When fats are mixed together, however, their varying alkali requirements
become modified, and once the saponification is begun with weak lye,
other materials are induced to take up alkali of a strength with which
alone they would not combine.

It is considered the best procedure to commence the pasting or
saponification with weak lye.

In order to economise tank space, it is the general practice to store
strong caustic lye (60 deg. to 70 deg. Tw., 33 deg. to 37 deg. B.) and to dilute it as
it is being added to the soap-pan by the simultaneous addition of water.

Many manufacturers give all their soap a "brine wash" to remove the last
traces of glycerine and free the soap from carbonates. This operation
takes place prior to "fitting"; sufficient water is added to the boiling
soap to "close" it and then brine is run in to "grain" it.

After resting, the liquor is withdrawn.

Having described the necessary operations in general, we will now
consider their application to the preparation of various kinds of hard
soap.

_Curd Soaps._--Tallow is largely used in the manufacture of white curd
soaps, but cocoa-nut oil sometimes enters into their composition.

The first three operations above described, _viz._, pasting, graining
out, and boiling on strength, are proceeded with; the clear boiling by
means of a closed steam coil is continued until the "head" is boiled out
and the soap is free from froth. A sample taken and cooled should be
hard. Boiling is then stopped, and, after covering, the pan is allowed
to rest for eight to ten hours, when the soap is ready for filling into
frames, where it is crutched until perfectly smooth.

_Curd mottled_ is usually made from melted kitchen stuff and bone
grease.

Its preparation is substantially the same as for curd soap, but the
clear boiling is not carried so far. The art of curd mottled soap-making
lies in the boiling. If boiled too long the mottling will not form
properly, and, on the other hand, insufficient boiling will cause the
soap to contain an excess of entangled lye. Having boiled it to its
correct concentration the pan is allowed to rest about two hours, after
which the soap is ready for framing, which should be done expeditiously
and the frames covered up.

Some lye, containing the impurities from the fats used, remains in the
interstices of the curd, unable to sink, and as the soap cools it is
enclosed and forms the mottling. The mottling may, therefore, be
co