The Romance of Modern Chemistry

ACIDS AND ALKALIS the shops. The liquid we buy contains a large proportion of water, but it would clearly be impracticable to buy and sell ammonia in the pure gaseous state. This convenient way of handling a substance in solution instead of in the pure, undiluted state is employed also in the case of some of the acids. Oil of vitriol, to be sure, is almost pure sulphuric acid, but “ aqua fortis ” is only a solution of nitric acid, and “ spirits of salt,” as a rule, does not contain more than one-third of its weight of hydrogen chloride, which is itself a gas. Ammonia, as an alkali, has the power of neutralising acids, and an interesting experiment which shows that the process of neutralisation leads to the formation of an entirely new substance, a salt, is the following:—A glass cylinder is filled with ammonia gas, and closed with a glass plate; a similar cylinder is filled with hydrogen chloride, and the two are placed mouth to mouth with the glass plate between. If the glass plate is slipped out, the colourless alkaline gas in the one cylinder and the colourless acid gas in the other immediately rush upon each other, and a white, powdery substance, sal ammoniac, is produced. Here we have the interesting case of two gases uniting to form a solid, entirely different in character from the original reacting sub- stances. Lime is another alkaline body, of which enormous quantities are required in the arts and manufactures, and yet the majority of people know very little about its valuable properties. Lime is the oxide of the metal calcium, and is obtained by strongly heating carbonate of lime, which nature supplies in profuse measure and in such various forms as marble, limestone, and chalk. We may note that from the point of view of ultimate chemical