Experiments on the Gas from Coal. 409 
‘produce less gas than might be obtained by 
a degree of heat somewhat higher. The 
‘best adapted temperature will probably be 
found to vary with different kinds of coal ; and 
I have been prevented from ascertaining 
it with respect to cannel, by the inconveni- 
ences that would arise from disturbing the 
regular arrangements of a large manufac- 
tory. From some experiments of Mr. Brande, 
it appears that the sudden application of the 
requisite heat evolves from coal much more 
gas, than the gradual heating of a cool re- 
tort up to the point of ignition.* 
In the experiments upon gas from Wigan 
cannel, the results of which are comprized 
in the first table, azotic gas was found in all 
the aériform products, from the beginning 
to the end of the operation. But in expe- 
riments on the gas, obtained at other times 
from the same substance, no appreciable 
quantity of azotic gas could be discovered till 
after the sixth hour of the process, when it 
began to appear, and progressively rose to 20 
parts in the hundred. Of this purity of the 
early products from azote, and appearance 
of it in the latter ones, Mr. Dalton was an 
eye witness on one occasion, when he was so 
* Journal of Science Vol. 1. page 75. 
VOL. ILI. eff 
