Mechanical Effect from Chemical Forces. 5 



In order to compare the foregoing result with the duty of 

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

 will admit that steam may be safely worked at a pressure of 

 14 atmospheres. The temperature of the boiler corresponding 

 to that pressure will, accorpling to the experiments of the French 

 Academicians, be 387° Fahr. The temperature of the condenser 

 might be kept at 80°. Reducing the above to temperatures 

 reckoned from the absolute zero, we obtain for the work evolved 

 by the combustion of each grain of coal, 



^^ 1261-45 (846-539 ) ^^Sy.^e foot-pounds. 

 846 



It would therefore appear, even in the extreme case which 

 I have adduced, that the performance of the steam-engine is 

 considerably inferior to that of the air-engine. The superiority 

 of the latter would have been still more evident had I also taken 

 an extreme case as an illustration of its ceconomy. It must, 

 moreover, be remarked that the heated air escaping from the 

 engine at a temperature so high as 219f ° might be made avail- 

 able in a variety of ways to increase still more the quantity of 

 work evolved. A part of this heated air might also be employed 

 in the furnaces instead of cold atmospheric air. 



We may also hope eventually to realize the great advantage 

 which would be secured to the air-engine by causing the air, in 

 its passage from the pump to the cylinder, to come into contact 

 with the fuel by the combustion of which its elasticity is to be 

 increased. It appears to me that the air might pass through a 

 number of air-tight chambers, each containing ignited fuel^ and 

 that whenever any one of the chambers required replenishing, 

 its connexion with the engine might be cut off by means of 

 proper valves, until by removing an air-tight lid or door the 

 chamber could be filled again with fuel. By means of suitable 

 valves, it would be easy to regulate the quantity of air passing- 

 through each chamber so as to keep its temperature uniform ; 

 and by a separate pipe, furnished also with valves, by which the 

 air could be carried from the pump to the upper part of the 

 chambers without traversing the fuel, the engine man would be 

 enabled to keep the temperatures of the chambers, as well as the 

 velocity of the engine, under proper control. 



