MINING AND PREPARATION OF CLAYS. 67 



bottom of the vat is drawn off by slip pumps and for- 

 ced by these into the presses. , 



The presses consist simply of flat iron or wooden 

 frames between which are flat canvas bags. These 

 bags are connected by nipples with a supply tube from 

 the slip pumps, and by means of the pressure from the 

 pumps nearly all of the water is forced out of the 

 kaolin and through the canvass. 



When all of the water possible, is squeezed out the 

 press is opened and the sheets of semi-dry kaolin are 

 taken out. It is then dried either on racks in the open 

 air or in a heated room. 



As for every ton of crude kaolin usually only about 

 two-fifths 01 one fourth of a ton of washed kaolin is 

 obtained, it is desirable to have the washing plant at 

 the mines, for it avoids the hauling of 60 to 

 70 per cent, of useless sand which has to be washed 

 out before the kaolin can be used or even placed on 

 the market. 



