536 Dr. R. Hare on the Ewplosiveness of Nitre. 



tion of the former, we may advert to aurum or argentum ful- 

 minans, or to the fulminates of mercury or silver; also to the 

 chloride or iodide of nitrogen, or perchloric aether. Com- 

 pounds of the last-mentioned kind, without confinement, break 

 the vessel on which they are exploded. They cannot be used 

 in gunnery, because the force in their immediate vicinity, in 

 proportion to its durability, is too great, so that they burst 

 the chamber before the ball moves an available distance. 

 The elements in these combinations are in a state of intense 

 chemical union, and can only leave that state for another, by 

 which gases and vapours are produced with an instantaneous 

 and almost irresistible expansibility. They require no con- 

 finement, because already confined by their reciprocal affini- 

 ties. In gunpowder and analogous mixtures, the ingredients 

 exist without any forcible coherence, so that an incipient re- 

 action causes a tendency to move apart, which prevents the 

 reaction from extending itself when there is no confinement. 

 This was strikingly shown by attempting to burn in vacuo a 

 small cylinder of consolidated gunpowder, made by intense 

 pressure within a metallic tube by a steel piston. This cylin- 

 der, about a half-inch in diameter and an inch in length, was 

 placed in contact with a platinum wire within an exhausted 

 receiver. The wire being ignited, a feeble combustion en- 

 sued. Subsequent examination showed that the cylinder was 

 only about half deflagrated, the unburnt portion remaining 

 unchanged. It had been extinguished spontaneously, after 

 being completely ignited at the end in contact with the incan- 

 descent wire. 



21. This was, no doubt, in consequence of the process 

 being effected in a rarefied medium. In order to compare 

 these observations with those which might be made by com- 

 bustion in pleno, I made a larger cylinder of gunpowder, 2 

 inches in diameter and 2 inches in height, by similar means, 

 and set fire to it by an iron rod ignited at one end. This I 

 caused to touch the top of the cylinder while standing upright 

 at the bottom of a cast-iron pot about 4 inches in diameter, 

 and a foot in depth. The combustion very much resembled 

 that of a rocket, commencing feebly, however, yet terminating 

 with a deflagration so rapid as to be almost explosive. The 

 augmentation of intensity I ascribe to the increased resist- 

 ance from reaction with the gas evolved, which pressed upon 

 the cylinder with a force like that which elevates a rocket. 



22. Finding that, in vacuo, a perfect combustion could not 

 be accomplished by the means above mentioned, I resorted 

 to an arrangement through which a cylinder of consoli- 

 dated gunpowder might be so supported by a rod sliding in 



