72 EARTH COLOURS where they are treated with lime and kieserite, whereby gypsum is formed, and the mass is put through a filter- press, which retains the solids and leaves the effluent clear. Filter-cloths which have become choked by use are spread on a table and scrubbed with water, or else … FIG. 19. washed in a special machine (Fig. 19), consisting of a rotary drum, with belt drive, the rotation circulating the water in the interior trough and enabling it to extract the dirt from the cloths. The flow and dis- charge of the water are controlled by valves, and the water may be warmed by…
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Internet Archive · Gerstein - University of Toronto · Public domain (published before 1931). Free to use for anything.
