owing reaction taking place:--

C_{6}H_{6} + C_{18}H_{34}O_{2} + H_{2}SO_{4} =
C_{6}H_{4}(SO_{3}H)C_{18}H_{35}O + H_{2}O.

On boiling the resultant product with water two layers separate, the
lower one consisting of a clear aqueous solution of sulphuric acid and
whatever benzene-sulphonic acid has been formed, while the upper layer,
which is a viscous oil, contains the benzene-stearosulphonic acid. This,
after washing first with hydrochloric acid and then rapidly with
petroleum ether, and drying at 100 deg. C. is then ready for use; the
addition of a small quantity of this reagent to a mixture of fat
(previously purified) and water, agitated by boiling with open steam,
effects almost complete separation of the fatty acid from glycerol.

The process is generally carried out in two wooden vats, covered with
closely fitting lids, furnished with the necessary draw-off cocks, the
first vat containing a lead coil and the other a brass steam coil.

In the first vat, the fat or oil is prepared by boiling with 1 or 2 per
cent. of sulphuric acid (141 deg. Tw. or 60 deg. B.) for one or two hours and
allowed to rest, preferably overnight; by this treatment the fat is
deprived of any dirt, lime or other impurity present. After withdrawing
the acid liquor, the fat or oil is transferred to the other vat, where
it is mixed with one-fifth of its bulk of water (condensed or
distilled), and open steam applied. As soon as boiling takes place, the
requisite amount of reagent is washed into the vat by the aid of a
little hot water through a glass funnel, and the whole is boiled
continuously for twelve or even twenty-four hours, until the free fatty
acids amount to 85-90 per cent. The amount of reagent used varies with
the grade of material, the smaller the amount consistent with efficient
results, the better the colour of the finished product; with good
material, from 1/2 to 3/4 per cent. is sufficient, but for materials of
lower grade proportionately more up to 2 per cent. is required. The
reaction appears to proceed better with materials containing a fair
quantity of free acidity.

When the process has proceeded sufficiently far, the boiling is stopped
and free steam allowed to fill the vat to obviate any discoloration of
the fatty acids by contact with the air, whilst the contents of the vat
settle.

The settled glycerine water, which should amount in bulk to 50 or 60 per
cent. of the fatty matter taken, and have a densi