According to this plan the sides of the chamber remain distinct from the basin-shaped floor, but descend into the acid lying there, so as to shut in the interior atmosphere. It has been noticed that especially this portion of the lead has been rapidly corroded when the acid contained much nitric acid, an eventuality often occurring through careless management. To avoid this, in many works the sides sre burnt to the bottom, so that all the acid is shut into the interior. When the process is properly conducted, however, this precaution is not necessary.
The steam required is generated in an ordinary boiler shown at N in Figs. 37 and 38. The lowest prcasure should be from 1 r to 2 atmospheres. The boiler is provided with a water puge, safety valve, and steam gauge, which latter may simply be a U-shaped open glass tube containing mercury. The water inlet is easily regulated through the copper tube u, Fig. 37, which, reaching to the roof beams, has more than sufficient height to overcome the pressure of the steam. This p'pe, opening out into a funnel at the top, is fed with water from the cistern O. A plug to, hanging ou the balance v, serves to regulate the outflow. When the float x, inside the boiler, sinks with the level of the water, the plug is lifted and the water can flow, but the plug is replaced so soon as the said float rises sufficiently.
The steam passes into the chambers by the copper pipe y, 2-in. bore. It enters near the gases, and in the same direction. The copper pipe terminates, in each case, just outside the chamber in a tap for regulating the amount of steam admitted, and provided with a gauge for that purpose. The other end of the tap is joined to a short piece of leaden pipe projecting about an inch into the chamber, and burnt to the chamber wall. In many works, the ste,am is introduced into the con nection pipes just at their commencement, so as to assist in mixing the gases and air.
Sometimes also, to economize fuel, the boiler is heated by the flame of the burning sulphur. In this way the heat of the gases in the chamber will be correspondingly diminished however, which may injuriously affect the conduct of the operation, especially in a small works during the winter seasen. Selious suspension of operations, too, may result from an injury to the boiler, which can easily happen. Therefore, heating the boiler in this manner is only advisable where fuel is
exfiessively dear, or where the climate is so hot that it is beneficial to reduce the temperature of the chamber gases.
It is scarcely necessary to state that the dimensions given above arc by no means constant, bid that they nre variable at plensure in accordance with the quantity of acid it is desired to make. The larger the works the lighter is the cost of eom,truetion in proportion to the make, and the the conduct of the operiition. Chambers may be found in most parts of England of far greater dimensions than those given above. In working them it is advisable not to have a corre spondingly enlarged sulphur kiln, but rather to use two smaller and to charge• them alternately. In this way the quantity of gas in the chambers is maintained at a more constant volume, as the sulphurous gas is less weakened by the periodical influx of air.
The brimstone-burner described above necessitates that the door shell be kept open for some time at each charge; in this way an excess of air is admitted just when the sulphur has burnt off. This is productive of bad results. For this reason many plans have been devised for differently arranged burners in which the evil might be lessened, but they have either not succeeded in accomplishing the desired end, or from possessing some new fault or difficulty have not come into general use.
The essential part of Kuhlmann's burner consists of four cast-iron retorts of the form used in making coal gas. In front are doors for admitting the brimstone, furnished with air holes, and behind are pipes for the escape of the gases. The gases pass from the retorts first into a large ante chamber in which they form a uniform mass, and, when sublimation takes place, deposit a soot like dust of sulphur.
Petrie invented a furnace which altogether does away with the intrc.duction of the sulphur through a door that needs opening. The sulphur is made to enter by a hopper or funnel placed on the top of the furnace. The ascending heat of the sulphur burning below brings down a new supply, so that the feeding is constantly kept up so long as the hopper is duly replenished. In front, the furnace has a perforated door for ventilation, and which is only removed for cleaning out the furnace.