38 .CLAYS AND CLAY INDUSTRY. 



The settling tanks are of wood, usually about 4 feet deep, 8 

 wide and 40 or 50 feet long. As soon as one is filled, the water 

 and clay is diverted into another. When the clay has settled, 

 most of the clear water is drawn off, and the cream-like mass 

 of clay and water in the bottom of the vat is drawn off by 

 means of slip pumps and forced into' the presses. These consist of 

 flat iron or wooden frames, between which are flat canvas bags. 

 The latter are either connected by. nipples with the supply tubes, 

 or else there may be a central opening in all the press bags and 

 frames, which, being in line, form a central tube when the press 

 is closed up. By means of pressure from the pumps, the slip 

 is then forced into the press, and the water is also* driven out of 

 it. It commonly takes about two hours to> fill a press. When 

 the water has been squeezed out the press is opened, and the 

 sheets of clay are removed from the press cloths and sent to the 

 drying room or racks. 



Air separation. — This is a method of cleansing clays which 

 has been rarely tried, yet in some of the cases where it has been, 

 used it is said to> have met with success. It is especially applic- 

 able to' those clays from which it is necessary to' remove simply 

 •coarse or sandy particles. The process consists, in brief, in feed- 

 ing the dry clay into a pulverizer, which reduces it to the con- 

 dition of a very fine powder. As the material is discharged 

 from the pulverizer into a long box or tunnel, it is seized by a 

 powerful current of air, which at once picks up the fine particles 

 and carries them along to the end of the airway, where they are 

 ■dropped into a bin. The coarser particles, which are too heavy 

 to' be picked up by the current, drop back and are carried through 

 the pulverizer once more. Such a method would be especially 

 applicable to' kaolins that are free from iron, but probably would 

 not be found adaptable to many of those containing ferruginous 

 particles. 



There are several forms of separators on the market. In the 

 Raymond pulverizer and separator, the material is pulverized in 

 the lower part of the machine and then thrown upward, the 

 finer particles being carried off by a fan to the discharge hopper, 

 the coarser ones falling back into the hopper. 



