"Again, as the volatile ammoniacal salt most curable from most animal matter (also of great antiquity) was found to agree with the other alkalies in taste, and in many chemical properties, though not in fixity, this ammoniacal salt was also termed an alkali, but volatile, in opposition to the two former, which remain unaltered in very considerable heat, and are therefore, comparatively, fixed. The volatile alkali is described under the article ."