GUNCOTTON. A name applied to certain cellulose products of the action of nitric acid on cellulose, discovered by Schdnbein in 1846. The molecular formula of cellulose (q.v.) is some un known multiple of and the action of nitric acid results in the substitution of a vary ing number of NO, groups for hydrogen atoms in the doubtless complex molecule of cellulose. The composition and chemical constitution of the re sulting compounds determine their properties (e.g. the solubility in organic liquids), and upon these, in turn, depend the practical uses to which the several compounds may be applied. The higher substitution products are generally called 'guncotton,' the lower ones 'pyroxylin.' In preparing the cellulose nitrates, purified cotton is treated with a mixture of nitric and i sulphuric acids. The mixture used in the case of guncotton consists of one part by weight of nitric acid, specific gravity 1.5, and three parts of sulphuric acid, specific gravity 1.845. For every pound of cotton 12 pounds of the acid mix ture are used, and the cotton is immersed and digested in it for twenty-four hours. After the acid has been removed from the cotton by wringing, the latter is pulped, washed, and com pressed into blocks. The acid liquids which have been expelled from the cotton after use are found to contain 79.91 per cent. of sulphuric acid, 9.52 per cent. of nitric acid, 1.04 per cent. of tetroxide of nitrogen, and 9.65 per cent. of water. This mixture is re-worked and is used again. For py roxylin and other of the lower cellulose nitrates weaker acids are used, according to the purpose for which the resulting product is intended.
The cellulose nitrate, known as pyrocellulose, used by the United States Navy in making smoke less powder, contains from 12.45 to 12.80 per cent. of nitrogen. Such cellulose nitrate has been made by dipping one pound of cotton (free from oil and mechanical impurities and containing about 7 per cent. of moisture) in 19 pounds of a mixture containing about 57 per cent. of sul phuric acid, 28.2 per cent. of nitric acid, and not more than 2 per cent. of nitrogen tetroxide. The acid mixture has an initial temperature of 25° C. (77° F.), and the crock containing the mixed acids and cotton is heated to 36° C. (97° F.), the action being maintained with one turning over of the cotton, for sixty minutes. After puri fication by wringing, washing, and steaming, to remove the acid, the nitrocellulose is freed from the water remaining in it by extraction with alcohol, and it is converted into a gelatinous mass by kneading or stirring in a Werner and Pflei derer mixing-machine with a mixture of ethyl ether and ethyl alcohol, two parts by weight of ether and one part by weight of alcohol being used for every three parts by weight of nitro cellulose. The subsequent processes have for their object the more intimate mixing of the material and straining off of the unconverted portions, the sbaning of the mass into grains. The latter still contain some of the solvent, par ticularly alcohol, the amount varying with the thickness of the walls. The very smallest grains
contain about 0.5 per cent., the larger grains often as much as 4 per cent. of the solvent.
The pyroxylin used for the manufacture of pyroxylin plastics, such as 'celluloid,' is made by clipping cotton or tissue paper in a mixture of sulphuric acid, 66 parts; nitric acid, 17 parts; and water, 17 parts; 100 pounds of the acid mixture being used for one pound of paper, and the immersion being continued from twenty to thirty minutes at C. The pyroxylin used in this art is of low nitration. containing about 10.18 per cent. of nitrogen. The pyroxylin used for collodion and in the making of varnishes contains about 11.11 per cent. of nitrogen, and is made by the use of stronger acids than those employed in the manufacture of the pyroxylin for plastics.
The perfection of the modern processes for the manufacture of guncotton are due principally to Baron von Lenk, of Austria, and Sir Frederick Abel, of England. Abel's improvement consisted chiefly in the reduction of the guncotton to a pulp by beating it in rag-engines, such as are employed in the manufacture of paper-pulp. The fibres of cotton consist of hollow, hair-like tubes. When immersed in the acid mixture, they become filled with it, just as capillary tubes of any other material would be, and cannot readily be freed from it. But the acid thus retained is capable of exercising further action on the fibres, and thus rendering the product unstable. Guncotton has thus frequently undergone spontaneous decom position in storage. By pulping the long-staple guncotton, Abel cut the fibres into very short tubes which permitted of the acids being readily washed out with water in a poacher, and thereby insured the stability of the product. Moreover, the moist pulp can be readily molded into any de sirable shape, and can be compressed to a density that may fit it best for use in military and naval mining. Thus the guncotton used for torpedoes in the United States Navy is compressed into rec tangular blocks, with chamfered corners, 2.9 inches in diameter and 2 inches in height, each block being provided with a hole one-half inch in diameter lying in its vertical axis. Such are obtained by first molding the wet pulp in a molding-press under a pressure of 100 pounds to the square inch, and then subjecting the molded blocks to a pressure of 6800 pounds to the square inch in a final press. Although one of the most powerful of explosive substances when fired by detonation, this military guncotton can, when clamp, be shaped with tools as wood is shaped, and in the preparation of the guncotton charges for use in the heads of the very large torpedo shells fired from the guns of the United States steamship Vesuvius, these compressed blocks of pulped guncotton were sawed with a fret saw and turned in lathes to shape the mass so as to con form to the particular shape of the heads of the torpedoes.