Dr. R. Hare on the Explosiveness of Nitre. 537 



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 

 wire appeared to burn feebly; nevertheless, by turning the 

 rod so as to cause the cylinder 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 temperature. This was ascertained by a thermo- 

 meter within the receiver, yet accessible 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 situated before a scale graduated into 480 

 parts. Of course, the whole contents being 240 cubic inches, 

 as above stated, each graduation represented half a cubic 

 inch. 



24. The igniting wire was soldered to the ends of brass 

 rods, of which one was soldered to the cap, the other secured 

 by collets of leather, so as to pass through the cap without 

 metallic contact. Consequently, connexion being made be- 

 tween this insulated rod and one pole of a battery, while the 

 other pole had a metallic communication with the cap, the 

 wire might at any moment be made the medium of a circuit 

 competent for its intense ignition. 



25. The upper end of the sliding rod supported a little 

 disc of sheet copper, and a little below that disc was sup- 

 ported, in like manner, a larger disc of the same material 

 perforated like a colander. 



26. Upon the upper disc, the consolidated gunpowder being 

 supported with all the above-mentioned arrangements, the 

 receiver was replaced. 



27. The air was withdrawn until the mercury in the gauge- 

 tube attained nearly the height of the column within an ad- 

 joining Torricellian tube, or that of a neighbouring barometer. 

 The height was recorded, likewise the temperature indicated 

 by the thermometer. The fall of the barometrical column of 

 mercury in the gauge-tube, resulting from the operation, was 

 not estimated until the mercury in the thermometer was in 



