MECHANICAL EFFECT FBOM CHEMICAL FORCES. 



177 



one working in atmospheric air of 15 lbs. pressure on the 

 square inch and 50" Fahr. I will suppose that the expansive 

 action in the cylinder is to exist through three-fourths of its 

 length. Then as the action of the compressing pump is the 

 reverse of that of the cylinder, the piston of the former must 

 traverse three-fourths of its length before the air is sufficiently 

 compressed to enter the receiver by its own pressure. The 

 temperature of the air entering the receiver, determined by 



Poisson's equation Jl = (^\ *"\ will be 439'''59 Fahr., 



and its pressure will be 105-92 lbs. on the square inch. 

 Supposing now that the volume of the cylinder is to that 

 of the pump as 4 to 3, the density of the air in the receiver 

 to that forced into it by the pump must be as 3 to 4 in order 

 to keep the quantity of air in the receiver constant. The 

 temperature of the air in the receiver will also require to be 

 kept at 739°* 12 Fahr. in order to maintain the pressure of 

 105-92 lbs. on the square inch. The air entering the cylinder 

 at the above pressure and temperature will escape from it at 

 the end of the stroke at the atmospheric pressure, and at the 

 temperature 219|°. 



It will be remarked that there are two ranges of tempera- 

 tures in the engine I have described, viz., that of the pump 

 and that of the cylinder. Owing, however, to the exact pro- 

 portion which subsists between the two, the same result is 

 arrived at by the application of Professor Thomson's formula 

 to either of them. Taking, therefore, the range of the cylin- 

 der, and converting the temperatures of the air entering and 

 discharged from the cylinder into the absolute temperatures 

 from the real zero by adding to them 459°, we obtain for 

 the work evolved by the consumption of a grain of coal, 



^ ^ 1261-45 (1 19812-67866) _ g^.g^ fo„,.pou„dB. 



1198-12 

 In order to compare the foregoing result with the duty of 

 a steam-engine approaching perfection as nearly as possible, I 



2a 



