420 Experiments on the Gas from Coal. 
being carefully avoided. The sulphuretted 
hydrogen is thus absorbed, and the carbonic 
acid, being left untouched, is afterwards ta- 
ken out from the same portion of gas by a 
similar use of solution of pure potash. 
2. To ascertain the proportion of olefiant gas 
in the residue left by potash. From 25 to 30 
hundredths of a cubic inch of chlorine gas 
are passed into a tube of the diameter of 
about .3,th of an inch, accurately divided 
into bundredths of a cubicinch; and the vo- 
lume of the chlorine is noted when actually 
in the tube, to avoid errors from its absorp- 
tion in rising through the water. To this is 
admitted half a cubic inch (equivalent to 50 
measures) of the gas under examination, and 
the mixture is left, excluded from the direct 
light of the sun and perfectly quiescent, for 
fifteen. minutes. At the expiration of this 
time, the remainder is noted, and the dimi- 
nution which has taken place being divided 
by 2, the quotient shews the quantity of 
olefiant gas in fifty measures of the mixture, 
This process, I am aware however, does 
not give results of perfect accuracy, for, in 
addition to other sources of fallacy, I find 
that chlorine begins to act on carburetted 
hydrogen much sooner than is generally 
SS oe 
