(38 Transactions of the American Institute. 



But steam boilers usually — and invariably when unprovided with 

 superheating apparatus — furnish " wet steam," and the weight of water 

 passing off unevaporated is sometimes greater than the real weight of 

 steam made. In order to make a reliable and valuable report upon 

 these points, it becomes necessary to determine what is the real 

 evaporation of each boiler and what weight of water passes over 

 unevaporated. 



Another extremely important fact, and one which should alone 

 induce the Committee to propose and the Institute to permit them to 

 adopt, an exact method of determining the true evaporative efficiency 

 of the steam boilers presented for their judgment, is that ignorant or 

 dishonest venders of peculiar forms of boilers have frequently deceived 

 the public and have imposed upon purchasers by apparently well sub- 

 stantiated statements that their boilers have, by actual test, evapo- 

 rated fourteen, fifteen, or even in some cases twenty pounds of water 

 per pound of fuel consumed — the purchaser being unaware of the 

 fact, so well known to scientific men and to engineers, that were it 

 possible to obtain one pound of coal absolutely free from all impurities 

 and composed of pure carbon, it would, if burned where no loss of 

 heat could take place, and with the feed water at a temperature of 212 

 degrees Fahrenheit, evaporate but about fifteen pounds of water, and 

 that under the usual circumstances of comparatively cold feed water and 

 high pressure of steam, and with waste of heat by the chimney and in 

 every direction by radiation, very much less than fifteen pounds must 

 be evaporated by the very best boiler that man can build. 



In order, therefore, to assist honest and skillful builders in prevent- 

 ing such injury of their business by those who would either know- 

 ingly or ignorantly take advantage of the lack of information possessed 

 by the public, the Committee considered it a duty and a privilege 

 to furnish, if possible, a weapon that might be made effective in pro- 

 tecting the public as well as manufacturers against such ignorance or 

 dishonesty. This they proposed to do by determining accurately the 

 performance of these five boilers, which they considered to include 

 some that rate among the best boilers made, and thus to furnish a 

 standard that should at all times be valuable for purposes of com- 

 parison. 



The method adopted by the Committee of Judges is an extremely 

 simple one in principle, and has often been before proposed by engi- 

 neers. Its earliest conception, probably, dates many years back. The 

 expense attending the building of the necessary apparatus and the 

 preparations for, and the prosecution, of such an exact investigation, 



