sary, in these crutching pans, and in that case they are merely
used for mixing the liquids with the hot soap prior to its passage along
wooden spouts (Fig. 8) provided with outlets over the frames, in which
the crutching is continued by hand. In the case of stiff soaps requiring
complete incorporation of liquor, the screw type is preferable, the soap
being forced upwards by the screw, and descending between the cylinder
and the sides of the pan, while the reverse action can also be brought
into play. The completion of crutching is indicated by the smoothness
and stiffness of the soap when moved with a trowel, and a portion taken
out at this point and cooled should present a rounded appearance. When
well mixed the resultant product is emptied directly into wheel-frames
placed underneath the outlet of the pan. It is important that the blades
or worm of the agitating gear be covered with soap to avoid the
occlusion of air and to prevent the soap becoming soft and spongy.

[Illustration: FIG. 8.--Wooden soap spout.]

_Liquoring of Soaps._--This consists of the addition of various alkaline
solutions to soap to produce different qualities, and is best performed
in the crutching machines, although it is in some instances carried out
in the frames. In the history of soap-making a large number and variety
of substances have been suggested for the purpose of accomplishing some
real or supposed desirable effect when added to soap. Many of these have
had only a very short existence, and others have gradually fallen out of
use.

Amongst the more practical additions most frequently adopted may be
mentioned carbonate of soda, silicate of soda, and pearl ash (impure
carbonate of potash). The carbonate of soda may be used in the form of
"soda crystals," which, containing 62.9 per cent. of water, dissolves in
its own water of crystallisation on heating, and is in that manner added
to the hot soap. In the case of weak-bodied soap, this addition gives
firmness and tends to increase the detergent qualities.

The soda carbonate may also be added to soap as a solution of soda ash
(58 deg. alkali) either concentrated, 62 deg. Tw. (34 deg. B.), or of various
strengths from 25 deg. Tw. (16 deg. B.) upwards. This solution stiffens and
hardens soap, and the addition, which must not be excessive, or
efflorescence will occur, is generally made at a temperature of 140 deg. F.
(60 deg. C.). Care should always be taken in the choice of solutions for