374 Dr Fyfe on the Illuminating Power of Coal and Oil Gas. 
Canal coal, at the manufactory of Messrs Phillips and Lee, and 
collected from an opening in a pipe between the retort and the 
tar-pit. When taken about half an hour from the commence- 
ment of the distillation, the olefiant was in some instances 13, in 
others 1 2 ; but as the distillation proceeded, it was so low as 7 ; 
and near the termination it did not contain any : consequently, 
had this gas been examined from the gasholder, the olefiant must 
have been considerably below 13 or 12, the good being mixed 
with the bad. In a former part of the paper, I have given 
the results of experiments performed at the Edinburgh Coal- 
Gas Works, with the view of ascertaining the quantity of olefiant 
in the gas at different times, after the commencement of the dis- 
tillation. 
At ph of hour it 
was 
14 
At hour and ph, 
- 
19 
At two hours and 
ph, 
17 
At three hours and ph, 
14 
At four hours and 
ph, 
5 
The gas, when tried from the gas-holder, yielded 17 ; for 
though that given off towards the termination was very bad, 
yet in the later stages of the distillation it comes off very slow- 
ly. The gas, then, of Dr Henry would not perhaps yield 
above 10, but let us take 12, which I am confident is more than 
it ought to be, the illuminating power, compared with average 
oil-gas, would be as 12 to 32, or as 1 to 2.66 ; if we consider it 
containing 11, then it is just 1 to 3. 
The opinion I have ventured to give, applies to the gases as 
now prepared, for it certainly would be going too far to say that 
oil-gas never can compete with coal-gas. From some experi- 
ments I have performed, I have every reason to believe that the 
illuminating power of oil-gas may be greatly increased : indeed, 
I have repeatedly succeeded in making a gas having more than 
three times the power of illumination even of the Edinburgh 
coal*gas. The experiments on this subject have been performed 
on a small scale, and are not yet sufficiently numerous to war- 
rant their publication : should circumstances permit me to ex- 
tend them, they may perhaps form the subject of another com- 
munication. I have found, in the making of gas from oil, that 
that disengaged after the supply of oil is cut off, possesses little 
