36 MR. JOHN GRAHAM ON CONSUMPTION 
at some parts of the bed than at others, 
such parts were supplied with extra quan- 
tities. This irregularity in the burning of 
boiler fires is one of the troublesome “ dis- 
turbing causes” in boiler experiments, the 
more so that such quick burning localities 
shift slightly with variations of the wind 
and other changes. ‘The fire-bars were 
always kept open, so that the ashpit was 
always bright and clear. The fire itself 
was “clinkered” at least once, and often 
twice in a day. 
18. This law, as regards rapid combustion, ‘was 
reversed on the small scale. In the usual evapo- 
rations commonly taking place in Print Works, 
where pans and open boilers are employed, vary- 
ing in capacity from ten to three hundred gallons, 
the rate of evaporation per pound of coal is very 
low, varying from two to four and a half pounds 
of water evaporated from 212° for one pound of 
coal; and the law of evaporation from such 
vessels is about as follows: If the time is reduced 
to one half, the evaporation per pound of coal will 
be reduced also, to the extent of from 10 to 20 p ct. 
19. The difference in the results obtained -by a 
change in the coal used amounted to .... .......... 
20. The same coal reputed to be from the same 
pit varied in its evaporating power to the extent of 
Il\pcé 
6 pct 
21. The higher the water stood in the boiler within cer- 
tain unknown limits, the better was the result. In some 
experiments this advantage was in the proportion of 1 per 
cent. for every six inches of depth of water. 
22. As regards the effect of pressure on evaporation, the 
general result of these experiments is in favour of the sup- 
