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the carbon and other constituents furnish their products to
the atmosphere—our 1,500 cubic feet of coal gas required to
produce one cubic foot of sulphurous acid, would, at the same
time, produce some 1,000 cubic feet of carbonic acid; and, in
addition to other far more abundant sources of dilution, the
sulphurous acid would be diluted with 1,000 times its volume
of carbonic acid. Accordingly, if you could measure the
proportion of carbonic acid gas in a room lighted by coal gas,
and take the 1,000th part of that proportion, you might form
some idea of the proportion of sulphurous acid gas existing
in the room. The highest result obtained by Professor
Roscoe, as I have told you, amounted to .32 per cent. of
carbonic acid, but how much of that was produced by the gas
burnt, and how much by tho respiration of the persons
present at the Theatre, I cannot tell you; but you may form
some notion of it by referring to the results of other experiments
made in crowded sleeping rooms with the windows
shut, and also in some barracks. In these cases the
proportion of carbonic acid, where no gas was burning,
approximated very closely to the amount found in the
gallery of the Theatre, where it was furnished alike
by the breaths of the individuals and the combustion of the
gas.
" Moreover, we can form some notion of it another way-
Speaking in round numbers again, every one of us produces
about two-thirds of a cubic foot of carbonic acid an hour,
which is the amount of carbonic acid gas that would be
produced by the combustion of one foot of coal gas, so that
every three individuals produce about as much as would be
produced by one burner burning 3 feet an hour. I think we
may take it for granted, therefore, that this .32 per cent.
found by Dr. Roscoe, was contributed as largely by the
individuals present as by the gas. We will assume, however,
that of the proportion found by Dr. Roscoe 0.2, or
nearly two-thirds of the whole, was produced by the combustion
of the gas, and the remainder by the breaths of the
people present.