Part 2 (1/2)

27. Always take the zinc from this fluid as soon as you have finished experimenting, or even if you have no use for the cell for a few minutes. The zinc and fluid are rapidly destroyed in b.i.+.c.hromate cells even when the circuit is open. Always wash the carbon and zinc as soon as you take them from the fluid.

APPARATUS 16.

_28. Battery Fluid._ For 2-fluid cells (App. 7), a saturated solution of copper sulphate (blue vitriol) is needed. Place some of the crystals in a gla.s.s jar, with water, stir them around, and add the sulphate as long as it is dissolved. A few extra crystals should be left in the stock bottle so that the solution will always be saturated.

APPARATUS 17.

_29. Vinegar Battery Fluid._ For a few of the experiments with detectors, etc., good strong vinegar does well as the exciting fluid.

This may be used with the copper and zinc or carbon and zinc elements.

The amount of current given with vinegar and App. 4 or 5 is sufficient to show many of the simpler experiments.

APPARATUS 18.

_30. Battery Fluid._ Strong brine, made by dissolving ordinary salt in water, will produce quite a little current with App. 4 or 5. The presence of the current is easily shown with the astatic detectors.

APPARATUS 19.

_31. Measures for Water, Acids, etc._ If you do not own a graduated gla.s.s, such as druggists use for measuring liquids, the following plan will be found useful. In the mixing of battery fluids, etc., while it is not necessary to be absolutely exact, it is necessary to know approximately what you are doing.

An ordinary gla.s.s pint fruit jar may be taken as the standard. This holds 16 fluid ounces, or 2 ordinary teacupfuls. A teacupful may then be taken as 1/2 pint, or 8 fluid ounces. You can probably find a small bottle that will hold 1 or 2 oz., and you can easily tell how much it holds by filling it and counting the number of times it is contained in the pint can.

A slim bottle holding 1/2 pint can be made into a convenient measuring gla.s.s by scratching lines on it with the sharp edge of a hard file. The lines should be placed, of course, so that they will show how much liquid you must put into it to make 1 oz., 2 oz., etc. Instead of the file marks, a narrow strip of paper may be pasted upon the bottle, and the divisions shown by lines drawn upon the paper.

APPARATUS 20.

_32. To Amalgamate Battery Plates._ To keep the zinc plates or rods in cells from being eaten or dissolved when the circuit is opened, they should be amalgamated; that is, they should have a coating of mercury.

The local currents (see text-book) aid in rapidly destroying the zinc, unless it is amalgamated. Do not amalgamate copper plates--merely the zinc ones.

33. Place a few drops of mercury in a b.u.t.ter dish. Dip the zinc into the solution of App. 14, then lay it upon a flat board. This is necessary with thin sheet-zinc, as it becomes very brittle when coated with mercury, and will not stand hard rubbing. If you also dip a very narrow piece of tin into the dilute sulphuric acid, you can use this as a spoon and lift one drop of mercury at a time from the b.u.t.ter dish to the zinc.

By tapping the tin upon the zinc, the mercury will leave the tin. Put the mercury only where the zinc will be under the solutions in the cell, then rub the drops around with a small cloth that has been dipped in the acid. The zinc will become very bright and silvery, due to the mercury.

Do not get too much mercury on it, just enough to give it a thin coat, as it will make the thin zinc so brittle that it will very easily break.

Amalgamate both sides of the zinc.

CHAPTER III.

MISCELLANEOUS APPARATUS AND METHODS OF CONSTRUCTION.

APPARATUS 21.

_34. For Annealing and Hardening Steel._ (See text-book for reasons why some parts of electrical apparatus should be made of hard steel, while other parts should be made of soft iron.)