51 



fuze its contents explode, and the explosion of the cotton 

 follows with great violence. Gun cotton may be detonated 

 whilst wet or even whilst frozen, provided a small mass of 

 dry cotton be placed in contact with the detonator, this 

 mass being known as the primer. 



The force of explosion so " detonated " is estimated at 

 six times that of powder, the explosive force when fired in 

 the ordinary way being only three times that of powder. 



The second and remaining " Explosive compound " of 

 practical importance is nitro-glycerine discovered in 1847, 

 by Sombrero, an Italian. 



To prepare it, ordinary glycerine is treated, certain pre- 

 cautions being carefully observed, with a mixture of strong 

 nitric and sulphuric acids. An oil is formed which is nitro- 

 glycerine, and on pouring the acid mixture into a large 

 volume of cold water, the oil falls to the bottom of the vessel, 

 and may be collected. As with gun cotton the greatest 

 care is taken to free the product from the last traces of 

 nitric acid, as the impure nitro - glycerine is liable to 

 spontaneous decomposition and subsequent explosion. 



Nitro-glycerine is exceedingly poisonous, a small quan- 

 tity swallowed by accident proving fatal in a few hours. 



The slightest blow will explode it, as I show by 

 pouring a single drop on an anvil and dropping a hammer 

 lightly on it, when a deafening report ensues. 



When first employed in blasting, a hole was drilled in 

 the rock, nitro-glycerine poured in and the hole filled up 

 with water, and the nitro-glycerine exploded by a detonating 

 fuze. Its explosive effect in blasting is given as equal to 

 that of ten -times its weight of powder. For convenience 

 of handling and transport it is converted into dynamite 

 which consists of nitro-glycerine absorbed by a porous earth 

 free from grit. Enough nitro-glycerine is added to the 

 earth to form a stiff dough, and it is then made up into 

 cartridges by enclosing it in parchment paper cases. It 

 may be fired by detonation in the ordinary way. I have 

 now, in conclusion, to mention that Fulminate of Mercury 



