transparent, distributed throughout the bulk
of the cotton (Monie., Cotton Fibre, 67). Mr Field says, "This is a
significant fact when it is known that from this cotton an extremely
soluble pyroxyline can be produced."

Pyroxyline of an inferior grade as regards colour only can be produced
from the cotton wastes of the trade. They must be scoured before they are
fit for nitrating. Paper made from the pulps of sulphite and sulphate
processes is capable of yielding a very soluble pyroxyline. It can be
nitrated at high temperatures and still yield good results. Tissue paper
made from flax fibre is also used after being cut into squares.

Mowbray (U.S.P., No. 443, 105, 3rd December 1890) says that a pure cotton
tissue paper less than 1/500 inch in thickness, thin as it is, takes on a
glutinous or colloid surface, and thus requires some thirty minutes to
enable the nitration to take place. With a thicker paper only the surface
would be nitrated. He therefore uses a fibre that has been saturated with
a solution of nitrate of soda, and afterwards dried slowly, claiming that
the salt crystallises in the fibre, or enters by the action termed osmose,
and opens up the fibre to the action of the acid. This process would only
be useful when the cotton is to be nitrated at a low temperature. At a
high temperature it would be unnecessary.

Dietz and Wayne (U.S.P., No. 133, 969) use ramie, rheca, or China grass
for producing a soluble pyroxyline. That made from ramie is always of
uniform strength and solubility, and requires a smaller quantity of
solvent to dissolve it than that made from cotton. Mr Field's experience,
however, is entirely contrary to this statement. Such is the influence of
the physical form of the fibre on the process of nitration, that when flax
fibre and cotton fibre are nitrated with acid mixtures of exactly the same
strength, and at the same temperature, the solution of the first is
glutinous or thick, and the second fluid or thin. By simply nitrating at a
higher temperature than the cotton, the flax will yield a pyroxyline
giving an equally fluid collodion.

The presence of chlorine in the fibre must be carefully avoided, as such a
fibre will yield an acid product which cannot be washed neutral. The fibre
must be dry before nitration; and this is best done, according to Mr
Field, by using the form of drier used in drying wool.

~Nitration of the Fibre.~--Mixed cotton and flax fibre in the form of
paper, from