cup. Into another cup pour a few drops of vinegar, an acid.
Dip your litmus paper first into one, then into the other, and
then back into the first. What color does the vinegar turn
it? the ammonia? Try lemon juice; diluted hydrochloric acid; a
_very_ dilute lye solution.

This is called the _litmus test_. All ordinary acids, if not too
strong, will turn litmus pink. All bases or alkalies will turn it
blue. If it is already pink when you put it into an acid, it will stay
pink, of course; if it is already blue when you put it into a base, it
will stay blue. But if you put a piece of litmus paper into something
that is neither an acid nor a base, like sugar or salt, it will still
stay the same color. So, to test for a base, use a piece of litmus
paper that is pink and see if it turns blue, or if you want to test
for an acid, use blue litmus paper. Do this experiment:

EXPERIMENT 110. With pink and blue litmus paper, test the
different substances named below to see which are acids and
which are bases. Make a list of all the acids and another list
for all the bases. Do not put down anything that is neither
acid or base. You cannot be sure a thing is an acid unless it
turns _blue_ litmus _pink_. A piece of pink litmus would stay
pink in an acid, but it would also stay pink in things that
were neither acid nor base, like salt or water. In the same
way you cannot be sure a thing is a base unless it turns
_pink_ litmus _blue_. Here is a list of things to try: 1,
sugar; 2, orange; 3, dilute sulfuric acid; 4, baking soda in
water; 5, alum in water; 6, washing soda in water; 7, ammonia;
8, dilute lye; 9, lemon juice; 10, vinegar; 11, washing powder
in water; 12, sour milk; 13, cornstarch in water; 14, wet
kitchen soap; 15, oil; 16, salt in water.

You may have to make the orange and sour milk test at home. You may
take two pieces of litmus paper home with you and test anything else
that you may care to. If you have a garden, try the soil in it. If it
is acid it needs lime.

_APPLICATION 81._ A boy spilled some greasy soup on his best
dark blue coat. Which of the following methods would have
served to clean the coat? to sponge it (a) with cold water;
(b) with water (hot) and ammonia; (c) with hot water and
vinegar; (d) with concentrated nitric acid; to sprinkle lye on
the spot and pour boiling water over it.

_APPLICATIO