3S3 
which it is obtained, was afresh brought prominently before 
me, at a period too near the time of our meeting to allow of 
its being submitted to any careful or detailed experiments. 
And though the data on this subject are accessible to every 
chemist, yet if practical men find anything like the difficulty 
in obtaining precise numerical statements from chemists which 
I find in obtaining replies to questions apparently simple, 
from workmen, in cases where there is no motive and no ap- 
parent wish for concealment, a short plain statement of the 
heating power, supposing the whole could be brought into 
use, of Coal, and of the Coke which it would furnish, may 
not be unacceptable. 
The difference between various kinds of coal is not so 
material to this inquiry as it might seem; provided we exclude 
Anthracite, or other native combustibles approaching more 
nearly to coke than coal in their composition. For the earthy 
contamination, or ash, remains in the coke, and adds to the 
incidental expenses of its carriage, &c., not in proportion to 
the weight of this, but of the original coal. 
I shall select, then, Newcastle coal, as analyzed by Thomas 
Richardson, of that place, with great skill and exactness. It 
consists, rejecting minute decimals, of 
Carbon 88 per cent. 
Hydrogen 5i „ 
Nitrogen and Oxygen 5^ „ 
Ashes „ 
Total 100 
According to Despretz, the heat given out during combus- 
tion is, with certain exceptions which still bear close relation 
to the law, and which do not aflPect the question before us, 
directly in proportion to the oxygen consumed, whatever be 
the combustible, and that heat he found to be sufficient to 
heat 28| lbs. of water from freezing to boiling. 
o 
