The Standard Electrical Dictionary Part 5

Aluminum.

A metal; one of the elements; symbol: Al.

Atomic weight: 27.4. Equivalent: 9.13. Valency: 3.

Specific gravity: 2.6. It is a conductor of electricity.

Relative resistance annealed, (Silver = 1) 1.935 Specific resistance at 0?C (32?F.) 2.912 microhms

Resistance of a wire at 0?C (32?F.) a) 1 foot long, weighing 1 grain, 0.1074 ohms.

b) 1 foot long, 1/1000 inch thick, 17.53 "

c) 1 meter long, weighing 1 gram, 0.0749 "

d) 1 meter long, 1 millimeter thick 0.03710 "

Resistance of a 1-inch cube at 0?C (32?F.) 1.147 microhms Electro-chemical equivalent. .0958 (hydrogen == .0105)

25 STANDARD ELECTRICAL DICTIONARY.

Amalgam.

(a) A combination or alloy in which one of the const.i.tuents is mercury.

Usually the term is applied to an alloy of a single metal with mercury.

Some metals readily form amalgams; such metals are: Gold, zinc, silver, lead and others; some, such as platinum and iron, form amalgams only under exceptional circ.u.mstances.

(b) The word is also applied to compositions for application to the cus.h.i.+ons of frictional electric machine in which cases it is often a misnomer. True amalgams used for this purpose are made as follows:

(a) Tin, 1 part; Zinc, 1 part; Mercury, 2 parts (Kienmayer).

(b) Tin, 2 parts; Zinc, 3 parts.

(c) Tin, 3 parts; Zinc, 5 parts; Mercury, 4 parts.

(d) Zinc, 1 part: Mercury, 4 parts; Mercury, 9 parts. [sic]

The tin, if such is used, (formula a, b and c) is first melted, the zinc is added in successive portions. The mercury, which must be heated, is slowly poured into the melted alloy after removal of the latter from the fire, and the mixture, while making, is constantly stirred. It is kept stirred or rubbed in a mortar until cold. Sometimes it is poured into water and kept in constant agitation until cold. It is thus obtained in a granular condition, and is pounded in a mortar until reduced to powder. It must be dried and kept in tightly stopped bottles and is applied to the cus.h.i.+ons after they have been greased. It is to be noticed that it is said that alloy (d) requires no pulverization beyond constant rubbing in a mortar as it cools. Sometimes the amalgam is shaken about in a wooden tray with chalk while cooling. The action of amalgams is not very clearly understood. Some claim that there is a chemical action, others that they simply act as conductors, others that they are more highly negative to the gla.s.s than the leather of the cus.h.i.+ons.

Graphite or sulphide of tin (mosaic gold) are sometimes used to coat the cus.h.i.+ons; it is these that are sometimes incorrectly called amalgams.

Amalgamation.

The application of mercury to a metal with which it forms an amalgam, or with which it amalgamates. Battery zincs are amalgamated in two ways. In the immersion method, the plate is dipped into an acid solution of mercuric chloride or nitrate. The latter is best. In the direct application method the plate is first wet all over with dilute acid and a little mercury is dropped upon it and is rubbed over the surface with a rag or, what is better, with a piece of galvanized iron. A very little mercury answers the purpose. The whole surface of the plate should be left as bright as silver. (See Action, Local.)

Amber.

Amber is a fossil resin, supposed to be a product of the extinct Pinites Succinifer and other coniferous trees. Most of it is gathered on the sh.o.r.es of the Baltic between Koenigsberg and Memel. It is also found in small pieces at Gay Head, Ma.s.s., and in New Jersey green sand. It is found among the prehistoric remains of the Swiss Lake dwellers. When rubbed with a cloth it becomes excited with negative electricity. The Greek word for it is electron, which gave the name electricity to the modern science. Thales of Miletus, 600 B. C., and Theophrastus, about 300 B. C., both mention its electric properties or power of attracting small objects when rubbed.

26 STANDARD ELECTRICAL DICTIONARY.

Ammeter.

The commercial name for an ampere-meter, an instrument designed to show by direct reading the number of amperes of current which are pa.s.sing through a circuit.

A great variety of ammeters have been invented, based on different principles. The definitions following this one give some idea of the lines of construction followed.

Synonym--Ampere meter.

Ammeter, Ayrton's.

A direct reading instrument for measuring current intensity.

A solenoid receives the current. In the axis of the solenoid an iron tube is suspended by a long spiral spring that pa.s.ses down within it, and the upper end of which spring is fastened to the gla.s.s top of the instrument. The tube is provided with proper guides so as to maintain a vertical position, and is free to rotate. Its upper end carries an index.

The whole operates as a magnifying device. A slight longitudinal displacement of the tube causes it to rotate through a considerable angle by the action of the spring. By properly proportioning the parts, the angle of displacement of the index is directly proportional to the current between 15? and 270? angular displacement.

The same instrument is wound for use as a volt-meter.

Its princ.i.p.al fault is its restricted range.

Ammeter, Commutator.

A commutator ammeter is one whose windings consist of separate strands, each of any desired number of turns, and provided with a commutating attachment for throwing them into series or into parallel as desired.

The essential condition is that all the wires shall be of equal resistance and of equal number of turns. Such an instrument can be used for heavy or light currents. Two sets of graduations are marked on its scale if it is a calibrated instrument. (See Calibration.) Commutator volt-meters are constructed on the same principle.

Ammeter, Cunynghame's.

A modification of the Siemens' electro-dynamometer. (See Electro-dynamometer, Siemens'.) An electro-magnet with very ma.s.sive core is excited by the current. As the core is of small reluctance the strength of the magnet is nearly proportional to the current strength.

Between the poles of the magnet a soft iron armature or induced magnet is pivoted. It carries a pointer so adjusted that when the axis of the soft iron magnet is at an angle of about 30? with the line joining the poles of the electro-magnet the pointer will indicate zero.

The soft iron armature is so ma.s.sive that the magnetism induced in it is proportional to the strength of the electro-magnet. Hence the couple exerted by the electro-magnet on the pivoted armature will be proportional to the square of the current.

The armature is retained in place by a spiral spring lying in line with its axis of rotation. The instrument is operated as a zero reading instrument. The current is pa.s.sed through it. The needle is deflected; it is brought back to zero by turning a milled head which twists the spring. The current will be proportional to the square root of the angle of displacement of the milled head. A scale with index is provided, giving directly the square roots of the angle over which the pointer is moved.

The same instrument is wound for use as a volt-meter.

27 STANDARD ELECTRICAL DICTIONARY.

Ammeter, Eccentric Iron Disc.

This ammeter comprises a cylindrical electro-magnet excited by the current to be measured. A disc of iron free to rotate is suspended on pivots below it. A piece is cut off the disc at one part of its periphery so as to give more metal to one side than to the other. In its zero position this portion of the disc swings towards the magnet. As the latter is more and more excited the other or more projecting portion of the disc turns towards it, being attracted like an armature, and moves against the force of gravity, the disc rotating. An index attached to the disc swings over the face of a graduated scale. The disc is so counterpoised that in its natural position the index points to zero.

Ammeter, Electro-magnetic.

An ammeter depending for its working upon the action of an electro-magnet, which is excited by the current to be measured.

Ammeter, Gravity.

An ammeter whose hand or index is drawn into the zero position by gravity, and whose displacement therefrom is produced by the action of the current to be measured.

Fig. 11. GRAVITY SOLENOID AMMETER.

Ammeter, Magnetic Vane.

A fixed plate of soft iron is placed within a coil. Facing it is a second disc free to move or swing on an axis. When the field is excited the two repel each other because like polarity is induced in each, and the motion of the movable disc indicates the strength of the current.