ACIDIFIABLE COMBUSTIBLES. 



jar D, fitted at its top E with a stop cock. 

 The capacity of the retort was 36 cubic inches. 

 This apparatus was attached to a mercurial 

 trough, so that the jar D could be placed 

 over the upright tube JB, C. The stop-cock F 

 being shut, I opened the stop-cock E, and with 

 my mouth sucked the air out of the jar till 

 only 5 cubic inches remained in it, over a co- 

 lumn of 8 inches of mercury; the stop-cock E 

 was then shut. I next took out the stopper G, 

 the stop-cock F remaining shut, and poured into 

 the retort a cubic inch of strong nitric acid. 

 100 grains of calcareous spar, in three or four 

 pieces were then dropped into the retort, and 

 the stopper being at the same instant put into 

 its place, the stop-cock F was opened. The 

 whole calcareous spar was speedily dissolved, 

 and the carbonic acid gas made its way into the 

 cylinder D. \Vhen the experiment was over, I 

 noted the volume of gas in the cylinder, the 

 height of the column of mercury below it (ge- 

 nerally about 1 inch), and the height of the ba- 

 rometer and thermometer at the time. Knowing 

 exactly the volume of air in the apparatus before 

 the experiment began, it was easy, by subtract- 

 ing it from the total quantity of air in the appa- 

 ratus after the experiment, to deduce the volume 

 of carbonic acid gas evolved. All the necessary 

 reductions being made, the volume of carbonic 

 acid gas evolved from 100 grains of calcareous 



Gl 



