Blasting of Rocks—Danger and Remedies. 139 
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 the gases, it is immediately wedged by the 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. A 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 aeid, 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 
when 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 well 
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 
