is
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
glass 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 butter 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 butter 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.)

35. To anneal or soften spring steel so that you can bend it without
breaking it, heat it in a candle, gas, or alcohol flame until it is
red-hot; allow the steel to cool in the air slowly.

36