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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
lc 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 2123 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 TV = 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 1A 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 0° 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
0D 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 a1, at B in Fig 3, have a length of 5
cms., then the resistance between the
terminal faces a1 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-53-— = 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 TV>3oV =: 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 0° 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 0°C, its resis-
tivity at 20° C. will be increased by 20
x 0.4=8 per cent., so that its resistivity at
this temperature will be 1.594 x £££=
1.721 microhms, approximately. At the
boiling point of water, or 100° C., its re-
sistivity will have become increased by
approximately 100 x 0.4 — 40 per cent.,
and its resistivity will be ±'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 0° C., the resistivity of the wire might
be 1.6 microhms, and a circular -mil -foot
of this wire would have a resistance of
9.625 ohms. If the diameter of the wire
were 0.01"; 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 -VoTi6!--
=0.9577 ohms at 0° C. If a current of two
amperes be sent steadily through this
length of wire, the drop in the wire would

HEATING OF 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 10°C. above
the surrounding air, or to 30° C. Then
the resistivity of the wire before the
current passed through it, would be
1.6 x |£|= 1.728 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 S19 $2 , or safety links, as they are
sometimes called, inserted in the circuit
of the two leads BB1 and AA1 , under
thumb screw clamps situated, at the ends
of the metallic blocks whiph form the
terminals of the leads B^ and A A1 .
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, A1.

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

and B, Bl . 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

$ir£uit. 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 wThich 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 TV°F., and,
therefore, an activity of one joule-per-
second, or one watt, can raise the tem-
perature of one cubic foot of air TV ° 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-

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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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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,

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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.

lnvFigs. 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

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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 25L 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 1°F. per
second. If this heater were placed at
work in a closed chamber, the temperature
acquired by the contained air would de-
pend upon the 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, wre 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. (5°C.) 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
P1. 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, C19 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
betwreen 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 betwreen
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 St £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
(C2H2), 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, Bl , 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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THIRD EDITION. GREA TL Y ENLAR GED.
A DICTIONARY OF

Electrical Words, Terms,
and Phrases.

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

AUTHOR OF

"Advanced Primers of Electricity"; '•'Electricity One
Hundred Years Ago and To-day,*' etc., etc.

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Electricity and Magnetism.

A Series of Advanced Primers.

By EDWIN J. HOUSTON, PH.D. (Princeton).

AUTHOR OF

"A Dictionary of Electrical Words, Terms and Phrases,"
etc.) etc., etc.

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During the Philadelphia Electrical Exhibition of 1884, Prof
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The Measurement of Electrical Cur-
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Primers of Electricity.

By EDWIN J. HOUSTON, PH.D. (Princeton).

AUTHOR OF

" A Dictionary of Electrical Words, Terms t and
Phrases" etc,, etc., etc.

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Electrical Transmission
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AND OTHER ADVANCED PRIMERS OF ELECTRICITY,
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AUTHOR OF

" A Dictionary of Electrical Words, Terms, and
Phrases" etc., etc., etc.

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and electrolysis, as well as the telephone, storage battery, etc., are
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ELECTRICITY

ONE HUNDRED YEARS AGO AND TO-DAY.

By EDWIN J. HOUSTON, PH.D. (Princeton),

AUTHOR OF

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cause and effect of various discoveries, and its personal references
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