e. Which
would have been best for her to use?

Make a list of as many acids as you can think of.

INFERENCE EXERCISE

Explain the following:

511. Sugar dissolves readily in _hot_ coffee.

512. The sugar disappears, yet the coffee flavor remains and
so does the sweetness of the sugar.

513. A tin spoon left overnight in apple sauce becomes black.

514. If one's clothes are on fire, rolling over on the ground
is better than running.

515. Lemon juice bleaches straw hats.

516. Will-o'-the-wisps glow at night, deceiving travelers by
their resemblance to moving lanterns.

517. Tomatoes should never be left in a tin can after it has
been opened.

518. Boiled milk tastes different from ordinary milk.

519. Your hands become very cold after you have washed things
in gasoline.

520. Wood decays more quickly when wet than when dry.

SECTION 55. _Bases._

Why does strong soap make your face sting?

How is soap made?

"Contains no free alkali," "Will not injure the most delicate of
fabrics," "99-44/100% pure,"--such phrases as these are used in
advertising soaps. What is meant by 99-44/100% pure? What is free
alkali? Why should any soap injure fabrics? What makes a soap
"strong"?

The answer to all these questions is that there are some substances
called _bases_, which are the opposites of acids, and some of which
are as powerful as acids. Lye, ammonia, caustic soda, and baking and
washing soda are common bases. The strong bases, like lye and caustic
soda, are also called _alkalies_. If you want to see what a strong
base--an alkali--will do to "the most delicate of fabrics," and to
fabrics that are not so delicate, for that matter, try the following
experiment:

EXPERIMENT 108. _To be done by the teacher._ If you get any
alkali on your skin or clothes, wash it off immediately with
vinegar or lemon juice.

Put half a teaspoonful of lye and a quarter of a cup of water
into a beaker, a small pan, or an evaporating dish. Bring it
to a _gentle_ boil. Drop a small piece of woolen cloth and a
small piece of silk cloth into it and let them boil gently
for a couple of minutes. What happens to them? Try a piece of
plain cotton cloth, and then a piece of cloth that is mixed
wool and cotton or mixed silk and cotton. What happens to
them? This is a very good test to determine whether any