ir use.

_Neutralising and Superfatting Material._--If desired, the final
neutralisation of free alkali can be carried out during the milling
process, any superfatting material being added at the same time. The
chief neutralising reagents have already been mentioned in Chapter VI.

With regard to superfatting material, the quantity of this should be
very small, not exceeding 6-8 ozs. per cwt: The most suitable materials
are vaseline, lanoline, or spermaceti.

[Illustration: FIG. 24--Hand soap-stamping press.]

(iii.) _Compressing._--The next stage is the compression and binding of
the soap ribbons into a solid bar suitable for stamping, and the plant
used (Fig. 23) for this purpose is substantially the same in all
factories. The soap is fed through a hopper into a strong metal
conical-shaped tube like a cannon, which tapers towards the nozzle, and
in which a single or twin screw is moving, and the soap is thereby
forced through a perforated metallic disc, subjected to great pressure,
and compressed. The screws must be kept uniformly covered with shavings
during compression to obviate air bubbles in the soap.

[Illustration: FIG. 25.--Screw press.]

The soap finally emerges through the nozzle (to which is attached a
cutter of suitable shape and size according to the form it is intended
the final tablet to take) as a long, polished, solid bar, which is cut
with a knife or wire into lengths of 2 or 3 feet, and if of satisfactory
appearance, is ready for cutting and stamping. The nozzle of the plodder
is heated by means of a Bunsen burner to about 120 deg. or 130 deg. F.
(49 deg.-55 deg. C.) to allow the soap to be easily forced out, and this
also imparts a good gloss and finish to the ejected bar--if the nozzle
is too hot, however, the soap will be blistered, whereas insufficient
heat will result in streaky soap of a poor and dull appearance.

(iv.) _Cutting and Stamping._--In cutting the soap into sections for
stamping, the cutter should shape it somewhat similar to the required
finished tablet.

Many manufacturers cut the soap into sections having concave ends, and
in stamping, the corners are forced into the concavity, with the result
that unsightly markings are produced at each end of the tablet. It is
preferable to have a cutter with convex ends, and if the stamping is to
be done in a pin mould the shape should be a trifle larger than the
exact size of the desired tablet.

[Illustration: FIG. 26--Pin mould.]