Report of the Committee on Steam Boilers. 71 



of water at the temperature of 212 degrees Fahrenheit, and under 

 atmospheric pressure. In comparing this result with the actual per- 

 formance on the test, it should be remembered that a large amount of 

 coal always falls through the grate unburned, and thus greatly reduces 

 the practical efficiency of all coals. The amount of this loss can only be 

 approximately estimated, and the Committee judge it to have averaged 

 at least fifteen per cent during these trials. 



The evaporative power 01 pure carbon, which has usually been 

 found to be capable of developing 14,500 British thermal units, is 

 fifteen pounds of water per pound of carbon, the water being eva- 

 porated under the pressure of the atmosphere at a temperature of 212 

 degrees Fahrenheit. All of the results obtained by the Committee are 

 reduced to similar standard measures of thermal units developed per 

 pound of combustible, and to the equivalent evaporation from 212 

 degrees Fahrenheit. It is by the comparison of these reduced obser- 

 vations, that the relative economic efficiencies of the competing steam 

 boilers are to be determined. 



The preparations for the trial having been completed, the following 

 letters of instruction were written, and forwarded to the Superin- 

 tendent of Machinery, by whom their contents were communicated 

 to the exhibitors, and the agreement of each to the proposed terms, 

 was a condition precedent to admission for competition. 



Fair of the American Institute, ) 

 New York, October Zlst, 1871. j 

 To the Superintendent of Machinery : 



Sir. — The Committee of Judges of Department V, Group I, having 

 determined to make a thorough test of the economic values, and of 

 the steaming capacities of the steam boilers entered for competition, 

 you are hereby authorized and instructed to make the necessary pre- 

 parations for such a test. 



The steam from each boiler, when under test, will be conducted 

 into a surface condenser of a capacity of at least eight hundred (800) 

 square feet of condensing surface ; the water of condensation will be 

 collected in a tank placed beneath the condenser, and there measured ; 

 the feed water will be measured by a meter, and the condensing water 

 will be measured in the same manner, the meters being previously 

 tested. 



The pressure of steam will be maintained constant (at seventy-five 

 [75] pounds), by means of a safety valve placed between the boiler 

 and the condenser, and the Committee desire that the safety valves 



