lation consumes ten acres of
wood lot per day, we see that all the rags in the world would be
inadequate to meet this demand alone, to say nothing of periodicals,
books, tissue paper, etc.

Chemistry plays a part in every phase of life; in the arts, the
industries, the household, and in the body itself, where digestion,
excretion, etc., result from the action of the bodily fluids upon
food. The chemical substances of most interest to us are those which
affect us personally rather than industrially; for example, soap,
which cleanses our bodies, our clothing, our household possessions;
washing soda, which lightens laundry work; lye, which clears out the
drain pipe clogged with grease; benzine, which removes stains from
clothing; turpentine, which rids us of paint spots left by careless
workmen; and hydrogen peroxide, which disinfects wounds and sores.

In order to understand the action of several of these substances we
must study the properties of two groups of chemicals--known
respectively as acids and bases; the first of these may be represented
by vinegar, sulphuric acid, and oxalic acid; and the second, by
ammonia, lye, and limewater.

202. Acids. All of us know that vinegar and lemon juice have a sour
taste, and it is easy to show that most acids are characterized by a
sour taste. If a clean glass rod is dipped into very dilute acid, such
as acetic, sulphuric, or nitric acid, and then lightly touched to the
tongue, it will taste sour. But the best test of an acid is by sight
rather than by taste, because it has been found that an acid is able
to discolor a plant substance called litmus. If paper is soaked in a
litmus solution until it acquires the characteristic blue hue of the
plant substance, and is then dried thoroughly, it can be used to
detect acids, because if it comes in contact with even the minutest
trace of acid, it loses its blue color and assumes a red tint. Hence,
in order to detect the presence of acid in a substance, one has merely
to put some of the substance on blue litmus paper, and note whether or
not the latter changes color. This test shows that many of our common
foods contain some acid; for example, fruit, buttermilk, sour bread,
and vinegar.

The damage which can be done by strong acids is well known; if a jar
of sulphuric acid is overturned, and some of it falls on the skin, it
eats its way into the flesh and leaves an ugly sore; if it falls on
carpet or coat, it eats its way into the ma