m. Pat. 61,329), the fat
being heated in contact with the reagent for about nine hours at
175 deg.-180 deg. C. under a pressure of some 18 atmospheres, but the process
does not appear to be of any considerable importance.

_Lime._--The use of lime for the saponification of oils and fats was
first adopted on the technical scale for the production of candle-making
material, by De Milly in 1831. The insoluble lime soap formed is
decomposed by sulphuric acid, and the fatty acids steam distilled.

The amount of lime theoretically necessary to hydrolyse a given quantity
of a triglyceride, ignoring for the moment any catalytic influence, can
be readily calculated; thus with stearin the reaction may be represented
by the equation:--

CH_{2}OOC_{18}H_{35} CH_{2}OH
| |
2CHOOC_{18}H_{35} + 3Ca(OH)_{2} = 3Ca(OOC_{18}H_{35})_{2} + 2CHOH
| |
CH_{2}OOC_{18}H_{35} CH_{2}OH
stearin milk of lime calcium stearate glycerol

In this instance, since the molecular weight of stearin is 890 and that
of milk of lime is 74, it is at once apparent that for every 1,780 parts
of stearin, 222 parts of milk of lime or 168 parts of quick-lime, CaO,
would be required. It is found in practice, however, that an excess of
3-5 per cent. above the theoretical quantity of lime is necessary to
complete the hydrolysis of a fat when carried on in an open vessel at
100 deg.-105 deg. C., but that if the saponification be conducted under
pressure in autoclaves the amount of lime necessary to secure almost
perfect hydrolysis is reduced to 2-3 per cent. on the fat, the treatment
of fats with 3 per cent. of lime under a pressure of 10 atmospheres
producing a yield of 95 per cent. of fatty acids in seven hours. The
lower the pressure in the autoclave, the lighter will be the colour of the
resultant fatty acids.

_Magnesia._--It has been proposed to substitute magnesia for lime in the
process of saponification under pressure, but comparative experiments
with lime and magnesia, using 3 per cent. of lime and 2.7 per cent. of
magnesia (_Journ. Soc. Chem. Ind._, xii., 163), show that saponification
by means of magnesia is less complete than with lime, and, moreover, the
reaction requires a higher temperature and therefore tends t