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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
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
tial circuit, its temperature would con
tinue to increase, because of the greater to be penetrated, and then heating the
current flowing, until the glower was iron to a glow.
destroyed. To prevent this increase of
current, a ballast resistance of fine iron Cracks in Concrete Wall
wire is connected in series with the
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.
TYPICAL DIAGRAM OF Nernst LAMP Circuit.
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 material certain oxides of the rare earths. The oxide is mixed in the form of a paste, then pressed through a small orifice into a string, which is subjected to a roasting process, forming the filament or glower material of the lamp. The glowers are cut the desired length and platinum terminals attached. As the glower is a non-conductor when cold, some form of heater is necessary to bring it up to a
perature, and thus prevents the increase of current through the glowers.
The accompanying figure shows complete connections for a 6-glower lamp. The current enters, say, at terminal 1, passes through the contacts of the cutout 4, to the heater circuit 5, then to contacts 4' and to the terminal 2. When the glowers become hot enough to conduct,
the current divides at 1', part of it passing through the glowers 6, the ballast 7, and the cut-out 3, to terminal 2. When the current in the glowers has reached its normal value, the contacts at 4 and 4' open, cutting out the heater coils entirely.
Making a Thermopile How is a thermopile constructed and used ? -F. H. N.
The thermopile is an instrument used in the production of such small, steady currents as are required for grading delicate ammeters and voltmeters. In conjunction with the galvanometer, it is also useful for registering minute variations of temperature in furnaces, where no ordinary thermometer could stand the melting power of the intense heat. In construction, the thermopile consists of one or more paired pieces of dissimilar metals. These metals are in the form of wires or blocks and are joined together at one end. Antimony and bis
The wires should then be placed in a vise, with the ends projecting so that they · may be twisted together with a pair of forceps. The twist is next soldered together. To prevent rusting, resin rather than the customary acid or soldering fluid is the best available material. The free end of the wires should now be drawn apart, so as to leave a space of some four inches between the extremities, as shown in the figure (a,b). These extremities are next connected to the terminals of a delicate galvanometer. If the galvanometer's pointer is then brought to 0°, on applying fire to the junction c, a current strong enough to deflect the pointer through 10° or 15° will be set up.
A dozen combinations of this kind will increase the power of the arrangement. In such case, vires of a length of four inches should be used. A twist of threefourths inch will suffice.
Tightening Steam Joints-Lime in Pipes
1: How can steam joints be made tight?
2: 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.
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.
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.
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 reason for this is that a liquid will boil at a lower temperature than in the surrounding atmosphere if the pressure is reduced. This well-known fact is taken advantage of in the boiling of syrups, etc. On its return, the piston is obliged
electro-magnet composed of a soft iron core of horseshoe shape wound with copper wire. The armature of the bell is mounted on a spring K, and carries a hammer H for striking the gong. On the back of the armature is a spring which makes contact at point D with a
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,
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 fluid 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 the result. This is mixed with the petrolatum by vigorous stirring.
The mixture is used in electrical work Fig. 2.
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 circuit, is shown in Fig. 2. P is the push
stead of having the tuyères at the very bottom of the converter so that the blast goes up through the metal, the air is blown at a low pressure upon the surface 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 Fig. 3.
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.
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 Men LAYING CONDUITS.
ditch; but conditions are occasionally 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