g02 Dr. Henry's Description of an "Apparatus for the 
The inferior gas, also, probably contains carbonic oxide ; 
for the quantity of oxygen gas, actually consumed, will be 
found, on calculation, less than it ought to be, if the carbon 
were not already combined with a portion of oxygen. 
The quantity of water, which was generated by combustion, 
was not determined experimentally, but is merely estimated. 
It must be acknowledged that the decomposition of the in- 
flammable gases cannot lead to unquestionable results, until 
the proportion of water, produced by their combustion, be also 
accurately ascertained. With the view of effecting this, I have 
already spent much time, and employed many contrivances, 
none of which have satisfactorily answered the purpose for 
which they were intended. 
7 . There appears to be a considerable difference in the 
specific gravity and combustibility of gas from various speci- 
mens of coal, even when taken at similar periods of the dis- 
tillation. The coal from Merthyr in South Wales, which 
burns without flame or smoke, yields a gas which contains, in 
an equal volume, scarcely half as much combustible matter 
as the gas from Wigan cannel. This will probably be found to 
be the case with respect to all coal of similar quality, among 
which may be reckoned the Kilkenny coal. The most impor- 
tant difference among the varieties of this mineral, connected 
with their application as sources of light, consists in the quan- 
tity of sulphureted hydrogen gas, which is mixed with their 
aeriform products ; and it unfortunately happens that the coal, 
otherwise best adapted to this purpose, yields generally the 
largest proportion of this offensive gas. The only effectual 
method of purifying the coal gas from sulphureted hydrogen, 
on the large scale of manufacture, will probably be found to 
