1824.] 
of the coal more than in the ratio of 
about two and a-half to one. I appre- 
hend the comparative illuminating power 
of the two gasses has been estimated 
usually upon too limited a scale, that of 
comparing the intensity of the lights 
within a few feet and calculating the 
square of the distance of each light 
from the object. It must be evident 
that the volume of the flame will have 
some effect on the number of luminous 
particles emanating from its surface. 
And although the intensity of the light 
would be greater within a given space 
from an oil-gas light, yet the aggregate 
quantity of light in a large apartment, 
or given area, would probably be greater 
from a coal-gas flame of large extent of 
surface, though of inferior lustre. The 
question of illuminating power there- 
fore seems to be of a compound nature, 
comprehending the relation which the 
area of the ignited body bears to. its 
intensity. That this is the actual state 
of the case seems to be fully borne out 
by the comparative lights of the street- 
lamps in all the towns of the kingdom 
which have been lighted with coal-gas 
and oil-gas. The latter may be com- 
pared to a spermaceti-candle with a 
small wick, which is very brilliant with- 
in a limited extent; but the coal-gas 
lamps having a much larger jet of gas 
( = four times the solid content of the 
oil-gas burners) the light, though not 
equally vivid to the eye, is capable of 
illuminating a much greater area of the 
atmosphere adjacent. 
But the quantity of oxygen consumed 
during the combustion of gas-lights, 
forms no small feature in the intensity 
of the light given out. (A perfect com- 
bustion of inflammable substances is 
scarcely ever obtained, for want of an 
adequate supply of oxygen.) Oil-gas 
consumes about three times its own 
bulk of oxygen, and coal-gas about twice 
its own volume. And it must'be evi- 
dent, that the more freely gas-lights are 
supplied with this indispensable agent, 
the more vivid will be the light afforded. 
It is the rapidity with which phosphorus, 
or iron, unites with oxygen at high 
temperatures which produces the in- 
tense and beautiful light we observe, 
when these substances are plunged into 
a jar of oxygen gas. 
Now as the atmospheric air is com- 
posed (in round numbers) of about one- 
fifth of its volume oxygen gas and four- 
fifth of azote, the quantity of air neces- 
sary to afford an adequate supply of 
oxygen for the perfect combustion of 
gas-lights may be easily computed. 
Comparative Value of Coal and Oil Gas. 
125 
In close apartments, there is usually 
a considerable deficiency of light, for 
want of a due circulation of the air to 
supply the lamps with fresh oxygen. 
While the carbonic, acid gas, produced 
by the combustion, is allowed to subside 
(being heavier than atmospheric air) in 
the lower. parts of the room and mix 
with the air to the great injury of the 
health of all those exposed to its dele- 
terious influence. Wherever artificial 
lights are used a good ventilation of the 
air ought to be preserved. And although 
this cannot always be acccomplished 
conveniently by leaving open doors or 
windows, it may be much more easily 
effected by having a pipe, of small di- 
mensions, communicating from the ex- 
terior of the building, and opening into 
any convenient part of the room, for the 
admission of atmospheric air; and ano- 
ther pipe, extending from the top of the 
light (as is now always done, where gas 
apparatus is properly constructed) to 
carry off the carbonic vapour produced 
by the combustion. 
Many of the gas-lampz in the interior 
of houses are provided with a hollow 
brass globe, or other ornamental figure, 
above the glass cylinder, which serves 
pretty effectually to condense the greater 
part of the sulphurous gas existing in 
coal-gas. But the density of carbonic 
acid gas being much greater than that of 
common air, a large portion of this de- 
leterious gas will descend, and remain 
dispersed in the air of the apartment, 
unless a current be produced to sweep 
the lower parts of the room and drive it 
off through an exit-pipe, either into a 
chimney or the open air. Adopting 
these precautions with regard to ven- 
tilation ; and never allowing a gas flame 
to project above the top of the glass 
cylinder; the inconveniences that have 
hitherto been complained of from the 
use of gas-lights would totally vanish. 
With regard to the comparative dis- 
advantages usually experienced between 
coal-gas and oil-gas it is not necessary 
for me to dwell; for the inconvenience 
in either case arises from negligence in 
not affording a proper ventilation. And 
although coal-gas contains rather more 
sulphur than oil-gas, and is consequently 
somewhat more liable to deface or tar- 
nish polished surfaces; yet the greater 
quantity of carbonic acid gas produced 
by the combustion of oil-gas will render 
the latter most injurious to health in 
close apartments. By judicious ventila- 
tion, however, both these evils are ef- 
fectually overcome. It is perhaps scarcely 
necessary 
