20 BOILER TESTS. 



ordinary with preliminary heating, the method is the same, 

 with the exception that the night evaporation is not included 

 in the total, and the boiler is heated for a time preparatory to 

 the beginning of the test. This is true also when the start and 

 stop is made with a thin fire. When the " kind of run " is 

 stated to be continuous, there is no interval in the production 

 of steam at noon-time ; and when it is spoken of as a factory 

 run, reference is made to the case where the usual noon-day 

 pause occurs. 



The " duration " of the test is the time required to evaporate 

 the total quantity of water, assuming the rate of evaporation 

 which occurs when the boiler is doing its normal work. It is 

 the quotient obtained by dividing the total evaporation by the 

 weight of water evaporated per hour. 



The quantity of " ash " is the refuse of the furnace and ash- 

 pits left after deducting the unconsumed coal which fails to 

 pass through a |-inch screen, and the percentage is found by 

 dividing this by the weight of dry coal consumed, and multi- 

 plying the decimal fraction thus found by 100. 



The quantity of " coal consumed per hour" is found by 

 dividing the total quantity by the number of hours determined 

 upon for the duration of the test. 



The quantity of " water evaporated per hour " is found by 

 taking the weight evaporated during those portions of the test 

 when the boiler is doing its normal work, say, in the case of a 

 factory working 10 hours per day, from 7.15 to 11.45 A. M., 

 and from 1.15 to 5.45 p. M., and dividing this quantity by the 

 number of hours covered by those periods. 



The " horse-power" is determined by first computing the 

 equivalent evaporation per hour, supposing the feed-water is 

 supplied at 100 decrees and evaporated at 70 pounds pressure, 

 and then dividing this quantity by 30. This is the horse-power 

 basis of rating established by the Committee on Boiler Trials, 

 appointed by the American Society of Mechanical Engineers. 

 The equivalent evaporation is found by multiplying the actual 

 hourly rate by the total heat of the steam, reckoned from the 

 temperature of the feed-water, and dividing the product by 



