METHODS OF WORKING CLAY DEPOSITS. 37 



along which it passes, dropping its sandy impurities on the 

 way and finally reaching the settling vats, into which the clay 

 and water are discharged, and where the clay finally settles. 



Details. — The disintegration of the clay is generally accom- 

 plished in washing troughs. These consist of cylindrical or 

 rectangular troughs, in which there revolves a shaft, bearing 

 a series of arms or stirrers (PI. IX, Fig. 1). The clay, after 

 soaking a short time in a pit, is shoveled into the washer, into 

 which a stream of water is also directed, and the revolving 

 blades break up the clay so that it goes more readily into sus- 

 pension. The water, with suspended clay, then passes out at the 

 opposite end from which the water entered. 



The troughing into' which the material is discharged is con- 

 structed of planking and has a rectangular cross section. Its 

 slope is very gentle, not more than 1 inch in 20 feet usually, and 

 its total length may be from 500 to 700 feet, or even 1,000 feet. 

 In order to economize space, it is usually built in short lengths, 

 which are set side by side, and thus the water and clay follow a 

 zigzag course. The pitch, width and depth of the troughing 

 may be varied to suit the conditions, for at some localities it is 

 necessary to* remove more sand than at others. If the clay con- 

 tains much very fine sand, the pitch must be less than if the 

 sand is coarse, since fine sand will not settle in a fast current. 

 In the case of very sandy clays, it is customary to place sand 

 wheels at the upper end of the troughing. These are wooden 

 wheels bearing a number of iron scoops on their periphery. As 

 the wheel revolves the scoops pick up the coarse sand which has 

 settled in the trough and, as the scoop reaches the upper limit of 

 its turn on the wheel, by its inverted position, it drops the sand 

 upon a slanting chute, which carries it outside the trough, 

 None of the New Jersey fire clays, which are washed, contain 

 sufficient sand to require the use of these wheels. 



By the time the water reaches the end of the troughing, nearly 

 all the sand has been dropped and the water and clay are dis- 

 charged into the settling tanks (PI. IX, Fig. 2), passing first, 

 however, through a screen of about 80' or 100 mesh. This 

 catches any particles of dirt or twigs and thus keeps the clay as 

 clean as possible. 



