322 NOTICES OF THE MEETINGS [May 20, 
The light emitted during the combustion of coal gas is due 
entirely to the first or illuminating class of constituents, which yield 
an amount of light proportional to the quantity of carbon contained 
in a given volume; thus, propylene and butylene yield respectively 
50 and 100 per cent more light than olefiant gas, because they 
contain respectively 50 and 100 per cent more carbon in a given 
volume. 
It would not be desirable to employ a gas containing only 
luminiferous ingredients, even if it were possible to manufacture 
such a gas, because it is exceedingly difficult to consume these 
constituents without the production of smoke attendant on imper- 
fect combustion. A diluting material is therefore necessary to 
give the flame a sufficient volume, so as to separate the particles 
of carbon farther asunder, and thus diminish the risk of their 
imperfect combustion. 
All the three diluents above-mentioned perform this office equally 
well; but if we study their behaviour during combustion we shall 
find that in a sanatory point of view hydrogen is greatly to be 
preferred. 
The two objections most frequently urged against the use of 
gas in apartments are, first, the heat which it communicates to 
the atmosphere, and, second, the deterioration of the air by the 
production of carbonic acid. Now, in their action upon the atmos- 
phere in which they are consumed, the above three diluents present 
striking differences in these two respects. 
One cubic foot of light carburetted hydrogen, at 60° F. and 30 in. 
barometrical pressure consumes two cubic feet of oxygen during its 
combustion, and generates one cubic foot of carbonic acid, yielding 
a quantity of heat capable of heating 5lbs. 140z. of water from 32° 
to 212°, or causing a rise of temperature from 60° to 80.8’ in a 
room containing 2,500 cubic feet of air. 
One cubic foot of carbonic oxide at the same temperature and 
pressure consumes during combustion 4 a cubic foot of oxygen, 
generates one cubic foot of carbonic acid, and affords heat capable 
of raising the temperature of 1lb. 140z. of water from 60° to 
66.6°. 
One cubic foot of hydrogen, at the same temperature and pressure, 
consumes 3 cubic foot of oxygen, generates no carbonic acid, and 
yields heat capable of raising the temperature of 1]b. 130oz. of 
water from 82° to 212° or that of 2,500 cubic feet of air from 
60 to 66.4°. 
This comparison shews the great advantage which hydrogen 
possesses over the other diluents, especially over light carburetted 
hydrogen, which is evidently a very objectionable constituent, and 
illuminating power, but a specimen of it brought from the coal strata beneath 
Chat Moss, Lancashire, shewed that it yields no more light than hydrogen or 
carbonic oxide when consumed from a j/ish-tail burner. 
