EXPLOSIVENESS OF NITRE. 15 



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, connection being made between 

 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 disk of sheet copper, and 

 a little below that disk was supported, in like manner, a larger disk of the same 

 material perforated like a colander. 



26. Upon the upper disk, 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 The air was withdrawn until the mercury in the gauge tube attained nearly 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 vs'ithin an adjoining Torricellian tube, or that of a neigh- 

 boring 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 statu quo. The difference in degrees caused in the height of 

 the barometric column, divided by two, gave the number of cubic inches of gase- 

 ous matter evolved. This difference was of course set down. 



28. In the next place, the temperature being carefully observed and recorded, 

 about two cubic inches of a strong solution of caustic potash was added. The 

 consequent absorption, as it declined in rapidity, was assisted by an agitation con- 

 sequent to moving up and down the rod, and the perforated disk attached to it. 

 When no more absorption could be observed to take place, judging by the quies- 

 cence of the mercurial column in the gauge, and when the temperature had 

 returned to the starting point, from which it had been disturbed by the heat gener- 

 ated through the reaction between the alkali and carbonic acid, the height of the 

 column was again recorded, and the difference of degrees, divided by two, were 

 estimated to give the number of cubic inches of carbonic acid generated. Allow- 

 ance was made for the mechanical effect of the bulk of the alkaline liquid in 

 lowering the mercurial column founded on actual measurement of the effect of a 

 like quantity of water ; the mercury being brought to the same height in the gauge 

 tube, in an experiment made for the purpose with atmospheric air. 



29. Three samples of Dupont's powder were obtained from the United States 

 Arsenal, severally designated cannon, musket, and rifle powder. Of each, 75 

 grains were pressed into an indurated cylindrical mass, as above described, and 

 successively burned in the exhausted receiver. 



The following are the results : — 



Cannon powder, gas evolved, .... 55 cubic inches. 



" " absorbed, 23J " 



Musket powder, " evolved, .... 52 " 



" " absorbed, , . . . . 21^ " 



