The Romance of Modern Chemistry

CHAPTER VIII ACIDS AND ALKALIS OF the various classes into which chemical com- pounds may be divided, acids form one of the largest and most important. They get their name from the sour taste which is supposed to characterise them, but this characteristic is by no means universal. From the chemist’s point of view, all acids are similar in that they contain the element hydrogen, this hydrogen being replaceable by a metal. In many cases we can actually follow the replacement of the hydrogen in an acid by a metal; as, for example, when a few pieces of magnesium ribbon, iron wire, or granulated zinc are put in hydrochloric acid—“spirits of salt,” as the druggist may call it. The acid and the metal attack each other, the latter disappears gradually and turns out the hydrogen, which comes bubbling off as a gas. What takes place might be expressed as follows:—metal acid-*a salt+ hydrogen, the salt left in solution being magnesium chloride, iron chloride, or zinc chloride, according as mag- nesium, iron, or zinc was the metal taken. The corrosive acid is, in a sense, destroyed by the metal, and the plumber’s description of zinc chloride as “killed spirits of salt ” is therefore quite to the point. The behaviour of acids in attacking or corroding metals is very general, and even domestic illustrations are avail- able. Vinegar is a household article, but it is well to 82