210 



THE POPULAR SCIENCE MONTHLY. 



acid gas are obtained by the decomposition of marble chips by a 

 fire of coke and a bath of sulphuric acid. The process of satura- 

 tion 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 sub- 

 stances are received. The presses consist of a number of four- 

 cornered plates or frames, over which cloths are stretched. The 



Fig. 9. — Centrifugal, Filter (Maumei)6). 



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 ver- 

 tical or a horizontal position, according as its effect is single, 



