acid and of nitrate, and after thoroughly mixing them, delivers them into
the still, where, under the influence of heat, they rapidly become a
homogeneous liquid, from which nitric acid continuously distils.

Mr Prentice says: "I may point out that while the ordinary process of
making nitric acid is one of fractional distillation by time, mine is
fractional distillation by space." "Instead of the operation being always
at the same point of space, but differing by the successive points of
time, I arrange for the differences to take place at different points of
space, and these differences exist at one and the same points of time." It
is possible with this plant to produce the full product of nitric acid of
a gravity of 1.500, or to obtain the acid of varying strengths from the
different still-heads. One of these stills, capable of producing about 4
tons of nitric acid per week, weighs less than 2 tons. It is claimed that
there is by their use a saving of more than two-thirds in fuel, and four-
fifths in condensing plant. Further particulars and illustrations will be
found in Mr Prentice's paper (_Journal of the Society of Chemical
Industry_, 1894, p. 323).




CHAPTER III.

_NITRO-CELLULOSE, &c._

Cellulose Properties--Discovery of Gun-Cotton--Properties of Gun-Cotton--
Varieties of Soluble and Insoluble Gun-Cottons--Manufacture of Gun-Cotton--
Dipping and Steeping--Whirling out the Acid--Washing--Boiling--Pulping--
Compressing--The Waltham Abbey Process--Le Bouchet Process--Granulation of