hloric or sulphuric acid. The former acid is
preferable, as the lime salt formed is readily soluble and easily
removed. The fat is agitated with a weak solution of acid in a
lead-lined tank by blowing in steam, and when the treatment is complete
and the waste liquor withdrawn, the last traces of acid are well washed
out of the liquid fat with hot water.

_Rosin._--Several methods have been suggested for bleaching rosin; in
some instances the constitution of the rosin is altered, and in others
the cost is too great or the process impracticable.

The aim of these processes must necessarily be the elimination of the
colouring matter without altering the original properties of the
substance. This is best carried out by converting the rosin into a
resinate of soda by boiling it with a solution of either caustic soda or
carbonated alkali. The process is commenced by heating 37 cwt. of 17 deg.
Tw. (11 deg. B.) caustic soda lye, and adding 20 cwt. of rosin, broken into
pieces, and continuing the boiling until all the resinate is
homogeneous, when an addition of 1-1/2 cwt. of salt is made and the
boiling prolonged a little. On resting, the coloured liquor rises to the
surface of the resinate, and may be siphoned off (or pumped away through
a skimmer pipe) and the resinate further washed with water containing a
little salt.

The treatment with carbonated alkali is performed in a similar manner. A
solution, consisting of 2-3/4 cwt. of soda ash (58 deg.), in about four
times its weight of water, is heated and 20 cwt. of rosin, broken into
small pieces, added. The whole is heated by means of the open steam
coil, and care must be taken to avoid boiling over. Owing to the
liberation of CO_{2} gas, frothing takes place. A large number of
patents have been granted for the preparation of resinate of soda, and
many methods devised to obviate the boiling over. Some suggest mixing
the rosin and soda ash (or only a portion of the soda ash) prior to
dissolving in water; others saponify in a boiler connected with a trap
which returns the resinate to the pan and allows the carbonic-acid gas
to escape or to be collected.

With due precaution the method can be easily worked in open vessels,
and, using the above proportions, there will be sufficient uncombined
rosin remaining to allow the resultant product to be pumped into the
soap with which it is intended to intermix it, where it will be finally
saponified thoroughly.

The salt required,