Dr Fyfe on the Comparative Value of Oil and Coal Gas . 181 
in its composition than oil-gas ; and hence, also, the great differ- 
ence in the statements of their illuminating power may have arisen, 
not from overrating that from oil, but from underrating that from 
coal, which is now, in general, of very superior quality. To come, 
therefore, to a conclusion with respect to their power of giving 
light, either the average of all the statements ought to be struck, 
or we ought to take best coal-gas, and put it in opposition to best 
oil-gas, as it must be the endeavour of different companies to 
adopt those means by which they may be obtained in greatest 
purity. If this be done, I suspect coal-gas will be found to pos- 
sess, or at least may be made in general to possess, about half the 
illuminating power of that from coal. In Edinburgh, where the 
coal-gas is of very superior quality, I have found it, as I have 
already stated, by the chlorine test, to be nearly as 1 to S, which 
I have confirmed by experiments, performed in the usual way, of 
producing the same light, and marking the quantity of gas con- 
sumed. 
We come now to the important question, Can oil-gas, in point 
of economy, compete with coal-gas ? and it is with a view of at- 
tempting to answer this, that I have dwelt so long on their 
comparative illuminating power. 
There can be no doubt, that if oil- gas could be afforded at 
as cheap a rate as coal-gas, it ought for many reasons to be pre- 
ferred. Much less capital is necessary to establish an oil-gas 
v/ork than one of coal ; the premises required are less exten- 
sive ; the gas-holders smaller, and there is no necessity for the 
expensive, and, unless properly managed, offensive purifying 
apparatus. Other circumstances would lead us to give it a de- 
cided preference ; but, with all these advantages, unless it be as 
economical as coal-gas, it of course cannot come in competition 
with it. Two advantages, it has been often stated, must in- 
duce many to prefer it to coal -gas, its less unpleasant odour, and 
its being free from all noxious ingredients, such as sulphuret- 
ted hydrogen, which renders the coal-gas so injurious to silver 
and plated goods. With respect to the odour, from all the 
trials I have made, I must confess, that there seems to be very 
little difference ; if any, it is certainly in favour of oil-gas ; but 
this, I conceive, ought not to be brought forward as any advan- 
tage which the one may possess over the other, because, if all 
