Improvements relating to the Manufacture of Nitro-cellulose or Pyroxylin.
Year: 1890

page_text: Date of Application, 23rd Dec., 1890-Accepted, 24th Jan., 1891
COMPLETE SPECIFTUATION.
[Communicated from abroad by GEORGE MORDEY MOWBRAY, of North Adams,
Massachusetts, United States of America. ¡
Improvements relating to the Manufacture of Nitro-cellulose or
Pyroxylin.
I, HENRY HARRIS LAKE, of the firm of Haseltine, Lake & Co., Patent Agents,
45 Southampton Buildings, in the County of Middlesex, do hereby declare the nature
of this invention and in what manner the same is to be performed, to be particularly
described and ascertained in and by the following statement:-
The method of manufacturing pyroxylin on a large scale as now practised is, to
select very fine, pure cotton tissue-paper unsized, of a thickness less than 5 of an
inch and immerse the same ir a bath of sulphuric and nitric acids of certain strength
and at a given temperature, say, about 85° F. for about thirty minutes, then to
remove the same from the acids bath, then expel the adherent acid, and then to wash
out all traces of acids.
Fine, pure, thin tissue-paper is preferred, because the instant the paper touches the
acids bath, it acquires a glutinous or colloid surface which impedes the thorough
conversion of the paper, thin as it is, and thus about thirty minutes, or there-
abouts, is necessary to enable the conversion to take place through only of an
inch thickness.
During the immersion in the acids, the paper has assimilated about forty per cent.
of nitric acid, yet at the end of the operation its bulk is less than before immersion, so
dense and parchment-like has it become.
It is this property of the thin film of converted nitro-cellulose of protecting the
paper beneath the surface from chemical action that has led to the selection of so
fine a paper, and has demanded so long an immersion, and each of these factors has
added to the cost of the pyroxylin or gun-cotton.
The object of my invention is to reduce the cost of the crude material used, by
substituting a waste product, such as cotton rags, cotton lint from the cotton-seed
hulls, and other materials in lieu of the more expensive unsized tissue-paper now used,
and to lessen the time which is now required for conversion, and at the same time to
produce a better, because a more uniform product.
These results I attain by taking advantage of the physical effect produced by
crystallizing a salt, (preferably a nitrate) in the cells of the fibre, which opens up
these cells to the action of-the acids bath, whereby, on the immersion of the material
in a bath of sulphuric acid, there is set free from the salt, (if a nitrate) nitric acid in
a nascent state, which instantly acts chemically on the adjacent walls of each cell
wherein the nitrate has crystallized. Thus 1 effect nitration more rapidly with less
costly material than is possible by the present method of immersing unsized tissue-
paper in the usual mixed acids bath, where the process of nitration is obstructed by
the superficial glutinous film of pyroxylin which forms on the surface of the fibrous
sheet of unsized tissue-paper the instant it touches the acids bath.
I do not confine myself to the use of any particular form of cellulose, whether
unsized paper, baled cotton, cotton yarn or textile fabric, as in cotton rags, or even
the cotton lint from cotton-seed hulls, however obtained. With either of these forms
of cellulose fibre properly cleansed, bleached and washed, if impregnated with a salt
not necessarily, but preferably a nitrate, a manufacturer can, by adopting my process,
make pyroxylin with less costly cellulose and overcome the inconvenience of that
superficial glutinous hindrance to nitration herein before described.
I have said it was not absolutely necessary to use a nitrate, 1 wish to be understood
by this assertion that any salt crystallized, or even water crystallized by freezing, in
the cells of the fibrous cellulose, facilitates nitration, by rendering the inner walls of
cellular tissue more readily accessible to the acids of the immersion bath.

page_text: .
Some salts it might be necessary to remove after crystallization and by washing,
therefore nitrates, sodic nitrates for instance, for its low price, its ready crystallization
and yield of nitric acid evolved in the acid bath in contact with its sulphuric acid, I
prefer to other salts.
To enable others skilled in the art to understand my invention, I will describe it for
two varieties of pyroxylin, viz., "gun-cotton," and "soluble pyroxylin" for explosive
and plastic purposes respectively.
For preparing textile cotton for explosive purposes, use for 100 parts of clean, dry,
bleached rags, 300 parts of boiling water and 25 to 50 parts of sodic nitrate; first
dissolve the sodic nitrate in pure, clean water, heat to a boiling point and gradually
introduce the rags, keeping up a moderate circulation of the mass, until no more air
bubbles leave the solution. Pass the rags through rollers to remove the excess of
saline solution.
The operator may estimate that rags as they leave the rollers in their wet condition
will retain twice their weight of solution, therefore, either by weighing the rags or
deducting the proportion of liquid left in the tank, he can calculate about the quantity
of sodic nitrate taken up by the textile fibre.
The rags from the impregnating tank, having passed through the rollers, are now
thrown on frames protected from dust, and allowed to dry gradually, in order to enable
the salt to penetrate by the action termed " osmose into the cells of the fibre and
there crystallize. They are then thoroughly dry and are ready for conversion into
nitro-cellulose.
The acids immersion bath for "gun-cotton" (tri-nitro-cellulose as it is known in the
art) should be as concentrated as possible, say, for sulphuric acid Sp. Gr. 1-84, for
nitric acid Sp. Gr. 152, and in the proportion of sulphuric acid 2 parts and nitric acid
1 part, both by weight..
For soluble pyroxylin (di-nitro-cellulose)-
For clean, dry, lileached rags 100 parts, use water 300 parts, and sodic nitrate
from 10 to 25 parts.
The directions herein before prescribed for impregnating are to be observed here.
The proportions, however, of acids and the strength of the acids immersion bath differ.
For example, sulphuric acid Sp. Gr. 1-845 07 pärts, nitric acid Sp. Gr. 1-520 17 parts,
water 16 parts.
If fine tissue is used and it is desired-to-avoid the fine opaque specks found therein
by the present process, a weak saline bath, consisting of 10 parts sodic nitrate to
100 parts of paper will suffice. The drying of the paper should not be too rapid, in
order that ample time may be given for the "osmose" action to take place.
Having now particularly described and ascertained the nature of the said inven-
tion and in what manner the same is to be performed as communicated to me
by my foreign correspondent I declare that what I claim is :-
The herein described improvement in the process of manufacturing the various
grades of nitro-cellulose or pyroxylin, which consists in crystallizing a salt, preferably
sodic nitrate, in the interstices of the cellulose material, whether simply fibrous, felted
or textile, and then converting the dried impregnated material by immersion in a
suitable bath of acids.
The process of manufacturing nitro-cellulose which consists in impregnating a
cellulose material with a solution of a salt, preferably sodic nitrate, drying the material
and crystallizing the salt in its interstices, then immersing it in a suitable bath of
sulphuric and nitric acid, and then washing and drying the nitro-cellulose, as set
forth.
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HASELTINE, LAKE & Co.,
45, Southampton Buildings, London, Agents for the Applicant.