]4 MEMOIR ON 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 vapors are produced with an instantaneous and almost irresistible 

 expansibility. They require no confinement, because already confined by their 

 reciprocal aflinities. In gunpowder and analogous mixtures, the ingredients exist 

 without any forcible coherence, so that an incipient reaction 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 metaUic 

 tube by a steel piston. This cylinder, 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 ensued. Subsequent examination 

 showed that the cylinder was only about half deflagrated, the unburnt portion 

 remaining unchanged. It had been extinguished spontaneously, after being com- 

 pletely ignited at the end in contact with the incandescent wire. 



21. This was, no doubt, in consequence of the process being eflfected in a rare- 

 fied medium. In order to compare these observations with those which might be 

 made by combustion in pleno, I made a larger cylinder of gunpowder, two inches 

 in diameter and two 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 four inches in diameter, 

 and a foot in depth. The combustion very much resembled that of a rocket, com- 

 mencing feebly, however, yet terminating with a deflagration so rapid as to be 

 almost explosive. The augmentation of intensity, I ascribe to the increased 

 resistance 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 cyhn- 

 der of consolidated gunpowder might be so supported by a rod sliding in a stuffing 

 box as to be pushed upwards against a wire ignited by a galvanic battery within/ 

 an exhausted receiver. When, by these means, the ignition of gunpowder was 

 attempted, it was not very readily accomplished. The part touching the wir^ 

 appeared to burn feebly ; nevertheless, by turning the rod so as to cause the cylin-4 

 der to revolve, and consequently to be assailed at various points, combustion was\ 

 induced and gradually extended, and at last completed satisfactorily. 



23. The receiver employed was held between two metallic plates, one forming 

 the bottom, the other the cap. Through the middle of the bottom the sliding rod 

 was introduced, so as to be in the axis of the cavity. It was secured by two 

 stuffing boxes, the object of the outer one being to enable the rod to pass through 

 the orifice of a vessel of oil, employed to prevent the possibility of air entering 

 through that next the cavity. The juncture of the cap with the receiver was 

 covered by cold water, which served to prevent leakage, and keep down the tem- 

 perature. This was ascertained by a thermometer within the receiver, yet acces- 

 sible to inspection. The cavity, thus secured against leakage, held 240 cubic 

 inches ; the contents being indicated by a column of mercury in a barometer tube 



