go Professor Abel [March 21, 



results appear to establish great superiority, iu point of violence of 

 action, or destructive effect, of the more rigid explosive agents (the 

 gun-cotton preparations). Thus, employing iron plates 1 inch 

 thick (supported upon an anvil with a central cavity), and 4 oz. 

 of each material unconfined, the charges being all about the same 

 diameter, exploded by detonators of equal strength, and simply resting 

 upon the upper surface of the plate, compressed gun-cotton produced 

 a considerable indentation of the upper surface of the plate, and long 

 cracks in the lower surface ; a species of nitrated gun-cotton, called 

 tonite, produced a much shallower indentation, though still a very 

 marked one, but did not crack the lower surface. Dynamite produced 

 only a very slight impression upon the plate, and none could be 

 detected by the eye on the plate upon which the blasting gelatine 

 was exploded. The difficulties, brought out by past experience, 

 which attend the contrivance of really comparative tests of the explo- 

 sive power of such substances as those under discussion, is well exem- 

 plified by the foregoing results, which were influenced to the maximum 

 extent by the physical characters of the several substances when applied, 

 as they were upon these iron plates, in a perfectly unconfined con- 

 dition, so that the particles were free to yield to the force of the 

 initiative detonation in proportion to their mobility. But, for this 

 very reason, these experiments afford excellent illustration of the 

 extent to which the development of detonation and the sharpness of 

 its transmission through the mass is influenced not only by the 

 inherent sensitiveness of the substance to detonation (or by its 

 chemical instability) but also by the degree of proneness of their 

 particles to yield mechanically to the force of a blow as applied by 

 an initiative detonation. Thus, although in comparing two substances 

 of similar physical characters, compressed gun-cotton and compressed 

 nitrated gun-cotton or tonite, the superiority of the pure compound 

 over the mixture, in point of sharpness and violence of action, is well 

 illustrated, a comparison of the result furnished by the weakest of the 

 four explosive agents tried, viz. tonite, with that of the substance 

 which should be superior to all the others in explosive force (i. e. the 

 blasting gelatine) demonstrates the important influence which the com- 

 paratively great rigidity of the mass in the one case exerts in favouring 

 the completeness and sharpness of its detonation in open air, and the 

 great disadvantage under which the other explosive is applied, arising 

 out of the plastic and therefore readily yielding nature of the material. 

 But if, by exposure to a moderate degree of cold, this plastic nitro- 

 glycerine preparation is made to freeze (for it partakes of the property 

 of the liquid itself of freezing at a temperature above the freezing 

 point of water, and becomes thereby converted into at least as rigid 

 a substance as the two descriptions of gun-cotton) its detonation upon 

 an iron plate produces an indentation, as well as a destructive effect 

 upon the lower surface of the plate, very decidedly greater than those 

 furnished by the corresponding amount of pure compressed gun-cotton. 

 Similarly, the effect produced by the detonation of dynamite upon a 



