The Passage of the Gases through the Chambers.—As the gases derived from the combustion of pyrites at the time of entering the chambers are lighter than those formed in the roasting of native sulphur under similar conditions, while on leaving the chambers they are somewhat heavier on account of their bolding somewhat more oxygen, it is evident that the increase of weight in the gases during their passage will be even greater in the case of pyrites than in that of brimstone. The following figures will show the proportions.
We have already seen that a litre of gas is increased in volume on its passage to the chambers to 1.346 litre as it enters the first chamber, and the weight of this litre will be 1.5230 grm., or 1 litre will weigh 1.1315 grm. This 1.098 litre of gas leaving the chambers will weigh, according to preceding calculations, 1.2861 grm., or 1 litre will weigh 1.1713 grm.
It is therefore evident that the same rule concerning the manner of conducting the gases through the chambers will bold good in this case as in that of acid made from brimstone.
In some cases, however, where the gases are first taken through a flue several hundred feet in length, in order to deprive them of their arsenic to a certain extent, they become cooled to such a degree that, together with the loss in weight of arsenious acid, they actually become lighter instead of heavier, and in consequence it has been necessary, as at Freiberg, to construct the chambers on the opposite plan, the gases entering in each case at the bottom and leaving at the top. But the gases in this case enter the chambers at a temperature so low as 27° (80° F.), and it is a question whether the acid can be so beneficially made at that degree. Further, they cannot hold more than 10.5 per cent. of the necessary water as steam.
Division of the Labour.—This depends entirely upon the class of kiln used, and has already been sufficiently treated uuder each kiln which has been described.
The "observation of the process" and "recovery of the nitrogen compounds," as described for the manufacture from brimstone, remain unaltered.
Working Results.—In consequence of the fact that the same quantity of sulphur from pyrites produces 1.314 times as much gas as native sulphur, the chamber space will have to be 1.314 times as great for the former as for the latter, or what comes to the same thing, the amount of sulphur burnt in the former case must be only of the amount of native sulphur burnt in a similar time.
The dilution of the chamber gas with nitrogen, owing to the oxidation of the metallic portions of the pyrites, has an evil effect in necessitating an augmented consumption of nitro. Instead of 6 per cent., which suffices for native sulphur, 10 per cent. upon the amount of sulphur oxidized from the pyrites will be requisite. These 10 parts of nitre are equivalent to 7.41 parts mono hydrated nitric acid, or parts of nitric acid at 69° Tw. The proportion of this which may be economized by the Gay-Lussac tower, remains the sathe as for brimstone.
When the pyrites used contains 46 per cent. of sulphur, 4 parts of which are left in the cinders, the 42 parts of sulphur converted will yield about 128 parts of sulphuric acid at 170° Tw., that is, 100 parts of sulphur converted give 804.76 parts of acid at Tw., or 288.43 parts of monohydrate. As the theoretical maximum possible make is per cent. of monohydrate, the loss amounts to 7.45 per cent., besides the sulphur wasted in the pyrites cinders. Having already.given full instructions concerning the manipulation of a brimstone acid works, and also enlarged upon all the points in which the conduct of the process with pyrites differs from that with brimstone, and the precise degrees of those differences, it will be easy to deduce the figures corresponding to any desired scale of manufactory.