Butyric Acid, , is a volatile fatty acid, first prepared by Chevreul, by treating butter with an Alkali (q.v.). It possesses the disagreeable odour of rancid butter, and it is to it, in part at least, that the perspiration of animals owes its unpleasant smell. It is a mobile liquid, specific gravity .974, the vapour of which is inflammable, burning with a blue flame. It is readily soluble in water and alcohol, possesses a sour burning taste and corrodes the skin. Butyric acid forms a whole series of salts, of which butyrate of sodium, , and butyrate of ethyl or Butyric Ether, , (q.v.), may be taken as typical examples.
While butyric acid itself and its inorganic salts (butyrates of sodium, calcium, &c.) have a disagreeable smell, it is interesting to note that the organic salts (butyrates of methyl, ethyl, &c.) have a pleasant odour, and are used in the manufacture of artificial fruit essences.
Butyric acid may be prepared by causing milk to undergo butyric fermentation. Chalk being then added, a butyrate of calcium is obtained, which, on treatment with hydrochloric acid and subsequent distillation, yields the pure acid.