The Standard Electrical Dictionary Part 123

Plate Condenser.

A static condenser having a flat plate of gla.s.s for dielectric. (See Epinus' Condenser.)

Plate Electrical Machine.

A frictional electric machine, in which a circular plate of gla.s.s is excited by friction with the cushions. It is the most recent type of frictional machine and has superseded the old cylinder machines. In its turn it is superseded by influence machines, really plate machines, but not so termed in practice.

Plate, Ground.

In a lightning arrester, the plate connected to the earth.

Plate, Negative.

In a voltaic battery, either primary or secondary, the plate which is unattacked by the oxygen or negative radical or element of the fluid. It corresponds to the carbon plate in the ordinary voltaic battery, and is the one charged with positive electricity.

Plate, Positive.

In a voltaic battery, either primary or secondary, the plate which is dissolved or attacked by the oxygen or negative radical or element of the fluid. It is the plate corresponding to the zinc plate in the ordinary voltaic battery, and is the one charged with negative electricity.

Plating Balance.

A balance or scales to which articles in an electroplater's bath are suspended. A weight exceeding by a known amount that of the article as immersed overbalances the article. When the plating is being deposited as soon as it exceeds the excess of weight of the counterpoise the balance tips, the article descends a little, the electric circuit is broken and the plating ceases. Thus the plating is automatically stopped when a predetermined amount of metal is deposited.

418 STANDARD ELECTRICAL DICTIONARY.

Plating Bath.

A vessel of solution for the deposition of metal by electrolysis as used in electro-plating.

Plating, Electro-.

The deposition of metal by electrolysis so as to coat the conducting surface of objects therewith. The full details of the many processes are very lengthy and cannot be given here.

The general principle includes a battery or source of electric current.

The object to be plated is connected to the negative terminal and is immersed in the solution. Thus with a battery the object is in electrical connection with the zinc plate. To the other terminal a metallic plate is connected. The object and the plate termed the anode being introduced into a suitable bath, the metal whose solution is in the bath is deposited upon the surface of the object.

The bath is a solution of the metal in some form that will lend itself to the electrolytic action. The anode is often a plate of the metal of the bath, so that it dissolves as fast as metal is deposited on the object, thus keeping up the strength of the solution.

The objects to be plated must be scrupulously clean, and great care must be taken to keep the bath uncontaminated.

When the object has a non-conducting surface, it is made conducting by being brushed over with plumbago q.v. In addition iron dust is sometimes dusted over it. This acts by precipitating the metal of the bath directly and thus giving a conducting basis for the metal to deposit on.

To avoid getting iron in a bath the object may be dipped in copper sulphate solution. This precipitates copper in place of the iron and leaves the article in good shape for silver or other plating.

Electro-plating, if made thick enough, gives a reverse of the article when separated therefrom. A direct copy can be got by a second plating, on the first plating after separation, or a wax impression can be employed.

Under the different metals, formulae for the baths will be found. (See also Quicking-- Steeling--Plating Balance.)

Platinoid.

An alloy of copper, nickel, zinc in the proportions of German silver with 1 or 2 per cent of tungsten. It is used for resistances. It has a specific resistance (or resistance per centimeter cube) of about 34 microhms. Its percentage variation in resistance per degree C. (1.8? F.) is only about .021 per cent., or less than half that of German silver.

This is its most valuable feature.

419 STANDARD ELECTRICAL DICTIONARY.

Platinum.

A metal; one of the elements; symbol, Pt; atomic weight, 197.4; equivalent, 49.35; valency, 4; specific gravity, 21.5.

It is a conductor of electricity.

The following data refer to the annealed metal at 0? C. (32? F.) Relative Resistance (Silver annealed = 1), 6.022 Specific Resistance, 9.057 microhms.

Resistance of a wire, (a) 1 foot long, weighing 1 grain, 2.779 ohms.

(b) 1 foot long, 1/1000 inch thick, 54.49 "

(c) 1 meter long, weighing 1 gram, 1.938 "

(d) 1 meter long, 1 millimeter thick, .1153 "

Resistance of a 1 inch cube, 3.565 Electro-chemical equivalent (Hydrogen = .0105), 0.5181.

The coefficient of expansion by heat is almost the same as that of gla.s.s. It can be pa.s.sed through holes in gla.s.s and the latter can be melted about it so as to hermetically seal its place of pa.s.sage through the gla.s.s. It is used in incandescent lamps for leading-in wires and other similar uses.

Platinum Black.

Finely divided platinum. It is made by boiling a solution of platinic chloride with excess of sodium carbonate and a quant.i.ty of sugar, until the precipitate is perfectly black and the supernatant liquid is colorless. It seems to possess a great power of occluding oxygen gas.

When heated to redness it becomes spongy platinum. The negative plates of a Smee battery are coated with platinum black.

Platinum-silver Alloy.

An alloy of 1 part platinum and 2 parts silver, used for resistance coils.

Relative Resistance (silver annealed = 1 ), 16.21 microhms.

Specific Resistance at 0?C. (32? F.), 24.39 Resistance of a wire, (a) 1 foot long, weighing 1 grain, 4.197 ohms.

(b) 1 foot long, 1/1000 inch diameter, 146.70 "

(c) 1 meter long weighing 1 gram, 2.924 "

(d) 1 meter long, 1 millimeter diameter, 0.3106 "

Resistance of a 1 inch cube, 9.603 microhms.

Percentage Variation per degree C. (1.8? F.) at about 20? C. (68? F.), 0.031 per cent.

Synonym--Platinum Alloy.

Platinum Sponge.

Finely divided platinum obtained by igniting platinum black, q.v., and also by igniting salts of platinum. It has considerable power of condensing or occluding oxygen. It will, if in good condition, set fire to a jet of hydrogen impinging upon it.

Plow.

Contact arms projecting downwards from the motors, trucks, or bodies of electric street cars, which enter the underground conduit through the slot and carry contact pieces or brushes, to take the current for driving the motors from the leads within the conduit.

420 STANDARD ELECTRICAL DICTIONARY.