EXPLOSIONS AND EXPLOSIVES. 781 



use in mining and engineering operations ; among others, the Hoosac 

 Tunnel and the works at Hallett's Point in New York harbor un- 

 doubtedly owed much to the powers of nitro-glycerine in hastening 

 their completion. The effect of a confined charge upon rock is to pul- 

 verize the portion near the blast-hole, the action being so sudden, 

 quick, and intense ; it is, therefore, found better not to tamp the hole, 

 a saving both of time and labor, allowing the gases a greater surface 

 upon which to act. Ordinarily the dynamite is contained in paraffined 

 paper cartridges, and is fired with a fulminate-fuse. 



Gun-cotton is formed by the action of nitric acid on cotton a 

 portion of the hydrogen being displaced in the cotton, just as it is 

 in the glycerine by the active constitution of the nitric acid. The 

 essential features of the process are the same as those of the manu- 

 facture of nitro-glycerine ; that is to say, a mixture of strong nitric 

 and sulphuric acids is made, the cotton exposed to its action, and the 

 excess of acid removed from the cotton by careful washing ; the sul- 

 phuric acid plays the same part, namely, that of taking up the water 

 formed, and so keeping the nitric acid at its full strength. As in 

 the former case, only perfect purity will insure safety ; the presence 

 of acid in the gun-cotton will ultimately cause decomposition and 

 explosion. Many accidents have taken place since the introduction 

 of gun-cotton to public notice some thirty-five years ago ; but, as in 

 the case of nitro-glycerine, all of them may be ascribed to imper- 

 fect washing, reference being had, of course, to instances of what 

 may be called spontaneous combustion. With the improved methods 

 of to-day, however, and the exercise of ordinary care, gun-cotton can 

 be rendered perfectly stable and safe, far safer for transportation than 

 nitro-glycerine in any of its forms ; when wet it can not be readily 

 exploded, and hence it is generally carried in that state, and either 

 dried for use or else exploded by the use of a dry primer of the same 

 material. It possesses, however, the disadvantage of rapidly absorb- 

 ing moisture, and hence it is extremely difficult to keep primers dry 

 unless they are prepared with great care. In a military point of view 

 this is no great objection, but commercially speaking it is, for the ex- 

 pensive water-proof cases would perhaps make its use financially im- 

 practicable. 



The details of the usual process of its manufacture are as follows : 

 cotton-waste is picked and cleaned, then dried at a high temperature. 

 After cooling, in quantities of about a pound, it is immersed in the 

 str6ng acid mixture contained in a trough surrounded by cold water; 

 after a short exposure it is removed, and the acid pressed from it as far 

 as practicable. After another immersion of twenty-four hours, it is 

 placed in a centrifugal strainer, by the rapid revolutions of which 

 nearly all the acid is expelled; it is then washed in a large amount of 

 water, and again placed in the strainer. When the acid-water no 

 longer remains, the gun-cotton is placed in the pulper, an oblong tub 



