The Library of Work and Play: Electricity and Its Everyday Uses

s of electric heating and should consult me freely about the matter. My telephone was kept busy, my laboratory w

heat produced by electricity reported it to the club. These were spread by the secretary in

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Fig. 70) and tucked away within the body of the iron. German silver offers about twice the resistance of iron when it is cold, but, at the temperature of the sad iron when in use, there is not mu

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ron, and according to the ammeter it passed 4 amper

/(28 ohms)

, or 1 cent for a hundred watts for an hour, or, on a 100-volt current, 1 cent for an ampere for a

elier one must know the voltage used in the building. If the voltage in use in the building is not the same as that stamped upon the iron, it is not safe to connect it. Not knowing this

enough current to melt it. The wire was seen to be at a very dull-red heat when examined in a dark room. Its temperature was about nine hundred degrees. At this temperature its resistance is about three times what it is when cold. We estimated by measurements that the iron contained about twenty-five feet of the wire. The boys then took twenty-five feet of No. 24 German silver wire and stretched it between two nails driven up in

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th of an inch thick, taking care to keep the successive turns half an inch apart. Asbestos paper was wra

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pported bottom side up makes a perfectly good hot plate. The particular hot plate which we examined had a three-point switch which gave three differ

/(112 ohms)

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keep food warm which has been already co

ond point the current goes through 56

/(56 ohms)

adapted to certain cooking processe

ird point the current goes through 28

/(28 ohms)

g in and boiled it 3 minutes. Using 4 amperes for 10 minutes cost two thirds of a cent. If it takes 7 minutes to boil a pint of water it would require 1 hour to boil a gallon upon this hot plate usi

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s consists of a hot plate with a cov

lator to sit upon it. The coffee percolator might sit upon any other hot plate or t

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require from 300 to 600 watts according to size. If used on the 110-volt current they take about 3 to 6 amperes, and if adapted to the 220-volt current they

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that we examined had a switch for three heats: low, requiring 360 watts-costs 3.6 cents per hour; me

p. It is large enough to hold four loaves of bread. It required 1520 watts for 40 minutes to heat it to the baking temperature a

so that it keeps a constant temperature of 103 degrees. Under these conditions chickens hatch from hens' eggs in three w

them if they come in direct contact. We proved this by opening the iron and touching paper to the wire while it was carrying the curr

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ntained a lot of fine wire covered by perforated mica. The wire became red hot when the push button in the handle was pressed. It took half an a

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o wires insulated from each other. One of these wires is attached to the outer shell of the plug, the other wire is attached to the central button of the plug. These make connections with the two separate dynamo wires in the socket. The current comes down one of the wires i

/(220 ohms)

s for soldering. They remain continually at the proper temperature and are free from corrosion. T

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t maintains a temperature of 180 degrees, and is an excellent substitute for a hot water bag. It contain

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cut off the current whenever too much passes for the copper conductor to carry without getting hot. The fuse wire melts at about six hundred degrees, while the copper will not melt until it reaches nearly two thousand degrees. This temperature is sufficient to set fire to wood, paper, and cloth. When any fuse melts, the current is cut off from all chandeliers, etc., in the particular circuit controlled by the fuse. This produces consternation among people who do not

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, may not be able to light the gas. The fact is that it is wholly a matter of temperature and kind of gas. Iron heated to dull red will not light the illuminating gas now being furnished in New York City, while iron at a bright red heat will do so. Iron may be hot enough to light illuminating gas but too cool to light gasolene vapour, which requires a dazzling white heat. Iron which is just under the temperature at which it giv

sionally be put in the handle

he resistance of wires

e more resistance it offe

eter of the wire the mo

for example, iron about six times as much as copper a

to five hundred degrees. It is the reverse with carbon, which offers more resistance when cold than when h

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s wire, when added to that of lamps, permits not more than one fifth of an ampere to pass, and this warms the wire slightly. The bar a b is composed of two strips of metal, brass above and iron below. Heat expands brass more than iron. The result is that when the current is turned on, the bar begins to curve downward until presently it t

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andle-power lamp; or two 16-candle-power lamps; or four 8-can

age or a circuit of more lamps. Suppose we have a 32-candle-power carbon filament lamp

/(110 ohms)

er wire of the electric flasher offers 330 ohms of resistance, and to

330 + 220 ohm

n might burn off before a made contact with b; if not the lamp would certainly burn out after the contact. If we undertook to operate with this flasher several 32-candle-power lamps instead of one u

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at circuit. Fig. 86 was drawn to explain the matter. The lamps l, l, l, etc., are connected in parallel. Each lamp makes a

ance. The result would be the same, if we should substitute for the ten pipes one pipe ten times as large in cross section. So it is with wires which are conducting electricity. Introduce two in p

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03 degrees. A screw in the metal strip c underneath the end of a may be set so that it will normally touch a. Suppose now the brass strip is underneath the strip of iron in a. As the hot plate warms up the egg chamber, the brass will expand more than the iron, and the bar will curve upward and break the connection with c. As soon as the current

maximum and minimum temperatures are regulated by law. The resistance wire may be seen in coils underneath the car seats. Electric street cars usually

= 1500 w = 1

1.5 cents per kilowatt hour to generate their supply

18 hours = 27

at 1.5 cents = 40

m apartment with at least 120 cubic feet of fresh air admitted per minute, will use on an average ten amperes of the 110-volt current. The cost will be about two dollars and fifty cents per day or sevent

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a plug which he could insert in place of a lamp in the chandelier. He placed this heater on the floor underneath the window and usually had 16-candle-power lamps in the sockets. He claimed that it was a jolly foot warmer and kept the room comfortable without other heat. He turned on from one to four lamps according to his need and replaced the 1

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n were cut so as to admit the glass globes of the lamps, but the sockets and keys were outside, so that it was convenient to turn on and off the lamps separately, thus using one half to two amperes of current, as desired. This rested upon another basin, b. Basin b was covere

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There are five indictments aga

t the house

easant flavours in the food into

regard to time and temperature a

too closely and are not

re wastef

l balance regarding the fifth item. But the remaining four items furnish a very hopeful field for research. I use the last word advisedly, and think it is just as applicable to high schoo

the bottom, so as to give access to the key sockets of the lamps, (Fig. 91). First upon the electric stove was placed a covered dish containing a roast of lamb. Above this was anoth

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of the dinner table when the guests gathered ar

oker heat the h

any heat about it until they laid their hands upon

? The process has been carried on fro

t no smell cou

g until now and served the meat and vegetable, leaving the p

arbitrarily decided to begin with temperature of 400 degrees, continue it for 20 minutes, then turn off all the electric current, and let the temperature fall gradually. This had been done at our convenience in the morning before school. At a quarter before t

escent lamps than from hot plates used in the same apparatus, and the electric

the heading, Applications of Electric Heating, since the electric lamps in general use

s length so as to make the proper relation between resistance and voltage, in order that enough current might pass to make it white h

n the room and you find that it is giving light enough to read by. But you notice that the light is growing dimmer, its colour is growing redder, and the ammeter indicates that less current is passing. I will cut off the current and let you examine the wire and you notice that a crust has formed upon it. This is d

educing the length would reduce the resistance, but reducing the resistance would allow more current to pass. If more current should pass it would make the wire hotter, and raising the temperature would increase the resistance, which would cut down the c

ch was ever more timely than this. Whereas there was practically no electric lighting before 1880, soon after that there began a phenomenal demand for carbon filament lamps. In 1890, 800,000 of these lamps were manufactured in

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It was the same size as No. 33 wire, which we also found by the wire gauge was the size of No. 90 sewing cotton. The diameter of No. 33 wire was given upon the wire gauge as .007 inch. When lighted, the filament of this lamp had looked to be about the size of No. 18 wire, which has a diameter of .04. That is, the filament when lighted looked six times as thick as it really was. Those who use sewing cotton learn quickly to know the siz

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SISTANCE OF

meter Re

10560 fee

" 2640

" 660

" 165

" 40

" 10

" 2.5

3 " 1

et equal

offer 75 ohms of resistance and therefore contain 30 feet of wire (30

ide the figures of the third column by six, and the table will answer for iron wire, o

Feet to

Copper Iron

ch 10560

" 2640

" 660

" 165

" 40 6

" 10

" 2.5

" 1 2

are not exac

lamp. When the 110-volt current was sent through the group of eight connected in series they seemed to give about the same light as the single 16-candle-power lamp. It is as though the filament of the 16-candle-power lamp had been cut into eight pieces, an

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rger (No. 30, diameter = .01 inch), so as to allow more current to pass. An 8-candle-power 110-volt lamp was substituted; one quarter of an ampere passed. A 4-candle-power 110-volt lamp was used; one eighth of an ampere passed. A 100-candle-power 110-volt lamp was substituted; three amperes of current passed through it. In all these cases the lamps which passed the larger current

alf a cent an hour. When the lamp was turned in its socket the current was switched off of the filament A, and on to the filament a. This took .03 of

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off the light entirely, seems to be a more satisfactory arrangement. One of the boys connected a wattmeter in the circuit with a hylo lamp and found that

much smaller than that in the 110-volt, 16-candle-power lamp. The pressure was twice as great as before, but the resistance was four times as great, and hence only half as

be noticed that the products of the two factors in each case are the same. The product of an ampere multiplied by a volt is a watt. In each of the above three cases the amount of electrical energy is 55 watts

half watts of electricity. Electricity for lighting purposes usually costs 10 cents per kilowatt hour, that is, 10 cents for 1000 watts for one hour, or one cent for 1

t. The ammeter showed 55 ampere. Hence the lamp is a 60-watt lamp, and requires one and a quarter watts per candle-

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showed that the current, which was one ampere at the beginning, grew steadily less as the filament grew smaller, until finally when it was about one quarter of an ampere, the circuit was broken by the filament burning in two. We removed the lamp from the socket and with a dropper tube introduced a little lime water, and shook it

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lamp is placed in the socket, the collar of the lamp is screwed into the collar of the socket, and the base of the lamp comes in contact with a brass spring in the bottom of the socket (Fig. 98). The spring is connected with one copper wire bringing electricity from the dynamo. The collar is connected with the other wire from the dynamo. This connection is made and broken by turning the key of the socket. The wires are made of copper since copper is a particularly good conductor of electricity. No electricity can flow unless this circuit is complete. Socket keys and wall switches make or close gaps in this circuit. No copper wires for carrying electric-lighting current are smaller than No. 12, which has a diameter of .08

110-volt pre

ugh a 32-candle-power lamp

gh a 16-candle-power lamp,

gh an 8-candle-power lamp, co

220-volt pre

ough a 32-candle-power lam

ugh a 16-candle-power lamp,

gh an 8-candle-power lamp, cos

this process, it offers greater resistance to the current, and as the amount of current grows less the proportion of light to current grows rapidly less, so that at last instead of paying for 3.5 watts of electricity per candle-power of light one must pay for perhaps seven or eight watts per candle-power. We pay fifteen cents apiece for 16-candle-power lamps, and it is economy to renew them about twice a year, if they are burned, say three hours a day, or a little

l as .002 of an inch, or No. 44. In order to furnish sufficient resistance to prevent the 110-volt current from melting, they often have a length exceeding two feet. This is laced back and forth within the small bulb. At the temperature of bright incandescence their resistance may be increased as much as fivefold and sometimes becomes ab

perature rises while non-conductors resist less as the temperature rises. Hence the ins

s the filament approaches its melting point, 6000 degrees, it becomes so good a conductor that it carries current enough to melt a fifteen ampere fuse. It is, therefore,

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One lower carbon was fastened into a clamp, and the other was touched to it, and then drawn away about three-eighths of an inch. A very brilliant light was produced. Probably

over 6000 degrees, which boils the carbon and fills the gap between the two pencils with a stream of carbon vapour. This conducts the current like the filament in an incandescent lamp. The air gap

(4.5 ohms)

.5 + 4.5 ohms)

part of this resistance-not mor

med, or, as we say, after the arc has been established. This mechanism is nothing else than electro-magnets which are operated by the lighting circuit itself. It may require thoughtful examination to recognize these as electro-magnets, i

nfluence of this field causes the iron rod to become a magnet with its south pole uppermost, and if the current is strong enough, and the field which it produces is strong enough,

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re of the magnetic field, and its lower portion is the armature. Yet this is ri

r cent. heat. The arc lamp gives 12 per cent. light and 88 per cent. heat. The carbon filament gives 4 per cent. light and 96 per cent. heat. When we have m

readily that it is used instead of kindlings for lighting a fire, carbon in the form of graphite in our so-called "lead" pencils and carbon as it is prepared for electric light pencils burns only very slowly

fit the large end of an argand lamp chimney and through a hole in this was passed one of the carbon rods (Fig. 101). A metal clamp made connections between this carbon and the negative wire from the dynamo. The other carbon, attached by a clamp to the positive wire, was thrust down into the upper end of the chimney until it touched the negative carbon, and then drawn upward a

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night if used in open arc lamps l

ark on paper. In all arc lamps carbon is distilled from the positive pencil, condensing upon the negative pencil as graphite, which is the material used in ma

wo, a fact that could not be detected while it was lighted because of the dazzling brightness of the arc. The neg

atus in which the light must be placed at the focus of a lens. That is, it is necessary to know from what point the ligh

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on. This is shown in Fig. 103 where for simplicity the lens is represented as a single piece. L represents a point of light which will naturally send its rays out in all directions as the radii of a sphere; m, m, m represents a bright reflecting surface which is given that peculiar curve called a parabola. It ha

nd send them forth parallel, and in addition it has a series of lenses which produce upon

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e also knew that it would only be used to flash a light, since if dry cells are required to furnish half an ampere continuously they soon run down. Behind the lamp there was a bright metal reflector-the lens and reflector are fairly well represented in Fig. 103. The filament of the lamp is connected with two small battery cells in the handle. These may be removed and replaced

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be. At one end, and in contact with one of these wires, is a small pool of mercury. By pulling the cord c the tube is tilted on the pivot p, so that a stream of mercury flows along the whole length of the tube and closes the electric circuit. When the tube falls back into its normal pos

ter Cooper-Hewitt, grandson of the fo

0-volt circuit. It is the longest step yet taken toward getting light without heat, but perhaps shows what we must expec

very much as one would put up a stove pipe or a job of plumbing. The joints are fused and made air-tight by playing a flame upon them after the pipe is up in place. This pipe is led around into all noo

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the terminals and the vapour becomes incandescent, filling the whole tube full of light. The first thing that the boys remarked was that altho

osed of one or several short rods of clay-like material. This is first heated by sending the electric current through resistance wire placed directly underneath it and connected in shunt with it. When it gets hot,

t fires from poor insulation are very rare. Less than one f

ductors touch one another at a mere point the electric current, in passing from one of these conductors to the other across such a narrow bridge, meets resistance and develops heat-sometimes heat enough to fuse the point, and either break the contact, or, what is more likely, start a minute arc at that point. In some cases this makes the apparatus dangerously hot, and in other cases it bridges the gap with a broader and better contact-a true ele