The Standard Electrical Dictionary Part 78

Generating Plate.

The positive plate in a voltaic couple, or the plate which is dissolved; generally a plate of zinc.

Synonyms--Positive Plate--Positive Element.

Generator, Current.

Any apparatus for maintaining an electric current. It may be as regards the form of energy it converts into electrical energy, mechanical, as a magneto or dynamo electric machine or generator; thermal, as a thermo-electric battery; or chemical, as a voltaic battery; all of which may be consulted.

Generator, Secondary.

A secondary or storage battery. (See Battery, Secondary.)

German Silver.

An alloy of copper, 2 parts, nickel, 1 part, and zinc, 1 part. Owing to its high resistance and moderate cost and small variation in resistance with change of temperature, it is much used for resistances. From Dr.

Mathiessen's experiment the following constants are deduced in legal ohms: Relative Resistance (Silver = 1), 13.92 Specific Resistance at 0? C. (32F.), 20.93 microhms.

Resistance of a wire, (a) 1 foot long, weighing 1 grain, 2.622 ohms.

1 foot long, 1/1000 inch thick, 125.91 "

1 meter long, weighing 1 gram, 1.830 "

1 meter long, 1 millimeter thick, 0.2666 "

Resistance of a 1 inch cube at 0?C. (32? F.), 8.240 microhms.

Approximate percentage increase of resistance per 1? C. (1.8? F.) at about 20? C. (68? F.), 0.044 per cent.

Gilding, Electro-.

The deposition of gold by an electric current, or electrolytically in the electroplating bath.

Gilding Metal.

A special kind of bra.s.s, with a high percentage of copper, used to make objects which are to be gilded by electrolysis.

278 STANDARD ELECTRICAL DICTIONARY.

Gimbals.

A suspension used for ships' compa.s.ses and sometimes for other apparatus. It consists of a ring held by two journals, so as to bc free to swing in one plane. The compa.s.s is swung upon this ring, being placed concentrically therewith. Its journals are at right angles to those of the ring. This gives a universal joint by which the compa.s.s, weighted below its line of support, is always kept horizontal.

Fig. 191. COMPa.s.s SUSPENDED IN GIMBALS.

Gla.s.s.

A fused mixture of silicates of various oxides. It is of extremely varied composition and its electric constants vary greatly. Many determinations of its specific resistance have been made. For flint gla.s.s at 100? C. (212? F.) about (2.06E14) ohms --at 60? C (140? F.) (1.020E15) (Thomas Gray) is given, while another observer (Beetz) gives for gla.s.s at ordinary temperatures an immeasurably high resistance. It is therefore a non-conductor of very high order if dry. As a dielectric the specific inductive capacity of different samples of flint gla.s.s is given as 6.57--6.85--7.4--10.1 (Hopkinson), thus exceeding all other ordinary dielectrics. The densest gla.s.s, other things being equal, has the highest specific inductive capacity.

Gold.

A metal, one of the elements; symbol Au. c .; atomic weight, 196.8; equivalent, 65.6; valency, 3; specific gravity 19.5.

It is a conductor of electricity.

Annealed. Hard drawn.

Relative Resistance (Annealed Silver = 1), 1.369 1.393 Specific Resistance, 2.058 2.094 Resistance of a wire at 0? C. (32?F.) (a) 1 foot long, weighing 1 grain, 57.85 58.84 ohms (b) 1 foot long, 1/1000 inch thick, 12.38 12.60 "

(c) 1 meter long, weighing 1 gram, .4035 .4104 "

(d) 1 meter long, 1 millimeter thick, .02620 .02668 "

Resistance of a 1 inch cube at 0? C.(32? F.) .8102 .8247

Approximate increase in resistance per 0? C., (1.8? F) at about 20? C. (68? F.), 0.365 per cent.

Electro-chemical equivalent (Hydrogen = .0105), .6888

279 STANDARD ELECTRICAL DICTIONARY.

Gold Bath.

A solution of gold used for depositing the metal in the electroplating process.

A great number of formulae have been devised, of which a few representative ones are given here.

COLD BATHS. HOT BATHS.

Water, 10,000 10,000 10,000 10,000 5,000 3,000 Pota.s.sium Cyanide, 200 -- 200 10 -- 50 Gold, 100 15 100 10 10 10 Pota.s.sium Ferrocyanide, -- 200 -- -- 150 -- Pota.s.sium Carbonate, -- 150 -- -- 50 -- Ammonium Chloride, -- 30 -- -- 20 -- Aqua Ammoniae, -- -- 500 -- -- -- Sodium Phosphate, -- -- -- 600 -- -- Sodium Bisulphite, -- -- -- 100 -- --

(Roseleur.)

In the baths the gold is added in the form of neutral chloride, Auric chloride (Au Cl6).

Gold Stripping Bath.

A bath for removing gold from plated articles without dissolving the base in order to save the precious metal. A bath of 10 parts of pota.s.sium cyanide and 100 parts of water may be used, the articles to be stripped being immersed therein as the anode of an active circuit. If the gilding is on a silver or copper basis, or on an alloy of these metals the same solution attacks the base and dissolves it, which is objectionable. For silver articles it is enough to heat to cherry red and throw into dilute sulphuric acid. The gold scales off in metallic spangles. For copper articles, a mixture of 10 volumes concentrated sulphuric acid, 1 volume nitric acid, and 2 volumes hydrochloric acid may be used by immersion only, or with a battery. The sulphuric acid in such large excess is supposed to protect the copper. For copper articles concentrated sulphuric acid alone with the battery may be used. This does not sensibly attack the copper if it is not allowed to become diluted. Even the dampness of the air may act to dilute it.

Graduator.

Apparatus for enabling the same line to be used for telegraph signals and telephoning.

One type consists in coils with iron cores or simply electromagnets.

These act to r.e.t.a.r.d the current in reaching its full power and also prolong it. This gives a graduated effect to the signals, so that the telephone diaphragm is not audibly affected by the impulses.

The telephoning current is so slight and so rapid in its characteristic changes that it is without effect upon the ordinary telegraph.

280 STANDARD ELECTRICAL DICTIONARY.

Gram.

The unit of weight in the metric system; accepted as the unit of ma.s.s in the absolute of C. G. S. system of units. It is the one-thousandth part of ma.s.s of a standard weight preserved under proper conditions in Paris, and supposed to be the ma.s.s of a cubic decimeter of distilled water at the temperature of the maximum density of water. The standard is the kilogram; the temperature is 3.9? C. (39? F.). The standard kilogram is found to be not exactly the weight of a cubic decimeter of water, the latter weighing 1.000013 kilogram.

If therefore the defined gram on the water basis is taken as the unit it varies very slightly from the accepted gram.