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ELEMENTARY ELECTRO-TECHNICAL SERIES 



ELECTRIC HEATING 



BY 

EDWIN J. HOUSTON, Ph. D., (Princeton) 

AND 
A. E. KENNELLY, Sc. D. 



NEW YORK 

THE W. J. JOHNSTON COMPANY. 

253 Broadway 

1895 



COPYRIGHT, 1895, BY 
THE W. J. JOHNSTON COMPANY. 



PREFACE 

IN preparing this volume on ELECTRIC 
HEATING, as one of a series entitled 
The Elementary Electro -Technical 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 
which 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- 



M289309 



IV PKEFACE 

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, process-es 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 

PAGE 

I. INTRODUCTORY 7 

II. ELEMENTARY PRINCIPLES . . 30 

III. ELECTRICAL HEATING OF BARE 

CONDUCTORS 37 

IV. ELECTRICAL HEATING OF COV- 

ERED 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 

INDEX 271 



ELECTRIC HEATING. 



CHAPTER I. 

INTRODUCTORY. 



ZOROASTER, the founder 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 



5 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- 



INTEODUCTORY. 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 space 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 




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burned in connection^with ja_ 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 ELECTEIC 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 



INTKODUCTOKY. 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 weight 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, and in so doing restore the 



14 ELECTRIC 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 quantity 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 ELECTBIC 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 




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to-and-fro at varying veKHSftfes. p . Some are v> 
moving faster than others ; for^tiurmg t&eir ^ 
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 ELECTRIC 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 



INTRODUCTORY. 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 ELECTRIC 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 further 
transform it. 



CHAPTER II. 

ELEMENTAKY 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 tc 
move. Work is never done by a force uu- 



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 by a 
body in falling, reference is had to certain 
units of work. 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 ELECTRIC 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 work performed by an electric current; 
for, as we 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 
man would have to expend his energy in 
doing the work would be very different in 



26 ELECTEIC HEATING. 

the two 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, 
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 joule -per - 
second, or the watt, and is equal to 0.738 



ELEMENTAKY PRINCIPLES. 27 

foot-pound-per-second, or l-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 = 10,500,000 
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, daring 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 already 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 







PRCFCRTY 

ELEMENTARY PRjfcir&LES. 29 



amount of work, this heat unit-may 
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. U., 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 
l c C. This heat is called the water- 
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 2 pounds weight, from 50 F. to the 
boiling point of 212 3 F., or through a tern- 



30 ELECTRIC HEATING. 

peratureof 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 ELECTEIC 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 coulomb; 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 ELECTRIC 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 



ELEMENTARY PRINCIPLES. 35 

watts. So in an electric circuit, the ac- 
tivity depends upon the flow of electricity 
per second through a given difference 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; i. 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-coulombs-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 KW. , 
is equal to 1.34 H.P., or, approximately, 
1J H.P. 



CHAPTER III. 

ELECTRICAL HEATING OF BAEE 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; i. e., 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 liy- 
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 BARE CONDUCTORS. 39 

of a given E. M. F. and against a given 
resistance in a circuit, was discovered by 
Dr. Ohm, of Berlin, arid is known as 
Ohm's 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: 

Tlie 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 T V = 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 ELECTBIC 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 = 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 -j. ampere - -f watt 
f = 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- 
su> e, or counter -hydraulic pressure, tending 
t j 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 back 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 current 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 



ELECTRIC HEATING. 



expended in the circuit, just as the prod- 
uct of the current strength and the E, 



\ /*N /7%\ f*\ / 


> 2 OHMS 
JGERMANSILYEB 
>WIRE 

^ 

















8 VOLTS 1 OHM 



TOTAL ACTIVITY OF' 
BATTERY 8 WATTS 



<$& 

'&* 

HHH 

8 VOLTS 1 OHM 
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 | ohm 




rtt *s 
( fy 



HEATING OF BAKE 

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 will 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 



ELECTEIC HEATING. 



tors, or electrolytic cells. For example, 
if the circuit represented in Fig. 2 have 




i-*****"^ j* efc&w flbs*^ 

\_f\ /r\ _ /*\ ft 


TOTAL PRESSURE AT 
^ MOTOR TERMINALS 
3/i VOLTS 

















8 VOLTS 



1 OHM 




TOTAL ACTIVITY OF 
BATTERY 6 WATTS 



OHM 



)LTS 

^AMPERE 
^ VOLT DROP 

9ig WATT ACTIVITY 



2 OHMS 
1 1 A 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 CONDUCTORS. 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 = | = | ampere. The drop in the 
resistance of the motor would be 2 x | = 
14 volts, and the total C. E. M. F. of the 
motor 2 + 14 == 34 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 34 x 
| == 2f watts. Of this activity that part 
will be expended in heat which is de- 
veloped in the resistance of the wire; 
namely, 14 x |= 1 watts, and the remain- 
ing, or 1J watts, = 2 x I = 14 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 BABE CONDUCTOES. 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 ELECTBIC HEATING, 

motor bo 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 
upon its resistivity, (or the resistance of a 
cubic 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 C., the freezing point 
of water: 

TABLE OF RESISTIVITIES. 

Substance. "Resistivity. 

Silver, annealed, . . . 1.500 microhms. 
Silver, hard drawn, . 1.53 



HEATING OF BAKE CONDUCTOES. 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 with variations in the tem- 
perature. Thus, the resistivity of pure 
soft copper is given as 1.594 microhms at 
D 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 T^^nr ohms. 



50 



ELECTRIC HEATING. 



If a wire having a cross -section of 1 sq. 
cm. as a 1 , at B in Fig 3, have a length of 5 
cms., then the resistance between the 
terminal faces a 1 and b\ will be 5 times 
as great as between the terminal faces of 
the cube at A, in the same figure, or 5 x 





FIG. 3. DIAGRAM REPRESENTING RELATION BETWEEN RE- 
SISTIVITY AND RESISTANCE. 

1.945 = 7.97 microhms. Again, if the wire 
were 5 centimetres ]ong, 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 CONDUCTORS. 51 

l - 5 3- = 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 ELECTRIC 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 
= 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 lo:_^ 
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 BAKE CONDUCTORS. 53 

a resistance per-foot of T V> 3 oV =: 0.001035 
ohm-per-foot at 20 C. The resistance of 
such a wire per mile would be 5*280 x 
0.001035 = 5.465 ohms. 

While the use of circular mils Is very 
convenient for wires 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 C. having a cross- 
section of 0.05 square centimetre would 
be 1..JL9.4 *.i_o^o_o microhms = 318,800 mi- 
crohms = 0.3188 ohm. 



54 ELECTRIC 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 



resistivity is 
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 ELECTBIC 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; i. 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 0C, 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 'J***s. = 2.232 
microhms. 

When the resistivity of a wire is 
known, either by actual measurement at 
the temperature of observation, or from 



58 ELECTEIC HEATING. 

its tabular resistivity at (PC. 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 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"; i. 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 -VoTi 6 !-- 
=0.9577 ohms at C. If a current of two 
amperes be sent steadily through this 
length of wire, the drop in the wire would 



HEATING OF BARE 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 ELECTRIC 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 10C. 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 ||= 1.728 microhms, and after 
the current has passed through it steadily 
1.6 x }% = 1.792 microhms, so that the 



HEATING OF BAKE CONDUCTORS. 61 

resistance of the heated wire 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 temperature 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 ELECTKIO HEATItfG. 

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 BARE CONDUCTORS. 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 surrounding air, 
whether 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 
will 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 will have 
become practically constant in about two 
minutes. As soon as this limiting tem- 
perature is reached the heat developed 
by the electric current in any length of the 
wdre, 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 BAKE CONDUCTORS. 67 

heat increases directly with the surface. 

For every degree centigrade of tem- 
perature elevation attained by the wire 
above the surrounding still air of a room, 
the heat lost by convection is, approxi- 
mately, 0.053 joules-per-second, per foot of 
length, so that if the wire has a temper- 
ature elevation of 20 C. , every foot will 
lose by convection, approximately, 1.06 
joules-per-second, or will lose heat energy 
at the rate of 1.06 watts. The loss by 
radiation will be approximately 0.004 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 ELECTKIC 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, when the 
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 
w^eather. 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 IV. 

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 COVERED 

the covering could be r erased "without 
allowing the electricity to escapeHfrom 
the wire, the temperature of the wire, 
under 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 ELECTRIC 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 COVERED CONDUCTORS. / 6 

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 
with 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 wire 
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 CONDUCTORS. /O 

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 ELECTKIC HEATING. 

tageous to subdivide the conductor; i. 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 
will 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 wire varies with its area of cross- 
section, decreasing as the area of cross- 
section increases, and vice versa. In 
other words, a small wire 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 COVEKED CONDUCTORS. 77 

a building, loses its heat entirely by con- 
duction, provided the walls of the panel 
or conduit are everywhere in contact 
with the external surface of the covered 
wire. 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 ELECTEIC 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 
fir epi'oof , it is important 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 COVERED CONDUCTORS. 79 

wire which can be grasped in the hand, 
say for a minute, 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 
would 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 ELECTRIC 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- 
perature 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 adcrpted 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 ELECTRIC 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 wire, 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 CONDUCTOKS. 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 25 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 



S ELECTRIC 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- 



DIESEL 

Of) 

FUSE WIR^ S PRCPEfft" V f C 

lent overload, sometimeMpiently great 



to melt even a stout cono&r< forming 
some portion of the circuiCVould 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, 
called 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 ELECTRIC HEATING. 

for, since, as we have seen, the amount of 
heat developed in any 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 will be de- 
veloped in, say one inch of fuse wire, the 
same amount of heat as would be liber- 
ated in, pei haps, 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 
simple 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 
the 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 lefc hand, the carrying capacity of 
the wires in amperes. It is to be ob- 
served, that although the cross -section of 



ELECTRIC HEATING. 



a wire is quadrupled when its diameter is 
doubled, yet the carrying capacity is not 



CARRYING CAPACITY 
AMPERES 



FUSE WIRES 



DIAMETERS 
MILS 

- 20 



31 
36 

50 
70 



32 

42 

56 

68 

78 

83 

96> 

TH 

130 

150 



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 WIKES. 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 in 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 WIKES. 



95 





FIG.?. COPPER-TIPPED FUSE WIRES. 

strip are often fused into copper clamps 
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. COPPER-TIPPED SAFETY FUSES. 



96 ELECTEIC 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- 
tween them as shown. 




FIG. 9. SAFETY FUSE-BLOCK. 

Fig. 10 shows a pair of strip safety 
fuses S 19 $ 2 , or safety links, as they are 
sometimes called, inserted in the circuit 
of the two leads BB 1 and AA 1 , under 
thumb screw clamps situated, at the ends 
of the metallic blocks whiph form the 
terminals of the leads B^ and A A 1 . 
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 1 . 




FiG.lO. PAIR OF SAFETY STRIPS, MOUNTED ON FUSE BLOCK. 

and B, B l . 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 WIKES. 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 



100 



ELECTRIC HEATING. 



B 




FIG. 12. MICA-COVERED FUSE-BOXES. 

carried off at right angles. In the event 
of any short-circuit 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 already mentioned, pass 
directly through the box. 



102 ELECTRIC HEATING. 

At B, 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 



ELECTRIC 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 WIKES. 



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. 17. CEILING BLOCK WITH SPRING CLIPS. 

fixture or circuit in which it is connected. 
Fig. 16 shows a form suitable for a ceil- 
ing fixture; i. e., an electrolier pendant 
from a ceiling and usually called a ceiling 
block. The supply 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 



$iruit. Fig. 18, 




inserts the fuse in 

shows such a screw - 

out and Fig. 19 shows various forms of 

socket attachments, or cut-out boxes, for 

such fuses. The cavities of the block 

containing the fuse wires are usually part- 





PIG. 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 WIEES. 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 (7, is removed to show 
the interior. In this case, the porcelain 



110 ELECTHIC 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 
w,w, is clamped under screws whose 
studs project through the fuse-block and 
enter into spring clips p, p\ when the fuse- 
block is thrown into position by its han- 
dle 7i, 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 upon 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, principal- 
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 ELECTKIC 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 WIKES. 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 ELECTRIC HEATING. 

cuit, the main fuse should blow out, while 
the branch fuse remains intact. 1 his 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 WIRES. 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 w T hich the fuses are blo\vn. 
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 ELECTRIC HEATING. 

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. 

ELECTRIC 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 safety of the ap- 
paratus, its freedom from fumes or dirt, 
and the ease with which it can be managed, 



118 ELECTRIC 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 



ELECTKIC HEATERS. 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 ELECTKIC 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 T VF., and, 
therefore, an activity of one joule-per- 
second, or one watt, can raise the tem- 
perature of one cubic foot of air T V 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 HEX5^. 

N^fc* 



PROPERTY CF '2 

^ 
121 





PIG. 3L 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 cwr 



ELECTRIC HEATERS. 



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 




FIG. 23. ELECTRIC CAR-HEATER. 

rnns. 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 




Fia. 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 connected in series, or in 
parallel -series, or some of them cut out 
from the circuit, thus permitting the 
amount of heat to be readily varied in or- 
der to meet the requirements of the 




^^^tes.'- 1 

FIG. 26. SIDE INTERIOR VIEW OF CAR- HEATER REGULAT- 
ING SWITCH. 

weather. Fig. 25 shows a form of reg- 
ulating switch of this character intended 
to produce five different strengths of 
current, and, therefore, five different rates 



ELECTKIC HEATERS. 129 

of producing heat in the car. The side 
view of the interior of the switch is shown 
in Fig. 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-HEATING KEGU- 
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 



ELECTEIC HEATING. 



The connections from the switch to the 
trolley wire and the ground through the 
various heaters, is 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 



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FIG. 28. DIAGRAM OP 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 



ELECTEIC HEATERS. 131 

entirely cut out of the circuit, so that the 
resistance of the series being diminished, 
the current strength and activity in the 
lemainder 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 
3J amperes in each series; /. e. t 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 



ELECTKIC HEATING. 




FIG. 29. CAB-HEATER. 



ELECTRIC HEATEES. 133 

12 amperes in all, and the activity about 
6 KW. 

Another form of car-heater is shown in 
Fig. 29. Here the heating coil shown at 
A, consists of a wire wrapped in one long 
spiral around the insulated grid or frame. 
The heating coil is enclosed in a perfor- 
ated iron cover shown at B, while at C, 

"I 
^3^m* , 




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 HEATING. 



Portable electric heaters, as their name 
indicates, are so constructed that they 
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 
lOJ in. wide, and is provided with three 
switches to regulate the temperature. A 




FIG. 32. 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- 



136 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. 33. 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 con- 
nection with the oar -heaters represented 



ELECTRIC HEATERS. 



137 




FIG. 34. ATMOSPHERIC HEATER. 



138 ELECTKIC HEATING. 

ln v 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 



ttfiTVCF 's 




FIG. 36, PORTABLE ELECTRIC HEATER. 



140 



ELECTRIC 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 HEATERS. 



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 ELECTRIC 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 
current 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 pnss, 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 ELECTRIC HEATING,. 

speed of the car, and with the direction 
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 



ELECTRIC 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 L 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 ai'e con- 
siderable. A stove fails to produce that 
uniform temperature 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 ELECTRIC 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- 
reetly to the surface of the body, for such 
medical treatment as would ordinarily 
employ hot water bags, the object can be 
muc*h more conveniently obtained by a 
suitably constructed electric heater tluin 
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 Fig. 39, because constructed of 
materials which enable it to be brought 
into intimate contact with the surface to 




ELECTKIC H 

be heated. The 
formed of German silver wire arrai 
shown in the figure, placed on asbestos 
cloth and suitably insulated. The space 




PIG. 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 ELECTRIC HEATING. 

mineral wool, or asbestos fibre, around the 
heating conductor and covering the mass 
with a suitable cover of cloth. 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 current 3 
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 HEATERS. 149 

either in the centre of the theatre or at 
the sides. Each fixed heater takes a cur- 
rent of nearly 3 amperes, 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 pointed 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 Lirge 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 HEATING. 

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- 



siji 




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 1F. 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 volume of air, A large 



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 only upon the 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 were 
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, w r e 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. 

An electric oven consists essentially of 
a small chamber, the air in which is prac- 
tically isolated, the walls being nearly 
air-tight and lined with some non-con- 
ducting material, so as to retain the heat. 

Fig. 41 shows a form of electric oven 
provided with 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 
through the walls. Two electric heating 
coils are shown within at A and B, respect- 
ively, one at the top and the other at the 
bottom of the oven. By means of the 
switch, shown at the right hand of the 
drawing, either or both can be operated. 
A thermometer is inserted through a small 
hole in the top of the oven, to show the 
temperature of the contained air. 

Fig. 42 shows another form of electric 



ELECTRIC COOKING. 155 

oven with three separate compartments 
and provided with a switch for operating 




FIG. 41. ELECTRIC OVEN. 

the same. The large compartment is 
about 13 inches wide. 



156 



ELECTRIC HEATING. 




FIG. 42. ELECTBIC OVEN. 



ELECTRIC COOKING. 157 




FIG. 43. ELECTRIC COFFEE HEATER. 



158 ELECTRIC HEATING. 

.... Fig. 43 represents a form of electric 
heater, suitable for heating a large quan- 
tity of coffee 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- 



ratus, out of contact 

ing separated from the same 

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 ELECTEIC 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 41 F. (5C.) and be raised, with- 
out actually boiling, to the boiling point, 
or 100 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 



ELECTRKT 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 
(i. 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 ELECTRIC HEATING. 

and, although in an air heater, any heat, 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 ifg- = 4| 
cents at 8 cents per kilowatt-hour, or near- 
ly 9 cents at 15 cents per kilo watt- hour. 

it is evident, from the preceding figures, 
that at the present price of electric power, 
the electric water heater could not be eco- 



ELECTEIC COOKING. 163 

nomically employed on a large scale. It 
is to be remembered, however, that these 
prices are for power 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 1J 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 
purposes. 



164 



ELECTRIC HEATING. 



Fig. 46 represents a form of electric 
chafing dish in which 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. 



ELECTRIC 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, in 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.T--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. Two 
forms of plug-switches for such purposes 
are shown in Fig. 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 supply mains. The in- 
sertion plug fits into the socket and con- 
nects two terminals from the flexible cord 



L ...:__ 

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 



ELECTRIC 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, 




not to carry off the 
the odors from the 
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; i. e., diverted 
from the material 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 ELECTEIC 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 



ELECTRIC 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 5 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 currents for heating in connection 




PIG. 54. ELECTRICALLY HEATED GLUE-POT. 

with heaters in cooking apparatus, a num- 
ber of others might be mentioned. For 
example, Fig. 54 represents an electric- 



176 ELECTRIC HEATING. 

ally heated glue-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, 



ELECTKIC COOKING. 177 

a sealing-wax heater, and Fig. 57, a curl- 
ing-long 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 energy of 60 
kilo watt -hours, or on an average of one 
half a kilowatt-hour per guest. 

The above company has notified the 
public that they w^ill 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 




ELECTKIC 

a banquet at which 

insignificant part is thus humorously de- 
scribedby 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 experiment which we 
some time 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 ELECTRIC 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: 

11 He conceited himself that the birds 
killed in this manner ate uncommonly 
tender." 



CHAPTER VTIL 

ELECTRIC 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 we will now discuss. 



182 ELECTKIC 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 welded 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 weld 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 ability to recognize precisely 
when the proper temperature has been 
reached in order to ensure the most 
effective joint. 



ELECTRIC WELDING. 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 
lirst 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 ELECTRIC HEATING. 

only more convenient and rapid than the 
ordinary process, but by its means, metals 
have been effectively welded, which 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- 



L 



V 





ELECTRIC 



section equals that of tHiiwelded por- 
tions of the bar. Judged 
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 welding 
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 whether 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 50,000 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 



ELECTRIC 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 ELECTBIC 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- down transformer, 
that is, a transformer in which the sec- 
ondary terminals supply a large current 
at a lower pressure, or a transformer in 



ELECTEIC WELDING. 191 

which the primary consists of a long, thin 




FIG. 58 DIRECT WELDER FOR WELDING BABY CARRIAGE 
TIRES AT THE RATE OF 1500 TO 3000 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 welding, 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 1 . The armature is driven by a belt and 
pulley Y. The armature has two windings. 
One is connected with the commutator (7, 
at the end of the shaft, and the brushes 
B, B, carry off a continuous, or commuted 
current, to the field magnet coils M, 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 



ELECTRIC WELDING. 193 

which rest heavy brushes to carry the pow- 
erful welding current to the two clamps 
P, P, mounted above the platform F F F. 
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 ELECTEIC 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 



ELECTRIC WELDING. 



195 




FIG. 59. DIRECT-WELDING APPARATUS. 



196 ELECTKIC HEATING. 

with their welds 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 M, 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, r, 
and brushes resting on the same. The 
strip S, to be welded, rests on the supports 
T, is then cut off at the right length and 
thfc two ends forced under the clamps p,p. 

Whenever large bars or rods are to be 
welded, indirect welders are used. Any 



ELECTRIC 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 required, 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 b, from the same shaft drives 



198 



ELECTRIC 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 




FlG. 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 
number of welds that the machine makes. 
The metallic mass or shell of the trans- 



ELECTRIC WELDING. 



199 



former T, is grounded 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 6r, supplies current to the magnets M, 
M, of the alternator. For this reason the 
alternator is called a separately -excited ma- 
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 two separate 
windings in its field magnets. The rings 
r, r, 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 \VELDING. 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 
welding transformer, the secondary coil con- 
sists of a single turn of very heavy copper. 
When a rapidly alternating current, 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, sayyi^^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 possess 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 



ELECTRIC 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 conductor slit between 
the clamps C,C, as shown. Within the 
groove formed by this secondary casting 



204 ELECTBIC 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 



ELECTRIC WELDING. 



205 



S S S S, of this transformer, is a copper 
casting made in two halves bolted together, 
serving as the secondary coil, and containing 
within it 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 ELECTKIC 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 welder, Fig. 64, has been devised. 
Here the proper degree of pressure be- 
tween the contact surf aces is automatical- 
ly applied, amounting for copper to 600 
Ibs. per square inch of welding cross- sec- 
tion, 1200 Ibs. per square inch for iron, 
and 1800 Ibs. 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 
clamps C, C 19 as the weld is effected, 



ELECTKIC WELDING. 



207 



causes a contact to be made under the 
control of the screw K, actuating the 




FIG. 64. AUTOMATIC WELDER. 

magnet M, which interrupts the main 
current. 

Indirect welders are made in a variety 
of forms. Generally, however, the ap- 



208 ELECTKIC HEATING. 

paratus is protected from dirt, dust and in- 
jury by a suitable casing. A form of 
automatic welder 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 




FIG. 65. AUTOMATIC WELDER. 



required; i. e., a trifle more than one mega- 
joule, and for a weld in copper one square 



210 



ELECTKIC HEATING, 



inch in cross-section, an expenditure of 
nearly one and one -half megajoules is 
required. 

Fig. 66 shows a form of welder intended 







FlG. 66. -WELDER FOR CARRIAGE TlRES. 

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 



ELECTRIC 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. 




.J 



FIG. 67. UNIVERSAL WELDER. 

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 



r 




FIG. 68. WELTER rcn CARRIAGE AXLES. 

//. 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 WELDING. 213 

for welding 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. 69. 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. 

Fig. 71 shows in detail some welds ef- 



214 



ELECTRIC HEATING. 




FIG. 70. WELDER FOR WHEEL-SPOKES. 



ELECTRIC WELDING. 



215 



fected by the preceding apparatus. Here 
the advantage possessed by an electric 
weld for telegraphic joints becomes ap- 
parent. According to the old process as 





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 welding, 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 thin strips welded 
together. At D, is shown a welded pipe 
which has been tested to the 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 segments and ready for 
welding; at F\ the same projectile after 
welding; G and H, wire cables welded; at 
K, an insulated wire with a welded joint. 
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. 



ELECTKIC WELDING. 



217 




FIG. 72. WELDER FOB SHRAPNEL SHELLS. 



218 



ELECTRIC 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 difficult to accomplish by any 




FIG. 73. PIPE-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 C,C, and the current is 



ELECTKIC WELDING. 219 

sent through the short length of pipe be- 
tween them, w^hich is thus raised to the 
wielding temperature except in the imme- 
diate neighborhood of the clamps. 

In the system of street passenger rail- 
ways, w^here the cars are driven by elec- 
tric motors w^hich take their current from 
trolley wires and tracks, a necessity exists 
for ensuring a continuous electric contact 
betw r een 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. Xo little diffi- 
culty has arisen in practice, owing to the 
imperfect contact thus ensured betw r een 
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 ELECTKIC 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 



the electric current has, of 




track. 



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 ap- 
proximately 500 volts, this current drives 
a motor -dynamo, or rotary transformer, 
placed on the car, and by this means the 
continuous current received from the 
trolley is converted into an alternating 
current and afterward delivered into the 
primary coil of the welding transformer. 

The car employed for this purpose is 
shown in Fig. 74. The welding transform- 
er, with its large clamps, is seen sus- 



222 



ELECTKIC HEATltf . 



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. 

motor in the car, the surface of the rails 
is ground by a revolving grinder for a few 
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. 



223 




FIG. 75. TRACK WELDER AT WORK. 



224 ELECTEIC HEATING. 

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 S, is 
represented in the figure with its two low- 
er extremities S^ $ 2 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 / /, is passed 
through or linked with both. The two 
heavy iron jaws J J, JJ, pivoted at F, are 



ELECTRIC WELDING. 225 

drawn apart by the spiral springs at the 
top, but are forced together by the hy- 
draulic pump M, so as to bring pressure 
transversely upon the chucks through the 
heads of the secondary terminals S t a . 
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 Ibs. per yard, 
when prevented from expanding and con - 
tracting, owing to the entire rail being in a 
single length, requires about 150,000 Ibs. 
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 th^ 
city of Boston, four miles of Providence 
girder street car rails, weighing 61 Ibs. 
per yard, were electrically welded 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 WELDING. 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 far 
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 ELECTRIC 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 other terminal, to a rod of hard carbon, 
which is brought into contact at the weld- 
ing surfaces and then separated a short 
distance fi'om 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 



ELECTRIC 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 welding^ or calking of plates 



232 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 voltaic 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 HEATING. 

means must necessarily be provided, in 
the combustion furnaces, for carrying off 
the 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, consequent- 
ly, all the heat developed is retained, 
with the exception of such losses as occur 
through 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 very frequently 
employed. 

The electric furnace assumes a variety 
of forms, one of which is shown in Fig. 77. 




ELECTRIC 

Here a voltaic carbon 
the source of heat, the arc being 
mitted to play in the interior of a crucible 
of refractory material, surrounded by a 
non-conducting mass, usually of fire- 




Pio. 



ELECTRIC FURNACE. 



brick. Since comparatively little heat 
escapes by conduction, the temperature 
which 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, lirst, 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 



ELECTRIC 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. 
Eeference 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 
surrounds this unaltered core. 



Another commercial application of the 



ELECTRIC FURNACES. 



241 



electric furnace in which 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 

COKE 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 



ELECTRIC 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. 

ble.Z?, and the masonry A, rest on a con- 
ducting plate 6, 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 d, 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 ELECTRIC HEATING. 

about 135 KW., or 180 H.P., can, it is 
claimed, produce daily in such furnaces a 
yield of one short tori, 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 2 H 2 ), 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 FOB THE PRODUCTION OF 
ALUMIMUM 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 l , filled with granulated copper. 
The charge in such a furnace is frequently 
a mixture of 50 Ibs. granulated copper, 
with 25 Ibs. of crushed cryolite, a mineral 
rich in aluminium, and 12 Ibs. 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 







en copper. When thc^fi^iace is cleared, 
50 Ibs. of alloy are obtam^L having. r from 
15 to 35 per cent, of aluminftrm- aad 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 current 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 current. In one process in which 
this is effected, the crucible, which con- 
sists of an iron box suitably lined with 
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 HEATING. 

by this carbon rod, and, after passing 
through the materials of the furnace, 
leaves 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 3500 amperes at a pressure of ap- 
proximately 35 volts, representing an ac- 
tivity of 122.5 KW. The furnace is so 
arranged that the metal can be tapped off 
and withdrawn 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 
charge 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, which 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 ELECTKIC HEATING. 

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 flow directly from the furnace 
into the mould when so desired. The 
chamber of the furnace is filled with a 
suitable mixture of ore, flux and redu- 
cing agent, and subjected to the influence 
of the electric current; or, the furnace is 
given a charge of the metal to be melted 
and a current applied sufficient 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 1 J tons of metal at a 



ELECTKIC FUKNACES. 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 Xeuhausen, 
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 Ibs. 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 iron 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 bring- 



254 ELECTBIC 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 



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 employed on war- 
ships, considerable difficulty has arisen in 
drilling the plates so as to permit them to 
be riveted together. The harveyized steel 



256 ELECTBIC 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 be made, but 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 APPLIB&HQNS. 257 

"\ 




nating current transformer, 
welding transformer. By this meansTcftr~ 
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 ELECTHIC 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 between 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 would 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 working 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. 261 

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 work done of about 4,000,000 joules 
or 1| KYVVhrg. = 200,000 joules-per- 



262 ELECTRIC HEATING. 

cubic-inch. A larger bar 3 feet long and 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, sin6e 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 



ELECTRIC 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 plunging 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. F. 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 ELECTBIC 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 . T he 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 the current strength 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 



- 



=$=======: SB * 




FIG. 85. END VIEW OF HEATING TANK. 

gravity of 1.2 at 84 F., and to every ten 
gallons 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 



ELECTBIC HEATING-. 



cers P, are connected with the positive pole 
of the source and hold the metal article 
M, so that this is partially submerged. 
The negative pole N, is connected with 




FIG. 86. PLAN OF HEATING TANK. 

the sheet lead lining of the tank. Fig. 86 
represents the same apparatus in plan 
view. 

THE END. 



INDEX. 



A. 

Abnormal Temperature Elevation of Circuits, How 

Avoided, 87, 89. 
Acetyline Gas, Illuminating Power of, 244. 

, Production of, from Calcium Carbide, 243, 244. 
Activity, Definition of, 26. 

, Muscular, Obtained from the Sun, 15. 

of Circuit, 41. 

of Electric Circuit, 35. 
- of Laborer, 27. 

, Unit of, 26. 
Aerial Dare Wires, Effect of Character of Surface on 

Temperature Elevation of, 6G. 
, Effect of Extent and Surface on Temperature 

Elevation of, 6fi. 
Affinity, Chemical, 9. 
Air Heater, Portable Elect- ic, 133, 134. 

, Resistance Offered by to Escape of Heat from 

Conductors, 59, 60. 



272 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-Secofid, 35. 
Annealing, Electric, of Harveyized Armor Plates, 

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 Heating of, 37-68. 



INDEX. 273 

Block, Ceiling, 105. 

, Porcelain, 87-98. 

, Safety Fuse, 86. 

, Cut-Out, 106, 107. 

Bond for Street Railways, 219. 
Box, Cut-Out, 107. 
Branch Fuse, 113, 114. 
British Heat Unit, 29. 

- Thermal Unit, 29. 

- Thermal Unit, Value of, 29. 

Buried Conductor, Permissible Temperature Eleva- 
tion of, 85. 

c. 

C. E. M. F., 42. 

, Development of, by Motor, 45. 

in Circuit, Distribution of, 42, 43. 
Cable Welder, 213. 
Calcium Carbide, Furnace for Manufacture of, 242, 

243. 

Calking, Electric, 231, 232. 
Calorie, Lesser, 29. 

Capacity, Carrying, of Conductor, 75. 
Car for Direct Welding, 222. 

- Heater, Electric, 125, 12G. 

- Heaier Regulating Switch, 127, 129, 21S. 
Heating, Cost of, 142-145. 



274 ELECTKIC HEATING. 

Carbon, Effect of Temperature on Resistivity of, 56,57. 
Carborundum, 237. 

Furnace, 238-241. 

Carriage Axle Welder, 212. 

-Tire Welder, 21 >, 211. 
Carrying Capacity of Fuse Wires, 92. 
Castings, Sharpness of, When Produced 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 Activity 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 Pound of, 10, 11. 
, Origin of Energy in, 12. 
Coal-Beds, {Store-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. 
, Temperature Elevation of, 62. 






INDEX. 



Conductors, Pure Metallic EffeclN&Xepiperature on 

Kes' stivity of, 56, 57. 
, Transmission, Nece sity for Maintain 
Temperature of, 69. 

Conduits for Insulated Wires, 77. 

Connections for Indirect Welding, 198. 

CoLvection, Approximate Amount of Heat Lost by 
Conductor per Foot of Length per Sec- 
ond, 67. 

, Loss of H eat by, 63. 

, Lnss of Heat, Practical Independence of Ex- 
tent and Character of Surface on Temper- 
ature Elevation of, 66, 67. 

Convectional Losses in Conductors, Effect of Motion 
of Air on, 68. 

Cooking, Electric, 151-180. 

Copper- Tipped Fuse Wiret>, 95. 

Cost of Car Keating, 142-145. 

Coulomb, or Unit of Electric Quantity, 32. 

Coulomb- Volts 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. 




276 ELECTKIC HEATING. 

Current Strength, Effect of, on Temperature Eleva- 
tion of Wire 80. 

Strength, Effective. 

Strength, Thermal, 62. 
Cut-Out Box, 107. 

Cylindrical Electric Heater, 120-122. 

D. 

Diameters of Fuse Wires, 92. 

Diamonds, Electric Furnace for the Production of 

Artificial, 253. 254. 
Difference of Electrical Pressure, Electrical Flow 

Produced by, 32. 

of Thermal Pressure, 72. 

of Water Level, Liquid Flow Produced by, 31. 
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. 277 

Earth-Buried Conductors, Lo&sof Heat by, 81. 

Economy of Electric Smelting, 252. 

Effective Thermal Resistance of Earth- Buried Con- 

ductois, 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* 1 

Heating, 124. 

- Heater, Advantages of, J19. 

- Radiator, 123. 

- Resistance, 38. 

- Source, Definition of, 24. 

Electricity and Heat, Relations between, 19, 20. 

Circumstances Regulating 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 Pound of Coal, 10, 11. 



278 ELECTRIC HEATING. 

Energy, of Coal, Origin of, 12. 

Storage of, in Water Reservoir, 30. 



F. 



Falling Water, Storage of Solar Energy in, 16. 

Fan, Electric, 1 54-150. 

Feeders, Ground, for Electric Railways, 220. 

Flexible Electric Hea er, 146, 147. 

Flow of Electricity, Circumstances Regulating, 37. 

of Water, Circumstances Regulating, 37. 
Foot-Pound-per-Second, Definiti m of, 26. 
Foor-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 ElectiicallyC oked Banquet, 178-180.' 
Full-Load 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, 238-241. 



INDEX. 279 



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 ( 'apacity of, 92. 

- \Vires, Composition of, 91. 
Wires, Diameters of, 9'2. 



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, Kelations between, 19, 20. 



280 ELECTRIC HEATING. 

Heat and Mechanical Work, Relations between, 
17, 18. 

Conduction, 63. 

, Dissipation of, 9. 

, Loss of, by Conduction, 63. 

, Loss of, by Convection, 63. 

, Loss of, by Eadiation, 64. 

, Nature of, 8. 

, or Molecular Oscillations, 9. 
- Unit, British, /J. 

, Unit of, 28, 29. 
Heater, Cylindrical, Electric, 120-J22. 

, 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, 119. 

, E ectric, Kequisites for, 119. 
Heating, Electric- Coil Conductor for, 122. 

, Electric, Tank for, 26'), 270. 

, Electric, Miscellaneous Applications of, 
255-270. 

, Electrical, of Bare Conductors, 37-68. 

, Electrical, of Covered Conductors, 69-86. 



INDEX. 281 

Heating of Conductor, Effect of Insulating Covering 
on, 69, 70. 

, Electrolytic, 267-269. 

Hemp Covered Wires, Permissible Temperature Ele- 
vation of, 85. 

Horse-Power and Kilowatt, Relative 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. 



282 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, 1G2. 
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 Calori", 23. 
Level, Electric, Difference of, 32. 
Links, Fuse, 94. 
Loss of He it by Conduction, 63. 

of Heat by Convection, 63. 

of Heat by Badi ition, 63, 64. 

M. 

Mechanical Work and Quantity of Heat, Relations 
between, 17, 18. 



INDEX. 283 

Megajoule, Definition of, 206. 

Metallic Ores, Electric Production of, 250, 251. 

Metals, Electric Fogging of, 258-260. 

, Electrical Working of, 259-270. 
Mica-Covered Fuse Boxes, 100, 101. 
Microhm, 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, Rule for Size of Wire in, 77, 78. 

N. 

Nature of Heat, 8. 

Negative Eesistivity, Temperature Coefficient of, 56. 

0. 

Oce in Cables, Temperature Elevation of, 86, 
Ohm's Law, 33. 

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. 



284 ELECTRIC HEATING:. 

Porcelain-Covered Fuse- Boxes, 102, 103. 

- Fuse-Block, 97, 98. 
Portable Electric Heater, 133, 134. 

- Electric Heater, 140, 141. 

Positive Resistivity, Temperature Coefficient of, 56. 
Press n re, Back 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 Resistivity, 54. 

Q. 

Quantity, Electrical, Unit of, 32. 

E. 

Radiation, Loss of Heat by, 63, 64. 
Radiator, Electric, 122, 123. 
Rails, Elec'rically Welded, 22G. 
Rate of Doing Work, or Activity, 26. 
Reduction, Electric, of Metallic Ores, 250, 251. 
Regulating Switch for Car Heater, 127-129. 
Reservoir of Water, Activity in, 34, 35. 



285 



Resistance, Electric, 38. 

, Hydraulic, 38. 

- , Thermal, of Insulating Covering, 71. 
Resistivity, Definition of, 48. 

, Effect of, on Pure Metallic Conductors, 56. 57. 

- , Effect of Temperature on, 5G, 57. 

, Influence of Annealing or., 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 . 
Rotary Transformer, 221. 

Rubber Covered Wires, Permissible Temperature 

Elevation in, 85. 
Rule for Size of Wire in Wooden Mouldings, 77, 78. 

s. 

Sad Iron, Electric, 176. 
Safety Fuse-Block, 96. 

- Fuses, 90. 

Stiips, 93. 

-- Transformer Fuse- Box, 109, 110. 
Screw Block, 107. 

Sealing- Wax Heater, Electric, 177. 
Secondary Coils of Transformer, 201. 
Separately -Excited Alternator, 200. 



286 ELECTRIC HEATING. 

Sharpness of Castings When Producdby Electrical- 
ly-Fused Metals, 251. 
Shrapnel Shells, Welder for, 217, 218. 
Size of Wire in Wooden Moulding, Rule for, 77, 78. 
Skillet, Electric, 160. 
Smelting, Electric, Economy of, 256. 
Socket Attachment, 107. 
Solar Energy, St >rage of, in Coal Beds, 13, 14. 

Energy, Stjrage of, in Falling Water, 16. 

Energy, f- torage of, in Wind, 16. 

Soldering, Electric, 230, 257-259. 
Source, E ecttic, Definition of, 32. 
Specimens of Electric Welding, 215. 
Steam Cooker, Electric, 167. 
Stearn 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. 



287 



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 Cuireut Strength 

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. 



ELECTRIC HEATING. 

Temperature, Elevation, Permissible, in Buried Con- 
ductors, 8i, 85. 

Tensile Strength of Electrically Welded Joints, 187. 
Therm, Defination of 29. 
Thermal Current Strength, 62. 

- Resistance, Effective, of Earth Buried Con- 

ductors, 81. 

- Resistance of Insulating Covering, 71. 
Unit, British, '29. 

Tin- Lead Alloys for Fuse Wires. 91. 
Transformer, Primary Coils of, 201. 

, Rotary, 22 1. 

, 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, 14, 
15. 



INDEX. 289 

Volt, or Unit of Electric Pressure, 32, 33. 

Ampere or Watt, 36. 

Coulornb-per-Second, 36. 

w. 

Wall Heater, Electric, 138. 

\Vater, Circumstances Regulating Flow of, 37. 

, Conditions Requisite for Causing Flow of, 31. 

Gram me- Degree-Centigrade, 29. 

- Heater, Electric, Low Economy of, 162, 163. 

in Reservoir, Capacity of, for doing Work, 30. 

Reservoir, Storage of Energy in, 30. 

, Resistance Offered by, to Escape of Heat 

from Conductors, 58, 59. 
Watt, Definition of, 26, 27, 

, or Volt-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. 



290 ELECTEIC HEATING. 

Welding, Advantages Possessed by Alternating Cur- 
rents in, 189. 
- Apparatus, Direct, 194-196. 

, Conditions Requisite foi Obtaining Efficient 

Joints by, 183, 184. 

, Definition of, 182, 183. 

, Electric, 181-232. 

, Electric, Advantages Possessed by, 185, 186 

t Electric, Use of C mtinuous or Alternating 

Cunentsin, 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 

f 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, 259-270, 

z. 

Zoroaster, 7. 



Elementary 
Electro -Technical Series. 

BY 

EDWIN J, HOUSTON, Ph.D, and A, E. KENNELLY, D.Sc. 



Alternating Electric Currents, Electric Incandescent Light- 
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