WORKING RESULYS.—The Proportion of Sulphur used in regard to the Chamber Space.—We have already seen that theoretically a very small amount of nitrous or hyponitric acid is necessary for the formation of a very large quantity of sulphuric acid from a mixture of sulphurous acid, oxygen, and steam. But an absorption of this acid by the sulphuric acid constantly takes place, and there is a certain, but not as yet correctly estimated, time necesssry in order to completely change a fixed volume of the gas mixture into sulphuric acid through the agency of the nitrogen compounds. The amount of sulphuric acid which forms in a certain time, or the volume of gas condensed into sulphuric acid in that time, is proportioned, up to a certain point and under equal conditions, to the increased consumption of nitrogen compounds. The time necessary for the conversion of a certain volume of gas into sulphuric acid will thus be diminished by increase of the nitrogen compounds, and augmented by their reduction.
In a chamber space of certain size, constantly filled with a mixture of sulphurous acid, air, and steam, and to which a certain quantity of nitrogen compounds is added, only a small amount of the volume of gas can condense in a certain time to sulphuric acid, and this increases up to a certain point with the increase of the nitrogen compounds. The quantity of sulphuric acid made in h given time depends therefore as much upon the amount of chamber space as upon the nitrogen compounds provided. Other conditions being unchanged, it stands in direct proportion to the space or to the amount of the volume of gas with which that space is filled. It can be increased by an increased consumption of nitre up to a certain point, and similarly, this consumption can be reduced to a certain degree if the chamber space be increased. There are limits to these points in practical working, based as much upon technical as upon financial grounds.
In the chambers we have described there are about 33,435 cubic feet (974 cm.) space, and with these it was found that the best working results were got when the amount of sulphur burnt in 24 hours was not more, but not much less, than 3 lb. per 100 cubic feet (•5 kilo. per 1 cm.),
under which conditions for each 100 parts of sulphur there were needed 6 parts of clean nitre, or 4.45 parts of monohydrated nitric acid, or 8.24 parts of nitric acid, of 1.340 sp. gr. at 15° C., or containing 54 per cent. of monohydrated acid. This daily consumption of sulphur could be increased to 3i lb. per foot without ill effect. In larger works generally much more sulphur is burnt in the same time and space. In this country it reaches, and sometimes exceeds. 5 lb., while in Germany and France it is seldom higher than 4i lb.
Theoretically the 3 lb. per 100 cubic feet in 24 hours, or • 5 kilo. per 1 cm., is arrived at by the following calculation. We have already seen that for each kilo. of sulphur burnt, 8345 litres of gas at 760 mm. and 50° C., and saturated with moisture, are conveyed into the chambers; then •5 kilo. sulphur produces litres of gas per cubic metre, or 1000 litres space—that is to say, the formation of the sulphuric acid from the gas introduced at the above rate of consumption will occupy about 51 hours.
The following calculations may servo to show the influence of the nitrogen compounds upon the production of the acid. One hundred parts of sulphur require for their conversion to 200 parts of sulphurous acid 100 parts of oxygen from the air. These 200 parts of sulphurous acid need further 50 parts of oxygen for their conversion to sulphuric acid, from which is lost by the reduction of the 3.812 parts of anhydrous nitric acid (derived from 6 parts of nitre) to 3.247 parts hyponitric acid, only •565 part, and but part is lost in reducing this to parts of nitrous acid.
On the supposition that the nitrogen compounds exist in the chambers as hypnnitric acid, the amount of oxygen taken from the air for the conversion of each 200 parts of sulphurous acid to sulphuric acid = 50 — 0.565 = parts, while each 3.247 parts of hyponitric acid only contain parts of oxygen. The hyponitric acid therefore permits the combination of the sulphurous acid with a volume of oxygen from the air which is 49435 = 21.9 times as great as 2 • 259 its own contents of oxygen.