COMPARISON OF DIFFERENT KINDS OF FUEL. 43 



4. COMPARISON OF DIFFERENT KINDS OF FUEL. 



There are two methods of treating the question of a com- 

 parison of different kinds of fuel. One method determines 

 the relative economy of the various fuels, when each is burned 

 under the conditions, regarding type and arrangement of boiler, 

 which will give the most favorable results. The other method 

 compares the various results obtained when the fuels are 

 burned in the same boiler, regardless of proportions and 

 regardless of the special adaptability of the boiler for the 

 economical use of any particular kind of fuel. The true 

 economy of a fuel depends to some extent upon its market 

 price. Changes which occur from time to time in the relative 

 market prices of different fuels, make one fuel the most eco- 

 nomical at one time, and another fuel at another time. It 

 becomes advisable, on that account, to change fuels when a 

 sufficient change of prices occurs. If this is done, it is not 

 usually practicable to make any material alteration in the boiler, 

 and as a consequence one design of boiler must answer for all 

 kinds of coal. It is for this reason that the second method 

 alluded to is the one selected for the treatment of the subject, 

 being, moreover, the one to which most of the tests conform. 



A comparison is first made on the basis of the number of 

 pounds of water evaporated from and at 212 degrees per pound 

 of coal. Anthracite broken coal is used as a standard, and the 

 comparison is made by determining the percentage of increase 

 or decrease in each case above or below the evaporation with 

 that coal. Table No. 7 gives a summary of the results of 

 those tests which can be treated in this manner. 



