, and holds 220 lbs. of mixed acids, and is surrounded on
three sides by a water space in order to keep it cool. The mixed acids are
stored in iron tanks behind the dipping tanks, and are allowed to cool
before use. During the nitration, the temperature of the mixed acids is
kept at 70 deg. F., and the cotton is dipped in quantities of 1-1/2 lb. at a
time. It is put into a tin shoot at the back of the dipping tank, and
raked into the acids by means of a rabble. It remains in the acids for
five or six minutes, and is then removed to a grating at the back, pressed
and removed. After each charge of cotton is removed from the tank, about
14 lbs. of fresh mixed acids are added, to replace amount removed by
charge. The charge now weighs, with the acids retained by it, 15 lbs.; it
is now placed in the pots, and left to steep for at least twenty-four
hours, the temperature being kept as low as possible, to prevent the
formation of soluble cotton, and also prevent firing. The proportion of
soluble formed is likely to be higher in hot weather than cold. The pots
must be covered to prevent the absorption of moisture from the air, or the
accidental entrance of water, which would cause decomposition, and
consequent fuming off, through the heat generated by the action of the
water upon the strong acids.

The excess of acids is now extracted by means of hydro-extractors, as at
Stowmarket. They are worked at 1,200 revolutions per minute, and whirled
for five minutes (10-1/2 lbs. of waste acids are removed from each charge
dipped). The charge is then washed in a very similar manner to that
previously described, and again wrung out in a centrifugal extractor
(1,200 revolutions per minute). The gun-cotton is now boiled by means of
steam in wooden tanks for eight hours; it is then again wrung out in the
extractors for three minutes, boiled for eight hours more, and again wrung
out; it is then sent to the beater and afterwards to the poacher. The
poachers hold 1,500 gals. each, or 18 cwt. of cotton. The cotton remains
six hours in the poachers. Before moulding, 500 gals. of water are run
into the poacher, and 500 gals. of lime water containing 9 lbs. of whiting
and 9 gals. of a caustic soda solution. This mixture is of such a strength
that it is calculated to leave in the finished gun-cotton from 1 to 2 per
cent. of alkaline matter.

By means of vacuum pressure, the pulp is now drawn off and up into the
stuff chest--a large cylindrical iron