570 TRANSACTIONS OF THE 



coals, flashes into steam, and is suddenly superheated. This 

 anhydrous steam, or steam, if heated in the absence of moving 

 water to 500 deg., (its pressure in the meantime being but 

 slightly changed,) will, upon the subjection of the proper quan- 

 tity of hot water become saturated steam, and instantly develope 

 the amazing force of 750 lbs. per square inch. This hot water 

 may be supplied from the water space around the heater, and it 

 may be absorbed by the high steam in the cylinder, at the mo- 

 ment of admission. The latent heat of steam diminishing as the 

 sensible heat increases, the quantity of fuel required would be 

 even less than enough to produce a similar degree of heat in the 

 same quantity of atmospheric air. And if it is true that expan- 

 sion is by volume and not by weight, we then have a force of 750 

 lbs. per square inch on the piston of a locomotive, at the trifling 

 cost of the fuel required to raise a heater full of steam at 15 lbs., 

 500 deg. 



But are these objections proportionate to the advantages ? 

 Manifestly not. 



This power is entirely under control. The combustion may 

 be instantly increased or stopped by the variable throw of the air 

 pump, and the saturating water may be regulated by a similar 

 and absolutely trustwortny apparatus. The coal itself being the 

 heating surface, direct contact is doubly advantageous. No in- 

 tervening tubes are turned out, and the heat which would other- 

 wise destroy them, is not delayed in its action. The grand ob- 

 jection attending air, under such treatment, is in the nature of 

 steam avoided, for its volume is 1700 times smaller than air, in 

 the form assumed when entering the supply pump. . Nothing 

 except the incombustible portion of the fuel is useless ; ,the se- 

 rious disadvantage of priming, condensation and cooling, by 

 opening the fire door, back pressure due to contracted exhaust 

 nozzles, the immense loss of exhaust heat, draft killing spark 

 arrestors, the weight of tubes and water, and the necessity of a 

 tender, which accompany ordinary locomotives, are in this case 

 entirely avoidable, while economy of space renders it possible to 

 place the entire weight of the engine and the feed-water on the 

 driving wheels. 



Thus, increased speed, which is now only attainable by rapid 

 destruction of rails, under the weight of ponderous machinery, 

 is possible at the wear and tear expense of ordinary freight 

 trains. 



Economy of space and weight are equally valuable in marine 



