Page:Treatise on Soap Making.djvu/35

19 to make a distinction between the salts formed by the union of an acid and an alkali, and those formed by the union of acids with earthy or metallic substances; for these will likewise unite with acids: and some of the compounds will likewise crystallise into regular figures; but because of their weaker union with these substances, the salts resulting from combinations of this kind are called imperfect.

All acids, the volatile sulphurous one excepted, change the blue infusions of vegetables, such as violets, to a red; and alkalis, as well as some of the imperfect neutrals, change them to a green.

This is the nicest test of an acid or alkali abounding in any substance, and seems the most proper method of determining whether a solution, intended to be neutral, really is so or not.