The lead chambers ([fig. 2]) are usually constructed entirely—sides, roof, and floor—of lead sheets, which are joined together by means of a hydrogen blowpipe. The sheets forming the roof and walls are supported, independent of the bottom, on a framework of wood. The capacity varies from 35,000 to 80,000 cubic feet. The floor forms a flat collecting surface for the chamber acid which lutes the chamber from the outer air. The necessary water is introduced into the chamber as steam or fine water spray.

The Glover and Gay-Lussac towers are lead towers. The Glover is lined with acid-proof bricks and filled with acid-proof packing to increase the amount of contact. The Gay-Lussac is filled with coke over which the concentrated sulphuric acid referred to above flows, forming, after absorption of the nitrous fumes, nitro-sulphuric acid.

Fig. 2a.—Lead Chamber System—Section through X X (after Ost)

Fig. 2b.—Lead Chamber System—Plan

As already stated, two Gay-Lussac towers are usually connected together, or where there are several lead-chamber systems there is, apart from the Gay-Lussac attached to each, a central Gay-Lussac in addition, common to the whole series. The introduction of several Gay-Lussac towers has the advantage of preventing loss of the nitrous fumes as much as possible—mainly on economical grounds, as nitric acid is expensive. But this arrangement is at the same time advantageous on hygienic grounds, as escape of poisonous gases containing nitrous fumes, &c., is effectually avoided. The acids are driven to the top of the towers by compressed air. The whole system—chambers and towers—is connected by means of wide lead conduits. Frequently, for the purpose of quickening the chamber process (by increasing the number of condensing surfaces) Lunge-Rohrmann plate towers are inserted in the system—tall towers lined with lead in which square perforated plates are hung horizontally, and down which diluted sulphuric acid trickles.

To increase the draught in the whole system a chimney is usual at the end, and, in addition, a fan of hard lead or earthenware may be introduced in front of the first chamber or between the two Gay-Lussac towers. Maintenance of a constant uniform draught is not only necessary for technical reasons, but has hygienic interest, since escape of injurious gases is avoided (see also Part III).