138 Blasting of Rocks — Danger and Remedies. 



2. Our object, then, is to repress the force to such a degree as to 

 accomplish our purpose ; which, in fire arms, is to give velocity to a 

 ball; but, in the case before us, it is to rend asunder the surround- 

 ing matter. In the old method of blasting rocks, this was most ef- 

 fectually accomplished, by ramming down pounded brick upon the 

 wadding. This closed the hole so thoroughly, that commonly, the 

 brick would remain undisturbed by the explosion, which of course, 

 spent itself upon the rock, and tore it asunder. 



In blasting logs, also, the same object was attained, by driving a 

 wooden pin into the hole above the wadding ; and here again the 

 pin often remained in its place, after die explosion which burst the 

 log. 



3. But, in Masting rocks, painful experience has shown, that great 

 danger of premature explosion is encountered, whenever firm suh- 

 stances are made use of to close the canal above the poivder ; and 

 multitudes have been killed outright, or dreadfully mutilated by these 

 casualities. 



4. The ingenious remedy, first proposed by the French, and em- 

 ployed, if I mistake not, by the Engineers of JYapoleon in construct- 

 ing his famous roads through the Alps, removed the danger of explo- 

 sion, but was not in every case effectual. — Mr. Blake has, however, 

 given us the rule, by which the desired effect may be rendered cer- 

 tain, and there can be no hesitation in applying it, as is indicated by 

 him, when the hole is bored to a certain depth. But, as the suc- 

 cess is not universal, and the reason and remedy were unknown to 

 the workmen, this method seems not to have been generally adopted 

 in this country. 



5. The method of Mr. Blake combines all the advantages of the 

 French mode, with another hnportant one, ivhich is peculiar to his 

 contrivance. — It is equally safe with the French method, (both are 

 perfectly safe,) and Mr. Blake's supplies the only deficiency in the 

 French mode. The latter was efi:ectual, evidently, because the re- 

 sistance afforded by the column of sand, when of a certain depth, 

 was sufficient to produce the necessary reaction upon the rock ; per- 

 haps the movement which would be given to the sand, by the first 

 expansive lift, when the powder was kindled, would even facilitate its 

 thorough and sudden inflammation, by giving room to the flame to 

 dart at once, into, and among the grains ; while the pressure would 

 force the flame to pervade, instantaneously, the whole magazine. 



