322 GUM TREE GUN COTTON GUM TREE. See BLACK GITM. GUJf. See CANNON, MTJBKET, and RIFLE. GFN COTTON, an explosive substance obtained by subjecting common cotton to the action of strong nitric acid, first brought to public no- tice in 1846 by Prof. Schonbein of Basel, Switz- erland. Several products are known under this name, possessing distinct properties, though differing slightly in constitution. Cotton fibre is nearly pure cellulose, Ci 8 H 3 oOi 6 , and by the action of the acid a number of equivalents of nitric oxide, N 2 O 4 , or NO 2 , are substituted for an equal number of hydrogen. The number of equivalents substituted varies from 6 to 9, according to the strength of the acid. Thus, the substitution of 9 equivalents would give C, 8 H a ,(NO 2 ) 9 Oi6, or more simply, C 6 H7(N0 2 ) 3 4 . Water is also generated in the reaction, by the union of hydrogen with the oxygen set free hi reducing nitric acid to oxide. In preparing the gun cotton, two or three parts of strong sulphuric acid are mixed with one part of nitric acid, to absorb this water and thus prevent further hydration of the nitric acid. The following formulas show the consti- tution of the products obtained by using two or three parts of sulphuric and one of nitric acid, while the quantity of water is varied : 1. With monohydrated acids : C 18 H 3 oOi6 + 9(HN- O3)=C 18 H ai (N0 3 ) fl 1 5 + 9H 3 O. 2. With 3 to 4 parts water: C 18 H 3 oO,6-i-8(HN03)=Ci 8 H 22 (N0 2 ) 8 16 + 8H 2 0. 3. With 4 to 5 parts water : C 18 H 9 o0 16 + 7(HN03)=C 18 H 23 (NO a ) 7 1B 7H 2 0. 4. With 5 to 6 parts water: Ci 8 H 3 oO 16 + 6(H NO)=C 18 H 24 (N0 2 ) a Oi 6 + 6H 3 O. The first va- riety is the well known detonating gun cotton. It is insoluble in common ether and alcohol, and is not attacked by acetic acid, but is solu- ble in acetic ether. The second is a less explo- sive variety, soluble in common ether with one eighth of alcohol added, but insoluble in acetic acid. The third is inflammable, but not ordi- narily explosive, and is soluble both in ether and in glacial acetic acid. This variety is used for collodion. The fourth is always dissolved in the acid, from which hitherto it has not been isolated. In the manufacture of gun cotton the substitutions are never exactly in accord- ance with the foregoing formulas, but most probably different degrees of substitution take place in the different molecules of the same mass of cotton ; and a careful analysis shows invariably an intermediate constitution, though in many cases one of the typical constitutions is very closely approached. Gun cotton is not readily distinguishable in appearance from the unaltered cotton ; but it is slightly harsher to the touch and the compression of the fingers. When moistened with a solution of iodine in potassium iodide, and touched with a drop of dilute sulphuric acid, it turns yellow, while unchanged cotton under the same test turns blue. The variety here to be considered is the detonating product, C n 7 (NO a )sO 6 . To pre- pare it the strongest commercial acids are re- quired, the nitric acid having a density of near 1-50, and the sulphuric a density of 1-847. An immersion of the cotton for a few seconds yields an explosive material ; but to insure the highest degree of explosiveness the immersion should be prolonged. Baron Lenk protracted it to 48 hours. On withdrawing it from the bath, as much acid as possible is squeezed out between porcelain plates, and the cotton is repeatedly and thoroughly washed in water. The fibres are capillary, and during the immersion the tubes absorb acid, which it is difficult to re- move entirely. As the so-called spontaneous ignition of gun cotton has been frequently at- tributed to the retention of acid, the original method of washing the unbroken fibre in water has been abandoned, and a new mode of treat- ment, devised by Mr. F. A. Abel, has been extensively applied in England. The fibre is first subjected to two or three rinsings in a large volume of water, and is freed from water as far as possible after each rinsing, by a cen- trifugal drying machine. It is then reduced to pulp by an engine similar to that used in reducing paper pulp. The access of water to the capillary tubes is thus greatly facilitated, and to insure the most searching purification, the pulp is transferred to a " poaching ma- chine," where it is beaten about, and kept sus- pended in a large volume of warm water, con- tinuously renewed, and rendered slightly alka- line at the close of the operation. This opera- tion lasts about 48 hours, and the quantity treated is half a ton. In this way a thorough intermixture of the products of many dippings is obtained, and the average constitution is ren- dered uniform. The pulp is then compacted into the desired forms by a preliminary mould- ing and a subsequent pressing by hydraulic power, ranging from four to six tons per square inch. On leaving the press the slab contains about 20 per cent, of water, in which condi- tion it may be safely cut with circular or band saws, and even hot iron may be used without danger to burn holes in it. When wet it may be kept for an indefinite period without change, and, whether wet or dry, it is affected by very few reagents. Its stability is supe- rior to that of gunpowder in every respect save the all-important one of immunity from inexplicable explosion. Repeated accidents have destroyed the confidence of all but the most sanguine in its safety. It was for a time supposed that the ingenious process of Mr. Abel had removed the causes of distrust ; but a terrible and unexplained explosion at Stow- market in 1871 revived the feeling, which still prevails. How far the repeated disasters at- tending the use and storage of gun cotton are due to the carelessness of those who have it in charge, is unknown, for it leaves no witnesses to testify to the origin of the explosions, and the very mystery which surrounds them, and our frequent inability even to conjecture a probable cause, are sufficient reasons for re- garding it as a treacherous servant. If massive gun cotton be ignited by a coal or flame of low
