.GUN-COTTON 761 



fuse is inserted in the dry disc, and its detonation determines that of all the remaining 

 discs, although the latter are absolutely immersed in, and in contact with, the water. 



In comparing the explosive action of equal weights of compressed gun-cotton and 

 of the ' nitrate ' mixture, it must be borne in mind that a considerable percentage of 

 the total mass of the latter is formed of a material of about one-sixth the cost of pure 

 gun-cotton. Thus a ' nitrate ' mixture, prepared with the full theoretical proportion 

 (about 38 per cent, by weight) of the oxidising agent, will not quite equal the effects 

 obtained from the same total weight of ordinary compressed gun-cotton. In other 

 words, the force of the explosion of, say, 100 Ibs. of a material which consists of 38 

 Ibs. of nitre and 62 Ibs. of gun-cotton will not equal that of 100 Ibs. of pure gun-cotton. 

 Here the loss of force due to the replacement of about one-third of the gun-cotton by 

 the salt used is not fully compensated for by the extra work obtained from the com- 

 plete oxidation of the remaining two-thirds of gun-cotton. If, however, about three- 

 fourths of the theoretical amount of the salt be employed, the mixture will, weight for 

 weight, equal ordinary compressed gun-cotton in explosive effect, although, as we have 

 said, a considerable proportion of the gun-cotton has, in the nitrated preparation, been 

 replaced by a comparatively inexpensive substance. Thus the use of nitrated gun- 

 cotton will be attended by material advantage in point of economy. 



But if equal volumes of highly-compressed gun-cotton, and of the ' nitrate ' or 

 * chlorate ' mixture, similarly compressed, are compared, the explosive force of the 

 latter will be found to be much greater. Chlorated gun-cotton is decidedly more 

 violent in its action than the nitrated mixture, but it is more costly to manufacture, 

 and more dangerous to store and use. The 'chlorate' salt is comparatively high in 

 price, and more of it is required to furnish the requisite amount of oxygen ; it is, 

 moreover, very susceptible of ignition by friction or percussion, and is, therefore, com- 

 paratively dangerous. For these reasons it does not compare favourably with the 

 ' nitrated ' preparations. Of the latter the best is that in which saltpetre is used. It 

 is the most readily prepared, and its tendency to absorb moisture is not appreciably 

 greater than that of ordinary compressed gun-cotton. 



Important experiments have been instituted jointly by the Special Committee on 

 Gun-cotton, the Torpedo Committee, and the Royal Engineers Committee, on the com- 

 parative explosive properties of ordinary gun-cotton, both in the dry and wet states, 

 and of nitrated gun-cotton under similar conditions. 



Some of these experiments are made by exploding under water equal weights of the 

 several substances under identical circumstances, and registering the resulting pressure 

 or blow by a ' crusher ' gauge somewhat similar to the pressure gauge used by the 

 Committee on Explosives in determining the explosive force of gunpowder in the 

 chamber of a gun. 



Experiments have also been made to ascertain the rapidity of detonation ; in other 

 words, the rate at which a string or row of gun-cotton discs placed close to one another 

 will successively explode if detonated at one extremity. For this purpose the beautiful 

 chronoscope invented by Captain Andrew Noble, F.K.S., has been successfully em- 

 ployed. This instrument is designed to measure very minute portions of time, and by 

 arranging the primary conducting wires at equal intervals along a long row of gun- 

 cotton discs a register is obtained of the time occupied in successively breaking the 

 wires as the explosive wave flashes along the row. It has thus been ascertained that 

 the rapidity of the detonation of gun-cotton is about 20,000 feet per second. , 



The expansive velocity of the gases generated by the explosion of gunpowder has 

 been reckoned at about 7,000 feet per second, so that, according to this estimate, gun- 

 cotton has about three times the explosive rapidity of gunpowder. It is probable that 

 the destructive force of an explosive substance bears a close analogy to the rapidity 

 with which the explosion is transmitted, and the experiments we allude to may furnish 

 most interesting and valuable results. But, whatever may be the method followed in 

 experiments, the considerable advantage which the nitrated gun-cotton possesses, both 

 in point of cost and power, added to the fact that it is so readily susceptible of igni- 

 tion by detonation, renders it highly probable that this preparation of gun-cotton will be 

 largely substituted for the ordinary compressed material in many of its applications. 



Moreover, the circumstance that carbonic oxide, a poisonous gas which is produced 

 in considerable amount upon the explosion of ordinary gun-cotton, is present in the 

 products of explosion of nitrated gun-cotton in scarcely higher proportion than in those 

 of gunpowder, appears likely to remove that objection to the employment of gun^ 

 cotton in military mines, which arose from the large quantity of carbonic oxide deve- 

 loped when heavy charges of gun-cotton were exploded. 



Abel has made a series of ingenious experiments on the combustion of gun-cotton. 

 He finds that when quantities of gun-cotton, varying from one to two grains, in the 

 form of a loose twist laid double, are ignited by means of a platinum wire in highly 

 rarefied atmospheres, they burn very slowly, presenting by daylight an appearance as 



