lphuric
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.

_Twitchell's Reagent._--In Twitchell's process use is made of the
important discovery that aqueous solutions of fatty aromatic sulphuric
acids, such as benzene- or naphthalene-stearosulphonic acid, readily
dissolve fatty bodies, thereby facilitating their dissociation into
fatty acids and glycerol. These compounds are stable at 100 deg. C., and are
prepared by treating a mixture of benzene or naphthalene and oleic acid
with an excess of sulphuric acid, the foll