114 > GAS LIGHTS. 
Gas Lights. quantity of light furnished is as the quantity of 
quantity of ligh quantity of oxy 
required to consume the gas. The carbonic oxide, which 
is already half saturated with oxygen, produces the 
least light, while the olefiant gas, as will be observed 
in the Table, requires the most. The gas from moist 
charcoal contains about 78 per cent. by weight of car- 
bonic oxide, the rest being principally hydrogen. On 
this calculation, the specific gravity of this gas comes 
out 6, hydrogen being 1. Its specific gravity by ex- 
periment, accowding to Cruickshank, is 5.4. Those from 
oak-wood and dried peat probably differ but little from 
the latter. This, however, might be ascertained near- 
ly, if we knew their specific gravities. The gas from 
cannel coal, when purified in the manner hereafter to be 
directed, consists’ almost wholly of carburetted hydro- 
gen. Its specifie gravity, derived by calculation from 
Dr Henry’s table, is 6.5. Carburetted hydrogen, on 
the authority of Mr Dalton, is 7.5,-hydrogen being 1. 
If Dr Henry’s experiment be correct, and 7.5 be the 
true specific gravity of carburetted hydrogen, then the 
cannel coal gas must contain free hydrogen, from its 
specific gravity being less than that of carburetted hy- 
drogen. The carbonic oxide, sulphuretted hydrogen, 
and sulphurous acid, which the coal gas will contain, 
if not purified, would contribute to increase the speci- 
fie gravity. 5 
Olefiant gas produces the most brilliant light of any 
other gas, which is to be attributed to its consisting en- 
tirely of hydrogen and carbon, and its great specific 
gravity. The gases, fiom the distillation of lamp oil 
and wax, in the way the coal is distilled, will be seen 
in the table to exceed the coal gas ; and that from wax 
nearly approaches the olefiant gas in the consumption 
of oxygen, and in the property of producing light. The 
substances, however, affording olefiant gas are too ex- 
pensive to be applied to the production of light by the 
process used for obtaining coal gas. 
., When the Lavoiserian theory was first advanced, it 
was generally thought that the light-and heat were fur- 
nished by the oxygen: hence, whatever might be the 
combustible body, the greatest light an:1 heat would be 
produced, the greater the quantity of oxygen which 
entered into combination in a given time ; and the in- 
tensity inversely as the space in which the combustion 
took place. It has since been held, and with good rea- 
son, that the inflammable body also contributes light 
and heat. 
There does not appear to be any just th of the 
YA, production of light and heat by combustion, but that 
- founded on the change of specific heat between the ma- 
terials of combustion and the body resulting from the 
combustion. We cannot, however, expect to derive 
much practical benefit from such a theory, till we are in 
possession of a correct table of the specific heat of bodies. 
Since chemists are sufficiently acquainted with four 
inflammable gases to obtain them in a state of purity, 
namely, hydrogen, carburetted hydrogen, carbonic 
oxide, and olefiant gas, we might, by afew experi- 
pm 4 some idea of the relative quantities of fight 
afforded by carbon and hydrogen. If we suppose 
these gases to consist of pure hydrogen, and still re- 
taining their respective densities, then the intensity and 
quantity of light would be directly as their densities, 
In as much, therefore, as their light differs from the ra- 
tios of their densities, may be attributed the relative 
quantities of light afforded by the bodies of which they 
are composed. 
Two small gazometers will be necessary for these 
experiments, the one to eontain hydrogen gas, and the Gas 
pee se 2m inflammable gas to be compared with it. Let ™ ud 
the pressure of each be exactly the same, and let the Method 
gas trom each pass through exactly the same sized aper- measurir 
ture, at the time it is burnt, The flames must now be the inten 
compared with each other, by making shadows in Stes of 
them fall upon a white surface); then remove the strong! gifferen: 
est light backward, till the shadows are of the same in gases. 
tensity. The squares of the distances of the flames, 
from their respective shadows, will express the ratio of 
the illuminating powers of the two flames. If, for in- 
stance, hydrogen were compared with olefiant gas, and. 
if the carbon of the latter contributed as much to. 
the illumination as the hy , then the ratio of the. 
squares of the distances of the flames from the shadows’ 
when the shadows were of the same intensity, would 
be as 1 to 11.85. If, however, the flame of the olefiant 
gas will not require to be shifted so far back, in order 
to make the shadows equal, then it will show that the 
carbon of this gas has not afforded the same light as so 
much hy would have done. If now the com 
rison be made between hydrogen and carburetted hy- 
drogen, the ratio of the squares of the distances, if 
latter gas were all hydrogen, would be as 1 to 7.5. But 
the distance of the flame of the carburetted hydrogen 
gas will probably fall short of the 4/7.5, owing to the 
carbon it contains ; but it contains a less proportion of 
carbon on the whole than olefiant gas, and therefore 
ought to produce more light, in proportion to its dens , 
sity, than olefiant gas. In these instances we have pres ; 
sumed, and with good ground, that a given weight of 
hydrogen, in its combination with oxygen, affords more 
light and heat than any other inflammable body. In 
these and all other instances of combustion, the absolute 
quantity of light and heat will be the same, whatever 
may be the density of the combustible body and the 
oxygen ; but the intensity may be much increased by 
diminishing the time of burning the same rome er 
matter, pre the space in which the combustion takes 
place. Hence we accumulate light and heat by means 
of bellows, and other means of furnishing oxygen, with 
t facility. We should also get a proportionate ef. 
ect by increasing the density of thé oxygen. If hydro- 
gen and oxygen were increased in their density by arti- 
ficial pressure, and presented to each other for combus« 
tion, the intensity of the light and heat would be in the 
complicate ratio of their increased density. If each 
were compressed into half the space, then the effect of 
their combustion would be four times the intensity of 
that in their natural state. In this way much greater 
intensity of both light and heat may be produced ‘than 
we have hitherto heard of. The carburetted hydrogen 
would much exceed olefiant in producing light, if 
its density were equal to the latter gas, because it con- 
tains more hydrogen than olefiant ; And if pure 
Phar art icingerde wh yt Ss gas, the inten- 
sity of its light would be nearly twelve times 
than when burnt in its ordinary state, and it would be 
to olefiant gas as about 7to 3. 
Cannel coal, and the most bituminous of the News 
castle coal, and many others in the country, when ex- 
posed to distillation at a red heat, furnish several gase-. 
ous products, the principal part of which is the carbu- 
retted hydrogen, a quantity of tar, and an aqueous 
fluid charged with carbonate of ammonia. The sepa- 
ration of the carburetted hydrogen, which when pure 
burns with great brightness, and without emell, is now 
effected with great success, on the largest scale, and the 
