OF COAL AND RATE OF EVAPORATION. 35 
13. A difference in the mode of firing only 
may produce a difference in the result of ......... 13 p ct 
I refer here to a difference such as will be pro- 
duced by withdrawing the regular and prac- 
tised stoker, and substituting for him an 
equally intelligent and careful man, but who 
has not been accustomed to the boiler or the 
coal employed. A man who is careless or 
dishonest will occasion a loss, the extent of 
which can scarcely be calculated. All inju- 
rious influences upon firing are greatly ag- 
gravated in very large fire-places (say of 
six feet by seven feet) from the physical in- 
ability of the stoker to keep the bars equally 
covered. 
14, The loss arising from the scale of sulphate 
of lime on the inner surface of the boiler, of not 
more than one-sixteenth of an inch, amounted to 14.7 p ct 
15. Neither wet coals, nor coals which had been 
out of the pit for three years, nor wet weather, nor 
a variation of temperature of the atmosphere from 
40° to 70°, produced any appreciable difference of 
result. 
16. Windy weather invariably gave a high re- 
sult. 
17. A moderately thick and hot fire, with a 
rapid draught, uniformly gave the best result. 
The coals used varying from the condition of dust 
to that of pieces four inches in diameter, it 
was found advantageous to keep the fire at a 
general thickness of from six to seven inches, 
in order to insure the bars being covered at 
all times ; and as it is found, that in all boiler 
fires the coals are consumed more quickly 
