The specific gravity of the gases passing up the vertical shaft on their way to the chambers will he lessened by the beat, and in consequence the draught will he increased hy the influx of air.
The temperature in the chambers assists and hastens the formation of sulphuric acid, so long as it is not allowed to exceed about 60° C. ; in a much higher temperature the nitrogen compounds may be reduced to nitrous oxide, or even to nitrogen itself. Further, the gases iu the.first chamber must be kept at such a temperature (according to experience, about 40-50) C.) that the water not yet forming hydrate (4H080,) may he maintained as steam, as its condensation weakens the sulphuric acid formed, and the nitric acid gas condensed at the same time is no longer available in the process.
In confirmation of these remarks, it has been found that it takes longer to get chambers into working order when commencing operations in cold weather than when Et start is made in warm weather, and that when the chambers have been subjeeted to cooling, either from atmospheric causes or from irregularities in the working, the acid produced at such a time is weaker than usual, and contains more nitric acid. In cold climates, too, the relative consumption of nitre is greater in winter than in summer. Hence it follows also that in very small works it becomes necessary to cover in the connection pipes between the kilns and the chambers, and often to place the chambers themselves in a closed building, so as to protect them from the ill effects of the weather. In warm ti 0111y C1111 the 0110011/0115 Safely bo left In small works, too, it is imperative that the moisture admitted to the chambers be really steam, and nut mero water as is sometimes the ease.
Draught and `apply of .1 ir.—Tho force of draught by which air is drawu into the sulphur burlier, and by which the kiln gases are drawn through the chamber system and out again (or what remains of them) into the atmosphere, has ilS much to do with the process as the temperature. This draught arises from several cans,•,, but principally from the str, nut of hot gasf s in the channel connecting the kilns and the chambers. A, the specific gravity of sulphurous ucid is more than doable that of air, it may be imag,ined that the kiln gases arc not lighter than air. But
it may be well to know what is their real specific weight. A, a basis for the calculation we must take the following figures.
A t n temperature of 0° U., and a barometrical pressure of 760 mute.
1 litre of dry air will weigh 1.2932 grin.
1 „ oxygen 1•4298 „ 1 „ nitrogen 1 „ sulphurous acid , 2 • 8731 „ 1 „ steam „ .. • 804343 ., Now one volume of oxygen forms, with the amount of sulphur burut in it, one volume of sulphurous acid, which requires a further half-volume of oxygen to form sulphuric acid. Then for every 14 volumes of sulphurous acid containing 14 volumes of oxygen, there are required am additional 7 volumes of oxygen to form sulphuric acid. This oxygen, however, is introduced to the isulphut-litn•ner as air containing 21 ports of ox)gt n mid 79 parts of nitiogen per cont. Then with (moll 14 7 = 21 volumes of oxygen there are ;fist) 79 volumes of nitrogen entering into the kilns, and thus the gas therein produced will consist, theoretically, of 14 snlpliurous ac.il 7 „ oxygon 79 „ uitmugen 100 -- Experience teaches that to get good working results an excess of oxygen is uecdful, which may innount to about 5 per cent.
If we represent the unkuown volume of this excess of oxygee necca•ary beyond the 100 volumes of gas mixture by x, then the amount of nitrogen added will be x. This must be added to the 79 volumes of nitrogen which are introduced by the 21 volumes of oxygen necessary to convert 14 volumes of sulphur into sulphuric acid. Thelerote the united volume of nitrogen and oxygeu required to he admitted to tho kilns for every 14 volumes of sulphurous acid so as to have an 79 100 excess of oxygen, will be x = 79 — 21 As x represents 5 per eont., or of this volume, we have then 1 100 79 5 x = + 21 — 20 + 5 1679 79'21 Hence follows, x — or, x then x = 20 10 = 5 18 volume. That is to .ay, besides the before-mentioned theoretical volume of gases, there is an excess of volumes of oxygen needed, together with its equivalent of nitrogen, which will be 5.15. volumed of '1 he volume of gases formed in the btu•ner and conducted thence into the chambers will be them composed as follows:— For every vols. sulphurous mid i + = 12•18 „ oxygen, and 79 + •50 = 98.50 „ nitrogen Total .. 124 • 68 volumes.