28 BOILER TESTS. 



No data are given on either type of vertical boiler to show 

 whether a considerable degree of superheating can be obtained , 

 and at the same time a high evaporative efficiency. It is 

 doubtful if the practical restrictions which the construction of 

 the boiler imposes will allow both of these objects to be real- 

 ized at the same time. 



It may be of interest, in passing, to note the effect produced 

 by superheating the steam in an independent superheater. 

 Under the head of Boiler No. 1, reference is made to a test on 

 a boiler fitted with an apparatus for this purpose. By increas- 

 ing the quantity of coal burned 17.8 per cent., this being the 

 coal used in the superheater, a superheating of 228 degrees was 

 obtained. On the basis which has been taken for computing 

 the value of the superheat, that is, a gain of one per cent, for 

 every ten degrees of superheating, this steam has a value of 

 24.8 per cent, over that of ordinary steam. Here is a net gain 

 of 7 per cent, in favor of the superheated steam when used for 

 motive power. 



2. GENERAL CONDITIONS WHICH SECURE ECONOMY. 



Glancing over Table No. 1, it appears that, in general, the 

 highest results are produced where the temperature of the 

 escaping gases is the least. An examination of this question 

 may be made by selecting those tests in which the temperature 

 exceeds the average, that is, 375 degrees, and comparing with 

 those in which the temperature is less than 375 degrees, taking 

 first those boilers in the table which are of the common hori- 

 zontal tubular type. It will be remembered that all of these 

 boilers use anthracite coal of either egg or broken size. The 

 tests with high temperature are given in Table No. 3, and 

 those with low temperature in Table No. 4. 



The average flue temperatures in the two series are 444 

 degrees and 343 degrees respectively, and the difference is 101 

 degrees. The average evaporations are 10 .40 pounds and 1 1 .02 

 pounds respectively, and the lowest result corresponds to the 

 case of the highest flue temperature. In these tests it appears, 

 therefore, that a reduction of 101 degrees in the temperature of 



