The Romance of Modern Chemistry

ACIDS AND ALKALIS colourless liquid becoming suddenly red on being poured into an apparently empty glass, and the same red liquid becoming colourless again when poured into another also apparently empty glass. As a class, alkalis are the opposite of acids, not only in regard to the indicators just mentioned, but in many other respects. The addition of an alkali to an acid destroys or neutralises the characteristic properties of the latter, and if the right quantity is added the solution then contains nothing but a salt—a kind of neutral substance which does not exhibit the behaviour either of an acid or of an alkali. The process of neutralisation may be represented in the following way : acid + alkali->a salt + water; from which it will be seen that the same sort of body is produced in this way as is formed by the action of an acid on a metal. In certain circumstances an alkali may obviously be used as an antidote to an acid; if, for instance, a drop of an acid is allowed to fall on clothing, the production of a stain, and ultimately a hole, may be prevented by the immediate application of an alkali, for the salt which is thus formed is quite harmless so far as any action on the cloth is concerned, and may be washed out with water. Again, if any acid has been swallowed, an alkaline substance is the thing to take. In both cases, however, the right alkaline substance must be chosen, otherwise the cure may be worse than the disease; for certain alkalis have a very powerful action on animal and vegetable tissues, destroying such things as skin and paper. Two alkalis of this description are caustic soda and caustic potash, which, although extensively used in the manufacture of hard and soft soap respec- tively, are perhaps not so familiar to most people as