THE APPLICATIONS OF EXPLOSIVES. 453 



Among experiments made to demonstrate the resistance of 

 structures to attack by a mob was one npon a safe twenty-nine 

 inches cube, with walls four inches and three quarters thick, made 

 up of plates of iron and steel, which were re-enforced on each edge 

 so as to make it highly resisting, yet when a hollow charge of dyna- 

 mite nine pounds and a half in weight and untamped waS detonated 

 on it a hole three inches in diameter was blown clear through the 

 wall, though a solid cartridge of the same weight and of the same 

 material produced no material effect. The hollow cartridge was 

 made by tying the sticks of dynamite around a tin can, the open 

 mouth of the latter being placed downward, and I was led to con- 

 struct such hollow cartridge for use where a penetrating effect is 

 desired by the following observations: 



In molding the gun cotton at the torpedo station, as stated 

 above, a vertical hole was formed in each cylinder or block in which 

 to insert the detonator, and in 

 the final press a steel die was 

 laid uj)on the cake so that an 

 inscription in letters and figures 

 was forced upon it. This in- 

 scription was indented in the 

 cylinders and was raised upon 

 the surfaces of the blocks. 

 When the gun cotton was fired 

 untamped, in testing it, the cyl- a 



inder or block was usually -^ 



placed with the inscribed face 

 resting on a polished iron plate k'«' 



/•?»■ 



or iron disk, and after firing, if Holes produced m Iron Plates by bored 



the gun cotton had detonated it 



was invariably found that not only was a vortexlike cavity produced 

 below the detonator, but that the inscription on the gun cotton 

 was reproduced on the iron plate, and, what was most singular, 

 when the inscription was indented in the gun cotton it was indented 

 in the iron plate, and when the inscription was raised on the sur- 

 face of the gun cotton it was reproduced raised on the surface of 

 the iron plate. In experimentally investigating this phenomenon 

 I eventually soaked several cylinders in water, so that I could bore 

 them without danger, and then bored holes of various diameters 

 and depths in them, until in the last instance I bored a vertical 

 hole an inch and three quarters in diameter completely through 

 the cylinder. These wet cylinders were each placed on a similar 

 iron plate, a similar dry disk was placed on each as a primer, and 

 they were successively fired, when it was found that the deeper 



