204- Mr. Haycraft oti the Specific Heat of the Gases. 



rent of gas through the tube was interrupted. Two smaller 

 turn-cocks also were fixed in the same tube, one on each side 

 of the larger turn-cocks : these, when open, communicated 

 with the external atmosphere. When, therefore, the large 

 turn-cock was closed, and the small ones open, the air would 

 necessarily, during the action of the machine, rush in at one 

 of the small turn-cocks, and be forced out of the other, so that 

 the air contained in the apparatus would be constantly re- 

 newed. In order, then, to fill the machine with the gas, 

 nothing more was necessary than to form a connection be- 

 tween the gasometer or receiver containing the gas and the 

 apparatus, by means of a tube connected to the small turn-cock 

 first mentioned, through which the air rushed in. In per- 

 forming this operation, however, I usually made use of an air- 

 pump to exhaust the apparatus, and then opening the turn- 

 cock communicating to the gasometer, filled it with the gas 

 required : after this operation had been several times repeated, 

 I found the gas contained in the machine to be nearly as pure 

 as that contained in the gasometer. 



By a slight consideration of this description of the appa- 

 ratus, which may be deemed rather prolix, and by an inspec- 

 tion of the plate, it will be perceived that two gases, contained 

 in the two parts of the machine, will be under circumstances 

 precisely similar ; the quantities of gas transmitted through 

 the calorimeters in a given time will be the same ; the tem- 

 perature of the surrounding media and the barometrical pres- 

 sure, will be equal ; the temperature also of the gases them- 

 selves must be the same, because they passed through the 

 same heating medium. In fine, the size of the tubes, cylin- 

 ders, calorimeters and valves, was the same in the two parts 

 of the machine. 



Therefore, the temperature communicated by the two gases 

 submitted to a comparative trial, will be the direct ratio of 

 their comparative capacities for caloric, provided there be no 

 disproportionate escape by absorption in the calorimeters, 

 arising from the different temperatures of surrounding bodies. 



This source of fallacy was obviated by the arrangement of 

 Count Rumford, who contrived that the temperature of the 

 surrounding medium should be as much above that of the ca- 

 lorimeter at the beginning, as it was lower at the end of the 

 experiments. 



The quantity of gas propelled through the calorimeter was 

 12 cubic inches during the action of the piston. Those actions, 

 as regulated by a second pendulum, which was suspended in 

 the apartment, being 1 20 every minute, the whole quantity 

 would be 1440 cubic inches of gas propelled through the ca- 

 lorimeter 





