198 MR HAYCRAFT on the Specific Heat of the Gases. 



describe in writing, may be easily understood by reference to 

 Plate VIII. Each action of the piston 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 construc- 

 tion. 



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 calorimeter, re- 

 turned to the cylinder, to be acted upon again in the same way. 

 The heating apparatus just mentioned, consisted 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 heating vessel three times before their 

 exit, more effectually to secure the Gases arriving at the tem- 

 perature of the water contained 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, how- 

 ever, was rather a matter of convenience than necessity, as it will 

 be easily perceived that, from the mode of conducting the expe- 

 riments, 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 cylinder; 

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



The apparatus, then, must be considered as consisting of two 

 distinct parts, exactly the counter parts of each other, each con- 

 veying an equal quantity of Gas through the same heating me- 

 dium, but through separate calorimeters. 



