e of
wool, and more if used hot than cold. Of the two, the ammonia will have
the least effect, especially if dilute, but borax is better than either.
The influence of a little sulphuric acid in the wool would be in the
direction of neutralising some of the ammonia or soda, and shellac, if
dissolved in the alkalis, would be to some extent precipitated on the
fibre, unless the alkali, soda or ammonia, were present in sufficient
excess to neutralise that sulphuric acid and to leave a sufficient
balance to keep the shellac in solution. Borax, which is a borate of
soda, would be so acted on by the sulphuric acid that some boric acid
would be set free, the sulphuric acid robbing some of that borax of its
soda. This boric acid would not be nearly so injurious to wool as
carbonate of soda or ammonia would.

The best solvent for shellac, however, in the preparation of the
stiffening and proofing mixture for hats, is probably wood spirit or
methylated spirit. A solution of shellac in wood spirit is indeed used
for the spirit-proofing of silk hats, and to some extent of felt hats,
and on the whole the best work, I believe, is done with it. Moreover,
borax is not a cheap agent, and being non-volatile it is all left behind
in the proofed material, whereas wood spirit or methylated spirit is a
volatile liquid, _i.e._ a liquid easily driven off in vapour, and after
application to the felt it may be almost all recovered again for re-use.
In this way I conceive the use of wood spirit would be both more
effective and also cheaper than that of borax, besides being most
suitable in the case of any kind of dyes and colours to be subsequently
applied to the hats.

_Wood Spirit._--Wood spirit, the pure form of which is methyl alcohol,
is one of the products of the destructive distillation of wood. The wood
is distilled in large iron retorts connected to apparatus for condensing
the distillation products. The heating is conducted slowly at first, so
that the maximum yield of the valuable products--wood acid (acetic acid)
and wood spirit--which distil at a low temperature, is obtained. When
the condensed products are allowed to settle, they separate into two
distinct layers, the lower one consisting of a thick, very dark tar,
whilst the upper one, much larger in quantity, is the crude wood acid
(containing also the wood spirit), and is reddish-yellow or
reddish-brown in colour. This crude wood acid is distilled, and the wood
spirit which dist