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23
You know that sulphurous acid is used for the bleaching of
silk, straw, &c., and for the preservation of catgut and things
of that kind, which, if corrosive, it would be quite unfit for.
Therefore, per it is not a corrosive substance, except in a
concentrated form, and then but very feebly.
"With regard to the amount of sulphur produced in the
combustion of gas, the Act of Parliament says that 100 cubic
feet of gas shall not contain of sulphur, in any form, more
than 20 grains. Now, the ordinary mode of estimating the
amount of sulphur in gas, consists in burning the gas somewhat
in this form f illustrating , and then collecting the products of
combustion, and estimating the sulphate of baryta obtainable
therefrom. The process is based upon the assumption that the
whole of the sulphur in the gas gets burnt. But we know
that the whole of the carbon does not, and neither does the
whole of the sulphur; so that in a process of this kind we
only estimate, so to speak, so much of the sulphur in the gas
as in the burning of the gas gets converted into sulphurous
acid. But in an experiment of this kind the gas is burnt
under very different conditions to those under which it is
burnt when we use it as an illuminating agent, and, so far as
I know, no experiments have been made to show the amount
of sulphurous acid produced by a certaiu number of cubic
feet of gas when burnt in the ordinary way. A great many
experiments have been made with the gas burnt in one small
jet, or from a Leslie's burner burning at a very slow rate;
but, so far as I know, there have been no experiments, at any
rate not satisfactory experiments, where gas has been burnt
at the rate of 5 cubic feet an hour, under the ordinary conditions
; and it must not be assumed that the amount of
sulphurous acid produced per cubic foot of gas is the same
when the gas is burnt in two such different manners. It may
be very different. So far, then, as regards the amount of
sulphurous acid produced, all I can tell you is, that when gas
is burnt somewhat in this way it gives rise to an amount of
sulphurous acid which corresponds to about the 20 grains of
sulphur allowed by the Act of Parliament. Very frequently