terial and leaves an
unsightly hole. The evil results of an accident with acid can be
lessened if we know just what to do and do it quickly, but for this we
must have a knowledge of bases, the second group of chemicals.

203. Bases. Substances belonging to this group usually have a bitter
taste and a slimy, soapy feeling. For our present purposes, the most
important characteristic of a base is that it will neutralize an acid
and in some measure hinder the damage effected by the former. If, as
soon as an acid has been spilled on cloth, a base, such as ammonia, is
applied to the affected region, but little harm will be done. In your
laboratory experiments you may be unfortunate enough to spill acid on
your body or clothing; if so, quickly apply ammonia. If you delay, the
acid does its work, and there is no remedy. If soda (a base) touches
black material, it discolors it and leaves an ugly brown spot; but the
application of a little acid, such as vinegar or lemon juice, will
often restore the original color and counteract the bad effects of the
base. Limewater prescribed by physicians in cases of illness is a
well-known base. This liquid neutralizes the too abundant acids
present in a weak system and so quiets and tones the stomach.

The interaction of acids and bases may be observed in another way. If
blue litmus paper is put into an acid solution, its color changes to
red; if now the red litmus paper is dipped into a base solution,
caustic soda, for example, its original color is partially restored.
What the acid does, the base undoes, either wholly or in part. Bases
always turn red litmus paper blue.

Bases, like acids, are good or bad according to their use; if they
come in contact with cloth, they eat or discolor it, unless
neutralized by an acid. But this property of bases, harmful in one
way, is put to advantage in the home, where grease is removed from
drainpipe and sink by the application of lye, a strong base. If the
lye is too concentrated, it will not only eat the grease, but will
corrode the metal piping; it is easy, however, to dilute base
solutions to such a degree that they will not affect piping, but will
remove grease. Dilute ammonia is used in almost every home and is an
indispensable domestic servant; diluted sufficiently, it is
invaluable in the washing of delicate fabrics and in the removing of
stains, and in a more concentrated form it is helpful as a smelling
salt in cases of fainting.

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