VOLATILE Alkali, a name given to one of the primary or elementary salts, the basis of all those which go by the name of ammoniacs. It is produced chiefly from animal-substances, especially urine, either by distillation with a strong heat, or by putrefaction. In its pure state it is a transparent elastic fluid like common air, but lighter in a considerable proportion; and in this state Dr Priestley has given it the appellation of alkaline air. It unites very readily with fixed air, and with all kinds of acids, forming with them various neutral salts according to their different natures. It unites also with water, which will imbibe one third of its weight of alkaline air. The mixture then is a caustic volatile spirit, the strongest that can be made, which unites with acids without any effervescence. If
fixed air is added, the spirit then contains volatile salt, and is said to be mild; though in fact it is now partly changed into a neutral saline mixture along with a quantity of caustic spirit. If a true caustic spirit is exposed to the air, part of the alkali will fly off; but part is also neutralized by the fixed air which it attracts from the atmosphere. The salt formed by an union of fixed air with volatile alkali is the most volatile of all the ammoniacal salts, and may be made perfectly neutral, though it is easily super-saturated with alkaline air, and is then extremely pungent. In this state it is called volatile salt, and is used in smelling-bottles; but the superfluous quantity of alkaline air soon flies off, and the salt remains neutral as before. Alkaline air in large quantities is fatal to animals, though in a small proportion it is a medicine of great efficacy in cases of fainting. It is very caustic; dissolves oils, and renders them soluble in water; prevents putrefaction; and is inflammable, but burns without any explosion. For the chemical properties of the volatile alkali, see CHEMISTRY, n° 319, & seq.