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stirring, the iceless device will be of lit- temperature at which it will conduct. tle practical value.

One form of heater is made of fine platinum wire wound upon a porcelain tube

as a support and covered with porcelain To Pierce Hard Metal

paste. The heater tubes are mounted Please explain how to drill a hole in very just above the glowers in the finished hard metal.-A. V.

lamp. The heating device is connected Good tools are requisite for drilling

across the circuit when the lamp is first in hard metals. A well-hardened drill

turned on, and must be cut out of circuit only should be employed. Have an

automatically when the glower becomes abundant supply of oil, and drive the

a conductor. This automatic cut-out is drill slowly but with as much force as

operated by means of an electro-magnet the point will bear. To harden the drill,

so arranged that current flows through heat to a dull glow in a charcoal flame,

its coil as soon as the glower conducts, and cool in mercury. The work will be

and opens a form of silver contact, cutfurther facilitated if the surface of the ting out the heater. The conductivity metal to be pierced is first nicked with

of the glower increases with its temperaa cold chisel. Chilled cast iron may be

ture; hence, if used on a constant-potensoftened by putting sulphur on the place tinue to increase, because of the greater

tial circuit, its temperature would conto be penetrated, and then heating the iron to a glow.

current flowing, until the glower was destroyed. To prevent this increase of current, a ballast resistance of fine iron

wire is connected in series with the Cracks in Concrete Wall

glower. The resistance of the iron wire Why is it that a concrete wall in which

increases rapidly with increase of temiron posts are set is sometimes cracked around the posts ?-H. T.

The concrete may not have been properly prepared, or it may have dried too quickly; perhaps, too, expansion joints were omitted. The wall, when newly laid, should be cut every 45 or 50 inches. These cracks should at once be filled with dry sand of a fine grain. The joints or cracks allow for the contraction or expansion of the concrete, which accompanies every change of temperature.

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The Nernst Lamp They have recently installed Nernst lamps in some of the stores in our town. Will you please explain this form of light and how it operates?-F. J. S.

The Nernst lamp is a form of incandescent lamp, using for the incandescent ma- TYPICAL DIAGRAM OF Nernst LAMP Circuit. terial certain oxides of the rare earths. The oxide is mixed in the form of a

perature, and thus prevents the increase paste, then pressed through a small ori- of current through the glowers. fice into a string, which is subjected to a The accompanying figure shows comroasting process, forming the filament or plete connections for a 6-glower lamp. glower material of the lamp. The glow- The current enters, say, at terminal 1, ers are cut the desired length and plati- passes through the contacts of the cutnum terminals attached. As the glower out 4, to the heater circuit 5, then to conis a non-conductor when cold, some form tacts 4' and to the terminal 2. When the of heater is necessary to bring it up to a glowers become hot enough to conduct, ·

the current divides at 1', part of it pass

The wires should then be placed in a ing through the glowers 6, the ballast 7, vise, with the ends projecting so that they and the cut-out 3, to terminal 2. When may be twisted together with a pair of the current in the glowers has reached forceps. The twist is next soldered toits normal value, the contacts at 4 and gether. To prevent rusting, resin 4' open, cutting out the heater coils en- rather than the customary acid or soldtirely.

ering fuid is the best available material. The free end of the wires should

now be drawn apart, so as to leave a Making a Thermopile

space of some four inches between the

extremities, as shown in the figure (a,b). How is a thermopile constructed and used ? -F. H. N.

These extremities are next connected to The thermopile is an instrument used the terminals of a delicate galvanometer. in the production of such small, steady If the galvanometer's pointer is then currents as are required for grading del- brought to 0°, on applying fire to the icate ammeters and voltmeters. In con- junction c, a current strong enough to junction with the galvanometer, it is also deflect the pointer through 10° or 15° useful for registering minute variations

will be set up. of temperature in furnaces, where no

A dozen combinations of this kind will ordinary thermometer could stand the increase the power of the arrangement. melting power of the intense heat. In In such case, vires of a length of four construction, the thermopile consists of inches should be used. A twist of threeone or more paired pieces of dissimilar fourths inch will suffice. metals. These metals are in the form of wires or blocks and are joined together at one end. Antimony and bis- Tightening Steam Joints-Lime in Pipes

How can steam joints be made tight? o

How can lime be removed from injectors and delivery pipes ?-A. G. R.

1: First, take white lead ground in oil; incorporate as

much black oxide (manganese) as possible; and add a small portion of litharge. Knead it with the hand, dusting the board with red lead. Make the mass into a small roll, and put the roll on the plate after having first oiled with linseed oil. It can then be smoothed and pressed into position.

2: Mix 1 part muriatic acid to 10 parts of soft water, and let the tube remain in the mixture over night.

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THERMOPILE.

Use of Loam Mould Under what conditions should a loam mould be used ?-P. 0. D.

Where the casting is large, and it would be too expensive to provide a pattern, loam moulds are employed. The casting, however, must be of a quite simple form, otherwise a pattern will be essential. Good results may be obtained by using a partial pattern with the loam mould. The basis of the mould is brick, over which the loam is spread.

muth have been more frequently employed than other metals. In some respects, however, copper and nickel are more satisfactory. These metals should first be cleaned with fine emery paper.

Stretching Barbed Wire

to drive through this steam. It often Could you suggest how to make a stretcher is unable to do this; and, as a result, for barbed wire ?-F. W. G.

work is brought to an abrupt standstill. Saw from hickory, oak, or other hardwood a piece three-quarters of an inch

Operation of Electric Bell
Please explain with diagrams the operation

of an electric bell.-S. E. G.
SIMPLE WIRE-STRETCHER.

The operation of an electric bell de

pends upon the principle that if a current thick by two and a-half or three inches

of electricity flows through a coil of wire wide, and of convenient length. Be sure wound upon an iron core, the core bethere is no knot in the wood that can

comes magnetized and will attract any weaken it. At one end, fasten an iron magnetic substance to itself. A diagramplate containing a notch the width of a matic representation of an electric bell barb. Now catch in the notch a barb is shown in Fig. 1, in which M is the close to a post, and brace the plated end of the stick against the post. An excellent leverage can thus be secured and the wire will be tightened.

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For a Pinched Tube How can I prevent the pinching of inner tubes in tires ?-C. R. K.

The tube should first be carefully wiped with a clean cloth that has been well charged with talc powder. Then slightly inflate the tube, to remove folds and wrinkles. In introducing it into the shoe, feel inside around the rim, and underneath the tube, to be sure all is smooth and right. If a fold is discovered that refuses to yield to rubbing, remove the tube and repeat the process.

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Pumping Hot Water Why is it that hot water canrot be successfully drawn through a pump?-W. H. A.

Under proper conditions, there is no reason why hot water cannot be pumped. But when the pump is not placed below the level of the supply, so that the water enters with little or no pressure, difficulty is likely to be experienced. When the piston rises, the pressure is reduced and the vacated space is flooded with steam. The electro-magnet composed of a soft iron reason for this is that a liquid will boil core of horseshoe shape wound with copat a lower temperature than in the sur- per wire. The armature of the bell is rounding atmosphere if the pressure is mounted on a spring K, and carries a reduced. This well-known fact is taken hammer H for striking the gong. On advantage of in the boiling of syrups, the back of the armature is a spring etc. On its return, the piston is obliged which makes contact at point D with a

FIG. 1,

backstop T. The action of the bell is as cuit with which it is connected in series. follows: When the circuit is closed Normally the springs are separated as through the bell, a current flows from shown, and the circuit is open. The bell terminal 1 around the cores of the elec- and the push-button are connected up in tro-magnet, through the spring K and series with the batteries as illustrated in contact-point D, then through backstop Fig. 3, in which P is the push, B the bell, T and terminal 2. The current magnę- and C the battery.

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Fig. 2.

Use of Soldering Paste
What is soldering paste, and how is it used?
-W. S. C.

Soldering paste consists of a mixture of grease and chloride of zinc. Vaseline or petrolatum is the grease commonly used, the latter being probably just as effective and costing less. The composition is mixed as follows: One pound of petrolatum, one fuid ounce saturated solution chloride of zinc. The chloride of zinc solution is made by dissolving as much zinc in strong hydrochloric acid as

it will take up. A thick, oily solution is R

the result. This is mixed with the pe0000

trolatum by vigorous stirring.

The mixture is used in electrical work as a flux for soldering, especially for

soldering copper wires. It is also used tizes the core, which causes it to attract

in other fields where corrosion is not de: the armature, and the hammer strikes

sirable. the gong. While in this position, however, the contact at D is broken, the current ceases to flow, and the cores lose their attractive force. The armature is, Tropenas Process of Making Steel therefore, carried back to its original

Castings position by the spring K, making con- Please explain or describe the Tropenas tact again, and the process is repeated. process of making steel castings ?-W. A. H. The bell will, therefore, continue to ring

The difference between this method as long as the circuit is closed.

and the ordinary method is that inThe bell-push, or means of closing the

stead of having the tuyères at the very circuit, is shown in Fig. 2. P is the push

bottom of the converter so that the blast goes up through the metal, the air is

blown at a low pressure upon the surface B

of the molten metal. At a point 4 to 7 inches above this set of tuyères, is another set which supplies air to burn the carbon monoxide coming out of the metal. In this method there is a great increase in the amount of heat produced, and the

steel is much hotter than if blown in the button; and when this is pressed upon, it usual (Bessemer) way. These converters brings the point of the spring S in contact are better adapted than an open-hearth with the spring R, thus closing the cir- furnace for making very small charges.

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FIG. 3.

Longest Subsurface Phone

By W. T. Walsh

ETWEEN the two great service rendered. Wind, nor rain, nor

cities on Lake Michigan, storm can disturb the cables. “A heavy Chicago and Milwaukee, snowfall brings down wires,” will never there will soon be in op- be said of the Chicago-Milwaukee teleeration the longest under- phone line. Moreover, many fine towns,

ground telephone system surburban in character, along the route, in the world. The feat of laying cables are preserved from the disfigurement of that would be capable of electrically unsightly poles and webs of tangled wire. transmitting the voice eighty-five miles, The work of construction is divided the distance from the Illinois to the Wis- between the Chicago and the Wisconsin consin city, would have been considered telephone companies. The southern problematical several years ago; thirty limits of Kenosha, Wis., indicate where

one shall leave off and the other continue the labor. Trenching and laying the cables are not the only things that have to be accomplished. An adequate system of drainage also is provided for, and this through a rolling country traversed by ravines and varying considerably in the character of the soil.

Several gangs of men, ranging in numbers from fifty to 100, began the work simultaneously at various points. Excavation, of course, was the first step. Ordinarily, two feet is the depth of the

ditch; but conditions are occasionally MEN LAYING CONDUITS. Chicago-Milwaukee telephone line.

such as to render three times this depth necessary.

Gullies, so frequently enmiles was something of which to boast. countered, must be filled; rivers and raBut in 1900, Prof. M. I. Pupin of Co- vines crossed by means of viaducts. lumbia University, invented the load coil This initial work completed, all was that bears his name, by which self-induc- ready for the installation of the conduits. tion is almost entirely overcome—that is, the current of one cable is prevented from setting up an induced current in a parallel cable. Professor Pupin's invention may be compared to a balance, for it acts in such a way that both cables remain about equally charged, rendering "cross-talk” impossible. The appliance has often been used in the past for longdistance overhead systems; for subsurface cables, however, the construction of the Chicago-Milwaukee line marks an epoch.

The advantages of the conduit method lie in the lessened cost of maintenance,

CONCRETE MANHOLE ON LINE OF CHICAGO-MILWAUKEE and in the increased efficiency of the

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TELEPHONE.

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