EXPLOSIONS AND EXPLOSIVES. 779 



where the proper care has been given to all the details of the manu- 

 facture. 



There are other methods of manufacture, differing, however, only 

 in the details, the principle of course being the same. 



When pure, nitro-glycerine is not very sensitive to friction, or even 

 to moderate percussion : if a small quantity be placed on an anvil and 

 struck with a hammer, that portion which is touched explodes sharply, 

 but so quickly as to drive away the other particles ; if, however, it were 

 even slightly confined, so that none could escape, it would all explode 

 or detonate. It must be fired by a fuse containing fulminate of mer- 

 cury (the compound used in percussion-caps), not being either readily 

 or certainly fired by gunpowder, the shock of the latter not being 

 sufficiently quick or sharp to detonate the nitro-glycerine. It is highly 

 probable that in this case, as in that of other high explosives, the 

 vibrations set up by the fulminate (which is not stronger than gun- 

 powder) are of just such a character as to find an answering chord, so 

 to speak, in the explosive, so that the desired effect is produced. This 

 would seem to be a correct theory, for it is not always the most pow- 

 erful explosive which most readily causes the explosion of another 

 body. For instance, although nitro-glycerine is much more powerful 

 than fulminate of mercury, yet seventy grains of it will not explode 

 gun-cotton, while fifteen grains of the weaker fulminate will readily 

 do so. The fuse generally used, then, for firing nitro-glycerine, is 

 composed of from fifteen to twenty-five grains of fulminate, and this 

 quantity is sufficient to detonate a large mass as well as a small one. 



If flame be applied to nitro-glycerine it will not explode, but burn 

 with comparative sluggishness. When frozen it is very difficult and 

 uncertain of firing. If the material be perfectly pure, it forms, upon 

 detonation, a volume of gases nearly thirteen hundred times as great 

 as that of the original liquid ; these gases are also further expanded, 

 by the heat developed, to a theoretical (though not practical) volume 

 ten thousand times as great as that of the charge. Practically speak- 

 ing, the forces exerted by gunpowder and nitro-glycerine are in the 

 proportion of one to eight. 



The great objection to nitro-glycerine, in its liquid state, is the dif- 

 ficulty of its transportation ; it is liable to leak from the packages in 

 which it is contained, and there have been several occasions on which 

 disastrous accidents have taken place owing to this circumstance. 

 The explosion of a large case on board of a steamer in Aspinwall some 

 twelve or fourteen years ago, and, about the same time, of a box in an 

 express-office in New York, caused great precautions to be taken with 

 regard to it, and also very great fear of it on the part of all transpor- 

 tation companies. Fortunately, it has been found that it can be car- 

 ried from place to place by mixing it with some absorbent substance, 

 which takes up a large quantity of it ; it is just as powerful in this 

 state, the presence of the absorbent having no deleterious effect. This 



