Blasting of Rocks — Danger and Remedies. 1 39 



In Mr. Blake's mode, this advantage is equally attained, and when 

 the wooden stopper begins to rise, in consequence of the expansive 

 effort of die gases, it is immediately wedged by tlie sand, which is 

 crowded between it and the walls of the cavity ; more sand presses 

 down from above, and thus a firm resistance is created, by the very 

 effort which the explosion makes to overcome it. It is a peculiar spe- 

 cies of valve, which operates at the moment when it is wanted, and 

 not before. It appears to me to combine in a sufficient degree, all the 

 advantages of the early, effectual, but dangerous mode of ramming in 

 brick fragments ; of the other more recent use of gypsum, and other 

 soft substances, and of the filling with sand. Should the experience 

 of the quarrymen confirm the certainty of the method, its safety being 

 perfect, this new mode of blasting will prove to that dangerous branch 

 of the arts, what the safety lamp has already proved to the coal 

 miners. 



Should any practical difficulties occur, such as are frequent in 

 new undertakings, however promising ; it is to be hoped that the at- 

 tempt will not be precipitately abandoned, as it is highly probable that 

 the united efforts of science and mechanical skill will overcome them. 



6. Jl few remarks on the theory of these accidental explosions, 

 and I shall have done. To any one acquainted with chemistry, it 

 will not appear very extraordinary, if we reason from the nature of 

 the elements concerned, that there should be cases in which gun- 

 powder explodes without a red heat. 



Gunpowder consists of highly inflammable bodies, charcoal and 

 sulphur, most intimately blended with three times their weight of 

 nitre. Nitre contains more than half its weight of nitric acid, and 

 nearly four fifths of this is oxygen. Oxygen is the great agent in 

 combustion, and it is rather wonderful than otherwise, that it should 

 lie in close union with dry inflammables, without acting upon them ; 

 it is the tiger, reposing peacefully with his prey, and attacking it only 

 w^hen he is roused : the proper stimulus to bring on the action in 

 gunpowder, is a red heat, but it is clearly possible, that much smaller 

 degrees of heat may answer the same purpose, and such degrees are 

 often rendered sensible, by mechanical action. Chemistry abounds 

 with similar cases. If, as has been repeatedly done, chlorate of pot- 

 ash be substituted for nitre, in the composition of gunpowder, no w^ell 

 informed man would dare to ram down a cartridge made of it, much 

 less to charge a rock with it in the ordinary way ; it would inevitably 

 explode, by a very gentle pressure : as was fatally experienced at 



