Experiments on the Gas from Coal. 417 
remove the sulphuretted hydrogen gas and 
other offensive ingredients, without abstracting 
an appreciable quantity of either of the carbu- 
retted hydrogen gases. It isnevertheless im- 
portant that the quantity of water, employed 
in washing the gas, should not beincreased be- 
yond whatisnecessary to give the mixture due 
fluidity, because, under equal circumstances, 
the power of water to absorb a gas is in di- 
rect proportion to the quantity employed. 
Such are the principal circumstances, that 
occurred to me as requiring to be investiga- 
ted, and to be at the same time capable of 
affording results, that may admit of general 
application, wherever coal gas is employed 
as a source of light. There are others of 
more limited utility, that may be left to be 
determined by those persons, who are inte- 
rested respecting them; such as the pre- 
ference due to different varieties of coal as 
sources of gas, andsometimes even to other 
inflammable substances, which, on account 
of local situation, may be entitled to prefe- 
rence over coal. The facts which have been 
stated supply, also, data for deciding other 
questions, which may be suggested by cir- 
cumstances of partial interest ;—for example, 
whether it may not be adviseable, in some 
cases, to collect only the first portions of 
VOL. III. Ggg 
