which of them were acids, you were really doing some work in chemical
analysis. Chemists actually use litmus paper in this way to find out
whether a substance is an acid or a base.

THE BORAX BEAD TEST. This is another chemical test, by which certain
substances can be recognized:

EXPERIMENT 113. Make a loop of wire about a quarter of an inch
across, using light-weight platinum wire (about No. 30). Seal
the straight end of the wire into the end of a piece of glass
tubing by melting the end of the tube around the wire.

Hold the loop of wire in the flame of a Bunsen burner for
a few seconds, then dip the looped end in borax powder. Be
careful not to get borax on the upper part of the wire or on
the handle. Some of the borax will stick to the hot loop. Hold
this in the flame until it melts into a glassy bead in the
loop. You may have to dip it into the borax once or twice more
to get a good-sized bead.

When the bead is all glassy, and while it is melted, touch it
lightly to _one small grain_ of one of the chemicals on the
"jewel-making plate." This jewel-making plate is a plate
with six small heaps of chemicals on it. They are: manganese
dioxid, copper sulfate, cobalt chlorid, nickel salts, chrome
alum, and silver nitrate. Put the bead back into the flame
and let it melt until the color of the chemical has run all
through it. Then while it is still melted, shake the bead out
of the loop on to a clean plate. If it is dark colored and
cloudy, try again, getting a still smaller grain of the
chemical. You should get a bead that is transparent, but
clearly colored, like an emerald, topaz, or sapphire.

Repeat with each of the six chemicals, so that you have a set
of six different-colored beads.

[Illustration: FIG. 187. Making the test.]

This is a regular chemical test for certain elements when they are
combined with oxygen. The cobalt will always change the borax bead to
the blue you got; the chromium will make the bead emerald green or, in
certain kinds of flame, ruby red; etc. If you wanted to know whether
or not certain substances contained cobalt combined with oxygen, you
could really find out by taking a grain on a borax bead and seeing if
it turned blue.

THE HYDROCHLORIC ACID TEST FOR SILVER. The experiment in which you
tested the action of light in effecting chemical change, and in which
you made a white po