acid gas are obtained by the decomposition of marble chips by a fire of coke and a bath of sulphuric acid. The process of saturation being complete, the juice is drawn through sand-catchers by means of a lye-pump, which conveys it under pressure into the filter-presses of the first saturation, where the precipitated substances are received. The presses consist of a number of four-cornered plates or frames, over which cloths are stretched. The
residuum is deposited between the plates or in the frames, as the case may be, while the fluid passes through the cloths before leaving the press, and is thus filtered.
From the presses the liquid mass passes to the evaporator. This consists of one or more cylindrical vessels, either in a vertical or a horizontal position, according as its effect is single.