NECESSARY EVAPORATION. 



by which the steam is ejected. The puffs from the blast-pipe must 

 be made at the rate of eight hundred per minute. 



If we assume that the contents of each cylinder is one cubic foot 

 and a quarter, then the boiler must supply to the cylinder per 

 minute 1000 cubic feet of steam. If this steam be assumed to 

 have a pressure of 50 Ibs. per square inch, then one cubic foot 



of water evaporated will produce about 500 cubic feet of such 

 steam ; and consequently, to supply 1000 cubic feet of steam per 

 minute to the cylinders, the boiler must evaporate two cubic feet 

 of water per minute, or 120 cubic feet per hour. This is a rate of 

 evaporation which would correspond to a stationary boiler of a 

 nominal power of 120 horses. 



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