A metal, one of the elements, atomic weight, 210 ; equivalent, 70; valency, 3; specific gravity, 9.9. It is a conductor of electricity.
Relative Resistance, compressed, (silver = 1) 87.23 Specific Resistance, 131.2 microhms Resistance of a wire (a) 1 foot long, weighing 1 grain, 18.44 ohms (b) 1 foot long, 1/1000 inch thick, 789.3 "
(c) 1 meter long, weighing 1 gram, 12.88 "
(d) 1 meter long, 1 millimeter thick, 1.670 "
Resistance of a 1-inch cube 51.65 microhms Electro chemical equivalent, .7350 (Hydrogen = .0105) (See Thermo-electric Series.)
FIGS. 62, 63. INCANDESCENT WIRE FUSE. ABEL"S PATENT.
FIG 64. VON EBNER"S FRICTIONAL ELECTRIC MACHINE FOR EXPLODING ELECTRIC FUSES OR DETONATORS.
Bi-telephone.
A pair of telephones arranged with a curved connecting arm or spring, so that they can be simultaneously applied to both ears. They are self-retaining, staying in position without the use of the hands.
83 STANDARD ELECTRICAL DICTIONARY.
Blasting, Electric.
The ignition of blasting charges of powder or high explosives by the electric spark, or by the ignition to incandescence (red or white heat) of a thin wire immersed in or surrounded by powder. Special influence or frictional electric machines or induction coils are used to produce sparks, if that method of ignition is employed. For the incandescent wire a hand magneto is very generally employed. (See Fuse, Electric.)
The cuts, Figs. 62 and 63, show one form of incandescent wire fuse. The large wires are secured to the capsule, so that no strand can come upon the small wire within the cavity.
The cut, Fig. 64, shows a frictional electric machine for igniting spark fuses.
Bleaching, Electric.
Bleaching by agents produced or made available by the direct action of electricity. Thus if a current under proper conditions is sent through a solution of common salt (sodium chloride), the electrodes being close together, the salt is decomposed, chlorine going to one pole and sodium hydrate to the other. The two substances react upon each other and combine, forming sodium hypochlorite, which bleaches the tissue immersed in its solution.
Block System.
A system of signalling on railroads. The essence of the system consists in having signal posts or stations all along the road at distances depending on the traffic. The s.p.a.ce between each two signal posts is termed a block. From the signal posts the trains in day time are signalled by wooden arms termed semaph.o.r.es, and at night by lanterns.
The arms may be moved by hand or by automatic mechanism depending in part on electricity for carrying out its functions. Thus in the Westinghouse system the semaph.o.r.es are moved by pneumatic cylinders and pistons, whose air valves are opened and shut by the action of solenoid magnets, q. v. The current of these magnets is short circuited by pa.s.sing trains, so as to let the valves close as the train pa.s.ses the signal post. The block system causes the semaph.o.r.e to be set at "danger"
or "caution," as the train enters the next block. Then the following train is not allowed to enter the block until the safety signal is shown. The Westinghouse system provides for two semaph.o.r.es on a post, one indicating "danger" as long as the train is on the next block; the other indicating "caution" as long as the train is on the next two blocks. The rails form part of the circuit, their joints being bridged by copper wire throughout the block, and being insulated where the blocks meet.
Block Wire.
In the block system a wire connecting adjacent block-signal towers or semaph.o.r.e poles.
Blow-pipe.
A name sometimes given to an electric experiment ill.u.s.trating the repulsion of electrified air particles from a point held at high relative potential. A metallic point, placed on the prime conductor of an electric friction or influence machine, becomes highly electrified, and the air becoming excited is repelled and acts upon the candle flame.
If the candle is placed on the conductor and a point held towards it the repulsion is still away from the point.
84 STANDARD ELECTRICAL DICTIONARY.
Blow-pipe, Electric Arc.
A name sometimes given to devices for using the voltaic arc to produce local heating effects. The directive action of the magnet may be used to force out the arc like a blow-pipe flame, or a blast of air may be directly applied for the same purpose.
Blue-stone.
A trade name for crystallized copper sulphate, used in Daniell"s and gravity batteries.
Boat, Electric.
A boat propelled by electricity. The electricity drives a motor which actuates a screw propeller. The current is generally supplied by a storage battery. When used on rivers charging stations are established at proper places. When the boat is used as a tender or launch for a steam ship, such as a war-vessel, the battery is charged by a plant on board the ship. From their noiselessness electric boats are peculiarly available for nocturnal torpedo operations, and the universal equipment of modern war-ships with electric lightning and power plants makes their use possible at all points. This type is often termed an electric launch, and most or all electric boats fall under this category.
Bobbins.
A spool of wood or other material wound with insulated wire. In a tangent galvanometer the bobbin becomes a ring, with a channel to receive the winding. As the ring is not infinitely large compared to the needle the tangent law is not absolutely fulfilled. It is most accurately fulfilled (S. P. Thomson) when the depth of the groove or channel in the radial direction bears to the breadth in the axial direction the ratio of square root of 3 to the square root of 2 or approximately 11 : 9
Body Protector.
A metallic short circuit connected with the wrists and lower legs of the human body, so that if by accident an active circuit is grounded by the hands and body of the workman wearing it, most of the current will pa.s.s through the wire conductors, thus avoiding the vital organs of the body.
Boiler Feed, Electric.
An apparatus by which an electric current acting on an electro-magnet, or other equivalent device, opens the water supply when the water level in a boiler sinks too low, and cuts off the water supply as the water level rises.
Boiling.
In secondary batteries the escape of hydrogen and oxygen gas when the battery is charged. The bubbling of the escaping gases produces the effect of boiling.
85 STANDARD ELECTRICAL DICTIONARY.
Boll.
An absolute, or c. g. s., unit of momentum; a gram moving at the rate of one centimeter per second; a gram-kine (see Kine); a unit proposed by the British a.s.sociation.
Bolometer.
An apparatus for detecting small amounts of radiant energy (radiant heat, so called). A coil suspended by a fine wire or filament so as to be free to rotate under the effect of force is made up of two parallel and equal wires, insulated from each other, but connected so that parallel currents sent through them go in opposite direction through each. This coil is hung in a strong electro-magnetic field produced by a large coil surrounding it. When a current pa.s.ses through the suspended coil no effect will follow, because the oppositely wound portions counteract each other exactly. In the circuit with one half of the suspended coil is an exceedingly thin strip of platinum wire. The other half of the coil has no strips. Both halves unite after leaving the coil. If now the strip of platinum is heated its conductivity is affected and its half of the coil receives less current than the other half. This disturbs the balance and the coil swings through a small arc.
This apparatus may be made very sensitive, so that an increase of temperature of 1/1400? F., 9/70000?C. (1/14000? F.) will be perceptible.
Another construction takes the form of a Wheatstone Bridge, q. v., in whose arms are introduced resistances consisting of bands of iron, .5 Millimeter wide (.02 inches), .004 millimeter (.00016 inch) thick, and folded on themselves 14 times so as to make a rectangular grating, 17 x 12 millimeters (.68 x .48 inch). The least difference of heat applied to the grating affects the galvanometer.
Synonym-Thermic Balance.
Boreal Pole.
The south pointing pole of the magnet. (See Austral Pole.)
Bot.
A colloquial expression for the English Board of Trade unit of Electrical Supply. It is formed of the initials of the words "Board of Trade." (See Unit, Board of Trade.)