STEAM BOILER TESTS — ROBB. l7 



Total heat of 1 lb. steam of at CO lbs. piessure, 1175.710 heat 

 units. 



Total heat of 1 lb. of feed water at 40°. 8. heat 



units. 



Example : 



10. X 1175.710—8. - 966 = 12.08 lbs. 



In comparing fuels, as with the efficiency of the boilers, the 

 quantity of water evaporated per pound of fuel, from and at 212° 

 should always be used. The actual quantity of water evaporated 

 per pound of fuel will differ with variations of temperature of 

 the feed-water entering the boiler, and also with the steam pres- 

 sure or temperature at which the steam leaves the boiler, but the 

 quantity evaporated per pound of fuel from and at 212° allows 

 for these variations and gives a true comparison of the value of 

 fuel if the efficiency of the generator is constant, or of the effici- 

 ency of the genei-ator if the calorific value of the fuel is known. 

 The temperature of saturated or dry steam always corresponds 

 with the pressure, but if from any cause the steam be not dry, it 

 will carry away less heat in proportion to weight, or, if the steam 

 be superheated by contact of the products of combustion with the_ 

 steam surface of the boiler, it will carry away more heat. In 

 either case the result of the test will be vitiated, unless the 

 quality of the steam be ascertained and accounted for. This is 

 usually done by means of a calorimeter, one of the b3st of which, 

 known as the " Barrus Calorimeter," was designed by Mr. Geo. 

 H. Barrus, of Boston. No attempt has been made to ascertain or 

 account for the quality of steam in the simple test given because 

 it would complicate the work, and it is intended that a profes- 

 sional test of the boiler should include this important item, and, 

 if the boiler is found abnormal in this respect, the expert should 

 either give direction? for the removal of the cause, or provide a 

 formula for the correction of the error due to wet or superheated 

 steam in future tests. 



The following table will be found useful in ascertaining the 

 equivalent rates of evaporation horse-power, etc. 



