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Encyclopedia Britannica - Main :: GUI-HAN |
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GUNCOTTON , an explosive substance produced by the action of strong nitric acid on cellulose at the ordinary temperature; chemically it is a nitrate of cellulose, or a mixture of nitrates, according to some authorities. The first step in the history of guncotton was made by T. J. Pelouze in 1838, who observed that when paper or cotton
starch
cotton
The smallest empirical formula
Guncotton is made by immersing cleaned and dried cotton waste in a mixture of strong nitric and sulphuric acids. The The composition of the cellulose nitrates was reviewed by G. Lunge (Jour. Amer. Chem. Soc., 1901, 23, p. 527), who, assuming the formula
recent
ordinary air temperature (15 C.), un which time it is almost fully nitrated, the main portion, say 90%, having a composition represented by the formula2 C6H702(NO3)2, the remainder consisting of lower nitrated products, some oxidation products and traces of unchanged cellulose and cellulose sulphates. The acid is then slowly run out by an opening in the bottom of the pan in which the operation is conducted, and water distributed carefully over its surface displaces it in the interstices of the cotton, which is finally subjected to a course of boiling and washing with water. This washing is a most important part of the process. On its thoroughness depends the removal of small quantities of products other than the nitrates, for instance, some sulphates and products from impurities contained in the original
original
Immediately after the discovery of guncotton SchSnbein proposed its employment as a substitute for gunpowder, and General von Lenk carried out a lengthy and laborious series of experiments intending to adapt it especially for artillery use. All these and many subsequent attempts to utilize it, either loose or mechanically compressed in any way, signally failed. How-ever much compressed by mechanical means it is still a porous mass, and when it is confined as in a gun the flame and hot gases from the portion first ignited permeate the remainder, generally causing it actually to detonate, or to burn so rapidly that its action approaches detonation. The more closely it is confined the greater is the pressure set up by a small part of the charge burning, and the more completely will the explosion of the remainder assume the detonating form. The employment of guncotton as a propellant was possible only after the discovery that it could be gelatinized or made into a colloid by the action of so-called solvents, e.g. ethylacetate and other esters, acetone
When quite dry guncotton is easily detonated by a blow on an anvil or hard surface. If dry and warm it is much more sensitive,to percussion or friction, and also becomes electrified by friction under those conditions. The amount of contained moisture exerts a coniderable effect on its sensitiveness. With about 2 % of moisture it can still be detonated on an anvil, but the action is generally confined to the piece struck. As the quantity of contained water increases it becomes difficult or even impossible to detonate by an ordinary blow. Compressed dry guncotton is easily detonated by an initiative detonator such as mercuric fulminate. Guncotton containing more than 15% of water is uninffammable, may be compressed or worked without danger and is much more difficult to detonate by a fulminate 2 This formula is retained mainly on account of its simplicity. It also expresses all that is necessary in this connexion. detonator than when dry.' A small charge of dry guncotton will, however, detonate the wet material, and this peculiarity is made use of in the employment of guncotton for blasting purposes. A charge of compressed wet guncotton may be exploded, even under water, by the detonation of a small primer of the dry and water-proofed material, which in turn can be started by a small fulminate detonator. The explosive wave from the dry guncotton primer is in fact better responded to by the wet compressed material than the dry, and its detonation ig somewhat sharper than that of the dry. It is not necessary for the blocks of wet guncotton to be actually in contact if they be under water, and the peculiar explosive wave can also be conveyed a little distance by a piece of metal such as a railway rail. The more nearly the composition of guncotton approaches that represented by CGH702(NO3)3, the more stable is it as regards storing at ordinary temperatures, and the higher the igniting temperature. Carefully prepared guncotton after washing with alcohol-ether until nothing more dissolves may require to be heated to 180-185 C. before inflaming. Ordinary commercial gun-cottons, containing from 10 to 15% of lower nitrated products, will ignite as a rule some 20-25 lower. Assuming the above formula to represent guncotton, there is sufficient oxygen for internal combustion without any carbon being left. The gaseous mixture obtained by burning guncotton in a vacuum vessel contains steam, carbon monoxide, carbon dioxide, nitrogen, nitric oxide, and methane. When slowly heated in a vacuum vessel until ignition takes place, some nitrogen dioxide, NO2, is also produced. When kept for some weeks at a temperature of 100 in steam, a considerable number of fatty acids, some bases, and glucose-like substances result. Under different pressures the relative amounts of the combustion products vary considerably, Under very great pressures carbon monoxide, steam and nitrogen are the main products, but nitric oxide never quite disappears. Dilute mineral
A characteristic difference . between guncotton and collodion cotton is the insolubility of the former in ether or alcohol or a mixture of these liquids. The so-called collodion cottons are nitrated celluloses, but of a lower degree of nitration (as a rule) than guncotton. They are sometimes spoken of as " lower " or " soluble " cottons or nitrates. The solubility in ether-alcohol may be owing to a lower degree of nitration, or to the temperature conditions under which the process of manufacture has been carried on. If guncotton be correctly represented by the formula C6H702(NO3)3, it should contain a little more than 14% of nitrogen. Guncottons are examined for degree of nitration by the nitrometer, in which apparatus they are decomposed by sulphuric acid in contact with mercury, and all the nitrogen is evolved as nitric oxide, NO, which is measured and the weight of its contained nitrogen calculated. Ordinary guncottons seldom contain more than 13 % of nitrogen, and in most cases the amount does not exceed 12.5 %. Generally speaking, the lower the nitrogen content of a guncotton, as found by the nitrometer, the higher the percentage of matters soluble in a mixture of ether-alcohol. These soluble matters are usually considered as " lower " nitrates. Guncottons are usually tested by the Abel heat test for stability (see CORDITE). Another heat test, that of Will, consists in heating a weighed quantity of the guncotton in a stream of carbon dioxide to 13o' C., passing the evolved gases over some red-hot copper, and finally collecting them over a solution of potassium hydroxide which retains the carbon dioxide and allows the nitrogen, arising from the guncotton decomposition, to be measured. This is done at definite time intervals so that the rate of decomposition can be followed. The relative stability is then judged by the amount of nitrogen gas collected in a certain time. Several modifications of this and of the Abel heat test are also in use. (See EXPLOSIVES.) . (W. R. E. H.) End of Article: GUNCOTTON If you wish, you can link directly to this article.
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