Electric Gas Lighting Part 6

Use care not to splash the solution, as it will burn the clothing and skin. If any does get on, a little animal grease or vegetable oil will quickly saponify it.

In the action of this cell the oxide of copper is reduced to metallic copper and the zincs consumed, it being intended that each element will require renewal at the same time. Upon picking into the oxide plate with a sharp-pointed instrument, if the plate is red throughout, it is exhausted; but, should it show black in its interior, it is still capable of a little more use, but is preferable to use a new plate whenever there is but little oxide left.

Never remove the oxide plates from the battery, and do not allow the solution to be less than one inch above oxide plates.

THE FULLER, OR BICHROMATE CELL.

Although not often necessary in gas-lighting work, there is at times a demand for a heavy current, such as in lighting a big building, where a large coil must be operated. At such times a bichromate of potash cell becomes of service. One of the types is shown in Fig. 56. _J_ is a jar containing electropoion fluid described below. _C_ is a carbon plate immersed in this fluid. _P_ is a porous cup holding the zinc, _Z_, and being filled with a solution of 18 parts common salt, 72 parts water, and one ounce mercury.

[Ill.u.s.tration: FIG. 56.]

The electropoion fluid for the outer jar is made by one pound bichromate of potash or soda to one gallon of water, mixing in a stone vessel. When dissolved, add three pounds commercial sulphuric acid carefully, a little at a time, and stir the mixture constantly as it gets hot. Always add the acid to the mixture; never attempt to pour the mixture into the acid, or trouble will result. The sodium salt is preferable to the pota.s.sium, owing to its greater solubility and its not forming _chrome alum_--a hard precipitate which sticks to jars, elements, etc., to their detriment.

[Ill.u.s.tration: FIG. 57.]

Fig. 57, a form of battery known as the Grenet battery, is used where there is no porous cup. The zinc element, _Z_, is mounted on a rod _R_ pa.s.sing through the cap _G_ of a gla.s.s jar, _J_, and can be raised or lowered into the electropoion fluid which the jar contains. This is a good scheme where the battery is liable to stand idle for a long period.

CARE OF OPEN CIRCUIT BATTERIES.

_Terminals._--Take care that the solutions do not splash over terminals; keep all terminals and binding post screws clean and bright. See that all wires are tightly clamped in terminals, also that their ends are clean. A loose contact is productive of infinite trouble. Examine connections that elements are in proper relation to each other. If in multiple, to produce large current--zincs together and carbons together. If in series, for high electromotive force--zinc to carbon, throughout battery.

_Zincs._--See that the zincs are clean; if crystals form, either reduce strength of solution with water, or sc.r.a.pe zincs clean, and watch if repeated. Examine screw which holds wire; it often corrodes, and makes poor contact in the thread.

A clever device for preserving a rod zinc from the acc.u.mulation of crystals is made by the manufacturers of the Samson cell. It consists of a thin paper tube which is slipped over the zinc. When the crystals acc.u.mulate so as to impair the cell, the tube is slipped off and a new one put on. This device increases the internal resistance of the cell but very slightly.

_Porous cups and carbons._--Wash in warm water. Carbons can be well soaked in warm water and dried in _sun_, in a place where they will not acc.u.mulate dust. Porous cups should be well soaked in warm water, and left to drain in a place exposed to dustless air. Examine binding post holes and screws.

_Solutions._--Do not make too strong. Use not more than six ounces, or more than four ounces avoirdupois, of chemically pure sal ammoniac to one cell Leclanche. Warm water can be used for making solutions, if desired. Some persons drop a teaspoonful of acetic acid in the cell; it is not recommended. If in a place where sal ammoniac cannot be procured, use temporarily common table-salt in same proportion; thoroughly well clean battery first.

Batteries should be kept in a cool dry place. Dry cells should stand upright, also in a cool place, and an examination made once in a while of the connections.