MECHANICS AND USEFUL ARTS. 101 



"My next experiment was in the 'heading,' for a period of 

 3 days. The average speed per month with powder had been 

 64 feet, blasting every 2 hours holes 20 to 30 inches deep. When 

 I commenced my experiment, the rock was excessively hard, and 

 the trial was very severe against me. I blasted 15 holes every 8 

 hours ; holes 30 to 36 inches deep. Within the 3 days I made 

 14^ feet. The next 3 days the rock happened to be better for 

 blasting, and powder was used, making 6 4-10 feet. Number of 

 nitroglycerine holes 132, and about 4,356 inches for the 14^ feet. 

 Number of powder holes 180, and about 4,500 inches drillino- 

 making 6 4-10 feet. '^ 



" In the same class of rock, I am of opinion that 'I can make at 

 least 35 feet per week in the heading, and in a month of 27 daj^s 

 about 158 feet; making 94 feet per month more than can be ac- 

 complished with gunpowder. 



" From these figures, the Hoosac Tunnel can be finished in less 

 than half the time and for less than half the expense by using ni- 

 troglycerine. From 8 to 10 years has been the estimated time for 

 completing the work, and the expense several millions of dollars. 

 From these economic considerations, the very able chief engineer 

 of that great enterprise is encouraged to belief in the early com- 

 pletion of the work by his adopting nitroglycerine." 



Though this substance possesses very important advantages 

 over gunpowder, as a blasting and destructive agent, the attempts 

 to introduce it as a substitute have been attended by most disas- 

 trous results, ascribable, in part, to some of its pi'operties, and 

 too evident instability of the commercial product, but principally 

 to the thoughtlessness of those interested in its application, who 

 apjjear to have been induced, either by undue confidence in its 

 permanence and comparative safety, or from less excusable mo- 

 tives, to leave the masters of shijjs, or others who had to deal 

 with the transport of the material, in ignorance of its dangerous 

 character. 



The precise cause of the fearful explosions of nitroglycerine 

 at Aspinwall and San Francisco will probaiily never be ascer- 

 tained ; but they are likely to have been due, at any rate, indi- 

 rectly, to the spontaneous decomposition of the substance, induced 

 or accelerated by the elevated temperature of the atmosphere in 

 those parts of the ship where it was stored. Instances are on 

 record in which the violent rujiture of closed vessels containing 

 commercial nitroglj'cerine has been occasioned by the accumula- 

 tion of gases generated by its gradual decomposition ; and it is 

 not improbable that a similar result, fiivored by the warmth of 

 the atmosphere, and eventually determined by some accidental 

 agitation of the contents of the package, was the cause of those 

 lamentable accidents. The great difficulties attending the purifi-: 

 cation of nitroglycerine upon a practical scale, and the uncer- 

 tainty, as regards stal^ility, of the material, even when purified 

 (leaving out of consideration its very poisonous character, and 

 its extreme sensitiveness to explosion by percussion, when in the 

 sofid form), appear to present insurmountable obstacles to its safe 

 9* 



