONDUCTOKS. 61 
 
 resistance of the heated wn^e will be 10.72 
 and the thermal activity in the heated 
 wire 4.288 watts. 
 
 It is, therefore, a simple matter to de- 
 termine the thermal activity in a given 
 conductor when the drop of pressure in 
 the conductor and the current strength 
 passing through it are observed; for, if the 
 drop in a wire, for example, be 5 volts, 
 and the current through the wire, 100 
 amperes, then the thermal activity in the 
 wire will be 500 watts. But it is by no 
 means a simple matter to determine what 
 temperature the wire will attain when 
 subjected' to this heating, since the wire 
 is constantly losing its heat at a rate which 
 depends upon a variety of circumstances. 
 
 When a current passes through a wire, 
 the heat developed by that current causes 
 
62 
 
 ELECTRIC HEATING. 
 
 it to increase its temperature. When a 
 body is heated above the temperature of 
 surrounding bodies, heat flows from the 
 former to the latter, just as water flows 
 from a higher to a lower level. The great- 
 er the elevation of temperatare of the 
 heated body, the more rapid will be the 
 passage of heat, or the greater the thermal 
 current strength. When the body is sup- 
 plied with heat at a steady rate, its tem- 
 perature continues to rise until the rate 
 at which it receives heat is balanced 
 by the rate at which it loses it. Conse- 
 quently, a time is reached when the tem- 
 perature of the body remains constant, 
 although the body is constantly receiv- 
 ing heat. When, therefore, an electric 
 current has been passing for a sufficient 
 length of time through a conductor, its 
 temperature will attain a definite eleva- 
 tion above that of surrounding bodies and 
 
HEATING OF BARE CONDUCTORS. 63 
 
 remain constant, the thermal activity 
 within the conductor being balanced by 
 the loss of heat from the surface of the 
 conductor. 
 
 Heat escapes from a body in three 
 ways; namely, 
 
 (1) By conduction to bodies in imme- 
 diate contact with its surface; as, for ex- 
 ample, when a heated wire is enclosed in 
 a mass of lead or rubber, the heat passing 
 directly across the surface of the wire 
 into the surrounding substance. 
 
 (2) By convection, which occurs only in 
 fluids; i.e., liquids or gases. Here, the 
 particles of fluid surrounding the hot body 
 become heated and are carried through 
 the fluid mass by currents, set up by dif- 
 ferences in density of the hotter and cool- 
 er portions of the fluid. 
 
 (3) By radiation, the heat passing out 
 
04 ELECTEIC HEATING. 
 
 from the heated surface in straight lines 
 just as light does, when a body becomes 
 incandescent. 
 
 As to which of the above methods of 
 loss of heat is the most effective in the 
 case of a wire heated by an electric cur- 
 rent, depends upon the character of the 
 surroundings of the wire, whether the 
 wire is bare or covered, and where it is 
 placed. 
 
 Circuit wires may be either bare or cov- 
 ered. Bare wires are only suitable for 
 suspension in air. Covered wires may be 
 placed in air, in water, or in the ground. 
 The character of the covering may also 
 vary in different cases. 
 
 It might be supposed that a bare wire 
 suspended in the air was the simplest 
 case to deal with. Such, however, is far 
 
HEATING OF BAEE CONDUCTOES. 65 
 
 from being the case; for not only does the 
 position of the wire itself greatly affect 
 the ease with which it loses heat, but al- 
 so the condition of the surroundin;;^: air, 
 w^hether at rest or in motion. 
 
 When a bare wire is supported horizon- 
 tally in the air of a room, and an electric 
 current is passed through it, this current 
 wall set up a certain drop of pressure in 
 the wire, and the product of this drop and 
 the current strength, will give the thermal 
 activity developed in the wire at the out- 
 set. 
 
 Under these circumstances the tem- 
 perature elevation of the wire wall have 
 become practically constant in about two 
 minutes. As soon as this limiting tem- 
 perature is reached the heat developed 
 by the electric current m any length of the 
 w^ke, such as an inch or a centimetre, will 
 be equal to the heat dissipated from its 
 
66 ELECTRIC HEATING. 
 
 surface by radiation and convection. The 
 amount of heat that will be radiated in a 
 given time, say one second, from a given 
 length of the wire, say one inch, will de- 
 pend upon the extent of free surface of the 
 wire in that length, upon the nature of 
 its surface, whether bright, blackened or 
 colored, smooth or rough, etc., and upon 
 the temperature elevation the wire has 
 attained. A rough, blackened surface will 
 radiate heat, approximately, twice as rap- 
 idly as a smooth, bright surface. 
 
 The heat which will escape from the 
 wire by convection, in the same length, 
 so far as is known, is practically the 
 same for all diameters of wire and for all 
 characters of surface, so that the loss by 
 convected heat does not depend upon the 
 surface, or only increases slightly with 
 the surface, while the loss by radiated 
 
HEATING OF BARE CONDUCTORS. 67 
 
 heat increases directly with the surface. 
 
 For every degree centigrade of tem- 
 perature elevation attained by the wire 
 Jibove the surrounding still air of a room, 
 the heat lost by convection is, approxi- 
 mately, 0.053 joules-per-second, per footof 
 length, so that if the wire has a temper- 
 ature elevation of 20^ C, every foot will 
 lose by convection, approximately, 1.08 
 joules-per-second, or will lose heat energy 
 at the rate of 1.06 watts. The loss by 
 radiation will be approximately 0.001 watt 
 per square inch of bright surface, per de- 
 gree centigrade of temperature elevation. 
 
 The total loss of heat in watts will, 
 therefore, be the temperature elevation of 
 the wire, in degrees centigrade, multiplied 
 by the number of feet, and by 0.053 for the 
 effective loss and the same temperature 
 
68 ELECTEIC HEATING. 
 
 elevation multiplied by the number of 
 square inches of surface and 0.004 for 
 the radiation loss. 
 
 When the air, in which a wire carrying 
 an electric current is suspended, is in a 
 state of motion, as, for example, w^henthe 
 wire is suspended out of doors, and ex- 
 posed to wind and air currents, the loss 
 of heat by convection from its surface is 
 greatly increased even in the calmest 
 wxather. Air currents carry off a large 
 amount of heat from the wire, so that the 
 temperature elevation of the wire for a 
 given current strength is considerably re- 
 duced. 
 
CHAPTER lY. 
 
 ELECTRICAL HEATING OF COVERED CON- 
 DUCTORS. 
 
 An electric conductor, when employed 
 to carry an electric current to a distance, 
 is intended to be -kept as cool as possible; 
 first, because a hot wire necessarily 
 means a wire in which energy that might 
 otherwise be utilized is being expended 
 uselessly as heat; second, because the re- 
 sistance of a hot wire is higher than that 
 of a cold wire and, consequently, more 
 energy is wasted in the wire to sustain a 
 given current; and third, because a wire 
 that is overheated by the current it car- 
 ries, may either destroy its insulation or 
 set fire to inflammable bodies in its vicin- 
 ity. On the contrary, an electric conduct- 
 
70 ELECTRIC HEATING. 
 
 or, which is intended for purposes of de- 
 veloping heat by the expenditure of elec- 
 tric energy, as in an electric heater, is do- 
 ing its best service when it is as hot as it 
 can become without danger of injury from 
 an excessive temperature. Since the 
 great majority of heated electric conduct- 
 ors are those in which heat is both an ob- 
 jection and a loss, it is necessary to ex- 
 amine the laws which control their heat- 
 ing, with a view of avoiding a dangerous- 
 ly high temperature. 
 
 Whether a covered wire be supported 
 in air, buried in the ground, or immersed 
 in water, it is evident that its heat must 
 first escape into the insulating covering, 
 before it can pass into the surrounding 
 medium. In other words, the insulat- 
 ing covering offers a certain resistance to 
 the escape of heat from the wire, and, if 
 
HEATING OF COYEEED CONDrCTOES. 71 
 
 the covering could be removed without 
 allowing the electricity to escape from 
 the wire, the temperature of the wire, 
 imder any given current strength, would 
 be less than that it attains with the cover- 
 ing in place. 
 
 The thermal resistance of any insulating 
 covering, on a round wire, depends on the 
 proportion of the diameter of the bare 
 conductor to the diameter of the covered 
 conductor, and on the nature of the insu- 
 lating material. As no two insulating 
 coverings offer exactly the same electric 
 resistance to the escape of electricity, so 
 no two insulating coverings offer exactly 
 the same thermal resistance to the es- 
 cape of heat from the wire. All good 
 electric insulators are good thermal non- 
 conductors, so that just as a considerable 
 difference of electric pressure is required 
 
72 ELECTKIC HEATING. 
 
 to force a given quantity of electricity 
 through a conducting coating on a wire, 
 so a considerable difference of thermal 
 pressure; i.e., difference of temperature, 
 is required between the inside and outside 
 of the coating to force a given quantity of 
 heat through the coating. When, therefore, 
 the insulating coating is thick, it is to be 
 expected that the temperature elevation 
 of the wire, for a moderate current 
 strength, will be appreciable. If, how- 
 ever, the covered wire be supported in the 
 air of a room, it will frequently happen 
 that the wire will be cooler than if devoid 
 of covering, for the reason that the advan- 
 tage gained by increased external surface 
 and the greater radiation therefrom, will 
 more than compensate for the additional 
 thermal resistance between the surfaces 
 of the wire and the air surrounding it. 
 The same is also more likely to be the 
 
HEATING OF COYEKED CONDUCTOKS. i6 
 
 case if the insulating covering of the wire 
 be blackened, since its radiation will there- 
 by be increased. 
 
 When a covered wire, instead of being 
 supported in air, is immersed in water, 
 the temperature elevation of the wire is 
 increased by reason of the insulating cov- 
 ering; for, if the wire could be covered 
 w^ith a very thin, electrically non-con- 
 ducting varnish, it would be almost im- 
 possible to raise the temperature of the 
 conductor, so rapid is the communication 
 of heat from the metal to the mass of 
 surrounding liquid, and so slow the 
 elevation of temperature in the liquid, if 
 its volume is large. With air, as we have 
 seen, the case is very different; the 
 thermal resistance of still air is often 
 large, while the thermal resistance of 
 water is very small. With wires sub- 
 
74 ELECTKIC HEATING. 
 
 merged in water it may be safely assumed 
 that the entire thermal resistance to the 
 escape of heat exists in the non-conduct- 
 ing covering, and that no thermal resist- 
 ance exists in the water outside it. 
 
 A covering of metal on the external 
 surface of an insulated wire, such, for ex- 
 ample, as a thin shell of lead spread over 
 the insulating material, does not offer any 
 appreciable thermal resistance. Metals 
 conduct heat so rapidly, as compared with 
 insulating substances, that the thermal 
 resistance in the metal may be neglected. 
 In fact a lead sheath aids in cooling a wdre 
 suspended in air, since it provides an in- 
 creased surface for loss of heat by radia- 
 tion and convection; or, in other words, it 
 reduces the effective thermal resistance 
 of the air. 
 
HEATING OF COVERED CONDUCTOBS. 75 
 
 The safe carrying capacity of a conductor 
 may be defined as the current strength 
 that can safely be permitted to pass 
 through it. The carrying capacity de- 
 pends upon the highest limit of tempera- 
 ture elevation permitted as consistent with 
 safety. In some cases, it is desirable, 
 from considerations of economy of in- 
 stallation, to press the electric activity of 
 a wire up to the limit of safety. In most 
 cases, however, it is too expensive to force 
 the activity of a wire to such a limit, for 
 the reason that the expense of the thermal 
 activity expended in the wire, at the 
 safety limit, renders a larger and more 
 costly wire, with a lower resistance and 
 diminished temperature elevation, eco- 
 nomical. In cases where it is desirable to 
 carry a powerful current with the mini- 
 mum cross-section or weight of conductor 
 consistent with safety, it is often advan- 
 
76 ELECTRIC HEATING. 
 
 tageous to subdivide the conductor; ^. e., 
 to employ two or more small wires in- 
 stead of a large single conductor. In the 
 case of a subdivided conductor, the tem- 
 perature elevation of each separate wire 
 wall be considerably less than the tem- 
 perature elevation of a single wire carry- 
 ing the entire current. This is for the 
 reason that the surface of a pound of a 
 given wdre varies with its area of cross - 
 section, decreasing as the area of cross- 
 section increases, and vice versa. In 
 other w^ords, a small wdre has a larger 
 surface, per pound, than a large one, and, 
 as is evident, the greater the surface, 
 the greater the rapidity with which the 
 heat generated within the substance of 
 the wire can escape. 
 
 An insulated wire placed in a wooden 
 moulding, or in a closely -fitting conduit in 
 
HEATING OF COVERED CONDUCTORS. 77 
 
 a building, loses its heat entirely by con- 
 duction, pro*vdded the walls of the panel 
 or conduit are everywhere in contact 
 with the external surface of the covered 
 wdre. In this case, the temperature ele- 
 vation of the wire, for a given current, is 
 greater than if the wire were immersed 
 in water, since the thermal resistance of 
 the walls of the panel is added to the 
 thermal resistance of the insulating cover- 
 ing. In almost all cases, however, the 
 temperature elevation is less than if the 
 wire were supported in air. Consequent- 
 ly, the effective thermal resistance of a 
 panel or conduit, is generally less than 
 the effective thermal resistance of the 
 air within a room. 
 
 The rule in common use for determin- 
 ing the size of wires to be placed in 
 wooden mouldings, is to allow 1000 am- 
 peres per square inch of area of cross- 
 
78 ELECTKIC HEATING. 
 
 section. This rule is easily applied, and 
 affords a convenient guide in the absence 
 of any special tables of reference. It 
 must be remembered, however, that the 
 rule implies that a large wire will lose its 
 heat as readily as a small one, and this, 
 as we have seen, is not the case, owing 
 to the reduction of surface per unit of 
 cross -sectional area or weight. Conse- 
 quently, a very large wire, selected accord- 
 ing to this rule, would be heated to a much 
 higher temperature than a very small 
 wire. In fact, the rule is not to be re- 
 garded as entirely safe beyond 250 am- 
 peres of current strength. 
 
 In buildings which are not absolutely 
 firepi'oof, it is imi3ortant that the conduct- 
 ors, which may be placed in them for 
 supplying electric light or power, shall 
 be so proportioned that their temperature 
 may never become dangerously high. A 
 
HEATING OF COVEEED CONDUCTORS. 79 
 
 wire which can be grasped in the hand, 
 say for a minnte, without marked discom- 
 fort from its heat, may be regarded as at 
 a safe temperature. The limiting tem- 
 perature, defined in this way, will of course 
 depend physiologically upon the condition 
 of the hand and the sensibility of the per- 
 son making the experiment, but roughly, 
 may be considered as in the neighborhood 
 of 50^ C. If we assume that the summer 
 temperature of the interior of a house is 
 30^ C. or 86^ F. , then to conform with these 
 requirements as to temperature, the limit- 
 ing temperature elevation for such a wire 
 w^ould be fixed as approximately 20^ C. 
 In other words, we must not allow the 
 current strength through the wire to ex- 
 ceed that necessary to elevate its temper- 
 ature 20^ C, since, otherwise, in summer, 
 the temperature attained by the wire at 
 full load would exceed 50^ C. In practice. 
 
80 ELECTEIC HEATING. 
 
 however, the limiting temperature allowed 
 by Fire Insurance Boards is sometimes 
 placed as low as 10^ C. at full load, so as 
 to allow margin for any accidental over- 
 loads that may occur unexpectedly. 
 
 If we double the current strength pass- 
 ing through a wire, under any given con- 
 ditions, we quadruple, roughly, the tem- 
 perature elevation of the wire. Thus, if 
 a wire in moulding be elevated 10^ C. 
 above surrounding temperatures by the 
 passage of its full-load current, then 
 twice that current strength will elevate its 
 temperature 40^ C, approximately, or 72° 
 F., and if the wire be originally at a tem- 
 ])erature of 78° F., its final temperature 
 with double full load will be 150° F, 
 
 Insulated wire for underground work 
 usually possesses in addition to the ordi- 
 
HEATING OF COVERED CONDUCTORS. 81 
 
 nary insulating material, a sheathing of 
 lead, and is either buried directly in the 
 ground, or is placed in a conduit. The ne- 
 cessity for obtaining a ready access to 
 wires for their examination has led to the 
 latter process being adopted in most cases. 
 In order to insure high insulation, the con- 
 duits frequently have air forced through 
 them, in which case their condition ap- 
 proximates to that of a lead-covered 
 wire supported in air. 
 
 Taking now the case of a wire buried 
 directly in the ground, the thermal resist- 
 ance to the escape of heat from the con- 
 ductor is not only that of the insulator, 
 but also that of the ground. If the ground 
 be moist, its effective thermal resistance is 
 reduced, but if it be dry, the thermal re- 
 sistance may be considerable. In almost 
 all cases, however, the thermal resistance 
 
82 ELECTEIC HEATING. 
 
 of the ground is less than the thermal re- 
 sistance of still air, so that a buried wire, 
 carrying a given current strength, will be 
 cooler than the same wire supported in 
 still air, although cases may occur in 
 which this statement does not hold good. 
 
 Intermediate between the condition of 
 a wire suspended in the air of a room, 
 and a wire in a conduit, in which there is 
 no attempt at forced ventilation, there is 
 the condition of a wire supported in a sub- 
 way. Here the air being at rest, the con- 
 ditions approximate, thermally at least, to 
 the case of a wire in the still air of a room. 
 
 When a wire has been electrically in- 
 active for a considerable period of time, 
 its temperature will necessarily coincide 
 with that of the surrounding air or other 
 material. When, however, the full-load 
 
HEATING OF COVERED CONDUCTORS. 83 
 
 current is sent through the wn^e, its tem- 
 perature will immediately begin to rise, 
 the rate of elevation of temperature being 
 a maximum at the outset, and diminish- 
 ing steadily as elevation of tempera- 
 ture is attained. From a theoretical stand- 
 point the wire never does reach the full 
 maximum temperature, but always ap- 
 proaches it. Practically, however, a wire 
 in air, reaches, say 95 per cent, of its maxi- 
 mum temperature in two minutes after 
 the application of the full-load current 
 strength. In water a wire reaches this 
 temperature in about ten minutes after 
 the full-load current is applied; in wood- 
 en moulding, in about fifteen minutes, 
 and, when buried in the ground, in about 
 twenty minutes. The larger the wire, 
 the greater will be its mass, and, conse- 
 quently, the longer the time required by 
 it to attain its full temperature elevation. 
 
84 ELECTRIC HEATING. 
 
 In the case of buried wires, the heat 
 has to be propagated slowly outward 
 from the wire through the mass of the 
 neighboring earth. The result is that, 
 while the layers of earth closely surround- 
 ing the wire will probably reach 95 per 
 cent, of their maximum temperature ele- 
 vation in half an hour, the layers situated 
 at a considerable distance from the wire, 
 although they will necessarily receive a 
 much smaller temperature elevation, yet 
 will require a much longer time for that 
 temperature elevation to be established, 
 and many hours may elapse before 50 per 
 cent, of the maximum temperature eleva- 
 tion is attained at a distance of say four 
 feet from a deeply buried wire. 
 
 The temperature elevation, which may 
 be permitted in a wire buried in the 
 ground, is determined by totally different 
 
HEATING OF COVERED CONDUCTORS. 85 
 
 conditions to those which limit the tem- 
 perature elevation of a wire placed in a 
 building; for it is evident that there is no 
 danger of setting fire to the ground. The 
 insulating material of a wire has, how- 
 ever, to be sufficiently plastic to allow the 
 wire to be bent or slightly stretched, and 
 this condition, together with good electric 
 insulation, is usually found in a substance 
 that will not permit of a high temperature 
 without injury. Even if it were possible 
 to operate a buried conductor at a high 
 temperature, such temperature would be 
 dangerous where the conductor emerged 
 from the ground. The temperature ele- 
 vation, in the case of hemp -covered wires, 
 is usually 2b^ C. and in rubber-covered 
 wires 20^ C. Most insulating materials, 
 long before they would be injured by the 
 heat, would be liable to soften, thus per- 
 mitting the conductor to sag, so that it 
 
86 ELECTKIC HEATING. 
 
 would no longer remain embedded central- 
 ly in the insulating material. Conse- 
 quently, the permissible temperature el- 
 evation is limited by the softening point. 
 
 As regards the temperature elevation of 
 ocean cables, employed in submarine 
 telegraphy, the question is at present de- 
 void of practical interest, since the cur- 
 rents which such cables carry are so very 
 feeble, say generally only a few milli-am- 
 peres, that the temperature elevation of 
 the conductor is entirely negligible. It is 
 worth pointing out, however, as an inter- 
 esting fact, that should occasion ever arise 
 for sending powerful currents through 
 submarine -cables, the fact that the entire 
 bed of the deep ocean is covered by a 
 layer of very cold water in the neighbor- 
 hood of 30^ F., would permit a ready 
 loss of heat. 
 
CHAPTER V. 
 
 FUSE WIRES. 
 
 A WIRE placed in a building, although so 
 proportioned relatively to the current 
 strength it has to carry, that, under ordi- 
 nary circumstances its temperature will 
 be perfectly safe, yet, owing to acci- 
 dental external causes, the current 
 strength may sometimes become enor- 
 mously increased, thereby heating the 
 wire to a dangerously high temperature. 
 If, for example, the wire has in its cir- 
 cuit a group of lamps, requiring normally 
 10 amperes of current from a pressure of 
 115 volts, then, if by some accident a short- 
 circuit be effected at the lamps, the cur- 
 rent strength through the lamps would 
 be much diminished, but the strength of 
 
88 ELECTKIC HEATING. 
 
 current in the wire, supplying the lamps, 
 might become enormously increased; for, 
 while the pressure on the mains would 
 remain practically the same, the resist- 
 ance in the circuit, if very small, would 
 permit, by Ohm's law, a very powerful 
 current to pass through it. 
 
 The effect of such an abnormally great 
 current would be to cause the amount of 
 heat liberated in the wire, forming the 
 short circuit, to be far greater than it 
 could dissipate without attaining a temper- 
 ature sufficiently high to make it red hot, 
 or even to melt it. If such a wire were 
 melted by an accidental short-circuit, not 
 only would there be danger of setting fire 
 to the wood-work, or other inflammable 
 material surrounding the wire, but there 
 might also be considerable trouble and 
 difficulty in replacing the wire after the 
 accident. Moreover, the effect of a vio- 
 
FUSE WIRES. 89 
 
 lent overload, sometimes sufficiently great 
 to melt even a stout conductor forming 
 some portion of the circuit, would be 
 liable to injure the dynamo or engine 
 driving it, or to overheat and consequent- 
 ly injure any electrical apparatus that 
 might be in the same circuit. In order to 
 avoid these difficulties the plan has been 
 universally adopted of inserting wires, 
 cdilled fuse wires, in the branch and main 
 circuits of any system supplied by a 
 dynamo. 
 
 A fuse wire is a wire or a strip of metal, 
 which has both a high electric resistance 
 per unit of length, and a low melting 
 point. If such a wire be in circuit with 
 a copper wire, and both are of such sizes 
 that they are able to carry the normal, 
 full-load current without overheating, it 
 will be evident that the fuse wire must 
 become much hotter than the copper wire; 
 
90 ELECTEIC HEATING. 
 
 for, since, as we have seen, the amount of 
 heat developed in auy circuit, the current 
 strength remaining the same, depends on 
 the resistance of the circuit, it is evident 
 that the same quantity of heat will be de- 
 veloped in such lengths of the fuse wire 
 and the copper wire, as have an equal 
 drop; i.e. , offer an equal resistance to the 
 current. Consequently, there wall be de- 
 veloped in, say one inch of fuse wire, the 
 same amount of heat as would be liber- 
 ated in, perhaps, ten feet of copper wire. 
 The fuse wire will, therefore, be raised to 
 the temperature at which it melts, long 
 before the temperature of the copper wire 
 would pass the danger point, and the 
 melting of the fuse wire would interrupt 
 the circuit and thus automatically cut off 
 the current. The meaning of the term 
 safety fuse is, therefore, evident, since the 
 simi^le introduction of such a wire into the 
 
FUSE WIKES. 91 
 
 circuit would absolutely prevent the pas- 
 sage through such circuit of a current 
 that would raise its temperature to a dan- 
 gerously high degree. It is fortunate 
 that so simple a plan as the mere inser- 
 tion of a safety fuse should be capable of 
 protecting electric conductors against the 
 consequences of accidental short circuits. 
 Like many other inventions, its value lies 
 largely in its extreme simplicity, and in 
 che certainty with which it can be relied 
 upon to operate effectively. 
 
 Fuse wires are composed of lead and 
 tin, or tin-lead alloy. These wires usu- 
 ally occur in the sizes shown in Fig. 4. 
 Here, on the right hand, the diameters of 
 the wires are given in circular mils, and 
 on the lef c hand, the carrying capacity of 
 the wires in amperes. It is to be ob- 
 served, that although the cross -section of 
 
92 ELECTRIC HEATING. 
 
 a wire is quadrupled \Yhen its diameter is 
 doubled, yet the carrying capacity is not 
 
 CARRYING CAPACITY FUSE WIRES DIAMETERS 
 
 AMPERES MILS 
 
 20 
 
 7 ^^ 
 
 15 
 18 
 
 '25 i ■ ■ 75 
 
 28 ' 85 
 
 9& 
 
 36 ^^ U1 
 
 50 , >30 
 
 Fig. 4.— Diameter and Carrying Capacities of Fuse 
 Wires. 
 
 quadrupled. The carrying capacity in- 
 creases faster than the diameter of the 
 wire, but less rapidly than its area of 
 cross -section. 
 
FUSE WIRES. 93 
 
 Safety fuses are not only employed in 
 the form of wires, but also in the form of 
 strips, as shown in Figs. 5 and 6. In 
 Fig. 5, the safety strips are connected to 
 the circuit by means of binding posts, the 
 studs of which pass through holes at each 
 
 Fig. 5.— Fuse Strips. 
 
 end. In Fig. 6, the ends of the strips are 
 slipped beneath the screw clamps, thus 
 avoiding the necessity for the removal of 
 the screw head, as would be the case in 
 the form shown m Fig. 5. 
 Fuse wires, such as shown in Fig. 4, 
 
94 ELECTRIC HEATING. 
 
 are placed in the circuit by simply wrap= 
 ping them around binding posts connected 
 with the circuit and firmly clamping the 
 connection with a screw head. This pres- 
 sure is apt to damage the wire and alter 
 
 Fig. 6.— Fuse Links. 
 
 its carrying capacity, thus causing it to 
 melt at a unduly low strength of current. 
 To avoid this, the ends of the wire or 
 
FUSE WIRES, 
 
 95 
 
 Fig. 7.— Copper-Tipped Fuse Wires. 
 
 strip are often fused into copper clam{)S 
 as shown in Figs. 7 and 8. Large safety 
 strips are usually of the form shown in 
 Fig. 8, the lead strip being riveted to the 
 copper end pieces. 
 
 Fig. 8.— Coppii:R-TippED Safety Fuses. 
 
96 ELECTRIC HEATING. 
 
 Fig. 9 shows a simple form of safety 
 fuse-block consisting of a slab of slate, or 
 other non-inflammable material, on which 
 are mounted two metal blocks B and B. 
 The circuit passes through these metallic 
 blocks, and the fuse wire is clamped be- 
 tw^een them as shown. 
 
 Fig. 9.— Safety Fuse-Block. 
 
 Fig. 10 shows a pair of strip safety 
 fuses S^, S,, or safetj/ links, as they are 
 sometimes called, inserted in the circuit 
 cf the two leads BB' and A A' , under 
 thumb screw clamps situated at the ends 
 of the metallic blocks which form the 
 terminals of the leads BB"^ and AA' . 
 These blocks are mounted on a non-con- 
 
FUSE WIRES. 
 
 97 
 
 ducting and non-inflammable plate, such 
 as a slab of slate, porcelain, or marble. 
 
 Fig. 11 represents a porcelain fuse-block 
 prepared for the reception of safety 
 links between the screw clamps A, A\ 
 
 B' 
 
 A' 
 
 Fig. 10.— Pair of Safety Strips, Mounted on Fuse- Block. 
 
 and B,B\ The two supply mains A and 
 B are electrically separated from each 
 other by the porcelain projecting ridge 
 RR, provided for this purpose. The pres- 
 *sure between these leads may be 100 or 
 200 volts, according to circumstances, and 
 
98 
 
 ELECTKIC HEATING. 
 
 were the ridge not present, the blowing 
 of the fuse might establish a dangerous 
 
 Fig. 11.— Porcelain Fuse-Box. 
 
 arc across the leads, or such arc might be 
 accidentally established during the proc- 
 
FUSE WIRES. 99 
 
 ess of connecting the safety links and 
 thus, perhaps, injure the attendant. 
 
 Fuse-boxes are generally provided with 
 a porcelain cover, though at times, for the 
 purpose of ready inspection, a transpar- 
 ent cover, such as glass or transparent 
 mica, is employed. Figs. 12 and 13 show 
 examples of fuse-blocks of the latter type 
 with the fuse wires or links in position. 
 The arrangement of the box will neces- 
 sarily vary according to whether the main 
 wires terminate in the box, or pass 
 through it. Thus at A, Fig. 12 , the mains 
 pass directly through the box in the 
 grooves on the left hand, but after being 
 bared of their insulation, have their con- 
 ductors clamped underneath the screws 
 whose heads are visible in the grooves. 
 Connections exist beneath the box from 
 these screws to the safety links on the 
 right-hand side and the branch wires are 
 
 LOFC. 
 
100 
 
 ELECTEIC HEATING. 
 
 A. 
 
 B 
 
 Fig. 12.— Mica-Covered Fuse-Boxes. 
 
 carried off at right angles. In the event 
 of any short -circnit between the branch 
 wires, one or both of the safety links is 
 
FUSE WIRES. 
 
 101 
 
 melted, but no accident in the main cir- 
 cuit can affect these fuses, since the main 
 
 Fig. 13.— Mica-Covered Fuse Boxes. 
 
 conductors, as abeady mentioned, pass 
 directly through the box. 
 
102 ELECTRIC HEATING. 
 
 At h, IS shown a form of safety fuse-box 
 through which the mains do not pass, but 
 terminate, say at the left, and the wires 
 supplied by such mains enter at the right. 
 
 At (7, a form is shown from which two 
 separate branch circuits issue from the 
 
 Fig. 14. — Fuse- Box Provided with Porcelain Cover. 
 
 box, half to the right and half to the left, 
 after being suitably connected to the 
 mains which enter and pass through the 
 centre of the box. 
 
 Practically similar forms are shown in 
 Fig. 13. 
 
FUSE WIRES. 
 
 103 
 
 Fig. 15.— Fuse-Box with Fuses in Cover. 
 
104 
 
 ELECTEIC HEATING. 
 
 In all these forms, a thin mica cover 
 serves to exclude dust, and, at the same 
 time, renders the conditions of the safety- 
 links externally visible. 
 
 Figs. 14 and 15 show forms of fuse- 
 boxes, provided with porcelain covers. 
 
 Fig. 16.— Ceiling-Fixture Fuse-Block. 
 
 The form shown in Fig. 14 is similar to the 
 box shown in Fig. 11, with the addition of 
 sides and cover. Fig. 15 shows a form 
 of box in which the safety links are sup- 
 ported on the cover, and the wires con- 
 
FUSE WIRES. 
 
 105 
 
 nected to the base, so that the attach- 
 ment of the cover to the base closes the 
 circuit through the links. 
 
 The form of fuse-box necessarily varies 
 with the current which has to be carried 
 through it, and with the character of the 
 
 Fig. it.— CEII.ING Block with Spring Clips. 
 
 fixture or circuit in whicli it is connected. 
 Fig. IC shows a form suitable for a ceil- 
 ing fixture; i. e., an electrolier pendant 
 from a ceiling and usually called a ceiling 
 block.' The supplj^ wires are connected to 
 the screws S, S, in the permanent block 
 
106 
 
 ELECTKIC HEATING. 
 
 which is attached to the ceiling, while the 
 wires connected to the electrolier are con- 
 nected to the screws B, B, in the cover. 
 Connection is secured through the two 
 safety fuses F, F, by screwing up the 
 cover against the block. A similar form 
 is shown in Fig. 17, in which, however, 
 connection is secured through spring 
 clips. 
 
 Fig. 18.— Plug Cut-Out. 
 
 The fuse wire is sometimes placed in a 
 screw- socket in order to ensure ease in 
 placing and replacing. Under these cir- 
 cumstances the electrical connections of 
 the fuse wire are such that the mere in- 
 sertion of the screw block in its socket 
 
FUSE WIKES. 
 
 107 
 
 inserts the fuse in the circuit. Fig. 18 
 shows such a screio -block fuse, or plug cut- 
 out and Fig. 19 shows various forms of 
 socket attcichmeiits, or ciit-ovt boxes, for 
 such fuses. The cavities of tlie block 
 containing the fuse wires are usually part- 
 
 FiG. 19.— CuT-OuT Boxes. 
 
 ly filled with plaster-of-Paris for the pur- 
 pose of excluding the air; for, when a fuse 
 wire suddenly melts or blows, the heated 
 air might escape explosively from the 
 cavity forcing particles of melted lead 
 outward. The effect of the plaster-of- 
 
108 ELECTEIC HEATING. 
 
 Paris on the action of the fuse, is to di- 
 minish its sensitiveness to a momentary 
 overload, for the plaster conducts heat 
 from the wire, and, therefore, a sudden 
 excess of heat will not so quickly bring 
 the wire to the melting point, although a 
 steadily continued current will eventual- 
 ly melt the fuse almost as readily as if 
 the plaster were absent. 
 
 When fuse-blocks are placed inside ap- 
 paratus, it becomes a matter of impor- 
 tance to insure convenience in inserting 
 and inspecting them, and when such ap- 
 paratus, as, for example, an alternating- 
 current transformer, employs dangerous- 
 ly high pressures, some means are neces- 
 sary in order to insure safety of attach- 
 ing the fuse wires to the fuse-block by 
 disconnecting them from the primary and 
 secondary terminals. A form of such a 
 
FUSE WIRES. 
 
 109 
 
 fuse -block is shown in Fig. 20. Here an 
 iron box BB, encloses a porcelain fuse- 
 
 FiG. 20.— Transformer Safety Fuse-Box 
 
 box, whose cover C, is removed to show 
 the interior. In this case, the porcelain 
 
no ELECTEIC HEATING. 
 
 fuse-blocks are detachable. One of them 
 is shown at F, detached, and the other at 
 F\ in place of the interior. The fuse wire 
 10, u\ is clamped under screws whose 
 studs project through the fuse-block and 
 enter into spring clips 7J, p\ when the fuse- 
 block is thrown into position by its han- 
 dle h, is connected with the external 
 circuit by a wire shown, and P\ connected 
 to the apparatus in the interior. Should 
 any short circuit exist in the apparatus, 
 the fuse will melt on the insertion of the 
 block, and the hand of the operator will 
 be protected from any particles of explod- 
 ed lead by reason of the shielding action 
 of the handle h. 
 
 The temperature at which a fuse wire 
 will melt, depends uijon its composition. 
 Some alloys can be used which will melt 
 at as low a temperature as 50^ C. As a 
 
FUSE WIRES. Ill 
 
 rule, however, the melting point is about 
 300° C. 
 
 The current strength which will melt a 
 fuse depends upon a variety of circum- 
 stances. It might be supposed that for a 
 given diameter of fuse wire, the length 
 of the wire forming the fuse would not 
 influence its melting point. Such, how- 
 ever, is not the case. A long fuse wire 
 will usually melt at a lower current 
 strength than a short fuse wire, princiijal- 
 ly for the reason that the heat generated 
 in a short wire is conducted by the metal 
 in the wire to the metallic masses form- 
 ing the clamps at each end, thus enabling 
 the heat in the wire to be dissipated more 
 rapidly than would be possible in the case 
 of a longer fuse. Similarly, the position 
 of a fuse wire, whether closely surrounded 
 in a practically air-tight chamber or free- 
 ly exposed to such currents of air as might 
 
112 ELECTRIC HEATING. 
 
 exist in its vicinity, would greatly effect 
 the current strength that melts it. So 
 also the position of the wire, whether ver- 
 tical or horizontal, its shape, whether 
 straight or curved, the shape of its cross- 
 section, the character of its surface, 
 whether rough or smooth, tarnished or 
 bright, all exert an influence on its carry- 
 ing capacity. As a rule, therefore, fuses 
 cannot be depended upon to melt at pre- 
 cisely the current strength for which they 
 are designed. 
 
 When an overload, or an unduly power- 
 ful current, exists in an electric circuit 
 for a very brief interval of time, as, for 
 example, when a short circuit occurs dur- 
 ing a small fraction of a second, a fuse de- 
 signed to melt at say, 10 amperes, may 
 carry 100 amperes or more without melt- 
 ing, when 10 amperes steadily maintained 
 
FUSE WIRES, 113 
 
 for one minute would insure the melting 
 of the fuse. This is for the reason that 
 heat has to be expended in the mass of 
 the fuse before its temperature can be 
 raised to the melting point. Consequent- 
 ly, an appreciable fraction of a second 
 may be required for even a powerful cur- 
 rent to develop this heat; while, when 10 
 amperes flow steadily through it, ample 
 time is afforded to bring up the tempera- 
 ture of the metal. 
 
 It sometimes occasions surprise that 
 when a dynamo supplies a distant branch 
 circuit through two fuses, one of which, a 
 large fuse near the dynamo, called the 
 main circuit fuse, is capable of carrying, 
 say 500 amperes, and the other, a small 
 branch fuse in a branch circuit, is capable 
 of carrying only 20 amperes, that on an 
 accidental short-circuit in the branch cir- 
 
114 ELECTKIC HEATIKG. 
 
 cuit, the main fuse should blow out, while 
 the branch fuse remains intact. This ac- 
 tion, by no means of common occurrence, 
 probably finds its explanation in the 
 fact that the main fuse has already been 
 heated by a full-load current of the gener- 
 ator, to a comparatively high temperature, 
 while the particular branch fuse is cold 
 since no current had been passing through 
 it prior to the accidental short circuit. 
 Under these circumstances, when a short- 
 circuit suddenly occurs between the 
 branch wires, the powerful rush of cur- 
 rent through both fuses may be able to 
 blow the larger fuse, before the smaller 
 one reaches the temperature of its melt- 
 ing point. 
 
 Since in most commercial electric cir- 
 cuits fairly considerable variations in the 
 strength of the current passing are apt to 
 
FUSE WIEES. 115 
 
 exist without constituting either a dan- 
 gerous or objectionable overload, if the 
 carrying capacity of the fuses is made too 
 near their normal-load current, consider- 
 able inconvenience may arise from the 
 frequency with which the fuses are blown. 
 For this reason, in good practice, fuses 
 are generally employed whose carrying 
 capacity is about fifty per cent, greater 
 than the full-load current. 
 
 In central stations supplying under- 
 ground systems of conducting mains, the 
 inconvenience above pointed out arising 
 from the blowing of fuses is so marked 
 that in many cases such fuses are omitted 
 entirely in the central station, and are 
 only inserted between the mains and the 
 consumers, as well as in all the branch 
 circuits of the house wirings. Should, for 
 example, a large feeder either become 
 
116 ELECTEIC HEATINGo 
 
 overloaded, or develop a short circuit at 
 some point underground, it would prob- 
 ably blow its fuse, and the extra load 
 would, therefore, be transferred to other 
 feeders. These in their turn would also 
 be liable to blow their fuses, until, in 
 some cases, the entire system of feeders 
 and mains might thus be cut off from the 
 dynamos. 
 
CHAPTER VI. 
 
 ELECTKIC HEATERS. 
 
 One of the commercial uses to which 
 electricity has lately been applied has 
 been the artificial heating of air in build- 
 ings on a comparatively small scale. 
 While this method of obtaining artificial 
 warmth has not yet reached such economy 
 as to permit it to be economically applied 
 to the heating of the air of large buildings, 
 yet the convenience arising from the facil- 
 ity with which the electric current can be 
 led to the electric heater, the comparative- 
 ly small size and portability of the latter, 
 the readiness with which the current can 
 be turned on and off, the safetj^ of the ap- 
 paratus, its freedom from fumes or dirt, 
 and the ease with which it can be managed, 
 
118 ELECTKIC HEATING. 
 
 have attracted no little attention, and its 
 use, in certain directions, is rapidly in- 
 creasing. While there is, perhaps, little 
 probability in the near future of large 
 electric plants being erected whose cur- 
 rent shall be entirely employed for the 
 production of heat, as in warming build- 
 ings, nevertheless, electric heaters are 
 likely to be extensively employed in con- 
 nection with already existing systems of 
 electric distribution for light and power. 
 
 Electric heaters are to-day in common 
 use in electric street railway cars, and 
 this is for the same reason that electric 
 lights are employed in these cars. Were 
 it not for the fact that the cars obtain their 
 propelling power from the electric cur- 
 rent, it is not at all likely that electrically 
 lighted and electrically heated cars would 
 have come into the general use they have 
 
ELECTEIC HEATEKS. 119 
 
 to-day; although in parlor cars on steam 
 railroads, electric incandescent lamps are 
 sometimes employed as luxuries. 
 
 Electric heaters, designed for the artifi- 
 cial warming of air, though made in a great 
 variety of forms, consist essentially of a 
 metallic conducting wire, generally of 
 galvanized iron, or German silver, loosely 
 coiled so as to possess a comparatively 
 extended radiating surface, and common- 
 ly supported in the air. 
 
 In order to obtain a sufficiently extend- 
 ed surface for radiation and convection, 
 and also to obtain the desired electric 
 resistance in the coil, within a limited 
 space, it is usual to wind the wire in a 
 loose spiral around a form or block of 
 earthenware, porcelain, or other similar, 
 non-inflammable material. 
 
 We have seen that a definite relation 
 
120 ELECTEIC HEATING. 
 
 exists between a given amount of electric 
 energy and the heat energy it is capable 
 of producing. It has been ascertained 
 that one joule of work, expended in pro- 
 ducing heat, will raise the temperature of 
 a cubic foot of air about y'g-^F., and, 
 therefore, an activity of one joule-per- 
 second, or one watt, can raise the tem- 
 perature of one cubic foot of air yV ^ F. 
 per second. 
 
 A simple form of cylindrical electric 
 heater for hot air is shown in Fig. 21. It 
 consists of a metallic strip, wound spiral- 
 ly on an insulated frame. Here, as in all 
 forms of air heater, the design is to obtain 
 as large a surface exposed to the air as 
 possible. Since the metal strip employed 
 is comparatively thin, the total mass or 
 weight of the metal in the heater is com- 
 paratively small, and the conductor is 
 rapidly heated by the passage of the cur- 
 
ELECTRIC HEATERS. 
 
 121 
 
 Fig. 21.— Cylindrical Electric Heater. 
 
122 ELECTEIC HEATING. 
 
 rent. But since the surface exposed to 
 the air is great, the heating coil never ac- 
 quires an excessively high temperature. 
 An electric heating coil best serves its 
 purpose when it rapidly imparts its heat 
 to the surrounding air, never itself acquir- 
 ing a dangerously high temperature. 
 
 The heating coil or conductor in an elec- 
 tric heater is not always in the form of 
 a strip. It sometimes takes the form of 
 a wire or spiral, either bare, or placed 
 within a metallic frame. 
 
 Fig. 22 represents a form of electric 
 heater or radiator resembling in appear- 
 ance an ordinary steam or hot water ra- 
 diator. Here the coils of the electric con- 
 ductor are placed within the metallic 
 frame. The exact length and dimensions 
 of the heater coils will depend upon the 
 amount of heat required, and on the elec- 
 
ELECTRIC HEATERS. 
 
 123 
 
 trie pressure employed in the building. 
 The same coil will, however, give practi- 
 cally the same amount of heat when con- 
 
 FiG. 22.— Electric Radiator. 
 
 nected with the same pressure of either 
 alternating or continuous current. 
 
 The advantages of an electric heater 
 are especially marked when employed in 
 cars propelled by electricity. Indeed, 
 
124 ELECTRIC HEATING. 
 
 the necessity for utilizing all the available 
 space in a street car for the accommoda- 
 tion of passengers, and for maintaining a 
 uniform temperature, with a minimum of 
 attention required from the conductor of 
 the car, renders the use of the electric cur- 
 rent for heating even more economical 
 than the use of a stove. This, of course, 
 arises largely from the fact that the stove 
 which can, in practice, be placed in the 
 limited space allotted to it in a car, must 
 necessarily be very uneconomical, more- 
 over, the large scale on which electric 
 power is generated in a central station for 
 propelling the cars, reduces the cost of 
 the electric energy so much that the elec- 
 tric heating of the car actually compares 
 very favorably in economy with what 
 would be required to heat it as effectively 
 by the direct burning of coal in a stove. 
 Fig. 23 represents a form of electric car 
 
ELECTEIC HEATEKS. 125 
 
 heater, in front elevation, and Fig. 24, the 
 back and interior of the same heater, 
 showing the electric coil in position. Four 
 or six of these heaters are employed in 
 each car, according to the size of the car 
 and the climate of the locality in which it 
 
 ■iieiiiiiiiiiiiiiiliipiiiiiiiSiifiiisAS 
 
 P^n!iiiiiPi|iiiiSiiii!ilU3l!i!!l!il 
 
 Fig. 23.— Electric Car-Heater. 
 
 runs. The heater is placed in a hole or gap 
 made in the riser, or vertical partition, be- 
 low the car seat. A cast-iron plate, fur- 
 nished with grid openings, placed in the 
 front of the heater and opening into the 
 car, serves the double purpose of prevent- 
 
126 ELECTRIC HEATING. 
 
 ing the dress of the passengers from com- 
 ing into contact with the heated coils, 
 and for permitting the ready escape of 
 the air through the apparatus. 
 
 An inspection of Fig. 24 will show that 
 the heating coil, employed in this particu- 
 lar form of car heater, consists of a close 
 
 Fig. 24. — Back and Interior of Electric Car-Heater. 
 
 spiral conductor, which is spirally wound 
 around a grooved porcelain tube, and is 
 supported at the centre and at the two 
 ends by porcelain washers. The back 
 of the heater is formed of sheet iron, 
 suitably provided with asbestos lining. 
 
ELECTRIC HEATERS. 127 
 
 Heaters employed on electric railroad 
 circuits take their current from the mains 
 at a constant pressure, generally 500 volts. 
 In order to vary the current passing 
 
 Fig. 25. — Car-Heater Regulating Switch. 
 
 through the four or six heaters generally 
 employed in each car, a switch is used, 
 by means of which the separate heater 
 
128 
 
 ELECTRIC HEATING. 
 
 coils can be couuected in series, or in 
 parallel-series, or some of tliem cut out 
 from the circuit, thus permitting the 
 amount of heat to be readily varied in 
 order to meet the requirements of the 
 
 Fig. 26. — Side Interioh View of Car-Heater Regu- 
 lating Switch. 
 
 weather. Fig. 25 shows a form of reg- 
 ulating sivitcli of this character intended 
 to produce five different strengths of 
 current, and, therefore, five different rates 
 
ELECTRIC IIKATERS. 
 
 129 
 
 of producing lieat in the car. The side 
 view of the interior of the switch is shown 
 in Fio;. 26; the front view of the interior 
 of the switch in Fig. 27. This switch 
 consists of a number of contact springs, 
 
 Fig. 27. — Front Interior View of Car-Heater Regu- 
 lating Switch. 
 
 whereby^ through the motion of a lever 
 attached to the barrel, the proper connec- 
 tions can be made for coupling the coils in 
 the five different arrangements required. 
 
130 
 
 ELECTRIC HEATIKG. 
 
 The connections from the switch to the 
 trolley wire and the ground through the 
 various heaters, are shown in Fig. 28. In 
 position No. 1 all the coils are connected 
 in series, so that the current has to pass 
 through each in succession. This position 
 
 AUTOMATIC cut Out 
 
 Fig. 28. 
 
 ^^^^^^^^^^^^^^^^^^^^^^^1 TOGROUNO 
 
 -Diagram of Wiring for Six Electric 
 Heater Equipment. 
 
 corresponds to the minimum current 
 strength, about 2 amperes, and, therefore, 
 to the minimum thermal activity, or rate 
 of developing heat; namely, about one 
 kilowatt. In position 2, two heaters are 
 
ELECTRIC HEATERS. 131 
 
 entirely cut out of the circuit, so that the 
 resistance of the series being diminished, 
 the current strength and activity in the 
 remainder are increased, and the four ac- 
 tive heaters will supply more heat to the 
 car than the six heaters in the first case, 
 the current being nearly 3 amperes, and 
 the activity nearly 1500 watts. In the 
 third position, the six heaters are con- 
 nected in two series of 3 each, so that the 
 current strength in each series is about 
 twice that in the first position, or about 
 3i amperes, in each series ; i. e., 7 amperes 
 or 3.5 KW. in the combination. The 
 fourth position connects two sets of two 
 heaters and cuts out two heaters entire- 
 ly. This gives about 4 amperes in each 
 series, or 8 in the combination, represent- 
 ing 4 KW. In the fifth position, three 
 rows of two heaters are employed, the 
 current in each row being 4 ampereS; or 
 
132 
 
 ELECTKIO HEATING. 
 
 B 
 
 miimtiHOiml 
 
 A 
 
 Mff ?(!({(f(((ffLft ff fffffytf 
 
 
 ^^^^m^mmm^mmm 
 
 Fig. 29.— Cab-Heater. 
 
ELECTRIC HEATERS. 
 
 133 
 
 12 amperes in all, and the activity about 
 6 KW. 
 
 Another form of car-heater is shown in 
 Fig:. 29. Here the heatino; coil shown at 
 A, consists of a wire ^vrapped in one long- 
 spiral around the insulated grid or frame. 
 The heating coil is enclosed in a perfor- 
 ated iron cover shown at JB, while at O, 
 
 Fig. 30. — Portable Air Heater. 
 
 the coil with its cover is shown in posi- 
 tion below the car seat. Here the air 
 enters the heater from the lower aper- 
 tures and issues from those above, 
 after passing over the heated wires. 
 
134 
 
 ELECTRIC HEATIKG. 
 
 Portcible electric heaters^ as tlieir name 
 indicates^ are so constructed that tliey 
 may be readily carried and temporarily 
 attached in any room where electric sup- 
 ply is obtainable. These are made in a 
 
 
 Fig. 31.— Portable Electric Heater. 
 
 variety of forms, but the principle in all 
 cases is the same. A wire of suitable 
 length and size is enclosed in the heater 
 and free access given to it from the 
 surrounding air. A form of cylindrical 
 heater is represented in Fig. 30. Other 
 
ELECTRIC HEATERS. 
 
 135 
 
 forms of portable heaters are shown in 
 Figs. 31, 32, 33 and 34. That shown in 
 Fig. 33 is 26 in. long, 7 in. in height, and 
 lOi in. wide, and is provided with three 
 switches to regulate the temperature. A 
 
 Fig. 82.— Portable Heater. 
 
 flexible attachment of the conductors to 
 the heater is shown in Fig. 34. Fig. 35 
 represents a small stationary heater in- 
 tended for attachment to a wall, corre- 
 
m 
 
 ELECTRIC HEATING. 
 
 Spending, it may be, in position, to the 
 ordinary hot-air register. 
 
 Figs. 36 and 37 show a form of electric 
 heater suitable for office or house work. 
 
 Fig. 83.— Portable Heater. 
 
 Fig. 36 shows the exterior, and Fig. 37, 
 the interior of the apparatus. The heat- 
 ing coils, six in number, are essentially of 
 the same type as those^employed in co73 - 
 nection with the car-heaters represented 
 
ELECTRIC HEATERS. 
 
 137 
 
 Fig. 34.— Atmospheric Heater. 
 
138 
 
 ELECTKIC HEATING. 
 
 in Figs. 23 and 24. The coils are wound on 
 vertical porcelain frames, as shown in Fig. 
 37, and are sometimes provided with atem- 
 perature-regulating switch in such a man- 
 ner that they may be connected in series, 
 or parallel -series, and so produce less or 
 greater activity. The stove case shown 
 in Fig. 36, is made of Russia iron. The 
 air enters at the bottom of the heater, 
 
 Fig. 35.— Wall Heater. 
 
 passes up over the heated wire, and 
 escapes at the top. 
 
 Electric air heaters may be employed 
 for a variety of purposes, as, for example, 
 for drying out the interiors of large cais- 
 sons or tanks. A form of heater suitable 
 for this purpose is represented in Fig. 38. 
 It consists, as shown, of a number of coils, 
 
ELECTRIC HEATERS. 
 
 139 
 
 Fig. 36.— Portable Electric Heater. 
 
140 
 
 ELECTEIC HEATING. 
 
 capable of being connected either in series 
 or in parallel. It is 33 in. long, 12 in. wide, 
 
 Fig. 37.— Portable Electric Heater, Inside View, 
 
 7 in. in height, and is intended for a pres- 
 sure of 110 volts with a maximum current 
 
ELECTRIC HEATEES. 
 
 141 
 
 strength of 42 amperes; i. e., a maximum 
 activity of 4.62 KW. 
 
 As we have already seen, the product 
 of the drop of pressure in a conductor 
 and the current strength, equals the ther- 
 mal activity in the conductor. Since in a 
 heating coil, the drop is entirely of this 
 
 Fig. 38. —Tank Heater. 
 
 nature, it is evident that all the energy of 
 the current passing through the coil must 
 appear in the circuit as heat, and all of 
 this heat energy must be given to the ex- 
 
142 ELECTKIC HEATING. 
 
 ternal air on the cooling of the coil. Con- 
 sequently, neglecting that small portion 
 which is dissipated by conduction to the 
 walls or floor, an electric air heater, as a 
 device for converting electric energy into 
 heat energy, may be regarded as a nearly 
 perfect machine. 
 
 The cost of operating a car-heater will 
 necessarily vary with the amount of ac- 
 tivity developed in the car, and this, of 
 course, will depend upon the number of 
 amperes passing through the coils and 
 the manner in which the coils are con- 
 nected by the regulating switch. If, for 
 example, there are four heaters in a car, 
 and their resistance is 62.5 ohms each, 
 then, when they are connected in series, 
 the total resistance of the heating circuit 
 will be say, 250 ohms. Assuming the 
 pressure to be uniformly maintained at 
 
ELECTRIC HEATERS. 143 
 
 500 volts, the current strength will be 2 
 amperes, and the thermal activity 1000 
 watts, or 1 KW. If the coils are connect- 
 ed in two rows of two each, the increased 
 cmn^ent which would flow through them 
 would increase the resistance of each coil, 
 by increasing its temperature, but as- 
 suming, for the sake of simplicity, that 
 this increase of resistance is negligible, 
 then the resistance of the coils, connected 
 in two rows of two, will be 62| ohms, and 
 a current of 8 amperes will p^iss, making 
 the activity 4000 watts, or four times as 
 great as in the preceding case. It is, 
 of course, impossible to determine from 
 these figures alone what the temperature 
 in the car will be, since the air is being 
 renewed by ventilation, and by the occa- 
 sional opening of the car door. Moreover, 
 the temperature produced will vary with 
 the temperature of the external air, the 
 
144 ELECTKIC HEATING. 
 
 speed of the car, and with the dh^ection 
 and intensity of the wind. Consequently, 
 in practice, it is necessary to provide for a 
 variable production of heat so as to meet 
 the requirements of a variable climate. 
 It is found that the^ average amount of 
 current required to warm the car, except 
 in extremely cold climates, is three am- 
 peres at a pressure of 500 volts, or 1^ 
 kilowatts. The cost of a KW. hour, when 
 supplied from a large power station to an 
 extended system of cars, is usually a little 
 over one cent and a half, per kilowatt - 
 hour delivered. At this estimate, the 
 average cost of heating a car in the winter 
 is about 2.25 cents per hour, or 40.5 cents 
 per car-day of 18 hours. The cost is 
 stated to vary from 25 cents to 50 cents 
 per car -day of 18 hours, according to the 
 number of cars and the nature of the 
 weather. It has been stated, from actual 
 
ELECTEIC HEATERS. 145 
 
 measurement in Boston, that cars having 
 two doors, 12 windows and 850 cubic feet 
 of space can be heated to an average tem- 
 perature elevation of 25" F. above the ex- 
 ternal air during severe wintry weather 
 by an expenditure of 2.5 KW. 
 
 Leaving out of consideration, however, 
 the cost of the electric heating of a car, 
 the advantages this method possesses 
 over heating by a coal or oil stove are con- 
 siderable. A stove fails to produce that 
 uniform temperatiu^e so necessary to the 
 comfort of the passengers, the centre of 
 the car being more powerfully heated 
 than the ends. The electric heater warms 
 the air near the floor of the car, where 
 warmth is most agreeable. Moreover, 
 the electric heater requires practically no 
 attention, does not necessitate the re- 
 moval of dust, ashes or coal, and occupies 
 
146 ELECTEIC HEATING. 
 
 no paying space. Consequently, where 
 electric cars are used, the electric heater 
 is coming into extended use, not only on 
 account of its greater popularity, but also 
 on account of its convenience. 
 
 When it is desired to apply heat di- 
 rectly to the surface of the body, for such 
 medical treatment as would ordinarily 
 employ hot water bags, the object can be 
 much more conveniently obtained by a 
 suitably constructed electric heater than 
 by any method which depends for its 
 heat on material warmed while away 
 from its body, since, in all such cases, 
 the cooling of the material necessitates its 
 repeated renewal. An electric heater, 
 suitable for local application to the body, 
 and called a flexible electric heater, is 
 shown in Pig. 39, because constructed of 
 materials which enable it to be brought 
 into intimate contact with the surface to 
 
ELECTEIC HEATEKS. 
 
 147 
 
 be heated. The heating coils B, are 
 formed of German silver wire arranged as 
 shown in the figure, placed on asbestos 
 cloth and suitably insulated. The space 
 
 Fig. 39. -Flexible Electric Heater. 
 
 surrounding the wires is filled with a 
 solution of silicate of soda, which, on 
 hardening, acts as a cement to hold the 
 different parts together. A cushion, or 
 flexible mass, is then made by packing 
 
148 ELECTEIC HEATING. 
 
 mineral wool, or asbestos fibre, around the 
 lieating conductor and covering the mass 
 with a suitable cover of clotli. The ad- 
 vantage of such a heater is that the heat 
 can be readily maintained. The appara- 
 tus shown in the figure, ordinarily re- 
 quires to be supplied with an activity of 
 about fifty watts. 
 
 The electric heater has recently been 
 adopted for the warming of the Vaudeville 
 Theatre in London, England. The advan- 
 tages of electric heating are specially 
 marked in the case of theatres, where 
 pure, warm air, without powerful currents 
 or draughts are the desiderata. The 
 heaters are two feet long and one foot 
 wide. Twelve of these are attached to 
 the skirtings round the walls, and twelve 
 to the partition in front of the orchestra. 
 Four large portable heaters are also em- 
 ployed with flexible attachments for use 
 
ELECTRIC HEATEES. 149 
 
 either in the centre of the theatre or at 
 the sides. Each fixed heater takes a cur- 
 rent of nearly 3 amijeres, at 100 volts pres- 
 sure, or develops an activity of nearly 300 
 watts, while the large, portable heaters 
 develop 1200 watts. When all are work- 
 ing, the total activity is 11,400 watts or 
 11.4 kilowatts. It is stated, however, 
 that, ordinarily, only two of the large 
 portable heaters require to be used, so 
 that the actual activity employed is 9 
 KW. The temperature of the auditorium 
 is stated to be raised 20^ F. by these heat- 
 ers after they have been working for a 
 reasonable length of time. The price 
 charged being 8 cents per kilowatt-hour 
 the cost of heating is 72 cents per hour, 
 and to warm -the theatre for four hours, 
 $2.88. 
 
 It is similarly proposed to warm the 
 stage by electric heaters to prevent the 
 
150 ELECTKIC HEATING. 
 
 inrush of cool air into the auditorium 
 when the curtain is raised. 
 
 To secure these results, it is only nec- 
 essary to heat the air of the stage to prac= 
 tically the same temperature as that of 
 the auditorium. 
 
 The advantages possessed by electric 
 heating, already jjointed out, are so 
 marked in the case of the theatre, that 
 with the general introduction of electric 
 lighting into such buildings, their electric 
 heating, either independently of or in con- 
 junction with other methods of heating, 
 is a possibility of the near future. 
 
CHAPTER VII. 
 
 ELECTRIC COOKING. 
 
 Although, so far as its general electrical 
 construction is concerned, an electric 
 stove differs in no respect from an electric 
 air heater, yet, there is this essential dif- 
 ference in the operation of these two 
 pieces of apparatus; namely, that while 
 the electric heater is so arranged as read- 
 ily to impart its heat to a large volume of 
 air in its neighborhood, the electric stove 
 is so arranged that it can only impart its 
 heat to a small volume of air confined in 
 Its interior. Consequently, for a given 
 amount of heat produced, the air sur- 
 rounding an electric heater acquires a tem- 
 perature much lower than that within the 
 stove. 
 
152 ELECTRIC HEATIlSra 
 
 Suppose any heating coil be taken, as, 
 for example, the coil shown in Fig. 40, 
 already described in connection with a 
 car-heater in Fig. 24. Let us suppose 
 that this coil has a resistance of 40 ohms 
 (hot). If a current of three amperes be 
 sent through it, the drop in the coil will 
 be 3 X 40 = 120 volts, and the electric ac- 
 
 FiG. 40. — Heating Coil. 
 
 tivity in the coil 3 X 120 = 360 watts, or 
 nearly half a horse power. This amount 
 of heat is capable of raising the temper- 
 ature of 20 cubic feet of air V F. per 
 second. If this heater were placed at 
 work in a closed chamber, the temperature 
 acquired by the contained air would de- 
 pend upon the voliune of air. A lai'ge 
 
ELECTRIC COOKING. 153 
 
 volume of air would acquire a lower tem- 
 perature than a small volume of air. But 
 the temperature attained would not de- 
 pend onl}^ upon tlie volume of air in the 
 chamber, but also upon the ability of the 
 chamber to retain its heat, that is, to al- 
 low no heat to escape by conduction, 
 radiation, or by convection, or open pas- 
 sages such as doors, windows, etc. For 
 example, if the walls of the chamber Avere 
 of cast iron, the temperature attained by 
 the air within the chamber would be 
 much lower than if the walls were thickly 
 lined with some non-conductor, such as 
 asbestos or felt. If, therefore, we know 
 the volume of air in a chamber and also 
 the rate at which heat escapes from it 
 through walls or apertures, we have all 
 the data necessary for the determination 
 of the resulting temperature of the con- 
 tained air. 
 
154 ELECTRIC HEATING. 
 
 All electric oven consists essentially of 
 a small cliamber, the air in which is prac- 
 tically isolated, the ^val]s being nearly air- 
 tight and lined ^vitli non-conducting mate- 
 rial, so as to retain the heat. 
 
 Fig. 41 shows a form of electric oven 
 provided Avith a wooden external case, 
 lined on the inside with asbestos or felt, 
 and covered on the inside with bright, tin 
 plate, which being a good reflector, tends 
 to prevent heat from being conducted 
 throno:h the walls. Two electric heating; 
 coils are shown within at A and jB^ resj)ect- 
 ivel}^, one at the top and the other at the 
 bottom of the oven. By means of the 
 switch, shown at the rio;ht hand of the 
 drawing, either or both can be operated. 
 A thermometer is inserted throngli a small 
 hole in the top of the oven, to show the 
 temperature of the contained air. 
 
 Fier. 42 shows another form of electric 
 
ELECTRIC COOKING. 155 
 
 oveD with three separate compartments 
 and jDrovided with a switch for operating 
 
 Fig. 41.— Electric Oven. 
 
 the same. The large compartment is 
 about 18 inches wide. 
 
156 
 
 ELECTRIC HEATING. 
 
 Fig. 42. — Electric Oven. 
 
ELECTKIC COOKING. 157 
 
 Fig. 43.— Electric Coffee Heater, 
 
158 
 
 ELECTRIC IIEATIJSTG. 
 
 Fig. 43 represents a form of electric 
 heater, suitable for lieating a large quan- 
 tity of coifee such as might be required 
 
 Fig. 44.— Electric Coffee Pot. 
 
 for use in a restaurant. Here the heater 
 coil is situated in the base of the appa- 
 
ELECTRIC COOKING. 
 
 159 
 
 ratus, out of contact with the liquid, be- 
 ing separated from the same by a metallic, 
 water-tight jacket. 
 
 Fig. 45,- Electric Kettle. 
 
 Fig. 44 represents a form of coffee -pot 
 intended to be heated electrically from a 
 pressure of 50 or 100 volts, absorbing, ap- 
 
160 ELECTKIC HEATING. 
 
 proximately, an activity of 500 watts. 
 The electric heater coil is contained in the 
 base of the pot. A flexible cord connects 
 it with the nearest lamp socket. 
 
 Fig. 45 represents a form of electrically 
 heated, four-quart tea-kettle. This ket- 
 tle requires an activity or about 700 watts 
 or nearly one horse-power, in order to 
 boil one quart of water in ten minutes. 
 
 If one gallon of water be put into an 
 electric tea-kettle, at say^ a tempera- 
 ture of 4P F. (5^C.) and be raised, vath- 
 out actually boiling, to the boiling point, 
 or lOO'^C, it would be elevated 95^ C. ; 
 there would be, consequently, 3786 cubic 
 centimetres elevated 95^ C. , (one gallon 
 containing 3786 cubic centimetres) or 
 3786 X 95 =359, 575 water-gramme-degrees- 
 centigrade of heat produced. But one 
 calorie, or a water-gramme-degree-centi- 
 grade, requires an expenditure of 4.18 
 
ELECTRIC COOKING. 161 
 
 joules, SO that the work required to be 
 done in raising a gallon of water to the 
 temperature of its boiling point, would be 
 359,575 X 4.18 =-- 1,503,000 joules. The cost 
 of electric power in large quantities is 
 usually about 8 cents per kilowatt-hour 
 (/. e, , one KW. supplied for one hour, or 
 3, 600, 000 joules), and, in very small quan- 
 tities, 15 cents per kilowatt-hour. 
 
 At 8 cents per KW. hour, the cost of 
 raising one gallon of water to the boiling 
 point would be 3J cents. At 15 cents 
 per KW. hour, the cost would be 6^ cents. 
 This assumes, however, that all the elec- 
 trically developed heat is utilized in rais- 
 ing the temperature of the water, which 
 of course, is not the case since some heat 
 is lost. For example, if we start with cold 
 water in a cold kettle, the metal in the 
 kettle will have to be heated before its 
 heat can be communicated to the water, 
 
162 ELECTEIC HEATING. 
 
 and, although in an air heater, anylieat, so 
 absorbed in the mass of metal of the heat- 
 er would be returned to the air; in a wa- 
 ter heater, this would not necessarily be 
 returned to the water heated; beside, dur- 
 ing the time required for the heating of 
 the water, which would be about fifteen 
 minutes for one gallon, the air outside 
 the kettle would be warmed and would 
 carry away some of the heat. The pro- 
 portion of useful heat developed to 
 total heat developed; or, as it is called, 
 the efficiency of the kettle, would proba- 
 bly be about 70 per cent. Therefore, the 
 actual cost of heating a gallon of water 
 would be, approximately, 3| x VV- = 4| 
 cents at 8 cents per kilowatt-hour, or near- 
 ly 9 cents at 15 cents per kilowatt-hour. 
 
 It is evident, from the preceding figures, 
 that at the present price of electric power, 
 the electric water heater could not be eco- 
 
ELECTBIO COOKING. 163 
 
 nomically employed on a large scale. It 
 is to be remembered, however, that these 
 prices are for ijower obtained from a cen- 
 tral station generating electricity from 
 coal, through the intervention of steam en- 
 gines, boilers and dynamos. With water 
 power, the cost would, probably, be much 
 less, and even with steam power, where it 
 is employed under the particular condi- 
 tions applying to street- car driving, on a 
 large scale, the cost to the central station 
 of a KW. hour is only about 1^ cents. 
 
 The cost of power developed for street- 
 car propulsion is less than that of power 
 developed for electric lighting for several 
 reasons. Among others, to its being more 
 continuously used, and to its being man- 
 ufactured on a larger scale for street 
 railway purposes than for lighting 
 puri)Oses, 
 
164 ELECTKIC HEATING. 
 
 Fig. 46 represents a forin of electric 
 chafing dish in Avhich the electric heat is 
 generated from a resistance coil, placed 
 in a water-tight compartment at the base, 
 where the wires enter. The apparatus is 
 designed to hold about one quart of water. 
 
 Fig. 46. - Electric Chafing Dish. 
 
 and requires to be supplied with an activ- 
 ity of about 500 watts. 
 
 Fig. 47 represents an electrically heated 
 stewing-pan for holding two quarts and 
 designed for a supply of 700 watts. 
 
ELECTKIC COOKING. 165 
 
 It will be evident, from an inspection of 
 the preceding figures, that, excepting the 
 electric stove, all the different types of 
 electric cooking apparatus are practically 
 of the same construction. In each, an 
 electric heating coil, embedded in a water - 
 
 Fig. 47 —Electric Stew pan. 
 
 tight manner, m a suitable part of the ap- 
 paratus, supplies the heat that would 
 otherwise be obtained from the ordinary 
 coal stove or range. For the sake, how- 
 ever, of showing the convenience with 
 which an electric heating coil or coils 
 
166 ELECTRIC HEATING. 
 
 can be made to serve the necessities 
 of the culinary art, Figs. 48, 49 and 50, 
 representing respectively an electric skil- 
 
 FiG. 48.— Electric Skillet. 
 
 let, cake griddle and cooker, are shown. 
 
 In electric cooking apparatus contact 
 with the supply mains is sometimes effect- 
 
 FiG. 49.— Pancake Griddles. 
 
 ed by the ordinary screw plug. It is pref- 
 erable, however, when much work of 
 this character is to be done, to employ 
 
ELECTRIC COOKING. 
 
 167 
 
 Fig. 50.— Electric Steam Cooker. 
 
 special connectors for this purpose. Tayo 
 forms of phig'Switches for such purposes 
 are shown in Fm, 51. One of these is for 
 
168 ELECTRIC HEATING. 
 
 attachment to the wall, and consists of a 
 disc of wood, or hard rubber, with a slot 
 containing a pair of separate springs con- 
 nected with the sui^ply mains. The in= 
 sertion plug fits into the socket and con- 
 nects two terminals from the flexible cord 
 
 Fig. 51.— Plug Switches. 
 
 leading to the heater with the spring clip, 
 thereby establishing the circuit. 
 
 The other switch shows a very conven- 
 ient method for connecting together two 
 pairs of flexible cords. Each flexible cord 
 
ELECTKIC COOKING. 169 
 
 terminates in a cylindrical block of wood 
 or rubber in which is a pin and hole. The 
 pin is connected with one terminal and 
 the spring metal lining of the hole with 
 the other terminal of the supply mains. 
 The opposite plug is similarly fitted and 
 the two are united by placing the pins in- 
 to the respective holes and pressing the 
 two together. 
 
 Although much remains to be accom- 
 plished in the way of improvements in 
 electric cooking apparatus, especially in 
 the direction of producing suitable heat- 
 ing coils that will last indefinitely with- 
 out deterioration or short-circuiting, yet 
 it will be evident that the advantages 
 arising from the use of electricity in the 
 kitchen are sufficiently great to warrant 
 the belief that this practical use of elec- 
 tricity will rapidly grow. An ideal kitch- 
 
170 
 
 ELECTRIC HEATING. 
 
 en, such as is capable of being furnished 
 by apparatus already in existence, is 
 
 Fig. 52. —Electric Kitchen. 
 
 shown in Fig. 52. Here an electrically 
 heated oven is provided with a hood, 
 
ELECTRIC COOKING. 171 
 
 not to carry off the smoke of the fuel, but 
 the odors from the cooking viands. A 
 switchboard enables the utensils on the 
 table to be connected with the supply 
 mains as desired. B, is a hot-water boil- 
 er in which water can be readily heated 
 electrically. 
 
 As we have already pointed out, the elec- 
 tric heater, considered as a device for 
 transforming electric energy into heat 
 energy, may be regarded as an extremely 
 efficient apparatus. This cannot be as- 
 serted to the same degree of electric cook- 
 ing apparatus, since, in such apparatus, 
 some of the heat is lost; /. e., diverted 
 from the materi-al to be cooked, and sup- 
 plied to the surrounding metal, air 
 or water. Since, however, all electric 
 heat is usually obtained by burning 
 coal in a central station, the cost of the 
 
172 ELECTKIC HEATING. 
 
 electric heat on a large scale is consider- 
 ably greater than the cost of the heat 
 necessary for the same amount of cook- 
 ing by the direct use of fuel in an ordinary 
 range. 
 
 The larger the scale on which cook- 
 ing is carried out, the greater the eco- 
 nomical advantage of an ordinary fuel 
 range over an electric range. 
 
 Under all circumstances, however, the 
 electric heater is the more convenient 
 and the more cleanly apparatus, and, 
 when employed on a small scale for cook- 
 ing, is often more economical than a coal 
 range. Consider, for example, the ease 
 of preparing a cup of coffee by electric 
 heating. Here, there is only required the 
 generation of an amount of heat slightly 
 in excess of that required to bring the 
 
ELECTKIC COOKING. 
 
 173 
 
 water to the boiling point. Contrast this 
 with the amount of fuel required to bring 
 a cooking range to the temperature at 
 which it can boil water. As regards con- 
 venience everything is in favor of the 
 
 Fig. 53. —Simple Electric Heater. 
 
 electric heater, since it requires only the 
 closing of an electric circuit, which may 
 be even done from another room, while 
 bringing the range into use, requires the 
 lighting of a fire, 
 
174 ELECTRIC HEATING. 
 
 A simple form of electric heater is rep- 
 resented in Fig. 53. Here the heat is 
 obtained from an incandescent lamp, of 
 size proportionate to the requirements of 
 each case. As will be seen, the lamp is 
 placed inside the hollow bottom of a cof- 
 fee pot or kettle, which is blackened so 
 as to absorb the heat. In this way 75 
 per cent, of the heat liberated by the lamp 
 is utilized in the heating of the water. 
 It is claimed that in the form shown, a 
 50-candle-power lamp, of say 200 watts 
 activity, will heat 2 ^ pounds of water 
 to the temperature of boiling point in 25 
 minutes, and that when the water is at 
 its boiling point it can be maintained at 
 this temperature by the activity of a 16- 
 candle-power lamp (about 50 watts), and 
 in some cases even less. 
 
 Beside the uses we have already 
 
ELECTRIC COOKING. 175 
 
 pointed out, of comparatively small elec- 
 tric cm-rents for heatins: in connection 
 
 Fig. 54.— Electrically Heated Glue-pot. 
 
 with heaters in cooking apparatus, a num- 
 ber of others might be mentioned. For 
 exami>le, Fig. 54 represents an electric- 
 
176 ELECTRIC HEATING. 
 
 ally heated glae-pot, with a switch at 
 the base, whereby the strength of current 
 may be regulated within certain limits. 
 This apparatus requires 700 watts for a 
 one quart size, and 500 watts for pint 
 
 Fig. 55. —Electric Sad Iron. 
 
 size, when heated at the maximum rate. 
 A much smaller activity is necessary to 
 keep the glue hot when once melted. 
 
 Fig. 55 represents a sad iron, requiring 
 about 250 watts for its operation, Fig. 56, 
 
ELECTRIC COOKING. 
 
 177 
 
 a sealing-wax heater, and Fig. 57, a curl- 
 ing -tong heater. The sad iron is operated 
 by a flexible cord attachment, but some 
 
 Fig, 56.— Sealing Wax Heater. 
 
 forms are made in which the sad iron is 
 free . from electric connections and is 
 merely laid upon an electrically heated 
 
 Fig. 57. —Electric Curling-Tongs Heater. 
 
 plate in order to acquire its heat by con- 
 duction. 
 
 As an illustration of what can be ef- 
 
178 ELECTRIC HEATING. 
 
 fected in the direction of electric cooking 
 we may mention a banquet recently 
 given in London, England, by the direct- 
 ors of an electric lighting company, to 
 120 guests, in which all the cooking was 
 performed electrically. They were ten 
 courses, which required for their prepar- 
 ation a total expenditure of euergy of 60 
 kilowatt-hours, or on an average of one 
 half a kilowatt-hour per guest. 
 
 The above company has notified the 
 public that they w411 charge 8 cents per 
 kilowatt-hour for cooking. Consequently, 
 this would place the expense of such a 
 banquet at 4 cents per guest for the ten 
 courses. Considering the convenience of 
 the process this charge cannot be re- 
 garded as exorbitant. 
 
 An electrically cooked banquet was not 
 a possibility in the time of Franklin, yet 
 
ELECTRIC COOKING. 179 
 
 a banquet at which electricity played no 
 insignificant part is thus humorously de- 
 scribed by him in a letter written in 1769: 
 "Chagrined a little that we have been 
 hitherto able to produce nothing in the 
 way of use to mankind; and the hot 
 weather coming on, when electrical experi- 
 ments are not so agreeable, it is proposed 
 to put an end to them for this season, 
 somewhat humorously, in a party of pleas- 
 ure on the banks of the Schuylkill. 
 Spirits, at the same time, are to be fired 
 by a spark sent from side to side through 
 the river, without any other conductor 
 than the water; an exxjeriment which we 
 sometime since performed, to the amaze- 
 ment of many. A turkey is to be killed 
 for our dinner by the electrical shock, and 
 roasted by the electrical jack, before a fire 
 kindled by the electrical bottle; when the 
 healths of all famous electricians, in En- 
 
180 ELECTKIC HEATING. 
 
 gland, Holland, France, and Germany, are 
 to be drank in electrified bumpers, under 
 the discharge of guns from 'the electrical 
 battery." 
 
 It may be of interest to our readers to 
 note in this connection, that Dr. Frank- 
 lin was not devoid of imagination, as may 
 be gathered from a remark he makes con- 
 cerning the turkey and other birds so 
 killed: 
 
 " He conceited himself that the birds 
 killed in this manner ate uncommonly 
 tender o" 
 
CHAPTER VIII. 
 
 ELECTEIC WELDING. 
 
 In the proportioning of electric coils 
 designed for heaters and cooking appara- 
 tus, care is taken that the electric resist- 
 ance is such that, with the electromotive 
 force employed, the resulting current 
 strength should not be such that the coils 
 shall reach an unduly high temperature. 
 In no form of such apparatus are the coils 
 allowed to reach an incandescent temper- 
 ature; i. e., a temperature at which they 
 glow, or begin to emit light. There are, 
 however, some very notable applications 
 of the heating power of an electric cur- 
 rent in which very high temperatures are 
 employed, which w^e will now discuss. 
 
182 ELECTEIC HEATING. 
 
 These are capable of being divided into 
 two sharply marked classes ; namely, 
 
 (1) Those in which a metal forming 
 part of an electric circuit is raised to its 
 welding temperature; that is, a tem- 
 perature considerably below the melting 
 point of the metal. 
 
 (2) Those in which metals, or refractory 
 substances, form portions of an electric 
 circuit, and a temperature is obtained as 
 high as is possible to produce under the 
 circumstances, this temperature at times 
 being the high temperature of the vol- 
 taic arc. 
 
 Apparatus of the first type find their 
 examples in various forms of welding ap- 
 paratus; those of the second type, in elec- 
 tric furnaces. 
 
 By the welding of two pieces of metal is 
 meant causing them to strongly cohere, or 
 
ELECTRIC WELDING. 183 
 
 hold together as a single piece, when pow- 
 erfully pressed together. Some few met- 
 als, like lead, for example, possess the 
 power of welding when cold. Thus, if two 
 freshly-cut surfaces of lead, free from 
 grease or oxide, are firmly pressed to- 
 gether, they will cohere so strongly that 
 the wielded joint may be as strong as other 
 portions of the metal. Other metals, such, 
 for example, as iron, copper, gold and steel, 
 cannot be caused to cohere or weld in 
 the cold by any pressure that can readily 
 be brought to bear on them. If, how- 
 ever, these metals be heated to their weld- 
 ing temperature, generally a tempera- 
 ture at which they become incandescent, 
 and then pressed together, either by quiet 
 pressure, or by the blow of a hammer, 
 they readily w^eld and cohere. 
 
 In order that welding may take place it 
 
184 ELECTEIC HEATING. 
 
 is necessary that the surfaces of the metal- 
 lic weld be clean and free from oxides or 
 other impurities. Such clean surfaces are 
 insured by the use of a suitable flux, as, for 
 example, borax, which removes the film of 
 oxide that so readily forms on the sur- 
 faces of glowing metal. 
 
 In the practical welding of one metal to 
 another, it has been found that the most 
 efficient welding is obtained when a cer- 
 tain temperature is reached but not 
 exceeded. In welding, carried on by 
 means of the heat of an ordinary fire, 
 the operator generally judges as to 
 when this temperature is reached, by 
 the color or appearance the metal ac- 
 quires, and much of the welder's art con- 
 sists in his abilitj'^ to recognize precisely 
 when the proper temperature has been 
 reached in order to ensure the most 
 effective jomt. 
 
ELECTKIC AYELDING. 185 
 
 The process of electric welding does not 
 differ in any mechanical point from the 
 welding of metals by the ordinary 
 heating process, save, only, that the heat 
 applied to the welding joint is of electri- 
 cal origin, and, instead of the welding 
 surfaces being separately heated in a fur- 
 nace, and subsequently brought together, 
 with the opportunity that their exposure 
 to the air affords for the formation of a 
 film of oxide over the surfaces to be united, 
 in the electric process the surfaces are 
 tirst heated by the passage of an electric 
 current through them while placed in 
 contact; and, when the welding tempera- 
 ture has been acquired, which even for 
 large masses of metals requires only a few 
 moments, are then suitably pressed to- 
 gether and the weld is affected. 
 
 The electric process of welding is not 
 
186 ELECTKIC HEATING, 
 
 only more convenient and rapid than the 
 ordinary process, but by its means, metals 
 have been effectively welded, v^hich it is 
 impossible to weld by the old process. 
 By the application of the electric welding 
 process not only can the ordinary metals, 
 such as iron, steel and copper, be readily 
 welded, but many metals which required 
 under the old process to be previously 
 bronzed, or covered by a layer of brass or 
 solder, can now be directly welded. The 
 following metals, for example, have been 
 successfully welded electrically; viz., 
 wrought iron, copper, gold, lead, zinc, tin, 
 silver, aluminum and cast iron, and some 
 of these metals have even been welded one 
 to another. 
 
 The practical efficiency of any welded 
 joint, of course, lies in the extent to which 
 the tensile strength of the welded cross- 
 
ELECTRIC WELDING. 187 
 
 section equals that of the unwelded por- 
 tions of the bar. Judged by this test, an 
 electrically welded joint possesses a 
 marked advantage over an ordinary welded 
 joint. Tests on the tensile strength of 
 welded bars have shown generally that 
 the bar is as strong at the welded joint 
 as at other cross -sections, which is far 
 from being the case in bars welded by the 
 ordinary process, since the difficulty in ap- 
 plying the heat uniformly, and wielding 
 the bar promptly, without the formation 
 of a deleterious scale, is greater in the 
 case of an ordinary weld. 
 
 The current employed in electric weld- 
 ing may be either continuous or alternat- 
 ing. The amount of heat liberated in a 
 given resistance, by a given current 
 strength, is the same w^iether the current 
 be continuous or alternating, although 
 
188 ELECTRIC HEATING. 
 
 large bars, especially of iron, offer a great- 
 er resistance to the alternating than to 
 the continuous current. 
 
 It is possible, therefore, to employ al- 
 ternating currents for electric heating and 
 this is, indeed, a very fortunate circum- 
 stance, since, when dynamo -electric ma- 
 chines are employed as the electric source, 
 the use of the commutator is thereby 
 obviated; for alternating -current gener- 
 ators employ no commutator, while 
 continuous -current machines necessarily 
 employ one. The enormous current 
 strength employed in welding large bars, 
 sometimes as high as 50,00Q amperes, 
 would necessitate the use of massive and 
 expensive commutators, while with the 
 use of alternating currents these are 
 dispensed with. 
 
 Extended practical experience in the 
 
ELECTKIC WELDING. 189 
 
 welding of metals, especially in large 
 masses, has demonstrated the fact that 
 not only does no inconvenience attend the 
 use of alternating currents in welding, 
 but that, on the contrary, such currents 
 actually possess advantages over contin- 
 uous currents. In order to obtain a good 
 joint, a certain temperature must be at- 
 tained by the welding surfaces and this 
 temperature should be as nearly uniform 
 as possible. With the use of the contin- 
 uous currents employed in such cases, the 
 loss of heat at the surfaces of the metal 
 causes the central portions of the mass to 
 attain a higher temperature, thus render- 
 ing it more difficult to obtain a good weld- 
 ing joint, over a large cross -section. By 
 the use of alternating currents, however, 
 a more uniform distribution of tempera- 
 ture over the cross -section of the welded 
 surfaces is obtained; for, although as be- 
 
190 ELECTRIC HEATING. 
 
 fore, the bar necessarily loses its heat 
 from the surface, yet, as is well known, 
 alternating currents tend to develop a 
 greater heat at the surface of a large mass 
 than at the central portions, and there is 
 thus ensured a more uniform heating of 
 the contact surfaces. Consequently, most 
 welding processes are now carried out by 
 the use of alternating currents. 
 
 The apparatus employed in electric 
 welding may be divided into two classes ; 
 namely, those in which the alternating 
 currents employed are generated directly 
 from a specially designed alternating-cur- 
 rent dynamo, and second, those in which 
 the currents employed are taken from the 
 secondary coil of a step-doton transformer j 
 that is, a transformer in which the sec- 
 ondary terminals supply a large current 
 at a lower pressure, or a transformer in 
 
ELECTRIC WELDING. 191 
 
 which the primary consists of a long, thin 
 
 a p 
 
 Fig. 58. —Direct Welder For Welding Baby Carriage 
 Tires at the Raie of 1500 to 2000 in ten Hours. 
 
 wire, and the secondary of a short, stout 
 wire. The first method is called the proc- 
 
192 ELECTRIC HEATING. 
 
 ess of direct loelding, and the second, that 
 of indirect welding. 
 
 Fig. 58 shows a direct welder employed 
 for welding the iron tires of baby car- 
 riages. Such a machine can make 1500 to 
 2000 welds in ten hours. It consists of an 
 alternating -current dynamo, or alterna- 
 tor, with two field magnets M, M, and the 
 armature A, revolving between the two 
 pole-pieces, one on each side as shown at 
 P' . The armature is driven by a belt and 
 •pulley Y. The armature has two windings. 
 One is connected with the commutator C, 
 at the end of the shaft, and the brushes 
 B,B, carry off a continuous, or commuted 
 current, to the field magnet coilsJf, M, for 
 their excitation. The other winding on the 
 armature consists of a single massive 
 turn of copper cable. Its extremities are 
 brought to the collecting rings R, R, upon 
 
ELECTEIC WELDING. 193 
 
 which rest heavy brushes to carry the pow- 
 erful welding current to the two clamps 
 P, P, mounted above the platform P PP. 
 These clamps can be caused to approach 
 or recede by the turning of the handle h. 
 The clamps P, P, hold the two rods d, d 
 which are to be welded together. The 
 alternating currents, generated in the 
 single turn of cable on the armature, are 
 carried directly to the rods which are 
 brought into end -to -end contact by the 
 movement of the clamps. Since the 
 clamps are attached to the rods to be 
 welded close to the welded ends, it is evi- 
 dent that only the portions between these 
 clamps and the welded surfaces, receive 
 the welding current and attain the welding 
 temperature. Moreover, in the immediate 
 neighborhood of the clamps the heat is 
 conducted away into the large metallic 
 masses around the clamps. On the ap- 
 
194 ELECTRIC HEATING. 
 
 plication of the current, the ends of the 
 bars to be welded are pressed steadily to- 
 gether and the pressure is increased as the 
 temperature rises. The current strength 
 employed in the welding circuit seldom 
 exceeds 4000 amperes, and the E. M. F. in 
 the circuit is only two or three volts. 
 
 In order to avoid the use of collector 
 rings for carrying off the heavy welding 
 currents, forms of direct welders have 
 been devised in which the armature is sta- 
 tionary, and the field is movable. In this 
 case, the ends of the heavy cable, wound 
 over the armature, are carried directly to 
 the welding clamps. 
 
 Another form of direct welder is illus- 
 trated in Fig. 59. This welder is spe- 
 cially adapted to the purpose of welding 
 strip-iron into hoops. Some of these hoops 
 are represented at the bottom of the figure 
 
ELECTKIC WELDING. 
 
 195 
 
 I PP 
 
 Fig. 59.— Dibect-Welding Appabatits, 
 
196 ELECTKIC HEATING. 
 
 with their Avelds at W. One of the mag- 
 nets of the alternator is shown at 
 M. The pole-piece P, embraces the 
 armature, which is driven by a belt on the 
 pulley Y. The whole machine can be 
 moved forward with the aid of the rachet 
 handle H, so as to tighten the belt, when 
 necessary. The rheostat R, enables the 
 strength of the current from the com- 
 mutator C, to the magnet coils J/, to be 
 readily controlled. On the platform F F, 
 are mounted the clamps p p, connected 
 with the ends of the turn of cable on the 
 armature, through the collector rings r, ?% 
 and brushes restmg on the same. The 
 strip S, to be welded, rests on the supports 
 T, is then cut off at the right length and 
 the two ends forced under the clamps p,p. 
 
 Whenever large bars or rods are to be 
 welded, indirect welders are used. Any 
 
ELECTEIC WELDING. 197 
 
 alternating- current machine can be em- 
 ployed for this purpose. The machines 
 usually employed give an E. M. F. of 300 
 volts, with a frequency of 50 cycles, or 100 
 alternations; i. e., 100 reversals of current 
 per second. This alternating E. M. F. is 
 led to the primary coil of a step -down al- 
 ternating-current transformer, and the 
 secondary coil of this transformer is 
 brought directly to the bars to be welded. 
 The E. M. F. in the secondary circuit 
 varies from 1 to 4 volts, according to the 
 character of the work to be performed, 
 the strength of current requn^ed, the melt- 
 ing point of the metal to be welded, the 
 size of the clamps, etc. 
 
 The connections of such an indirect 
 welder are represented in Fig. 60. The 
 alternator A, is driven by a belt B. A 
 small belt h, from the same shaft drives 
 
198 
 
 ELECTEIC HEATING. 
 
 the exciter E, which supplies the current 
 for the field magnets of the alternator A, 
 through the controlling rheostat R. The 
 current from the collecting rings of the 
 alternator armature, is carried through the 
 
 Fig. 60. —Connections of Indirect Welding. 
 
 switches S, S, and the register g, to the 
 primary coil of the welding transformer T. 
 A register is employed to count the 
 numiber of welds that the machine makes. 
 The metallic mass or shell of the trans- 
 
ELECTEIC WELDING. 
 
 199 
 
 former T, is gTOuncled by the ground con- 
 nection G, in order to prevent any shock 
 
 Fig. 61.— Constant Potential Dynamo. 
 
 from being accidentally obtained from the 
 apparatus, by the operator. 
 
 Fig. 61 represents an alternator, with 
 six poles, intended for indirect welding. 
 Here a separate continuous current genera- 
 
200 ELECTRIC HEATING. 
 
 tor G, supplies current to the magnets M, 
 M, of the alternator. For this reason the 
 alternator is Qdlledidi separately 'exciteclvcL^' 
 chine. There is, however, on the alter- 
 nator shaft, a commutator c, which serves 
 to commute part of the current from the 
 armature A , and supplies this rectified or 
 commuted current to the field magnets, 
 in order to compensate for the drop in the 
 pressure at the terminals of the armature, 
 when the machine is running at full load. 
 The machine is, therefore, said to be com- 
 pound-wound; i. e., contains tw^o separate 
 windings in its field magnets. The rmgs 
 r, 7% carry the current to the primary coil 
 of the welding transformer at a pressure 
 of about 300 volts. The handle H, is for 
 tightening the belt on the main pulley P, 
 by driving the generator forward on the 
 guides g, g. This machine has a capacity 
 of about 60 KW., or, at 300 volts pres- 
 
ELECTRIC WELDING. 201 
 
 sure, will give a current of about 200 
 amperes. 
 
 Without entering into a minute ex- 
 planation of the function of an alternating- 
 current transformer, it is sufficient to state 
 that it consists essentially of two coils of 
 wire, placed side by side, called respect- 
 ively the primary and secondary coils sur- 
 rounding a core of laminated iron. One of 
 these coils consists of many turns and the 
 other of a few turns. In the case of the 
 icelcling transformer, the secondary coil con- 
 sists of a single turn of very heavy copper. 
 When a rapidly alternating ciu^rent, that 
 is, a current which is rapidly changing its 
 direction, is sent through the primary coil, 
 currents, alternating equally rapidly, are 
 generated by induction in the secondary 
 coil. The relation existing between the 
 E. M. F. that is caused to act on the primary 
 coil and the E. M. F. produced by indue- 
 
202 ELECTRIC HEATING. 
 
 tion in the secondary coil, will depend up^ 
 on the relative number of turns or loops of 
 wire in each. If, for example, the primary 
 contains 100 turns and the secondary a sin- 
 gle turn, then, if the E. M. F. impressed 
 upon the primary coil from the machine 
 above described be 300 volts, there will be 
 induced in the secondary coil an E. M. F. 
 of about three volts. But, since the resist- 
 ance of this single turn of very heavy 
 copper is exceedingly low, the resistance 
 of the secondary coil may be, sayy^^o^^th 
 of an ohm. The current strength which 
 would flow through the secondary circuit 
 might, therefore, be 21,000 amperes, a cur- 
 rent that would necessarily jjossess large 
 heating power; namely, 3 x 21000 = 63,000 
 watts activity. 
 
 Fig. 62 shows a form of welding trans- 
 former. A core /, of laminated iron, made 
 
ELECTKIC WELDING. 
 
 203 
 
 up of a number of thin sheets piled to- 
 gether, is looped with a massive copper 
 casting S S S S, which serves as a single 
 
 Fig. 62.— Welding Transformer. 
 
 turn of secondary conauctor slit between 
 the clamps C\C\ as shown. Within the 
 groove formed by this secondary casting 
 
204 ELECTEIC HEATING. 
 
 is placed an insulated coil of wire forming 
 the primary coil, but not shown in the fig- 
 ure. This transformer is, in reality, 
 double, a second transformer being placed 
 at the back, and only part of which is 
 seen. Its construction, however, is iden- 
 tical with that just described. When 
 an alternating electric current is sent 
 through the primary coils, powerful cur- 
 rents are set up by induction in the heavy 
 single copper turn forming the seconda- 
 ries of these transformers as soon as their 
 circuit is closed through ^the clamps and 
 bars to be welded. 
 
 For very large work, which it would be 
 impracticable to bring to the transformer, 
 the transformer is so designed that it can 
 be readily brought to the work. For this 
 purpose the form of transformer shown in 
 Fig. 63 has been devised. The outer shell 
 
ELECTEIC WELDING. 205 
 
 S S S S, oi this transformer, is a copper 
 casting made in two halves bolted together, 
 serving as the secondary coil, and containing 
 wdthinit the primary coil. By this means 
 
 Fig. 63. — Large Welding Transformer . 
 
 the primary coil is protected from injury. 
 Insulation is maintained not only by in- 
 sulating the wire of the primary coil in 
 the usual way, but also by filling the inte- 
 
206 ELECTRIC HEATING. 
 
 rior of the copper box with oil. The iron 
 core, not shown in the figure, is linked both 
 with the primary and secondary coils 
 through the opening 0. 
 
 In order to decrease the skill required 
 for making an effective welded joint, the 
 automatic lo elder. Fig. 64, has been devised. 
 Here the proper degree of pressure be- 
 tween the contact surfaces is automatical- 
 ly applied, amounting for copper to 600 
 lbs. per square inch of welding cross-sec- 
 tion, 1200 lbs. per square inch for iron, 
 and 1800 lbs. per square inch for steel. 
 The rods to be welded are placed in the 
 clamps C, C, , and are pressed together by 
 the action of the weight W. The trans- 
 former T, supplies from its secondary 
 coil the current strength required for ef- 
 fecting the weld. The movement of the 
 clami:)S C, C\, as the weld is effected, 
 
ELECTRIC WELDING. 
 
 207 
 
 causes a contact to be made under the 
 control of the screw K, actuating the 
 
 ^ 
 
 
 ^ ^ 
 
 Fig. 64.— Automatic Welder. 
 
 magnet J/, wdiich interrupts the main 
 current. 
 
 Indirect welders are made in a variety 
 of forms. Generally, however, the ap- 
 
208 ELECTEIC HEATING. 
 
 paratus is protected from dirt, dust and in- 
 jury by a suitable casing. A form of 
 automatic ic elder is shown in Fig. 65, 
 which is intended for the welding of 
 copper wire. 
 
 The amount of power, which must be 
 expended in effecting a weld, depends 
 both upon the material and upon its cross- 
 sectional area. If we double the cross - 
 sectional area, we increase the amount of 
 work to be expended by about 150 per 
 cent, that is to say, we more than double 
 the necessary expenditure of work. In 
 order to weld bars of iron and steel one 
 square inch in cross -section, nearly one 
 megajoule; i. e., nearly 1,000,000 joules 
 must be expended, or somewhat more 
 than 1 of a KW. hour. For a weld in 
 brass, of one square inch in cross-sec- 
 tion, about the same amount of work is 
 
ELECTEIC WELDING. 
 
 209 
 
 \k^^ 
 
 f m 
 
 .1 
 
 Fig. 65.— Automatic Welder. 
 
 required; /. c\, a trifle more than one mega- 
 joule, and for a ^veld in copper one square 
 
210 
 
 ELECTEIC HEATING. 
 
 inch in cross -section, an expenditure of 
 nearly one and one-half niegajoules is 
 required. 
 
 Fig. 66 shows a form of welder intended 
 
 Fig. 66. -Welder for Carriage Tires. 
 
 for welding carriage tires. The welding 
 transformer is situated in the interior of 
 the box upon which the clamps are 
 mounted. Here the pressure is applied 
 
ELECTKIC WELDING. 
 
 211 
 
 hydraulically from the cylinder G, under 
 the action of the handle H. The tire to 
 be welded is gripped in the clamps C, C. 
 
 Fig. - 67. —Universal TVelder. 
 
 Fig. 67 shows a universal welder adapted 
 to a variety of work, and of 40 kilowatts 
 capacity, so that at 2 volts E. M. F., the 
 full-load current would be approximately 
 
212 
 
 ELECTRIC HEATING, 
 
 20,000 amperes, or 20 kilo-amperes. In 
 this apparatus, as in the preceding, the 
 pressure is applied hydraulically from the 
 piston G, under the control of the handle 
 
 
 ^ 
 
 
 
 -..X, 
 
 .J 
 
 !F- 
 
 _^ 
 
 m":.: ^MM 
 
 ^ 
 
 W 
 
 rir 
 
 _„ .. _ ___ ..J 
 
 Fig. 68.— Welder for Carriage Axles. 
 
 ff. The handles h, h, are for operating 
 the clamps C, C . 
 
 Fig. 68 shows a form of welder suited 
 for welding wagon and carriage, axles. 
 
 Fig. 69 shows a welder for steel wire 
 cable or for bars of iron or steel. 
 
 Fig. 70 represents a form of welder 
 
ELECTRIC AVELDING. 213 
 
 for weldino' steel spokes to their hubs. 
 A circular platform is mounted above 
 the transformer, as shown, and the 
 four clutches grip as many spokes at a 
 time. Water is supplied, through the 
 
 /: 
 
 Fig. C9.— Welder for Cable or Bars. 
 
 flexible pipes shown, to the upper 
 clamps, which are hollow, so as to keep 
 their temperature from becoming ex- 
 cessive under constant use. 
 
 Ym. 71 shows in detail some welds ef- 
 
214 
 
 ELECTEIC HEATING. 
 
 . - r 
 
 Fig. 70.— Welder for Wheel-Spokes. 
 
ELECTRIC WELDING. 
 
 215 
 
 fected by the i)receding apparatus. Here 
 the advantage possessed by an electric 
 weld for telegraphic joints becomes ap- 
 parent. According to the old process as 
 
 OLD AND NEW TELEGRAPH 
 WIRE SPLICE 
 
 ~1i 
 
 jf 
 
 THIN STRIP WELDED 
 
 B 
 
 B 
 
 WELDED SHAPE 
 
 PROJECTILE REAC 
 FOR WELDING 
 
 THIN STRIP WELDED 
 
 (e 
 
 3) 
 
 w 
 
 WIRE CABLE 
 
 CAST-IRON RETUfiN BEND 
 WELDED TO WROUGHT-IRON PIPE 
 
 C 
 
 > 
 
 = CaaSi^ 
 
 PROJECTILE FORMED 
 OF TWO PARTS 
 
 K" 
 
 Fig, 71.— Specimens of Electric "Welding. 
 
 shown on the left in the illustration, the 
 wire was twisted and soldered as indi- 
 cated while according to the new method 
 of weldino;. the ends of the wires are 
 
216 ELECTKIC HEATING. 
 
 abutted and welded together, as shown in 
 the lower right hand portion of the cut. 
 
 The extent of telegraphic welds may be 
 inferred by the fact that a single firm, man- 
 ufacturing telegraphic wire, makes on the 
 average 600 welds daily by this method. 
 At B and C, are shown tliin strips welded 
 together. At D, is sliown a welded pipe 
 which has been tested to tlie bursting 
 point and which has burst not at the 
 weld, but beyond it. At E, is a coil of 
 pipe containing welded joints; at F, a pro- 
 jectile made in segn^ents and ready for 
 welding; at F\ the same projectile after 
 welding; G and if, wire cables welded; at 
 K, an insulated wire with a welded jomt. 
 Of course, such welded joints can only be 
 effected conveniently in the factory, as 
 the welding apparatus is not usually avail- 
 able in the field. 
 
ELECTRIC WELDING. 
 
 217 
 
 T 
 
 *E%'-'4S;^fjs#gJs!" '#g^J#^--ig^} 
 
 Fig. 72.— Welder for Shrapnel Shells. 
 
218 
 
 ELECTEIC HEATING. 
 
 Fig. 72 shows a special form of weld- 
 ing machine for welding the hard steel 
 points of shrapnel shells to their soft steel 
 bodies. This is an operation that would 
 be very diflficult to accomplish by any 
 
 Fig. 73.— Fipe-Bending Apparatus. 
 
 other method. Fig. 73 represents a form 
 of welding apparatus designed to heat a 
 short length of pipe to enable the same to 
 be readily bent. The pipe is held in the 
 screw clamps CC, and the current is 
 
ELECTRIC WELDING. 219 
 
 sent through the short length of pipe be- 
 tween them, which is thus raised to the 
 welding temperature except in the imme- 
 diate neighborhood of the clamps. 
 
 In the system of street passenger rail- 
 ways, where the cars are driven by elec- 
 tric motors which take their current from 
 trolley wires and tracks, a necessity exists 
 for ensuring a continuous electric contact 
 between the separate rails constituting 
 the tracks. This is effected, in practice, 
 by connecting the abutting ends of the 
 rails by means of stout copper wires, or 
 bonds, as they are termed. No little diffi- 
 culty has arisen in practice, owing to the 
 imperfect contact thus ensured between 
 the surfaces of the bond wires and the 
 rail, a considerable resistance being intro- 
 duced into the circuit of the rails from 
 this lack of good connection, as well as 
 
220 ELECTEIC HEATING. 
 
 from the liability to corrosion through 
 galvanic action. Not only is a contin- 
 uous conductor necessary for the eco- 
 nomical transmission of electric current 
 over the line, but also to reduce to a 
 minimum the electric corrosion of the 
 gas and water-pipes, or other masses of 
 metal situated along the line in the 
 neighborhood of the railroad tracks. 
 Again, unless the contact between adjoin- 
 ing rails is electrically good, the advan- 
 tages gained by buried cables, or ground 
 feeders, to constitute a return circuit, 
 is materially diminished. 
 
 An attempt has been made to overcome 
 these difficulties by rendering the entire 
 length of rail constituting the track one 
 continuous metallic conductor. This is 
 done by welding the abutting ends of 
 the rails together, while in place, on the 
 
ELECTEIC WELDING. 221 
 
 track. Since the rails are welded in place, 
 the electric current has, of course, to be 
 carried to the weld. To this end, the 
 necessary welding appliances are placed 
 on a special car which either takes its 
 current from the trolley wire, or from any 
 alternating- current circuit that may be in 
 the neighborhood. When the continuous 
 current from the trolley wire is employed 
 for this purpose, the pressure being ai)- 
 proximately 500 volts, this current drives 
 a motor-dynamo, or rotari/ transformer, 
 placed on the car, and by this means the 
 continuous current i^eceived from the 
 trolley is converted into an alternating 
 current and afterward delivered into the 
 primary coil of the welding transformer. 
 
 The car employed for tliis purpose is 
 shown in Fig. 74. The welding transform- 
 er, with its large clamps, is seen sus- 
 
222 ELECTEIC HEATIKG. 
 
 pended from a beam at the rear end of the 
 car. The same transformer is shown 
 more clearly in Fig. 75, which represents 
 the welding transformer in place, in actual 
 work upon a track weld. By means of a 
 
 Fig. 74. —Track- Welding Car. 
 
 m(!)tor in the car, the surface of the rails 
 is ground by a revolving grinder for a f ew^ 
 inches on each side of the joint, so as to 
 prepare a clean surface of iron on which 
 the weld is to be produced. Two iron 
 
ELECTRIC WELDING. 
 
 228 
 
 Fig. 75. —Track Welder at Work. 
 
224 ELECTRIC HEATIjSTG. 
 
 chucks are then placed in position, one on 
 each side of the joint, and the electric cur- 
 rent is forced from the Jaws of the welder 
 through the chucks and across the two 
 ends of the rails. By this means the 
 chucks and rail ends are brought to- 
 gether up to the welding temperature. 
 Hydraulic pressure is exerted upon the 
 chucks by the hand pump P^ shown on the 
 right. When the weld is effected, the two 
 chucks and the two ends of the rail form 
 one solid mass. The massive secondary 
 copper casting, or single turn S S S Sy is 
 represented in the figure with its two lower 
 extremities jS^ jS^ forming the terminals 
 which are brought into contact with the 
 chucks. The primary coil is contained 
 within the secondary shell or box, and 
 the laminated iron core I J, is passed 
 through or linked with both. The two 
 heavy iron jaws JfJ^ JJ^ pivoted at F^ are 
 
ELECTEIC WELDIISra. 225 
 
 drawn apart by the spiral springs at the 
 top, but are forced together by the hy- 
 draulic pump Mj so as to bring pressure 
 transversely upon the chucks through the 
 heads of the secondary terminals S S . 
 
 J 12 
 
 It will be seen, therefore, that the rails are 
 not pushed together, end to end, but are 
 welded transversely. 
 
 Fig. 76 represents the appearance of a 
 welded rail, after the operation is com- 
 pleted. The area of this weld is from 
 12 to 16 square inches. The current 
 strength required from the trolley wire 
 may reach 275 amperes, representing an 
 activity of about 137.5 KW. This is de- 
 livered from the motor-dynamo, or rotary 
 transformer, as an alternating current at 
 a pressure somewhat in excess of 300 
 volts, and, after allowing for the 
 losses of power in the rotary transformer, 
 
226 ELECTEIC HEATING. 
 
 as well as in the welding transformer, 
 about 120 KW. can be delivered to the 
 
 Fig. 76. — Welded Rails. 
 
 track, representing a current strength of 
 very nearly 60,000 amperes. The welding 
 
ELECTRIC WELDING. 227 
 
 transformer is oil-insulated, so that the 
 whole apparatus can be worked in the 
 rain. Water is circulated through the 
 jaws, in order to cool them when at work. 
 Under favorable circumstances, four joints 
 can be made per hour. 
 
 A street rail, weighing: 70 lbs. per yard, 
 when prevented from expanding and con- 
 tracting, owing to the entire rail being in a 
 single length, requires about 150,000 lbs. 
 tensile strength to withstand the stresses 
 produced in it by the expansions and 
 contractions, following changes in tem- 
 perature due to the seasons. An elec- 
 tric weld requires more than 250,000 
 pounds to break it. Consequently, a 
 track is not likely to break at a weld 
 owing to the stresses produced by tem- 
 perature variation. It is necessary, how- 
 ever, in practice, to keep the track firmly 
 
228 ELECTRIC HEATING. 
 
 from bending in summer, by securely 
 fastening it to the sleepers. 
 
 In order to cite an example of the 
 practical application of electric track 
 welding, it may be mentioned that in the 
 city of Boston, four miles of Providence 
 girder street car rails, weighing 61 lbs. 
 per yard, were electrically wielded in the 
 summer of 1893 in one continuous length. 
 . It had been the general belief, up to the 
 date of this experiment, that a track so 
 .welded could not resist the tendency of 
 its own expansion and contraction to pull 
 it to pieces. These four miles remained 
 in good condition until the following 
 winter, when they broke in about 80 
 places, but, in nearly all cases, it is inter- 
 esting to note that these fractures did not 
 occur at the joints, but about four to eight 
 inches from them, These fractures were 
 
ELECTRIC ^yELBING. 229 
 
 repaired by being electrically welded. 
 The track lasted intact through the sum- 
 mer of 1894, but again broke the following 
 winter in about 30 places. It is a curious 
 fact that these breaks did not occur at 
 regular intervals, but several would usu- 
 ally appear within a few feet, and then 
 none, perhaps, for half a mile. It is 
 claimed that the difficulty referred to in 
 the preceding paragraph can now be 
 overcome. 
 
 In all the methods of welding thus fai^ 
 described, a single process is employed; 
 namely, the parts to be welded are 
 brought into contact and a powerful 
 electric current is sent through the con- 
 tact surfaces until they are raided to the 
 welding temperature. The temperature 
 is never allowed to reach the fusing point. 
 Another method of welding, which dif- 
 
230 ELECTKIC HEATING. 
 
 fers radically from the preceding, consists, 
 practically, in bringing the metals to be 
 welded to the fusing point. This is ac- 
 complished by the use of the voltaic arc 
 as follows ; one terminal of the source of 
 current, preferably a storage battery of 
 between 50 and 100 volts E. M. F., is con- 
 nected to the metals to be welded, and 
 the othei terminal, to a rod of hard carbon, 
 which is brought into contact at the weld- 
 ing surfaces and then separated a short 
 distance from them, so as to form an arc 
 between the metal and the end of the car- 
 bon electrode. By this means, a partial 
 fusion is obtained, which results in an 
 electric soldering; or, as it is sometimes 
 called, a welding at the joint. This meth^ 
 od of uniting the ends of metal bars or 
 rods, is not unlike the burning process as 
 applied to lead, in which two abutting sur- 
 faces or ends of lead sheets are united by 
 
ELECTEIC WELDING. 231 
 
 the aid of a blow-pipe flame. It is evi- 
 dent that this method is not capable of as 
 many applications as is the method pre- 
 viously described, since the heat, being 
 only superficially applied, is incapable of 
 giving to joints of any considerable cross- 
 section, that uniformity of temperature on 
 which a good weld is dependent. The 
 process, however, possesses some advan- 
 tages, and has been successfully applied 
 to the filling of blow holes in castings. It 
 is evident that masses of metal intro- 
 duced at the fusing temperature into such 
 blow holes, under the action of the elec- 
 tric arc, tend to render the mass of metal 
 fairly homogeneous, provided the precau- 
 tion has been taken to previously heat 
 the casting to a dull redness. 
 
 The same process has been applied to 
 longitudinal loelding, or calking of plates 
 
132 ELECTRIC HEATING. 
 
 that have already been riveted, in order to 
 make a water-tight joint and instead of 
 employing a calking tool. As before, 
 however, the process is limited to the 
 case of comparatively thin plates. 
 
 Another method, also dependent on the 
 heat of the voltaic arc, consists in de- 
 flecting, by the aid of an electromagnet, 
 the arc existing between two carbon points 
 and directing the flame against the sur- 
 faces to be welded. This apparatus con- 
 stitutes, in fact, an electric blow-pipe. 
 
CHAPTER IX. 
 
 ELECTRIC FURNACES. 
 
 The intense heat of the Yoltaic arc, 
 forming, as it does, the most powerful 
 source of heat known, led many investi- 
 gators, at a very early date, to apply it 
 in various metallurgical processes. These 
 processes were, as a rule, carried out in 
 what may be properly styled electric fur- 
 naces. That is, in furnaces, the heat of 
 which was obtained electrically, either by 
 means of the voltaic arc, or by the heat of 
 intense incandescence of such refractory 
 substances as graphite or carbon. It may 
 be well to point out, in this connection, 
 that the electric furnace differs radically 
 from any furnace in which the heat is ob- 
 tained by ordinary combustion, in that 
 
234 ELECTRIC HEATilS^G. 
 
 means must necessarily be provided, in 
 the combustion furnaces, for cariying off 
 tlie products of combustion. This not 
 only ensures an inefficient form of fur- 
 nace, but also necessitates the cooling 
 or chilling of the furnace by the loss of 
 heat, and by the ingress of cold air. In 
 marked contrast with this, in an elec- 
 tric furnace, no essential gaseous prod- 
 ucts of combustion are formed in the 
 production of the heat, and, consequently, 
 all the heat developed is retained, with 
 tlie exception of such losses as occur 
 thi'ough the walls of the furnace by con- 
 duction. Electric furnaces have been 
 known in the art as early as 1848, and 
 since that time have been veiy frequently 
 employed. 
 
 The electric furnace assumes a variety 
 of forms, one of which is shown in Fig. 77, 
 
ELECTRIC FURNACES. 
 
 235 
 
 Here a voltaic carbon arc is employed as 
 the source of heat, the arc being per- 
 mitted to play in the interior of a crucible 
 of refractory material, surrounded by a 
 non-conducting mass, usually of fire- 
 
 Fig. 77. — Electiuc Furnace. 
 
 brick. Since comparatively little heat 
 escapes by conduction, the temperature 
 Avhich may be attained in the interior is 
 exceedingly high. This particular form of 
 furnace was employed to ascertain the 
 temperature at which carbon boils. 
 
236 ELECTBIC HEATING. 
 
 Although constructed in a variety of 
 forms, all electric furnaces may be di- 
 vided into two classes; namely, first, those 
 in which the operations carried on are 
 effected by means of the intense heat 
 electrically produced, and, second, those 
 in which the operations are effected by 
 electrolysis; i. e., the power possessed by 
 an electric current, under certain con- 
 ditions, of effecting chemical decomposi- 
 tions. By far, however, the greater num- 
 ber of commercial electric furnaces 
 belong to the first class. 
 
 In all electric furnaces the heat is 
 obtained either by means of the electric 
 arc or by electric incandescence. Since 
 carbon is one of the most refractory sub- 
 stances known, it is generally employed 
 either as the material between which the 
 arc is formed, or as the substance for 
 
ELECTRIC FURNACES. 237 
 
 leading the current into the furnace. 
 Since, as is well known, the carbon arc is 
 the most intense source of artificial heat 
 we possess, and the peculiar construction 
 of the electric furnace permits this heat 
 to be readily accumulated, the tempera- 
 ture reached is the highest artificially 
 obtainable. Consequently, under these 
 conditions, chemical processes become 
 possible on a commercial scale, that here- 
 tofore could only be conducted on a 
 small scale in laboratory research. 
 
 As an example of a commercial process 
 carried on under the intense heat of the 
 electric furnace, we may mention the 
 manufacture of a compound of silicon and 
 carbon, known in commerce as carborun- 
 dum. This material is carbon silicide, a 
 molecule of which consists of an atom of 
 silicon united to an atom of carbon. This 
 
238 
 
 ELECTRIC HEATING. 
 
 product is of considerable commercial 
 value in the arts, owing to its great hard- 
 ness, and is extensively used as an abra- 
 sive material, as a substitute for emery and 
 corundum, and has even been employed 
 
 Fig. 78.— Longitudinal Section of Carborundum Fur- 
 nace. 
 
 in the place of diamond dust, for the 
 polishing of gems. 
 
 The furnace employed for the produc- 
 tion of carborundum is shown in longi- 
 tudinal section, as charged ready for the 
 passage of the current, in Fig. 78. It 
 
ELECTEIC FURNACES. 239 
 
 consists substantially of a rectangular 
 chamber, whose walls are formed of brick 
 and fire-clay. The furnace chamber is 
 charged with a central core of granular 
 coke, surrounded by a mixture of carbon, 
 sand, salt and sawdust. In order to ef- 
 fectively connect the electric source with 
 the central carbon core of the charged 
 furnace, carbon rods or terminals are 
 placed at each end of the furnace and 
 brought into good electrical connection 
 with the core by means of a filling of fine 
 carbon tightly packed around them. 
 When a powerful electric current is sent 
 through this furnace, a chemical action 
 occurs, under the influence of the intense 
 heat, whereby a combination is effected 
 between the carbon mainly of the central 
 core and the silicon of the sand, with the 
 formation of a silicide of carbon called 
 carborundum. 
 
240 
 
 ELECTRIC HEATING. 
 
 A cross-section of the furnace, prior to 
 the passage of the current, is shown in 
 Fig. 79, and another cross-section, after 
 the passage of the current, in Fig. 80. 
 Reference to the latter figure will show 
 
 Fig. 79. — Section through Furnace before Passage 
 OF Current. 
 
 that a portion of the coke core still re- 
 mains unaltered, while carborundum in the 
 crystalized and uncrystalized states sur- 
 rounds this unaltered core. 
 
 Another commercial application of the 
 
ELECTRIC FURT^ACES. 
 
 241 
 
 electric furnace in wliicli the product is 
 obtained by high temperature, is in the 
 process for the manufacture of calcium 
 carbide. In this process the product is 
 obtained by the prolonged action of an 
 
 CARBORUNDUM, NOT CRYSTALLIZED 
 CARBORUNDUM CRYSTALS 
 «OKE CORE — 
 
 Fig. 80. — Section through Furnace after Passage 
 OF Current. 
 
 electric arc on a mixture of lime and car- 
 bon, placed inside a suitably formed 
 smelting furnace, formed of refractory 
 materials. The form of the furnace is 
 shown in Fig. 81. The outer shell A, 
 
242 
 
 ELECTEIC HEATING. 
 
 consists of a cylindrical fire-brick cover or 
 bench, inside of which is placed a crucible 
 B, of carbon or graphite. Both the cruci- 
 
 FiG. 81.— Furnace for Production of Calcium Carbide. 
 
 ble5, and the masonry A, rest on a con- 
 ducting plate &, of metal, to which one of 
 the terminals of the dynamo is connected, 
 the other terminal being connected to the 
 
ELECTRIC FURNACES. 243 
 
 carbon bar or pencil C, forming the mova- 
 ble electrode of the furnace. The furnace 
 is provided with the cover E, formed of a 
 single or double carbon plate. This is in- 
 sulated from the body of the furnace B, 
 by means of a plate of non-conducting 
 material F. The material to be acted on 
 is placed at the bottom of the furnace, 
 and heat applied by means of a current 
 passing between the electrode C, and the 
 crucible B. A screw-thread shaft G, at- 
 tached to the carbon, permits the adjust- 
 ment of the central electrode in the nut 
 h. A tap hole is provided at rf, for dis- 
 charging the products of the furnace from 
 time to time. During operation, this hole 
 is closed by a plug of clay or other suit- 
 able material. 
 
 An alternating current of from 4000 to 
 5000 amperes under a pressure of from 35 
 to 25 volts, representing an activity of 
 
244 ELECTKIC HEATING. 
 
 about 135 KW., or 180 H.P., can, it is 
 claimed, produce daily in such furnaces a 
 yield of one short ton, or 2000 pounds of 
 calcium carbide at a cost of about $15. 
 
 No little attention has recently been at- 
 tracted to the preparation of calcium car- 
 bide, from the fact that when thrown into 
 water, it is capable of yielding acetylene 
 gas, a combination of hydrogen and carbon 
 (C^HJ, which possesses a high illumi- 
 nating power when burnt in air. Either 
 a continuous or an alternating current 
 may be employed in its production. One 
 of the most important uses to which 
 acetylene can be applied is the enrich- 
 ment of ordinary illuminating gas, so as 
 to increase its light-giving power. 
 
 Up to the present time, perhaps, the 
 most important application of the electric 
 
ELECTRIC FURNACES. 
 
 245 
 
 furnace is to the production of aluminium, 
 either pure or alloyed with copper. 
 
 Fig. 82 represents a section of an elec- 
 tric furnace which produces aluminium 
 bronze alloy; i. e. , aluminium alloyed with 
 copper. This furnace consists essential- 
 ly of a rectangular chamber of fire-brick 
 
 Fig. 82. —Electric Furnace for the Production of 
 Aluminium Alloys. 
 
 provided with carbon electrodes entering 
 the charged chamber. 
 
 A convenient size for such a furnace has 
 an interior length of five feet, a width of 
 one foot, and a height of one foot. The 
 charge occupies the centre of this space in 
 a mass roughly 3 feet long, 7 inches wide 
 and 3 inches high, the space between 
 
246 ELECTRIC HEATING. 
 
 the charge and the wall being filled with 
 limed charcoal. The furnace employs a 
 carbon arc as the source of heat, the arc 
 being formed between the carbon elec- 
 trodes which lead the current through the 
 furnace. In the figure these electrodes 
 are shown at A-r A — , the arc being formed 
 between them at D. The electrodes pass 
 through openings in the ends through 
 boxes B, B^ , filled with granulated copper. 
 The charge in such a furnace is frequently 
 a mixture of 50 lbs. granulated copper, 
 with 25 lbs. of crushed cryolite, a mineral 
 rich in aluminium, and 12 lbs. of charcoal. 
 The current strength varies from 1200 to 
 1500 amperes, and is maintained at a 
 pressure of about 50 volts for 5 hours. 
 Under these circumstances, the ore of 
 aluminium is reduced in the presence of 
 highly heated carbon, and the reduced 
 metal enters into an alloy with the molt- 
 
ELECTRIC FURNACES. 247 
 
 en copper. When the furnace is cleared, 
 50 lbs. of alloy are obtained having from 
 15 to 35 per cent, of aluminium and a 
 small quantity of silicon. 
 
 In another process, by means of which 
 the aluminium is obtained in a pure state, 
 the decomposition is effected by elec- 
 trolysis. Here the curi'ent is led through 
 an electrolytic bath of alumina dissolved 
 in a double fluoride of aluminium and 
 potassium, maintained in a fused state by 
 the heat evolved during the passage of 
 the curi'ent. In one process in which 
 this is effected, the crucible, which con- 
 sists of an iron l)ox suitably lined w^ith 
 carbon forming the cathode or negative 
 electrode, is charged with the ores of 
 aluminium, and a carbon rod, standing 
 vertically in the centre, forms the anode, 
 or positive electrode. The current enters 
 
248 ELECTRIC HEATIIS^G. 
 
 by tliis carbon rod, and, after passing 
 through the materials of the furnace, 
 leav^es it at the negative or external sur- 
 face by means of the iron frame suitably 
 connected to the other pole of the dyna- 
 mo. The current strength employed is 
 about 2500 amperes at a pressure of ap- 
 proximately 35 volts, representing an ac- 
 tivity of 123.5 KW. The furnace is so 
 arranged that the metal can be tapped off 
 and ^vithdrawn as it is formed, so that 
 the process is a continuous one, fresh ore 
 being added from time to time. The effect 
 of the current is not only to keep the 
 chai'ge in the furnace molten by the heat 
 produced in the passage through the fur- 
 nace, but also to reduce the metal from 
 the ore by electrolytic action. By these 
 means the metal obtained is very nearly 
 pure. The iron box is usually cubical in 
 shape, and is two feet deep. It has an 
 
ELECTRIC FURNACES. 249. 
 
 opening beneath, whicli is supplied with a 
 plug of carbon or clay to permit of the 
 pouring off of the metal. 
 
 The electric furnace has been employed 
 in obtaining a number of rare metallic 
 substances among which chromium may 
 be mentioned. 
 
 In the use of electric furnaces for me- 
 tallurgic purposes many advantages arise 
 from the fact that a vacuum can readily be 
 maintained within the furnace during the 
 operation. For this reason metals ob- 
 tained in the fused state from their ores 
 by electric reduction, or metals fused 
 in air-tight furnaces by the application 
 of heat of electric origin, produce sharper 
 and much more homogeneous castings 
 than those melted when exposed to the 
 air. Moreover, such castings are devoid 
 of troublesome blow holes and blasts, 
 and are denser than ordinary castings* 
 
250 ELECTRIC HEATIlSrG. 
 
 In one form of electric furnace, the ore 
 is not only reduced to the metallic state, 
 by the, action of the current, but is also 
 cast directly from the furnace, within 
 which a vacuum is maintained. This fur- 
 nace consists of an air-tight chamber, pro- 
 vided with an inclined hearth, arranged so 
 as to permit the reduced and molten 
 metal to flowdirectly from the furnace 
 into the mould when so desired. The 
 chamber of the furnace is filled with a 
 suitable mixture of ore, flux and reduc- 
 ing agent, and subjected to the influence 
 of the electric current ; oi', the furnace is 
 given a charge of the metal to be melted 
 and a current applied suflficient to melt it, 
 while in the presence of a vacuum. 
 
 The practical limit of size proposed for 
 such a chamber is 40 feet in length and 
 capable of holding li tons of metal at a 
 
ELECTRIC FURNACES. 251 
 
 charge. By working such a chamber with 
 a current of about 30,000 amperes, at 
 fifty volts pressure; i. e., at an activity 
 of about 1500 KW., somewhat less than 
 the activity already employed in the alu- 
 minium electric furnace at Neuhausen, 
 the entire charge can be fused and run off 
 in about a quarter of an hour. Such a 
 furnace would, therefore, be capable of 
 turning out a ve:'y large number of cast- 
 ings in a single day. 
 
 It might be supposed that the electric 
 melting of metals would be more expen- 
 sive than the ordinary method employing 
 the regenerative furnace, but, bearing in 
 mind the fact that all the heat developed 
 by the electric current can be liberated 
 exactly where it is wanted, .and that the 
 loss of heat in such a furnace is very small, 
 it is evident, that even where water-power 
 
252 ELECTRIC HEATING. 
 
 is not obtainable, this method might com- 
 pete with coal on a commercial basis. 
 For example, it has been estimated that 
 in order to smelt a short ton of iron in 
 the Siemens -Martin regenerative furnace, 
 from 1000 to 1400 pounds of coal are re- 
 quired. By the electric process here de- 
 scribed, assuming that coal is burned to 
 drive the dynamo and operate the air 
 pump employed in maintaining the vac- 
 uum, the same work can, it is claimed, be 
 done by the consumption of from 720 to 
 800 lbs. of coal. 
 
 In the use of a furnace of the above 
 type for the direct production of pig iron 
 from iron ore, the resulting iron can be 
 made to contain much less carbon that in 
 that produced by the ordinary blast fur- 
 nace, since the ingredients can be much 
 more closely proportioned in the elec- 
 
ELECTRIC FURNACES. 253 
 
 trie furnace than in the ordinary blast 
 furnace. Experiments made have pro- 
 duced pig ircm containing less than 3 per 
 cent, of total carbon. 
 
 The electric furnace has been employed 
 for the artificial production of very small 
 diamonds. When carbon is melted and 
 vaporized in the electric furnace, it con- 
 denses in the form of graphite with the 
 specific gravity of about 2. Indeed this 
 same process occurs in every arc lamp, the 
 carbon being volatilized at the positive 
 electrode, a portion of this vapor con- 
 densing in the form of a nipple of graph- 
 ite on the cooler, negative or opposite 
 electrode. In order to produce the dia- 
 mond, great pressure is necessary. This 
 can be obtained by forming a solution of 
 carbon in molten iron, and allowing the 
 iron to solidify suddenly, thereby brings 
 
254 ELECTRIC HEATING. 
 
 ing sufficient pressure upon the contained 
 carbon to crystalize the latter into dia- 
 monds. A molten solution of carbon and 
 iron, obtained in an electric furnace, is 
 suddenly poured into lead that has just 
 been separately melted. The iron and 
 carbon, being lighter than molten lead, 
 float to its surface in the form of globules, 
 and solidify. These globules, when dis- 
 solved in suitable acids, will leave as a 
 residue the diamond crystals which are 
 unfortunately very minute, but have all 
 the physical properties of larger natural 
 gems. 
 
CHAPTER X. 
 
 MISCELLANEOUS APPLICATIONS OF ELECTRIC 
 HEATING. 
 
 Beside the difFerent commercial appli- 
 cations of heat of electric origin, which we 
 have already described, there are others of 
 great interest that would appear to have 
 a reasonable probability of coming into ex- 
 tensive use in the near future. We will, 
 therefore, devote the consideration of the 
 closing chapter to some of the more inter- 
 esting of these applications. 
 
 In the manufacture of harveyized armor 
 plates, now extensively employedon war- 
 ships, considerable difficulty has arisen in 
 drilling the plates so as to permit them to 
 be riveted together. The harveyized steel 
 
256 ELECTEIC HEATING. 
 
 plate, as is well known, is so extreme- 
 ly hard, that the ordinary drill has no 
 effect whatever on it. Attempts have 
 been made to soften, or anneal, these 
 plates at the points where the drill holes 
 have to bemade,bnt although the intense 
 heat of the oxy-hydrogen blow-pipe has 
 been tried for this purpose, it has been 
 found to be insufficient. For this reason 
 a strip around the edges of the plate had 
 to be left unhardened, so as to permit of 
 the drilling, and this was an element of 
 weakness. It has been found, however, 
 that under the intense heat of the voltaic 
 arc, even the harveyized plate was an- 
 nealed, or restored to the soft condition, 
 then readily permitting penetration by 
 the drill. This method of electric anneal- 
 ing is carried out specifically as follows: 
 Blocks of copper are laid on the surface 
 of the plate and connected with an alter- 
 
MISCELLANEOUS APPLICATIONS. 257 
 
 nating current transformer, resembling a 
 welding transformer. By this means, on 
 the passage of the current, intense heat 
 is developed in the plate between the two 
 electrodes or masses of copper. The 
 temperature is then slowly lowered by re- 
 ducing the current strength. This has 
 the effect of withdrawing the temper, or 
 annealing the plate between the two 
 blocks of copper. It has been found that 
 alternating currents are more favorable 
 for the concentration of the heating effect 
 than continuous currents, a fact due to 
 the inductance in the iron. 
 
 The heat of the voltaic arc has been em- 
 ployed in a process of electric casting al- 
 ready described and mentioned as a proc- 
 ess of electric soldering. This process is 
 applicable to the cases of repairing fly- 
 wheels, steam cylinders, connecting-rods, 
 
258 ELECTEIC HEATING. 
 
 etc. It consists essentially in the em- 
 ployment of the voltaic arc taken be- 
 tween two metal electrodes. One of the 
 electrodes, consisting of the mass of the 
 metal to be repaired, is fixed, and the 
 other, the movable electrode, is made of 
 the metal which is to be fused and em- 
 ployed in the repairing. Under these 
 conditions, the arc is formed betw^een the 
 metal to be repaired and the metal em- 
 ployed in the casting or filling of the 
 intervening space, the latter melting, 
 and dropping into the interstices of the 
 metal to be filled with the metal and 
 then soldered or welded. 
 
 This process requires about 8 amperes 
 per active square millimetre of the metal 
 electrode. The usual diameter em- 
 ployed for the electric soldering tool is 
 from 6 to 10 millimetres. It is neces- 
 sary that the metal which receives the 
 
MISCELLANEOUS APPLICATIONS. 259 
 
 molten application should itself be raised 
 to a red heat, as, otherwise, the molten 
 metal introduced \YOuld chill too rapidly, 
 and thus prevent an effective junction. 
 
 Probably one of the most valuable mis- 
 cellaneous applications of electric heating 
 is to be found in the various processes 
 which have been designed for the electric- 
 al loorking and forging of metals. In these 
 processes the metal is brought by heat of 
 electric origin to the temperature re- 
 quired for its working, shaping or forging. 
 
 In this, as in other commercial applica- 
 tions of electric heating, one of the most 
 marked advantages obtained is found in 
 the fact that the heat is developed in the 
 exact locality where it is needed, and not 
 elsewhere; is developed only to the ex- 
 tent it is needed, and not to an unneces- 
 sary extent; and, moreover, only at the 
 
260 ELECTRIC HEATING. 
 
 time when it is needed. Instead of re- 
 quiring a long previous heating in the 
 forge or furnace with a waste of fuel, the 
 metal is quickly heated by the electric 
 current. Moreover, heat of electric ori- 
 gin is capable of much finer and closer 
 regulation than is heat of the ordinary 
 forge or furnace. Then again, automatic 
 devices may be readily introduced where- 
 by the current can not only be controlled 
 as to amount, but also can be cut off as 
 soon as a certain temperature is reached. 
 This will be found a matter of consider- 
 able advantage in cases where the metals 
 to be worked require tempering, since 
 the heat to which they are subjected 
 can be made absolutely uniform, irre- 
 spective of the size of the piece to be 
 heated. Moreover, the bar can be heated 
 uniformly throughout all portions of its 
 area of cross -section. 
 
MISCELLANEOUS APPLICATIONS. 2G1 
 
 A decided advantage in electric forging 
 lies in the rapidity with which the heating 
 can be obtained; for, if the power applied 
 be ample, the bar to be forged can be 
 brought up to the forging temperature in 
 less than a minute. At the same time it is 
 to be remembered that no very large bars 
 have yet been treated electrically. This 
 process has so far been applied mainly to 
 the production of comparatively small 
 cross-sections of metal, although, of course, 
 it is only a question of the amount of 
 electric power to permit the process to be 
 carried on in larger sizes. 
 
 The power required to heat an iron or 
 steel bar one square inch in cross -section 
 and 20 inches long is about 27 KW. and 
 requires about 2^ minutes, representing a 
 total w^ork done of about 4,000,000 joules 
 or Ih KW.-hrs. = 200,000 joules-per- 
 
262 ELECTKIC HEATING. 
 
 cubic-inch. Alargerbar 3 feet long anJ 3 
 inches in diameter, would require about 
 75 KW. over ten minutes, or 45 megajoules 
 =14 KW. hours, or nearly 180,000 joules- 
 per-cubic-inch. 
 
 Two distinctly different methods are in 
 use for obtaining the electrical heating of 
 the material to be shaped or forged; name- 
 ly, heating it by passing a. sufficiently 
 powerful current through it while in the 
 air, and passing an electric current from 
 it into a mass of surrounding conducting 
 liquid. The former process, as in electric 
 welding, requires the use of a powerful 
 current strength at a low pressure and is 
 best obtained by means of an alternating- 
 current transformer. The latter process, 
 on the contrary, requires comparatively 
 small current strength, but a compara- 
 tively high electrical pressure. 
 
MISCELLANEOUS APPLICATIONS. 
 
 263 
 
 Fig 83.— Electric Forge and Electric Cooking Range. 
 
264 ELECTRIC HEATING. 
 
 Fig. 83 represents the apparatus em- 
 ployed when the former method of heat- 
 ing is adopted. T T, is a large alternat- 
 ing-current transformer for reducing a 
 current of comparatively high pressure to 
 one of very low pressure, but of corre- 
 spondingly increased strength. In the 
 particular case represented the primary 
 coil of the transformer receives about 40 
 KW. at full load at a pressure of 1500 volts 
 and consequently a current strength of 
 about 24 amperes. The secondary coil 
 delivers nearly 40 KW. at full load at a 
 pressure of about 4 volts and, consequent- 
 ly, with a current strength of about 10,000 
 amperes. The secondary terminals of 
 the transformer are connected with the 
 copper massive conductors 1 and 2 ; 3 and 
 4; 5 and 6; and 7 and 8; any pair being se- 
 lected according to the character of the 
 work to be heated. These conductors 
 
MISCELLANEOUS APPLICATIONS; 265 
 
 terminate beneath in clamps or holders 
 suitable for different sizes of work. Bars 
 to be heated are shown at B, bridging 
 across the distance between the two elec- 
 trodes or clamps. The attention of the 
 reader is called to the electrical cooking 
 range shown at the right, not because it 
 has any connection with the forging proc- 
 ess, but from the fact that it differs 
 from the electric cooking ranges de- 
 scribed in the earlier chapter of this 
 book, since its heating coils are properly 
 proportioned to produce the required tem- 
 perature within it from a large current 
 strength and a low pressure of, say four 
 volts, instead of from a high pressure of 
 perhaps 100 volts, and a correspondingly 
 reduced current. 
 
 A number of samples of work done by 
 the hammer on metal heated electrically 
 
266 
 
 ELECTEIC HEATING. 
 
 Fig. 84. —Samples of Forgings Electrically Heated. 
 
MISCELLANEOUS APPLICATIONS. 267 
 
 by this process is shown in Fig. 84. 
 
 The second method for heating consists 
 in plnnging the metal to be heated be- 
 neath the surface of the conducting liquid, 
 when held in a metal clamp connected with 
 the negative pole of a continuous -current 
 source of E. M. I'. The metal to be heated 
 is made the negative pole, and the ves- 
 sel containing the liquid is provided with 
 a metal lining of lead connected with the 
 positive pole. Under these circum- 
 stances the current passes from the liquid 
 to the metal to be heated. The current 
 strength employed is sufficient to produce 
 free electrolysis of the liquid with the 
 production of free hydrogen gas at the sur- 
 face of the metal to be heated, the high 
 resistance of which causes so intense a 
 heat at this surface as to practically set up 
 an electric arc over its surface. The heat 
 so produced rapidly penetrates the mass 
 
268 ELECTEIC HEATING, 
 
 of the metal and raises its temperature. 
 It is to be observed that this method 
 can only be employed with a continuous 
 current. The heating process is con- 
 ducted without any oxidation of the metal 
 to be heated, its surface being thoroughly 
 protected by the enveloping mass of hy- 
 drogen. The metal surface of the vessel 
 containing the liquid becomes oxidized by 
 electrolysis during the operation of the 
 process, and has to be renewed from time 
 to time. The main resistance in this liquid 
 tank exists at the surface of the metal, in 
 the film or layer of hydrogen, and, conse- 
 quently, it is at this surface that the heat 
 is almost entirely liberated. Consequent- 
 ly, the amount of current employed is 
 automatically regulated by the surface 
 area of the immersed metal, the larger the 
 surface the greater the current strength 
 which will flow. The pressure employed 
 
MISCELLANEOUS APPLICATIONS. 269 
 
 for such a liquid heater may be from 100 
 to 500 volts, and th^ cmTent strqno th from 
 45 amperes upward. 
 
 In order to render the liquid conduct- 
 ing, a suitable conducting salt such as sal 
 soda is dissolved in the water to a specific 
 
 
 [LEAD rUATE 
 
 Fig. 85.— End View if Heating Tank. 
 
 gravity of 1.2 at 84^ F., and to every ten 
 gallon.^ of the solution five pounds of 
 borax are added. 
 
 Fig. 85 represents an end view in cross- 
 section of the tank employed. The pin- 
 
270 
 
 ELECTPaC HEATING. 
 
 cers P, are connected with the positive pole 
 of the source and hold the metal article 
 il/, so that this is partially submerged. 
 The negative pole N, is connected with 
 
 +POLE 
 
 Fig. 1 
 
 -Plan of Heating Tank. 
 
 the sheet lead lining of the tank. Fig. 86 
 represents the same apparatus in plan 
 view. 
 
CHAPTER XL 
 
 THE ELECTRICAL THAWING OF FROZEN 
 WATER IN PIPES. 
 
 The rapid spread of electric supply 
 systems duriug the past decade has ren- 
 dered possible the use of electric heatiug 
 for the thawing of ice in water pipes that 
 liave been exposed to an unexpectedly 
 low temperature durhig winter. When 
 the water in a pipe freezes, it expands 
 nine per cent, in volume. At the same 
 time it liberates a good deal of heat. In 
 other words, a considerable amount of 
 heat must be abstracted from water at the 
 freezing temperature, in order to convert 
 it into ice. This heat must be returned 
 
272 ELECTRIC HEATING. 
 
 to ice ill order to liquefy it or change it 
 back from the solid to tlie liquid state at 
 the same temperature. In order to thaw 
 the ice, the latent heat of liquefaction 
 must be given to it, before the tempera- 
 ture can be raised. The amount of heat 
 required would be sufficient to raise the 
 same weight of water at an ordinary room 
 temperature as far as the boiling point. 
 More precisely, the quantity of heat re- 
 quired to thaw a given weight of ice, or 
 convert it from ice to water, would raise 
 the water from a room temperature of 
 20.5^ Oto 100" 6; just short of ebullition. 
 
 In many cases an alternating current 
 can be caused to flow through a length of 
 pipe containing ice. The heat generated 
 by the current in the resistance of the 
 metallic walls of the pipe supplies the 
 heat of liquefaction to the ice within. 
 
THAWING OF FROZEN WATER IN PIPES. 273 
 
 Fig. 87 represents tlie connections for 
 the method commonly used for thawing 
 out a frozen water service-pipe. A trans- 
 former T, preferably of 10 to 15 KW 
 capacity, has a resistance R and an am 
 meter A inserted in the primary circuit, 
 
 B > 
 < o 
 
 -o- 
 
 Fuses 
 
 -®- 
 
 -<D- 
 
 Hoiise 
 
 -(^ 
 
 s^^v/N/V 
 
 Service Pipe 
 
 ± 
 
 Water Main 
 
 Fig. 87. 
 
 The secondary circuit is closed tlirougli a 
 switch S and the frozen service-pipe. 
 Connection is secured through a hj^drant 
 ^in the neiQ;hborhood to the water main. 
 If no hj^drant is available in the neighbor- 
 
274 ELECTRIC HEATING. 
 
 liooci some other service-pipe from the 
 same main may be used. A voltmeter V 
 and a recording watt-hour meter M may 
 also be conveniently used, although they 
 are not indispensable. The resistance H 
 may be a water-barrel with salt added to 
 the water in order to improve the con- 
 ductivity^, and two iron plates, or masses 
 of metal, as electrodes inserted in the 
 barrel. A dry cord fastened to one 
 electrode enables the depth of its immer- 
 sion to be regulated by the operator with- 
 ont danger of shock. The transformer 
 should preferably supply 50 volts to the 
 secondary circuit, since the range of 
 secondary voltage required is usually from 
 5 to 25 volts according to the length and 
 size of the pipe to be thawed out. 
 
 The current strength found desirable to 
 thaw out 1/2'' lead pipe is about 200 am- 
 
THAWING OF FROZEIN^ WATER 11^ PIPES. 275 
 
 peres. This current has usually to be 
 applied for a time varying between 10 
 minutes and half an hour, according to 
 circumstances. The amount of energy 
 consumed is commonly less than one KW.- 
 hour ; so that the cost of the electrical 
 energy expended in thawing an ordinary 
 house-pipe is relatively small. For such 
 sizes of pipe a 2-KW. transformer may 
 suffice if the secondary voltage be 50-volts. 
 For thawing out a water-main the cur- 
 rent strength required will be considerably 
 greater. A type of Westinghouse port- 
 able air-cooled pipe-thawing transformer is 
 shown in Fig. 88. 
 
 In some cases a service-pipe or a small 
 water pipe within a house may be thawed 
 out by a current taken directly from the 
 lighting mains through a water-barrel re- 
 sistance, as shown in Fig. 89. In such a 
 
276 
 
 ELECTRIC HEATING. 
 
 case care must be taken tLat tlie ligLtiiig 
 mains are of sufficient size tlirougliout to 
 
 Fig. 88. 
 
 carry the required current. In this illus- 
 tration, II is the adjustable water rheostat, 
 
TIIAWIIN^G OF FROZEX WATER IX PIPES. 277 
 
 A tlie ammeter, S the switch, and H an 
 available hj^lrant on the Avater main, the 
 
 -O- 
 
 Fiises 
 
 — o- 
 
 -(Ey 
 
 -^ 
 
 V 
 
 House 
 
 @ 
 
 Water Main 
 
 Fig 89. 
 
 service from which to the house is sup- 
 posed to be frozen. 
 
INDEX. 
 
 Abnormal Temperature Elevation of Circuits, How 
 
 Avoided, 87, 89. 
 Acetyline Gas, Illuminating Power of, 244. 
 
 , Production of, from Calcium Carbide, 'M3, 24.4. 
 
 Activity, Definition of, 26. 
 
 , Muscular, Obtained from the Sun, 15. 
 
 of Circuit, 41. 
 
 of Electric Circuit, 35. 
 
 of Laborer, 27. 
 
 , Unit of, 26. 
 
 Aerial Bare Wires, Effect of Character of Surface on 
 
 Temperature Elevation of, 6Q. 
 , Effect of Extent and Surface on Temperature 
 
 Elevation of, 6G. 
 Affinity, Chemical, 9. 
 Air Heater, Portable Electiic, 183, 134. 
 , Kesistance Offered by to Escape of Heat from 
 
 Conductors, 59, 60. 
 
280 ELECTRIC HEATING. 
 
 Alloys, Effect of Temperature on Resistivity of , 56,57. 
 
 . Lead-Tin, for Fuse Wires, 91. 
 
 Alternating Current, Definition of, 201. 
 Alternating Currents, Advantages Possessed by, for 
 
 Electric Heating, 189, 190. 
 Alternator for Indirect Welding, 199, 200. 
 
 , Separately-Excited, 200. 
 
 Aluminum, Alloys, Furnace for Production of, 
 
 244-247. 
 
 , Metallic, Electric Production of, 247-249. 
 
 Ampere or Coulomb -per-Secoiid, 35. 
 
 Annealing, Electric, of Harveyized Armor Plat s, 
 
 255-257. 
 
 , Influence of, on Resistivity, 54. 
 
 Armor Plates, Harveyized, Electric Annealing of, 
 
 255, 256. 
 Atlantic Liner, Activity of Driving Engines of, 27. 
 Atmospheric Heater, 137. 
 Automatic Welder, 206-208. 
 
 B. 
 
 B. T. U., 29. 
 
 Back Electric Pressure, 41. 
 
 Banquet, Franklin's Electrically Cooked, 178, 180. 
 
 Bare Aerial Wires, Temperature Elevation of, 45, 46. 
 
 Conductors, Electrical Heatii g of, 37-68. 
 
INDEX. 281 
 
 Block, Ceiling, 105. 
 
 , Porcelain, 87-98. 
 
 , Safety Euse, 96. 
 
 , Cut-Out, 106, 107. 
 
 Bond for Street Eailways, 219. 
 Box, Cut-Out, 107. 
 Branch Fuse, 113, 11 4. 
 British Heat Unit, 29. 
 
 Thermal Uuit, 29. 
 
 Thermal Unit, Value of, 29. 
 
 • Buried Conductor, Permissible Temperature Eleva* 
 tion of, 85. 
 
 c. 
 
 G. E. M. E., 42. 
 
 — — , Development of, by Motor, 45. 
 
 • in Circuit, Distribution of, 42, 43. 
 
 Cable Welder, 213. 
 
 Calcium Carbide, Eurnace for Maoufactuie of, 242, 
 
 243. 
 Calking, Electric, 231, 232. 
 Calorie, Lesser, 29. 
 
 Capacity, Carrying, of Conductor, 75. 
 Car for Direct Welding, 222. 
 
 Heater, Electric, 125, 126. 
 
 Healer Kegulating Switch, 127, 129, 218. 
 
 Heating, Cost of, 142-145. 
 
282 ELECTRIC HEATING. 
 
 Carbon,Effect of Temperature on Resistivity of, 56,57. 
 Carborundum, 237. 
 
 Furnace, 238-241. 
 
 Carriage Axle Welder, 212. 
 
 Tire Welder, 210, 211. 
 
 Carrying Capacity of Fuse Wires, 92. 
 Castings, Sharpness of, When Pioduced from Elec- 
 trically Fused Metals, 251. 
 Ceiling Fixture, Fuse-Block, 104, 105. 
 Chafing Dish, Electric, 164. 
 Chemical Affinity, 9. 
 Circuit, Activity of, 40. 
 
 , C. E. M. F. and Activrity of, 46, 47. 
 
 , Distribution of C. E. M. F. in, 42, 43. 
 
 , Wires, Bare, 64. 
 
 , Wires, Covered, 64. 
 
 Circular Mils, Definition of, 52. 
 Coal, Energy in Pou.d of, 10, 11. 
 
 , Origin of Energy in, li. 
 
 Coal-Beds, ^^tore-houses of Solar Energy, 13, 14, 
 
 Coffee Heater, Electric, 157. 
 
 Coffee-Pot, Electric, 158. 
 
 Compound-Wound Machine, 200. 
 
 Conduction, Loss of Heat by, 63. 
 
 Conductor, Carrying Capacity of, 75. 
 
 , TemiDcrature Elevation of, 62. 
 
INDEX. 283 
 
 Conductors, Pure Metallic, Effect of Temperature on 
 Ees'stivity of, 56, 57. 
 
 , Transmission, Necessity for Maintaining Low 
 
 • Temperature of, 69. 
 
 Conduits for Insulated Wires, 77. 
 
 Connections for Indirect Welding, 198. 
 
 Convection, Approximate Amount of Heat Lost by 
 Conductor per Foot of Length per Sec- 
 ond, 67. 
 
 , Loss of Heat by, 63. 
 
 • , L.Mss of Heat, Practical Independence of Ex- 
 tent and Character of Surface on Temper- 
 ature Elevation of, 66, 67. 
 
 Ccnvectional Losses in Conductors, Effect of Motion 
 of Air on, 68. 
 
 Cooking, Electric, 151-180. 
 
 Copper- Tipped Fuse Wires, 95. 
 
 Cost of Car I eating, 142-145. 
 
 Coulomb, or Unit of Electric Quantity, 32. 
 
 Coulomb-Yolts or Unit of Electric Work, 33. 
 
 Counter E. M. F., 41. 
 
 E. M. F., how Produced, 44-45. 
 
 Counter- Hydraulic Pressure, 40, 41. 
 
 Covered Conductors, Electrical Heating of, 69-86, 
 
 Curling-Tongs Heater, Electric, 177, 178. 
 
 Current, Electric, Work done by, 33. 
 
284 ELECTRIC HEATING. 
 
 Current Strength, Effect of, on Temperature Eleva- 
 tion of Wire 80. 
 
 Strength, Effective. 
 
 Strength, Thermal, 62. 
 
 Cut-OutBox, 107. 
 
 Cylindrical Electric Heater, 1-20-122. 
 
 Diameters of Fuse Wires, 92. 
 
 Diamond-, Electric Furnace for the Production of 
 
 Artificial, 253, 254. 
 Difference of Electrical Pressure, Electrical Flow 
 
 Produced by, 22. 
 
 of Thermal Pressure, 72. 
 
 of Water Level, Liquid Flow Produced by, 3L 
 
 Direct Welder, 191-193. 
 
 Welder, Electric, 223. 
 
 Welding Apparatus, 194-196. 
 
 Welding Car, 222 . 
 
 Dissipation of Heat, 9. 
 
 Doctrine of the Conservation of Energy, 20, 
 
 Drop, Definition of, 43. 
 
 E. 
 
 E. M. F., 35. 
 
 , Counter, 41. 
 
 , Impressed, 41. 
 
INDEX. 285 
 
 Earth-Buried Conductors, Lo&sof Heat by, 81. 
 
 Economy of Electric Smelting, 252. 
 
 Effective Thermal Kesistance of Earth-Buried Con- 
 ductors, 81. 
 
 Efficiency of Electric Kettle, 152. 
 
 of Steam Engine, 11. 
 
 Electric Boiling of Water, Cost of, 161. 
 
 Car Heater, 125, 126. 
 
 Circuit, Activity of, 35. 
 
 Cooking, 151-180. 
 
 Cooking, Advantages of, 172, 173. 
 
 Heaters, 117-150. 
 
 Heater, Advantages Possessed by, for Ca^* 
 
 Heating, 124. 
 
 Heater, Advantages of, 119. 
 
 Kadiator, 123. 
 
 Eesistance, 38. 
 
 Source, Definition of, 24. 
 
 Electricity and Heat, Kelations between, 19, 20. 
 
 Circumstances Kegulating Flow of, 37. 
 
 Electrolysis, Definition of, 236. 
 Electrolytic Heating, 267-269. 
 Electromotive Force, Definition of, 32. 
 Elements of Work, 22. 
 Energy, Conservation of, 20. 
 in Pouud of CocjI, 10, 11, 
 
286 ELECTKIC HEATING. 
 
 Energy, of Coal, Origia of, 12. 
 
 Storage of, in Water Keservoir, 30, 
 
 F. 
 
 Falling Water, Storage of Solar Energy Id, 16. 
 
 Fan, Electric, 154-156. 
 
 Feeders, Ground, for Electric Eailways, 220. 
 
 Flexible Electric Hea er, 146, 147. 
 
 Flow of Electricity, Circumstances Kegulating, 37. 
 
 of Water, Circumstances Eegulating, 37. 
 
 Foot-Pound-per-Second, Definition of, 26. 
 
 Foot-Pounds, 23. 
 
 Force, Definition of, 21. 
 
 , Electromotive, Definition of, 32. 
 
 Forging, Electric, 263, 264. 
 
 , Electric, of Metals, 259, 260. 
 
 , Electi ic. Samples of, 266. 
 
 Franklin's Electrically C oked Banquet, 178-180. 
 
 FuU-Iioad Current, Temperature Elevation uuder,80. 
 
 Furnace, Electric, 233-254. 
 
 , Electric, Definition of, 233. 
 
 , Electric, for Manufacture of Calcium Carbide, 
 
 242, 243. 
 
 , Electric, for the Manufacture of Carborun- 
 dum, 238-211. 
 
INDEX. 287 
 
 Fuse-Box, Ceiling Fixture, 104, 105. 
 
 Boxes, Mica-Covered, 100, 101. 
 
 Boxes, Porcelain-Covered, 102, 103. 
 
 , Branch, 113, 114. 
 
 — Links, 94. 
 
 , Main-Circuit, 113, 114. 
 
 Screw Block, 107. 
 
 Wire, Definition of, 89. 
 
 Wire Strips, 93. 
 
 Wires, 87-115. 
 
 Wires, Copper-Tipped, 95. 
 
 Wires, Carrying Capacity of, 92. 
 
 Wires, Composition of, 91 . 
 
 Wires, Diameters of, 92. 
 
 Fuses, Safety, 90. 
 
 G. 
 
 Glue-Pot, Electrically Heated. 175. 
 Ground-Feeders for Electric Railways, 220. 
 
 H. 
 
 Harveyized Armor Plates, Electric Annealing of 
 
 255-257. 
 Heat and Electricity, Relations between, 19, 20. 
 
288 
 
 ELECTEIC HEATING. 
 
 Heat and Mechanical Work, Pielations between, 
 
 17, 18. 
 
 Conduction, 63. 
 
 , Dissipation of, 9. 
 
 , Loss of, by Conduction, 63. 
 
 , Loss of, by Convection,. 63. 
 
 , Loss of, by Kadiation, 64. 
 
 , Nature of, 8. 
 
 , or Molecular Oscillations, 9. 
 
 Unit, British, '^.9. 
 
 , Unit of, 28, 29. 
 
 Heater, Cylindrical, Electric, 120-1^2. 
 
 , Electrical, Advantages of, 119. 
 
 , Electric Tank, 141, 142. 
 
 , Electric Wall, 138, 
 
 , Flexible Electric, 146, 147. 
 
 , Portable Electric, 140, 141. 
 
 Heaters, Electric, 117-150. 
 
 , Electric, Essential Construction of, il9, 
 
 , Electric, Kequisites for, 119. 
 
 Heating, Electric Coil Conductor for, 122. 
 
 , Elect' ic. Tank for, 26^, 270. 
 
 , Electric, Miscellaneous Applications of, 
 
 255-270. 
 
 , Electrical, of Bare Conductors, 37-68. 
 
 , Electrical, of Covered Conductors, 69-86. 
 
INDEX. 289 
 
 Heating of Conductor, Effect of Insulating Covering 
 on, 69, 70. 
 
 , Electrolytic, 267-26D. 
 
 Hemp Covered Wires, Permissible Temperature Ele- 
 vation of, 85. 
 
 Horse-Power and Kilowatt, Kelative Values of, 36. 
 
 , Definition of, 26 27. 
 
 Hydraulic Resistance, 38. 
 
 I. 
 
 Impressed E. M. F., 41. 
 
 Indirect Welder, 197, 198. 
 
 Welding, 192. 
 
 Welding, Connections for, 198. 
 
 Insulated Wires, Conduits for, 77. 
 
 Wires in Conduits, Temperature Elevation of, 
 
 77. 
 
 — Wires, Mouldings for, 76, 77. 
 
 Insulating Covering, Effect of, on Electrical Heating 
 of Conductor, 69. 
 
 Covering, Effect of Thickness of, on Tempera- 
 ture Elevation, 72. 
 
 Covering, Thermal Resistance of, 72. 
 
 International Unit of Activity, 26, 27. 
 
 J. 
 
 Joints, Welded, Tensile Strength of, 187. 
 
290 ELECTRIC HEATING. 
 
 Joule, 33. 
 
 , Definition of, 24, 25. 
 
 per-Second, 26, 27. 
 
 , Value of, in Foot-Pounds, 25. 
 
 K. 
 
 Kettle, Electric, 158. 
 
 , Electric, Efficiency of, 162. 
 
 Kilowatt, 36. 
 
 Kitchen, Electric, 169-171. 
 
 L. 
 
 Laborer, Activity of, 27. 
 Law, Ohm's, 39. 
 
 Lead Sheathing of Wires, Influence of, on Tempera- 
 ture Elevation of, 74. 
 Lead-Tin Alloys for Fuse Wires, 91. 
 Lesser Calorie, 29. 
 Level, Electric, Dififerencie of, 32. 
 Links, Fuse, 94. 
 Loss of Hcdt by Conduction, 63. 
 
 of Heat by Convection, 63. 
 
 of Heat by Eadiation, 63, 64. 
 
 M. 
 
 Mechanical Work and Quantity of Heat, Relations 
 between, 17, 18. 
 
INDEX. 291 
 
 Megajoule, Definition of, 208. 
 
 Metallic Ores, Electric Production of, 250, 251. 
 
 Metals, Electric Forging of, 258-260. 
 
 , Electrical Working of, 259-270. 
 
 Mica-Covered Fuse Boxes, 100, 101. 
 IMicrohm, Definition of, 48. 
 Mil, Definition of, 51, 52. 
 Mils, Circular, Definition of, 52. 
 Molecular Oscillations or Heat, 9. 
 Motor, Electric Development of Counter E. M. F. 
 by, 45. 
 
 , Dynamo, 221. 
 
 Mouldings for Insulated Wire, 76, 77. 
 
 , Wooden, Kule for Size of Wire in, 77, 78. 
 
 ■ N. 
 
 Nature of Heat, 8. 
 
 Negative Eesistivity, Temperature Coefficient of, 56, 
 
 0. 
 
 Oce..n Cables, Temperature Elevation of, 86. 
 Ohm's Law, 39. 
 
 P. 
 
 Pan-Cake Griddles, Electric, 166. 
 Physical State, Influence of, on Resistivity, 54. 
 Pipe-Bending Apparatus, Electric, 218. 
 Plug-Switch for Electric Heaters, 168, 169. 
 
292 ELECTKIC HEATING, 
 
 Porcelain-Covered Fuse- Boxes, 102, 103. 
 
 Fuse-Block, 97, 98. 
 
 Portable Electric Heater, 133, 134. 
 
 Electric Heater, 140, 141. 
 
 Positive Eesistivity, Temperature Coefficient of, 56. 
 Pressure, Beck Electric, 41. 
 
 , Counter- Electric, 41. 
 
 , Counter- Hydraulic, 40, 41. 
 
 , Electric, Difference of, 32. 
 
 , Hydraulic, 40, 41. 
 
 , Unit of Electric, 33. 
 
 Primary Coils of Transformer, 201. 
 Purity, Influence of, on Eesistivity, 54. 
 
 Q. 
 
 Quantity, Electrical, Unit of, 32. 
 
 K. 
 
 Radiation, Loss of Heat by, 63, 64. 
 Badiator, Electric, 122, 123. 
 Rails, Electrically Welded, 226. 
 Rate of Doing Work, or Activity, 26. 
 Reduction, Electric, of Metallic Ores, 250, 251. 
 Regulating Switch for Car Heater, 127-129. 
 Beservoir of Water, Activity in, .34, 35. 
 
INDEX. 293 
 
 Eesistance, Electric, 38. 
 
 , Hydraulic, 38. 
 
 , Thermal, of Insulating Covering, 71. 
 
 Resistivity, Definition of, 48. 
 
 , Effect of, on Pure Melallic Conductors, 56, 57. 
 
 , Effect of Temperature on, 56, 57. 
 
 , Influence of Annealing on, 54. 
 
 , Influence of Physical Sta.e on, 54. 
 
 , Influence of Purity on, 54. 
 
 of Alloys, Effect of Temperature on, 56, 57. . 
 
 of Carbon, Effect of Temperature on, 56, 57. 
 
 Eotary Transformer, 221. 
 
 Rubber Covered Wires, Permissible Temperatuie 
 
 Elevation in, 85. 
 Rule for Size of Wire in Wooden Mouldings, 77, 78. 
 
 s. 
 
 Sad Iron, Electric, 176. 
 Safety Fuse-Block, 96. 
 
 Fuses, 90. 
 
 Strips, 93. 
 
 Transformer Fuse- Box, 109, HO, 
 
 Screw Block, 107, 
 Sealing- Wax Heater, E ectric, 177. 
 Secondary Coils of Transformer, 201. 
 Separately- Excited Alternator, 200. 
 
294 ELECTEIC HEATING. 
 
 Sharpness of Castings When Producdby Electrical- 
 ly-Fused Metals, 251. 
 
 Shrapnel Shells, Welder for, 217, 218. 
 
 Size of Wire in Wooden Moulding, Kule for, 77, 78. 
 
 Skillet, Electric, 166. 
 
 Smelting, Electric, Economy of, 256. 
 
 Socket Attachment, 107. 
 
 Solar Energy, St )rage of, in Goal Beds, 13, 14. 
 
 Energy, Storage of, in Falling Water, 16. 
 
 Energy, Storage of, in Wind, 16. 
 
 Soldering, Electric, 230, 257-259. 
 
 Source, E'ectric, Definition of, 32. 
 
 Specimens of Electric Welding, 215. 
 
 Steam- Cooker, Electric, 167. 
 
 Steam Engine, Efficiency of, 11. 
 
 Step-Down Transformer, 190. 
 
 Stew Pan, Electric, 165. 
 
 Street Railway, Bonds for, 219, 
 
 Strips, Fuse Wire, 93. 
 
 , Safety, 93. 
 
 Subdivided Conductors, Temperature Elevation of. 
 75, 76. 
 
 Subway, Temperature Elevation of Wires in, 82. 
 
 Sun, Prime Source of Muscular Activity, 15. 
 
 Switch, Car Heater Regulating, 127. 
 
 ' for Electric Fan, 155. 
 
INDEX. 295 
 
 T. 
 
 Table of Resistivities, 48, 49. 
 Tank for Electric Heating, 269, 270. 
 
 Heater, Electric, 141, 142. 
 
 Temperature, Effect of, on Pure Metallic Conductors, 
 
 56, 57. 
 
 , Effect of, on Resistivity, 56, 57. 
 
 , Effect of, on Resistivity of Alloys, 56, 57. 
 
 Elevation of Circuits, Abnormal, How Avoid- 
 ed, 87, 89. 
 
 ■ Elevation of Conductor, 62. 
 
 Elevation of Conductor. Effect of Thickness 
 
 of Insulating Covering on, 72. 
 
 Elevation of Conductors in Conduits, 77. 
 
 — — Elevation of Ocean Cables, 86. 
 
 Elevation of Subdivided Conductors, 75, 76. 
 
 Elevation of Wire, Effective Curreut Streogth 
 
 of, 80. 
 Elevation of Wire, Maximum Time Required 
 
 for. 83, 84. 
 
 Elevation of Wire, Safe, 79. 
 
 Elevation of Wires in Subway, 82. 
 
 Elevation Permissible in Hemp-Covered 
 
 Wires, 85. 
 Elevation Permissible in Rubber-Covered 
 
 Wires. 85. 
 
296 ELECTErC HEATING. 
 
 Temperature, Elevation, Permissible, in Buried Con- 
 ductor.^, 8i, 85. 
 
 Tensile Strength of Electrically Welded Jo'nts, 187. 
 
 Thawing of Water Pipes, 271. 
 
 Therm, Definition of, 29. 
 
 Thermal Current Strength, 6^. 
 
 Resistance, Effective, of Earth Buried Con- 
 ductors, 81. 
 
 Resistance of Insulating Covering, 71. 
 
 Unit, Eritish, 29. 
 
 Tin-Lead Alloys for Fuse Wires, 91. 
 
 Transformer, Primary Colls of, 201. 
 
 — , Rotary, 221. 
 
 , Safety Fuse Box, 109. 110. 
 
 , Secondary Coils of, 201. 
 
 , Step-Down, 190. 
 
 , Welding, 201-206. 
 
 u. 
 
 Unit, British Heat, 29. 
 
 Heat, 29. 
 
 of Activity, 26. 
 
 of Activity, International, 26, 27. 
 
 Units of Work, 23. 
 Universal Welder, 211. 
 
 V. 
 
 Vegetable Food, Store-houses of Solar Energy, U, 
 15. 
 
INDEX. 297 
 
 Volt, or Unit of Electric Pressure, 32, 33. 
 
 Ampere or Watt, 36. 
 
 Couloinb-per-Second, 36. 
 
 w. 
 
 Wall Heatht, Electric, 138. 
 
 Water, Circumstances Eegulating Flow of, 37. 
 
 , Conditions requisite for Causing Flow of, 31. 
 
 Gram me- Legree-Cent' grade, 29. 
 
 Heater, Electric, Low Economy of, 16z, 163. 
 
 in Eeservoir, Capacity of, for doing Work, 30. 
 
 Eeservoir, Storage of Energy in, 30. 
 
 , Eesistance Offered by, to Escape of Keat 
 
 from Conductors, 58, 59. 
 Watt, Delinition of, 26, 27. 
 
 , or Yolt-Ampere, 36. 
 
 Welder, Automatic, 206-208. 
 
 , Direct, 191-193. 
 
 for Cables. 213. 
 
 for Carriage Axle, 212. 
 
 for Carriage Tires, 210, 211. 
 
 for Shrapnel Shells, 217, 218, 
 
 for Wheel Spokes, 214. 
 
 , Indirect. 197, 198. 
 
 , Universal, 211. 
 
298 ELECTBIC HEATING. 
 
 Welding, Advantages Possessed by Alternating Cur- 
 rents in, 189. 
 
 Apparatus, Direct, 194-196. 
 
 , Conditions Requisite for Obtaining Efficient 
 
 Joints by, 183, 184. 
 
 , Definition of, 182, 183. 
 
 , Electric, 181-232. 
 
 , Electric, Advantages Possessed by, 185, 186 
 
 , -Electric, Use of Continuous or Alternatiug 
 
 Curientsin, 187, 188. 
 
 Transformer, 201-206. 
 
 Wheel Spokes, Welder for, 214. 
 
 Wind, Storage of Solar Energy in, 16. 
 
 Wires, Bare Circuit, 64. 
 
 , Covered Circuit, 64. 
 
 , Fuse, 87-115 
 
 ■ , Safe Temperature Elevation of, 79. 
 
 Work, Definition of, 22. 
 
 — done by Electric Current, 33. 
 
 , Elements of, 22. 
 
 , Units of, 23. 
 
 . Unit of. Electric, 33. 
 
 Working of Electrical Metals, 259-270o 
 
 z. 
 
 Zoroaster, 7. 
 

 
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