lAr on the llkminating Vower of Coal-Gas, SB'S 
from coal, that nothing but the most unquestionable facts can be 
expected to satisfy the public mind with regard to its truth. 
These facts have already been stated. They do not consist of a 
few insulated and doubtful trials, made with a particular kind 
of coal-gas carefully prepared on the small scale, from selected 
materials for a special purpose : but they may be said to be the 
average result of a numerous and extensive series of experi- 
ments, conducted for months together, under every variety of 
circumstance by which that result could be affected in the largest 
establishment. They furnish, therefore, data for a legitimate 
extension of all the consequences which they involve, in their 
application to the economy of coal-gas, as contrasted with that of 
oil-gas. Of these consequences, it is not the least important, that 
9600 cubic feet of coal-gas, when duly prepared, are capable of 
emitting a light equal to that of 8100 candles, for at least five 
hours, or of 40,500 candles for one hour. 
If this result be compared with the light afforded by oil-gas‘, 
of which IJ cubic feet, (as stated by Taylor and Martineau)^^ 
yield a light equal to that of ten candles for an hour, it would 
appear, that one cubic foot of oil-gas affords a light equal to 6| 
candles for an hour ; while an equal volume of coal-gas gives a 
light equal to 4/^ ca^^idles, during the same length of time. The 
illuminating power of the two gases, bulk for bulk, is thus as6| 
to 4 or as 8 to 5 nearly. This result coincides almost exact- 
ly with the conclusions to which I was led by the experiments 
recorded in the last number of this Journal ; and ought to be 
the more satisfactory, as it has been deduced by a mode of in- 
vestigation totally difierent. 
With regard to the probability of extracting from coal a spe- 
cies of carburetted-hydrogen, which shall contain a larger propor- 
tion of olefiant gas than has hitherto been obtained, I am dis- 
posed to indulge the most sanguine hopes. I conceive myself 
justified in cherishing this expectation, from observing the vast 
quantity of carbonaceous matter which escapes during the de- 
composition of the coal ; and from considering the evident pos- 
sibility of causing it, in a state of nascent volatilization, to unite 
in larger proportion, with the hydrogenous element, with which, 
even by the most approved' methods of carbonization, it still 
combines only in a partial manner. One mode of effecting this 
