Experiments on the Gas from Coal, 407 
greater facility of preserving an uniformtem- — 
perature, in all chemical processes which are 
carried on upon a scale of magnitude. 
The temperature to which the coal is sub- 
jected, must necessarily be a point of the 
greatest importance to the quantity and qua- 
lity of the aériform products ; for while too 
low a heat distils over, in the form of a con- 
densible fluid, the bituminous part of the coal 
which ought to afford gas, too high a tempe- 
rature, on the contrary, occasions the produc- 
tion of a large relative proportion of the 
lighter and less combustible gases. It would 
be a great step in the improvement of the 
manufacture of coal gas, if the whole of the 
hydrogen could be obtained in combination 
with that proportion of charcoal which con- 
stitutes olefiant gas; and it is satisfactory to 
know, that no impediment to this arises 
out of the proportion of the hydrogen and 
charcoal present in coal. If this object 
be ever accomplished, it will probably be by 
the discovery of means of uniformly sup- 
- porting such a temperature, as shall be ade- 
quate to the production of olefiant gas, and 
shall never rise above it; and some proba- 
bility of success is perhaps derivable from 
the fact, that M. Berthollet, by the careful 
decomposition of oil, which in my experi- 
