OF COAL AND RATE OF EVAPORATION. ou 
position that the rate of evaporation of water per pound of 
coals increases with and bears some ratio to the pressure 
under which the steam is generated. In connection 
with this idea I may mention a singular fact which may be 
supposed to give it support, or ‘may, perhaps, find some 
other practical explanation. Tf a boiler be used exclusively 
for the purpose of heating water and liquors in a dyehouse, 
and be capable of working that dyehouse just sufficiently 
when the steam is at 10 Ibs. pressure, it will be found 
unable to do so when the pressure falls to 7 lbs., and still 
less able to do its work when the pressure further falls to 
QL lbs. By repeated experiments on the large scale I find 
that the loss incurred by working steam at 21 lbs. as com- 
pared with steam at 10 Ibs., an equal quantity of coals 
always being burned in the same time, is as follows : — 
Available power of the boiler to heat dye cisterns : 
With the steam at 10 lbs. pressure—=100 
= s 7 Ibs. pressure= 92 
zy 5 2% lbs. pressure— 77 
I have not experimented at higher or lower pressures 
than those stated. 
23. While we may reasonably look for advantage from 
improvements in the construction of the fireplace, in the 
management of the fire itself, in the construction of the 
flame-bed and in adaptation of draught, in the form of the 
boiler, in the addition of separate supplementary heating 
surface, and in cleanliness, and by all these means effect a 
great saving in the consumption of coals, we cannot at the 
same time expect much saving from extension of flue space 
when allowed to coat with soot, nor from a greater length 
of boiler than four times the length of the fire-place. 
94. With a view to the prevention of the “scaling” of 
boilers, or the coating with sulphate and carbonate of lime 
and mud, I have experimented with the following sub- 
stances: caustic soda, quicklime, muriatic acid, soap liquor, 
