_Sulphuric Acid._--The hydrolysing action of concentrated sulphuric acid upon oils and fats has been known since the latter part of the eighteenth century, but was not applied on a practical scale till 1840 when Gwynne patented a process in which sulphuric acid was used to liberate the fatty acids, the latter being subsequently purified by steam distillation. By this method, sulpho-compounds of the glyceride are first formed, which readily emulsify with water, and, on treatment with steam, liberate fatty acids, the glycerol remaining partly in the form of glycero-sulphuric acid. The process has been investigated by Fremy, Geitel, and more recently by Lewkowitsch (_J. Soc. of Arts_, "Cantor Lectures," 1904, 795 _et seq._), who has conducted a series of experiments on the hydrolysis of tallow with 4 per cent. of sulphuric acid of varying strengths, containing from 58 to 90 per cent. sulphuric acid, H_{2}SO_{4}. Acid of 60 per cent. or less appears to be practically useless as a hydrolysing agent, while with 70 per cent. acid only 47.7 per cent. fatty acids were developed after twenty-two hours' steaming, and with 80 and 85 per cent. acid, the maximum of 89.9 per cent. of fatty acids was only reached after fourteen and fifteen hours' steaming respectively. Using 98 per cent. acid, 93 per cent. of fatty acids were obtained after nine hours' steaming, and after another seven hours, only 0.6 per cent. more fatty acids were produced. Further experiments have shown that dilute sulphuric acid has also scarcely any action on cotton-seed, whale, and rape oils. According to Lant Carpenter, some 75 per cent. of solid fatty acids may be obtained from tallow by the sulphuric acid process, owing to the conversion of a considerable quantity of oleic acid into isoleic acid (_vide_ p. 12), but in the process a considerable proportion of black pitch is obtained. C. Dreymann has recently patented (Eng. Pat. 10,466, 1904) two processes whereby the production of any large amount of hydrocarbons is obviated. In the one case, after saponification with sulphuric acid, the liberated fatty acids are washed with water and treated with an oxide, carbonate, or other acid-fixing body, _e.g._, sodium carbonate, prior to distillation. In this way the distillate is much clearer than by the ordinary process, and is almost odourless, while the amount of unsaponifiable matter is only about 1.2 per cent. The second method claimed consists in the conversion of the fatty acids into their methyl esters by treatment with methyl alcohol and hydrochloric acid gas, and purification of the esters by steam distillation, the pure esters being subsequently decomposed with superheated steam, in an autoclave, with or without the addition of an oxide, _e.g._, 0.1 per cent. zinc oxide, to facilitate their decomposition.