186 BOILER TESTS. 



The tests on Boiler No. 51 show the performance of this 

 type of boiler under various conditions, when burning anthra- 

 cite broken coal. Test No. 102 was made under the ordinary 

 working conditions. Test No. 101 was made with damper 

 wide open, so as to work the boiler to its maximum capacity. 

 Test No. 103 was made under similar conditions to that of No. 

 102, with the single exception that the water line was carried 

 to a higher point. The amount of water heating surface on 

 this test was 1159 square feet, and that of steam heating 

 surface 208 square feet, the ratios of these surfaces to the 

 grate surface being respectively 25.4 and 4.(> to 1. 



The evaporative results given in the Table take no account 

 of the superheated condition of the steam. The amount of 

 superheating in the case of Test No. 102 was 90 degrees. 

 What allowance should be made for the superheat depends 

 upon the character of the work which the steam is called upon 

 to perform. The increased value of superheated steam is 

 never less than the equivalent of the excess of the heat which 

 it contains over saturated steam, whatever the use to which it 

 is applied. For operating engines it has been found that the 

 value of superheat is at least double that of heat expended in 

 evaporation. If an allowance for superheating is made on 

 Test No. 102 according to the heat added, the equivalent 

 evaporative result per pound of combustible from and at 212 

 degrees is increased from 9.5(3 to 9.94 pounds. This result 

 is not so high as that obtained from horizontal tubular boilers, 

 working under favorable conditions. The temperature of the 

 escaping gases on this test, which is 480 degrees, is excessive 

 for anthracite coal, and it is evident that the inferior result is 

 due, in a measure, at least, to the waste heat at this point. 



The effect of increasing the water heating surface and re- 

 ducing 1 the amount of superheating is seen in the results of 

 Test No. 103. The amount of superheating is only 14 degrees, 

 and the temperature of the escaping gases is reduced to 434 

 degrees. The evaporative result is higher than that given on 

 the low water test, being 10.07 from and at 212 degrees per 

 pound of combustible, the increase amounting to about 5 per 



