Dr Fyfe on the Illuminating Power of Coal and Oil Gas. 373 
Thus, I would propose to call the coal-gas of Edinburgh at pre- 
sent offered for sale 15 ; the oil-gas of Leith 16 ; that of Mr 
Milne 35 or 32, according to the proportion of its olefiant gas. 
The conclusion at which I have arrived with respect to the 
illuminating power of coal and oil gas, is the same as that stated 
in my last paper, — of course, the answer to the question, Can 
oil- gas compete with coal-gas ? must also be the same. The 
price of the coal-gas of this place is 12s., the lowest at which 
oil-gas has been sold is 40s., per 1000 cubic feet. If, then, we 
take the illuminating power as 1 to 2 ; that is, that one foot of 
the latter will go as far as two of the former (and this is giving 
it higher than it is in general made on a large scale in oil-gas 
establishments), a light which costs the consumer 40s. may be 
had from coal-gas for 24s. But this, as I have mentioned, is 
giving it every advantage. If we consider the light given by a 
burner consuming a cubic foot per hour, as equal to that of 8 
candles (short sixes), the illuminating power, compared with 
Edinburgh coal-gas, is only as 1.7 to 1 ; consequently a light 
which costs 40s., can be supplied by the other for a little more 
than 20s. 
Unless, then, oil-gas can be offered for sale at a much lower 
price than it has hitherto been sold for, it cannot compete with 
coal-gas. 
The preceding remarks must not be considered in a general 
point of view ; they apply alone to the gases as made at Edin- 
burgh, at least with respect to coal-gas. Oil-gas, I have already 
mentioned, seems, when manufactured on a large scale, to be 
nearly uniform in its composition *, which is not the case with 
coal-gas, its illuminating power depending on the coal employed ; 
hence the superiority of the Edinburgh gas. 
Dr Henry, in his paper in the Annals of Philosophy for Sep- 
tember 1821, has stated the quantity of olefiant gas in a coal- 
gas ; so that we are enabled to fix its illuminating power, and 
compare it with oil-gas. The gas was prepared from Wigan 
* Good oil-gas I have stated to contain about 32 of olefiant gas ; whereas that 
made at Leith has only 16. The inferiority of this gas seems to be occasioned by 
the imperfect state of the apparatus, several defects having been discovered, but 
which, I understand, it is intended to remedy immediately, and by which it is ex- 
pected the gas will be much improved. 
