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The acids and alkalis are generally thought to be entirely opposite in their nature to one another.
Some, however, imagine them to be extremely similar, and to be as it were parts of one substance violently taken from each other. Certain it is, that, when separated, they appear as opposite to one another as heat from cold.
Their opposite action, indeed, very much resembles that of heat and cold, even when applied to the tongue; for the alkali has a hot, bitter, burning taste, while the acid, if not considerably concentrated, always gives a sensation of coldness. In their action, too, upon animal substances, the alkali dissolves, and reduces the part to a mucilage (or clammy, glutinous, ropy substance); while the acid, if not very much concentrated, tends to preserve it uncorrupted. If an alkaline salt, and moderately strong acid, in
