Page:The New International Encyclopædia 1st ed. v. 09.djvu/419

* GUNCOTTON. 369 GUNCOTTON. composition and clieniieal constitution of the re- sulting compounds determine their properties (e.g. the solubility in organic liquids), and ipon 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 'pyro.vylin.'- In preparing the cellulose nitrates, purified cotton is treated with a mi.xturc of nitric and sulphuric acids. The nii.xturc used in the case of guncotton consists of one part b.y 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 Tfl.Ol per cent, of sulphuric acid, 0.52 per cent, of nitric acid, 1.04 per cent, of tetroxide of nitrogen, and 9.05 per cent, of water. This mixture is re-worked and is used again. For py- rox,vlin and other of the lower cellulose nitrates weaker acids are used, according to the jiurpose 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 30? 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 nitrocellulo.se is freed from the water remaining in it by extraction with alcohol, and it is converted into a gelatinous mass bv 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 shaping 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 dipping 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 30° 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 mamif:u/ture 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 Fiederick Abel, of England. Abel's improvement consisted chiellj- in the reduction of the guncotton to a pulp by beating it in rag-engines, such as are employed in the manufacture of paper-jiulp. The fibres of cotton consist of hollow, hair-like tubes. Wlien iunuersed in the acid mixture, they become filled with it, just as capillary tubes of any other material would be, and cannot readil.v' be freed from it. But the acid thus retained is capable of exercising further action on the fil)res, and thus rendering the product unstable. (Juncotton has thus frcquentl.v undergone spontaneous decom- position in storage. B.v puljiing the long-staple guncotton, Abel cut the fibres into very short tubes which permitted of the acids being readily waslied out with water in a poacher, and thereby insured the stabilil.v 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 militar.v 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 blocks 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 damp, be shaped with tools as wood is shaped, and in the preparation of the guncotton charges foi- 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. The stability of guncotton or its permanency during storage is tested by exposing it to an agreed temperature and noting its behavior. This is preferably done by the method devised by Abel, in which the gimcotton is placed in a test tube which is partly immersed in the water contained in a w^ater bath, the mouth of the test tube being closed by a cork stopper from which a piece of partly moistened test paper is suspended by means of a platinum wire. When the guncotton begins to decompose, it gives ofT nitrogen oxides, which are absorbed by the moisture on the test paper and re- act with the reagents with which the paper is cov- ered to produce a color, and as only the lower half of the paper is moistened, the color first appears as a brown line at the point of demarcation be- tween the wet and dry parts of the paper. In making the test the water in the bath is heated up to the agreed-upon temperature, and main- tained at that temperature by means of a tem- perature-regulator. The test tube, filled and fitted as above described, is plunged into the water bath to the prescribed depth and a stop-watch started. A piece of paper upon which a line of the agreed depth of color has been drawn (known as the standard-tint paper) is placed beside the test