CARNOT S THEOKY OF THE MOTIVE POWER OF HEAT. 



573 



per hour. The economy may be estimated from these data, as in the other cases, 

 on the assumption which, with reference to these, is the most probable we can 

 make, that the evaporation produced by a pound of best coal is 7 lbs. of steam. 



58. The following Tables afford a sjmoptic view of the performances and 

 theoretical duties in the various cases discussed above. 



In Table A the numbers in the second column are found by dividing the 

 numbers in the first by 8| in cases (1.), (2.), and (5.), and by 7 in cases (4.), (6.), 

 and (7.j, the estimated numbers of pounds of steam actually produced in the dif- 

 ferent boilers by the burning of 1 lb. of coal. 



The numbers in the third column are found from those in the second, by 

 dividing by 618, in Table A, and 614 in Table B, which are respectively the 

 quantities of heat required to convert a pound of water taken from the hot well 

 at 30°, into saturated steam, in the boiler, at 140 or at 121°. 



With reference to the cases (3.), (4.), (6.), (7.), the hypothesis of Table B is 

 probably in general nearer the truth than that of Table A. In (4.), (6.), and (7.), 

 especially upon hypothesis B, there is much uncertainty as to the amount of eva- 

 poration that will be actually produced by 1 lb. of fuel. The assumption on which 

 the numbers in the second column in Table B are calculated, is, that each pound 

 of coal will send the same number of units of heat into the boiler whether hypo- 

 thesis A or hypothesis B be followed. Hence, except in the case of the French 

 contract, in which the evaporation, not the fuel, is specified, the numbers in the 

 third column are the same as those in the third column of Table A. 



Table A. Various Engines in which the temperature of the Boiler is 140°, and 



that of the Condenser 30°. 



Theoretical Duty for each Unit of Heat transmitted. 4AQ foot-pounds. 



VOL. XVI. PART V. 



( I 



