1874.] Economy of Fuel. 75 
time, of from 40 to 50 per cent of that which was previously 
burnt. 
Irrespective, however, of other circumstances, a great 
waste of fuel may be caused by bad firing; the fire being 
kept too thick, or too thin, or irregular. If too thick, the 
carbonic acid that is generated by the combustion of the 
lower part of the fuel, with which the air first comes in 
contact, is changed in its passage through the upper part of 
the fuel into carbonic oxide, by absorbing from the fuel a 
second equivalent of carbon. If carbonic oxide gas, thus 
generated, does not meet with free atmospheric air, at a 
suitable temperature in the upper part of the furnace, it 
must remain unconsumed, and will pass through the flues 
or tubes of the boiler, and make its escape into the air, 
carrying with it the valuable unconsumed carbon of the coal 
in a gaseous form. And when it is remembered that under 
ordinary circumstances every pound of coal burnt into car- 
bonic acid is capable of evaporating about 13 lbs. of water 
from 212°, while a pound of coal converted into carbonic 
oxide is capable of evaporating only 4 lbs. of water, it will be 
seen how necessary it is that no mismanagement of the fire 
should cause a portion of the fuel thus to escape unburnt up 
the chimney. 
We have thus pointed out the extent to which, and the 
principal means by which economy of fuel has been attained 
in the manufacture of iron, and for steam purposes. The 
results hitherto attained are, however, still very far from 
what theoretically should be practicable; but there can be 
little doubt that the same influences which have been at 
work to produce established results, will continue to act in 
the same direction, and with equally beneficial effects, until 
very much better value is obtained out of coal, although it 
would be unreasonable to hope that the full theoretical 
value should ever be actually attained.; and, indeed, as has 
been already shown, such a result would be impossible. 
Lastly, a few words with reference to the waste of fuel in 
domestic consumption. Nothing could be more extravagantly 
absurd, from an economical point of view, than the present 
system of open fire-places, and the method of setting them. 
From published returns for the year 1872 it appears that, 
taking the statistics of the metropolitan district as a guide, 
on an average, 12% cwts. of coal is consumed per annum for 
each person of the population for domestic services. In the 
preceding year the average was slightly higher, but prior to 
that it was below that average; so that it appears, in the use 
of fuel for domestic purposes, so far from there having been 
