STEAM. 



Pure steam is, in fact, a transparent and invisible elastic fluid 

 like air, and this explains how it is, that in the tube, A B, the 

 space below the piston, after the evaporation of the water, appears 

 to be empty. It is, however, no more empty than if it were filled 

 with air. It is filled with the invisible elastic vapour into which 

 the water has been converted by the heat which has been applied 

 to it. 



9. It remains now to show what is the quantity of mechanical 

 force evolved in this conversion of water into steam, and what 

 quantity of heat has been absorbed in producing it. 



From what has been stated above, it appears that the water in 

 passing into vapour has swelled into 1669 times its original bulk, 

 being subject to a compressing force of 15 Ib. upon the square 

 inch. In thus expanding, the weight of 15lb. has been raised 

 140 feet, an effect which is mechanically equivalent to 140 times 

 15 Ib., that is 2100 Ib. raised one foot. 



10. To estimate the quantity of heat absorbed in producing this 

 effect, let us suppose that in the commencement of this process, 

 the water under the piston has the temperature of 32, and that 

 the lamp, or other source of heat, which is applied to it acts with 

 such uniformity as to impart exactly the same quantity of heat 

 per minute. 



Let the time which elapses between the first application of tho 

 lamp and the moment at which the water attains the temperature of 

 212 and begins to be evaporated, be observed, and also the interval 

 between the commencement of evaporation and the total disap- 

 pearance of the water. It will be found that the latter interval is 

 5| times the former. It follows consequently that to convert water 

 at 212 into steam requires 5| times as much heat as is necessary 

 to raise the same water from 32 to 212, or what is the same, the 

 quantity of heat which would convert water at 212 into steam 

 would increase the temperature of th'e same water by 5| times 

 ISO", that is by 990, if it had remained in the liquid state. 



It follows also, that to convert water at 32 into steam will take 

 6| times as much fuel as would be sufficient to boil the same 

 water. 



11. It may be asked, what becomes of the enormous quantity of 

 heat thus imparted to the water during the process of its evapo- 

 ration, seeing that the water itself receives no increase of tempe- 

 rature, being maintained steadily at 212, and that the steam into 

 which it is converted has the same temperature ? This is answered 

 by showing that the entire quantity of heat which thus disappears 

 to the thermometer is absorbed by the steam, and must in fact be 

 regarded as the immediate cause of its maintaining the elastic or 

 vaporous form. That it is actually contained In the steam, though 



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