Mr. Haycraft on the Specific Heat of the Gases. 203 



forced a quantity of air through the tubes; thus, by means of 

 one additional valve, the apparatus would act upon exactly 

 twice the quantity of air that could be acted upon in a pump 

 of the ordinary construction. 



The pipes immediately connected with the four valves ter- 

 minated in two tubes ; through one of which the air, during 

 the action of the apparatus, was propelled with a constant and 

 almost uniform current, while, through the other, the same 

 air having passed through the heating apparatus and the calo- 

 rimeter, returned to the cylinder, to be acted upon again in 

 the same way. The heating apparatus just mentioned con- 

 sisted of a metallic vessel, about 16 inches long, containing 

 hot water, through which the tubes passed, containing the air 

 propelled from the cylinders : those tubes traversed the heat- 

 ing vessel three times before their exit, more effectually to 

 secure the gases arriving at the temperature of the water con- 

 tained in the vessel. By means of a lamp placed under this 

 vessel, I could raise the temperature of the water to any point 

 required. This last arrangement, however, was rather a mat- 

 ter of convenience than necessity, as it will be easily perceived 

 that, from the mode of conducting the experiments, a fixed 

 point of temperature was not required. 



There were also two calorimeters, similar in construction to 

 those of Messrs. De la Roche and Berard before described. 

 Each of these was connected with the tube containing the gas, 

 propelled by its cylinders through the heating apparatus, and 

 likewise with that through which the air flowed to the cylin- 

 der ; these tubes were all of metal, and air-tight. 



The apparatus, then, must be considered as consisting of 

 two distinct parts, exactly the counterparts of each other, 

 each conveying an equal quantity of gas through the same 

 heating medium, but through separate calorimeters. 



The tubes communicating between the heating vessel and 

 the calorimeters were one inch in length. In these tubes there 

 was an opening, through which could be introduced a delicate 

 thermometer, for the purpose of ascertaining the temperature 

 of the gases as they entered the calorimeters. 



Each of the calorimeters was inclosed in a polished metallic 

 case, for the purpose of preventing, as much as possible, the 

 absorption or escape of caloric during the process. These 

 latter were also placed in a box containing water, which was 

 repeatedly agitated, that the calorimeters might not be affected 

 by the unequal temperatures of the walls of the apartment. 



For the purpose of facilitating the operation of filling the 

 apparatus with the gas operated upon, there was a turn-cock 

 fixed in the course of each returning tube, by which the cur- 

 C c 2 ren 



