The process is complete in 2 to 4 weeks. Gartner, working according to this process with 150 kilogrammes of lead in a chamber 1·26 metre long, 0·78 metre high and 0·78 metre wide, obtained good white lead in 28 days. The apparatus designed by H. Kirberg for the manufacture of white lead is illustrated in Figs. 12, 13 and 14. The lead plates are hung upon the laths, _a_, in the chambers; the supports of the laths, _b_, go through the slits, _c_, in the supports, _d_, and project through the walls at _e_. The carriers, _b_, hang from bolts by brass wire. By striking the end of the laths, _e_, they are made to swing so that the white lead loosely adhering to the lead plates is shaken off and fresh surfaces of metal are exposed. The openings in the walls through which the ends of the laths project are closed by indiarubber. In order to prevent the production of dust when the chambers are emptied, water is introduced in a fine spray upon the lead plates from the copper tubes, _v_, placed under the roof of the chamber. The water washes off the remains of the white lead from the plates. [Illustration: FIG. 14.] In a similar manner, the white lead process may be carried out in a shorter time when the gases enter the chamber under increased pressure; but this is attended with difficulties, since continuous supervision of the apparatus and of the tightness of the chamber is necessary. [Illustration: FIG. 15.] The apparatus of W. Thompson (Fig. 15) consists of a chamber, _A_, constructed with a false roof, _B_, to carry off the condensed vapours, and provided at both sides with doors, through which the waggons, carrying the lead, are introduced and removed. The pipes, _n_, which convey air and carbonic acid, are provided with branches, _e_, which reach to the sides of the chamber, and are joined to the perforated tubes, _D_. The pipes, _n_, are provided with reservoirs, _b_, which prevent the too rapid entry of the air or carbonic acid, and at the same time give a sufficient heating surface. Upon the waggon, _E_, are the frames, _v_, which support the lead plates. The plates may be solid or gratings; they are 3 to 12 millimetres thick, and are arranged at intervals of about 25 millimetres in the frames. The troughs, _F_, for the reception of the acetic acid are filled from the reservoir, _Z_. The steam pipe, _C_, effects the evaporation of the acid; the steam pipe, _d_, heats the chamber at the commencement of the process, and also when _C_ is out of use. When the chamber is filled with lead, the troughs, _F_, are filled with acetic acid of 5 per cent. strength. The chambers are closed, and steam is led through _C_ and _d_ until the temperature in the chamber reaches 25° to 50° C., and the evaporation of the acid begins. Then air is forced in under a small pressure through _n_, _e_, _D_ during 3 to 4 days, after which follows a mixture of equal parts of carbonic acid and air, continued until the formation of white lead is complete.