202 Mr. Haycraft on the Speci/ic Heat of the Gases. 



tube passed to conduct the gas. Previous, however, to its en- 

 tering the calorimeter, the gas was heated, by a particular 

 contrivance, to the boiling temperature. 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 reciprocating 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 comparative 

 trials the capacity of the different gases was inferred. 



This last method was superior to that of Dr. Crawford, in- 

 asmuch as greater quantities of gas could be employed. In 

 other respects it was far inferior, because the experiments were 

 not, strictly speaking, comparative. Atmospheric air, whose 

 capacity was their standard of comparison, was subjected to 

 trial, and the results were remarked. The other gases, at dif- 

 ferent periods, with the surrounding media of different tem- 

 peratures, and under different barometrical pressures, were 

 examined ; this plan involved endless and very difficult calcu- 

 lations, in order to adjust those differences. But the greatest 

 imperfection in those experiments, was the neglect of depriv- 

 ing the gases of their watery vapours previous to their exami- 

 nation. The apparatus itself would not admit of this, because 

 the water employed in the process would necessarily keep the 

 gas and the whole apparatus in a state of moisture. Besides, 

 this very great source of error was materially increased by the 

 high temperature to which the gases were exposed, being a 

 condition in which they are disposed to unite with a greater 

 quantity of watery vapour than at ordinary temperatures. 

 Considering the subject in this point of view, therefore, the 

 experiments of Messrs. De la Roche and Berard may be sup- 

 posed to determine the capacities of the different gases united 

 with watery vapour at the boiling point, but by no means of 

 those gases in their dry state, and at ordinary temperatures. 



The apparatus now to be described will perhaps be found to 

 unite the advantages and avoid the defects of both methods. 



It consisted of two hollow brass cylinders (see Plate II.), 

 in each of which was a piston attached to a spindle by means 

 of two levers of equal length ; to the spindle was attached an- 

 other lever, terminating in a handle, to be moved by an assist- 

 ant. Each cylinder was closed at each end, excepting where 

 the tubes were attached, which served to conduct the gases. 

 By means of four valves to each cylinder, fixed in such a way 

 as, though difficult to describe in writing, may be easily un- 

 derstood by reference to Plate II., each action of the piston 



forced 



