154 OF THE POWER OF STEAM, [SECT. iv. 



diameter is unity, we have 2,860,000 Ibs. raised 1 foot for the utmost power 

 of a cylindric foot of water converted into steam. To deduct from this there is 

 the waste steam, the friction of the piston, and the resistance of the uncon- 

 densed vapour. I shall not attempt at present to compute the extent of these 

 deductions, for it would be premature, but shall give an analytical form to the 

 calculation, for the purpose of applying it to the expansive and other species of 

 engines. 



303. Iff be the force of the steam in inches of mercury, and t its temperature, 

 the weight of a cubic foot in grains is 



5700 / 

 459 + t ' 



Now a cubic foot of water, at the lowest temperature it is likely to be when con- 

 densed, will be 436500 grains ; hence, 



436500 (459 + t) .. 76-58 (459 + t) 

 5700 / / 



is the bulk of the steam when that of the water is unity. 



Now neglecting the taking of unity for the bulk of the water, we have 7075 / 

 = the force of steam on a square foot ; and we have 



70-75/ x 76-58(459 + = 5418(459 + t) 



for the Ibs. 1 cubic foot of water converted into steam, of the temperature t, 

 would raise 1 foot high, without reduction for loss by friction, uncondensed 

 vapour, or waste. 



This conclusion, that the power of steam is independent of its elastic force, 

 is the same as resulted from the more popular mode of investigation, (art. 

 294.) 



304. But if/* be the force corresponding to the temperature of the condensed 

 water, or of the condenser, then 



5418 (459 + t)f _ t h e resistance. 



For the condensed steam is limited to the space which the whole occupied in 

 its elastic state, and therefore offers a resistance proportional to its force acting 



through that space. Thus we found the space - - ; and the force is 



70'75/'; consequently, the resistance of the uncondensed steam is 



5418 (459 + *)/' 



