854 Transactions of the American Institute. 



inch of our evaporating surface "will be maintained. It cannot \m 

 otherwise, for the pressure, and hence temperature, in the her- 

 metically sealed tube will be controlled entirely by the temperature, 

 and corresponding pressure, in the generator, because condensa- 

 tion is more rapid than evaporation, and hence all the heat which 

 can be made to enter the end of the tubes which is over the fire is 

 instantly disposed of in the generator, subject to the above condi- 

 tions. 



Here, then, we have a theoretically perfect boiler, with every 

 part, at the exact temperature required, although that temperature 

 is a variable one; for when the pressure in the boiler is high the 

 temperature of the heating tubes will also be high, simply because 

 they can then become hot; but when the pressure in the boiler is 

 low, the film of water which surrounds the tubes abstracts their 

 heat so rapidly that they can only maintain the equilibrium, and 

 hence the boiler can never by any possibility become colder or 

 hotter in any part than is due to the pressure of steam it is car- 

 rying. 



I have endeavored to explain some of the defects of our present 

 method of evaporation, and have demonstrated that much of its 

 surface is necessarily useless. That the great body of water, involv- 

 ing an extended surface, maintained at a fearful risk, is not simply 

 a nuisance, but a definite evil, swallowing up the mechanical 

 eftects of the fuel, far beyond what is generally supposed. If a 

 very large part of the heat is not resolved into mechanical motion 

 'in the boiler, the question, what does become of it, must remain 

 unanswered. 



The plan here proposed, appears to be free from all of those 

 defects. It is the most effectual way to utilize the heat from the 

 furnace. It is the only way to maintain the desired temperature 

 equally throughout the whole generator. It is light, comparatively 

 inexpensive, and absolutely free from danger. And if it does not 

 attain to the above theoretical results, it is evidently more efficient 

 than are the boilers now in use, especially on the farm, where sim- 

 plicity and absence of weight is a necessary element of success. 



I have already constructed a boiler on the above principles, and 

 with considerable success. It weighs thirty-five pounds when fully 

 charged for work, and with a moderate fire evaporates a cubic foot 

 of water per hour under ninety pounds steam. And although far 

 from perfect, in ita mechanical details, still I am persuaded this is 

 the direction from which we may reasonably hope for success in 



