It is evident, then, that the gases must be introduced just under the ceiling of the chamber, and they must escape at a point as near the bottom as is convenient. When the first condition is neglected, and the gases are admitted near the bottom, a great loss of draught is caused by the reduction of the height of the vertical kiln flue, and consequently a waste is incurred, because the gases are so slow in passing through the chamber system. When the gases from the first chamber are not drawn out below, but at the top, a very great loss is unavoidable. With such an arrangement the gases in the first chamber do not sink regularly, but a great part of them will stream just under the ceiling into the connection pipe and immediately into the second chamber, whilst in that part of the first chamber space lying below the exit, stagnation takes place, as it becomes more and more filled with nitrogen. An opportunity of observing how great this loss might actually be in practice was presented in a works in Tuscany, wherein the connection pipe left the first chamber near the ceiling and took the gases into the top of the second chamber. The working results obtained for a long time were so unusually bad as to amount to only 150 parts of monohydrated acid from every 100 parts of sulphur burnt during the period that the connections were left iu this way ; yet the moment that a change was made in this respect, and the gases were withdrawn from near the bottom of the first chamber and admitted near the top of the second, the product was increased to 285 parts per 100.
It is therefore unnecessary to say that the lead-strving plan adopted by some manufacturers, in which lead c.urtains were suspended reaching alternately to the bottom and to the top of the large chamber, was built upon false principles. We cannot, however, recommend the arrangement of curtains in any disposition, on account of the rapid corrosion to which they are subjected.
It is found more profitable in practice not to attempt to produce all the acid in one chamber, but lather to be content with allowing the majority to condense in a first chamber, aud to convey the gases from the first chamber before they have become exhausted into a second chamber, and from this into a third, both of much smaller dimensions than the first, because they have to receive a much less volume of gas. With such chambers, also, the gases should always be allowed to enter above and escape below, and this is still mote necessary when, as is usual, fresh steam is admitted at each step, whereby their temperature is increased and their density diminished, so that during their stay in the small chambers they undergo a new reduction in tetuperature and increase in density.
The above-described manner of conducting the gasea through the chambers is based on tbe increase of their density through cooling, and which is modified in many ways by the condensation of parts of the gas and of the steam. It will therefore be interesting to compare the densities of
the gases entering the first chamber and escaping from the last, in order to satisfy ourselves whether the increase of their density really has anytlaing to do with the course of the process.
We have already seen that 1 litre of the dry gas, composed of sulphurous acid, oxygen, and nitrogen, found in the first chamber, weighs 1.4547 grm. at 0° C. and 760 nam. B. Further, we have found that the volume derived from V at 0° C. and 760 mm. B., when saturated with steam at C. rem is V' = (273 + - 273 (b — e) V ; 760 when e is the tension caused by saturation with steam at t° C. Finally, we have shown that the temperature of the gases immediately after entering the first chamber is at 50° C., and that this temperature is equal to 92 mm. Whence we know that each 1 litre of the gas at 0° C. and 760 mm. B. in the first chamber will be increased by 760 1; the saturation with steam at 50°C. to V' = (273 + 50) ; = 1.346 litre.
273 (760 — 92) As 1 litre of steam at 0° C. and 760 rem. (weighing grm.) prodnces at 50° C. and ; 92 min. a volume of 1(273 + 50) 760= 9'7739 litres. Then, according to the proportion 273; 92 : 0'804343 = : x, each 1.346 litre of steam at 92 mm. weighe 0.1108 grm. The total weight, thereforo, of 1'346 litres of gas at 50° C. and 760 rem., and saturated with moisture, is 1.4547+ = 1.5655 grm., or 1 litre of the gas mixture weig 1 65 hs = grm.
We have now to reckon in the same way the weight of the gases which leave the last chamber, containing the superfluous oxygen and nitrogen in the dry proportion of litre oxygen and 0.95 litre nitrogen in each litre, but saturated with moisture. Tii be sure that we do not make their specific gravity too high we will take the temperature at 20' C., as it is generally lower. As at 0° C. and 760 min. 1 litre of dry oxygen weighs 1.4298 grm., and 1 litre dry nitrogen 1.2562 grm., then 1 litre of the mixed gases at the same temperature and pressure will weigh 0.05 ; 1.4298 + 0.95 ; 1.2562 = 1.26488 ; grm. But taking into consideration the tension (273 +20); 1; 760 = 1 • 09S litre.
17'391 derived from the saturation with steam at 20° C., we have 273 (760-17 391) Also 1 litre of steam at 0° C. and 760 rum., weighing 0.804343 grm., becomes at 20° C. and 1 (273 + 20) 760 mm. = 46.902 litres. Then, according to the proportion 273; 17.391 46•902 : = 1.098 r, each litre of steam weighe, at 17.391 ram., 0.0188 grm. Then the combined weight of 1.098 litre of the gas at 20° C. and 760 mm., and saturated with steam, = 1.2649 + = 1.2837 grm., or 1 litre of this compound weighs = 1.169 grm. It is therefore heavier than tho 1 litre of etcam-saturated gas mixture on its entering the first chamber, whose weight, as we have seen, was only 1.163 grm.