ISO APPENDIX. 



the utilization of 965.7 British thermal units per pound of 

 water so evaporated." 



The unit of commercial boiler horse-power adopted by 

 the Committee of 1885 was the same as that used in the re- 

 ports of the boiler-tests made at the Centennial Exhibition 

 of 1876. The Committee of 1885 reported in favor of this 

 standard in language of which the following is an extract : 



" Your Committee, after due consideration, has deter- 

 mined to accept the Centennial standard, and to recommend 

 that in all standard trials the commercial horse-power be 

 taken as an evaporation of 30 pounds of water per hour 

 from a feed-water temperature of 100 degrees Fahr. into 

 steam at 70 pounds gauge-pressure, which shall be consid- 

 ered to be equal to 34^- units of evaporation ; that is, to 34^ 

 pounds of water evaporated from a feed-water temperature 

 of 212 degrees Fahr. into steam at the same temperature. 

 This standard is equal to 33,305 thermal units per hour." 



The present Committee accepts the same standard, but 

 reverses the order of two clauses in the statement, and 

 slightly modifies them to read as follows: 



In all standard trials the commercial horse-power shall 

 be taken as 34^ units of evaporation; that is, 34^ pounds 

 of water evaporated from a feed-water temperature of 212 

 degrees Fahr. into steam at the same temperature. This 

 standard is equivalent to 33,317 British thermal units per 

 hour. It is also practically equivalent to an evaporation of 

 30 pounds of water from a feed-water temperature of 100 

 degrees Fahr. into steam at 70 pounds gauge-pressure.* 



* According to the tables in Porter's Treatise on the Richards Steam- 

 engine Indicator, an evaporation of 30 pounds of water from 100 degrees 

 Fahr. into steam at 70 pounds pressure is equal to an evaporation of 34.488 

 pounds from and at 212 degrees; and an evaporation of 34^ pounds from 

 and at 212 degrees Fahr. is equal to 30.010 pounds from 100 degrees Fahr. 

 into steam at 70 pounds pressure. 



The "unit of evaporation" being equal to 965.7 thermal units, the 

 commercial horse-power = 34.5 X 965.7 = 33.317 thermal units. 



