408 Experiments on the Gas from Coal. 
ments afforded a mixture of gases, succeeded 
in obtaining olefiant gas in a state of pu- © 
rity.* | 
With the view of ascertaining how low a 
degree of heat is adequate to the production 
of gas from coal, I placed a small iron re- 
tort, containing cannel, in melted solders of . 
various composition, without obtaining more 
than the common air of the vessel. The re- 
tort, charged with fresh materials, was then 
immersed in melted lead, but after expelling 
the common air, no more than a few bubbles 
of gas came over, and that only when the 
lead, by being kept over the fire, had -ac- 
quired a temperature about its fusing point. — 
On restoring this temperature by adding fresh 
metal, the evolution of gas was always sus- 
pended. TI placed also, one of Mr. Wedge- 
wood’s hydrometer pieces in contact with a 
retort which was at work at Mr. Lee’s manu- 
factory, and which shewed only a dull red 
or blood coloured heat; but, after remaining 
in that situation half an hour, a contraction 
of barely one degree of the scale had taken 
place. This temperature, however, I sus- 
pect is rather too low, and has a tendency to 
distil over too much tar, and consequently to 
* Mémoires de la Sog, d’Arcueil, ii, 84. 
