196 MR HAYCRAFT on the Specific Heat of the Gases. 



scription of it. Dr CRAWFORD'S method consisted of inclosing 

 two different Gases (previously exposed to muriate of lime, 

 for the purpose of depriving them of their watery vapour) in two 

 close vessels of equal size and weight ; these being heated to ex- 

 actly the same temperature, by a very ingenious contrivance, 

 were at the same time plunged into two vessels, containing wa- 

 ter of a lower temperature : these vessels were also of the same 

 size, form, and weight : then, by means of accurately adjusted 

 thermometers, he ascertained the comparative rise of tempera- 

 ture occasioned by the two Gases, and hence he determined 

 their specific heats. 



I know of no imperfection in this mode, excepting that the 

 quantities of the Gases were so small, that the results could not 

 be obtained with sufficient accuracy. 



This defect is entirely obviated by the method adopted by 

 Messrs DE LA ROCHE and BERARD : their apparatus consisted of 

 a column of water, so adjusted as to act with a constant and equal 

 pressure in a close vessel containing air ; which being gradually 

 expelled by the superincumbent water, pressed on the outward 

 surface of a bladder containing the Gas whose capacity was to be 

 examined. From this bladder the Gas was propelled through 

 the calorimeter : this consisted of a vessel containing water of a 

 low temperature, through which a spiral tube passed to conduct 

 the Gas. Previous, however, to its entering the calorimeter, the 

 Gas was heated, by a particular contrivance, to the boiling tem- 

 perature. After leaving the calorimeter, it was conducted, by 

 means of turn-cocks, into another bladder ; the latter was acted 

 upon in the same way as the former. By means of this recipro- 

 cating action, Messrs DE LA ROCHE and BERARD could cause 

 225.2 cubic inches of Gas, heated to the boiling temperature, to 

 pass through the calorimeter every minute. The temperature 

 communicated was ascertained by a thermometer, and from com- 

 parative trials, the capacity of the different Gases was inferred. 



