in physics, is commonly used to denote a mixed body, whose integrant parts are easily dissipated by fire or heat; but is more properly used for bodies whose parts are easily separated from each other, and dispersed in air.

Volatile Alkali, in the new French nomenclature ammoniac, one of the three alkaline salts. It consists, as Mr Berthollet and several other chemists have proved, of 807 parts in 1000 of azot, and 193 of hydrogen. Several experiments, published by Dr Priestley, led the way to this analysis, though he himself did not see their result. It is chiefly procurable from animal substances by distillation, during which process the azot and hydrogen necessary to its formation unite in proper proportions; it is not however procured pure by this process, being mixed with oil and water, and mostly saturated with carbonic acid. To separate these substances, it is first combined with an acid, the muriatic for instance, and then disengaged from that combination by the addition of lime or pitch. In its greatest degree of purity it can only exist in a gaseous form, at least in the common temperature of the atmosphere. It was at first obtained chiefly from urine, and was therefore called sal urina; afterwards from horns, especially from those of the hart, hence its name, sal cornu cervi, "hart's horn." See CHEMISTRY INDEX.