MECHANICS AND USEFUL ARTS. 117 



tie too straig-lit, they were in this respect not so convenient as the 

 field-rifle ; but one soon gets accustomed to this. These little 

 drawbacks are far more than outweighed by the many good 

 qualities of the Peabody. The ammunition, of Swiss manuiacture, 

 was excellent ; not one shot of 300 missed lire, so that in this 

 respect also we can be perfectl}^ satisfied, and Switzerland may 

 congratulate herself upon her possession of her 15,000 American- 

 made Peabody guns." 



NITRO-GLTCERINE. 



From a paper read a short time ago by Edward P. North, C. E., 

 before the American Society of Civil Engineers, of New York 

 city, we make the following extracts on the properties and uses 

 of nitro-glycerine : — 



•' The efiect of nitro-glycerine differs from that of powder in 

 consequence, I suppose, of its greater force and quickness of explo- 

 sion, in that, that powder, when fired, when the line of least re- 

 sistance is a vertical one (the bore also being vertical, and the rock 

 homogeneous), will form a tolerably uniform crater, with the sides 

 sloping according to the hardness of the rock. When the line of 

 least resistance is a horizontal one, and not too long, the rock be- 

 ing solid, the blast will throw out what is before it, leaving the 

 back uncracked, and no sign of action below the bottom of the 

 hole. 



*' Nitro-glycerine, on the contrary, in the first case, will form a 

 well, and, if the rock is not too hard, the bottom diameter will be 

 greater than the top. Nor, as far as I have seen, will the action 

 ever be concentrated on the line of least resistance, but will ex- 

 tend back from the hole and downward to a greater or less dis- 

 tance, according to the hardness of the rock. I think that this 

 action of nitro-glycerine, in connection with the fact that its explo- 

 sive force is uninfluenced by the presence of water, will tend to its 

 being the only explosive agent used in all subaqueous operations ; 

 for, with any depth of water, it will be unnecessary to drill holes, 

 but only to sink a flask of nitro-glycerine on the rock and fire it." 



Its advantages are : — 



" 1st. That, being of greater strength, there is a great saving in 

 drillers' wages, as fewer holes have to be made, and the charge 

 of nitro-glycerine can be put into the rock much more compactly. 

 For instance, if, to break up a certain rock, 1 foot of depth in the 

 bore-hole was required with nitro-glycerine, 13 feet would be re- 

 quired with powder, which would necessitate 6 feet of additional 

 drilling if but 1 hole was used ; but 13 feet of powder could not 

 be exploded in a 2-inch or 2^-inch hole so that it would be effect- 

 ive, on account of the slowness with which it burns, so that addi- 

 tional holes would have to be drilled, with in each an allowance 

 of at least two-thirds of the depth for tamping. With gun-cotton 

 there would not be so much difference, 



" 2d, That nitro-glycerine is not injured, either permanently or 

 temporarily, by water or moisture, which enables us to use water 



