acle and reserved for use in the
saponification of other material, and the soap is then ready for the
final operation of "fitting".

(_d_) _Fitting._--If the operations just described have been properly
performed, the fitting should present no difficulty. The soap is boiled
with open steam, and water added until the desired degree of closing is
attained. As the water is thoroughly intermixed throughout the mass the
thick paste gradually becomes reduced to a smooth, thin consistence.
Samples are tested from time to time as to their behaviour in dropping
off a hot trowel held sideways; the thin layer should drop off in two or
three flakes and leave the surface of the trowel clean and dry. The soap
is then in a condition to allow the impurities to gravitate. According
to the required soap, the fit may be "coarse" ("open") when the flakes
drop off the trowel readily, or "fine" ("close") when the flakes only
leave the trowel with difficulty.

If the dilution with water has been allowed to proceed too far, and too
fine a fit is produced, which would be denoted by the layer of soap not
leaving the trowel, a little caustic lye or brine may be very carefully
added and the whole well boiled until the desired condition is obtained.

A good pressure of steam is now applied to the pan, causing the contents
to swell as high as possible, this greatly facilitating the settling of
impurities; steam is then turned off, the pan covered, and the boil
allowed to rest for several days.

The art of fitting consists in leaving the contents of the pan in such a
condition that, on standing, all the impurities precipitate, and the
settled soap, containing the correct amount of water, is clear and
bright.

The above is a general practical outline of the ordinary soap-boiling
process. It may be modified or slightly altered according to the fancy
of the individual soap-maker or the particular material it is desired to
use. Fats and oils not only vary in the amount of alkali they absorb
during saponification, but also differ in the strength of the alkali
they require. Tallow and palm oil require lye of a density of 15 deg. to 18 deg.
Tw. (10 deg. to 12 deg. B.), but cocoa-nut oil alone would not saponify unless
the lye was more concentrated, 33 deg. to 42 deg. Tw. (20 deg. to 25 deg. B.).
Cotton-seed oil requires weak lyes for saponification, and, being
difficult to saponify alone even with prolonged boiling, is generally
mixed with animal fat.