106 
> For the pein Magaxine. 
tiie yosetove 
Boi? 
Onothe Ini paawatinc Power, of Kaa 
rosiioos oi & Om. Gas. yo 
ERHABPS, no)question. -has . more 
incdivided «the ‘opinion, of scientific 
men than that of the illuminating 
power, -and,'consequently,. the value of 
the inflammable gases obtained from the 
distillation, of, oil and coal. It is, in- 
deed, \caleulated to render the judg- 
ment, of those gentlemen, who make 
scientific pursuits a profession, of little 
weight or authority, either as to oral 
or written testimony, when we find 
such extraordinary discrepancies as in 
the -present case; some authorities 
having stated the illuminating power 
of oil-gas to be from three and a half to 
four times greater than that of coal- 
gas.* While others, with Professor 
Leslie at their head, have not allowed 
oil-gas to exceed coal-gas, i in illuminat- 
ing power, more than about the ratio 
of 150 to 100.+ 
Now, however extraordinary it might 
at first view appear, both these state- 
ments may be correct as to the facts 
deduced from the experiments con- 
ducted by the respective parties, though 
they are certainly very far from satis- 
factory, or even correct, as general 
statements of the comparative “Wlumi- 
nating power of the two kinds of gas, 
considered as an article of general de- 
mand with the consumer. The fact 
appears to be, that different parties 
have undertaken to espouse different 
interests in the investigation of this 
important branch of civil economy ; 
and, in so doing, have, in some mea- 
sure, sacrificed the dignity of genuine 
science, by making a sort of ea parte 
statement of the case, 
It is well known to every person 
conversant with the coal-trade, how 
greatly the quality of different speci- 
mens of coal varies, and even that ob- 
tained from the same coal-seam at dif- 
ferent stations. While some varieties 
are best adapted for producing coke, 
others, having less solidity and greater 
inflammability, are better calculated for 
affording gas. Not only the quantity, 
but sie” quality of gas also varies very 
considerably, from different specimens 
Of coal; the quantity of sulphur existing 
* Ann. Phil., vol. vi. p. 404. Experi- 
Me of Messrs. Davy, Faraday, and Phil- 
. ps. z. € } ne 
’ + Coal-gas° Company’s Report—Jul 
1924. wot : 
Coal and Oil Gases compared. 
[Sept. 1, 
in some samples rendering them quite 
unfit, to. be eh ae fay "een 
without, . a,, eonsinerenlg ner 
trouble incurred i in poly 
render it. fit for use. 
known, that the variety ie, 
ist by, 
or Wigan, Coal, produces gas of: oe 
superior quality to.that from » New, 
castle and Durham. coal eee. or ain- 
deed from any other of the English co ol- 
lieries; and that the Pa, ‘tn 
the south of Scotland yield varieties ‘of 
coal even superior in quality, especially 
for gas-making, to that of the Lanca- 
shire coal-field. Now these facts being 
(it must be presumed) well known to 
every person in any way ‘connected 
with gas-works, it. certainly appears 
very remarkable that scientific men, 
who undertake experiments to estimate 
the value of the respective gases, should 
omit taking these points into their con- 
sideration. Thus, in the experiments 
of Messrs. Davy and Co., coal-gas -of 
inferior quality, or about 400° spec. 
grav., was compared with oil-gas of the 
best ‘quality, or above 900; and Mr. 
Leslie compared the best coal. -gas of 
the Edinburgh works, about 700. spec. 
grav., with oil-gas of inferior quality, 
or but little exceeding a spec. gray. 
800. : 
Although the value, or illuminating 
power of each species of gas, be not 
found in exact ratio to the specific 
gravity — oil-gas having, ceteris payi- 
bus, greater ‘iWuminating power ; yet, 
for a general estimate, the density af- 
fords a pretty fair criterion of the value 
of each kind of gas: consequently, 
whenever a comparison is instituted of 
the respective advantages afforded to 
the public from the use of either kind, 
the specific gravity of the gas should al- 
ways be expressed. 
It is, therefore, with some ghee 
I find, in the July number of is Edin- 
burgh. Philosophical Journal, a more 
able investigation of this important 
question than has hitherto been re= 
sented to. the public. The authors of 
the paper (Drs. Christison and’ ‘Tur- 
ner{) appear to have viewed the. ques- 
tion in all its bearings, during the ela- 
borate experiments they conducted, 
determining the comparative ‘value of 
the two gases. : 
They selected the photometer of 
Count Rumford in preference : y the 
+ This report was. ste 
before the Royal Society of Ediz 
