CLAYS OF KEW YORK 801 



iron scoops on their periphery. As the wheels revolve the scoops 

 catch up a portion of the sand which has settled in the trough, and, 

 as each scoop reaches the upper limit of its turn on the wheel, it, 

 by its inverted position, drops the sand outside the trough. These 

 sand wheels are a help, but it is often necessary in addition to keep 

 a man shoveling the sand from the trough. 



If the sand is finer it is not dropped so quickly, and, distributed 

 more evenly along the trough, does not clog it up so fast. 



The zigzag arrangement of the troughing has been objected to 

 by some, as it produces irregularities in the current, causing the 

 sand to bank up in the corners, at the bends and at certain points 

 along the sides of the troughing. (E. Hotop. Tlionindustrie zeit- 

 ung. 1893) The effect is to narrow the channel, and consequently 

 increase the velocity of the current, thereby causing the fine sand 

 to be carried still farther toward the settling tank. This difficulty, 

 which is not often serious, has been obviated either by having the 

 troughing straight or by allowing the water and suspended clay 

 as they come from the log washer to pass through a section of 

 straight trough, and from this into another, of the same depth but 

 5 or 6 times the width, and divided by several longitudinal par- 

 titions. The water and the clay then pass into a third section, 

 twice as wide as the second, and divided by twice the number of 

 longitudinal divisions. By this means the water moves only in a 

 straight course, but as it is being continually spread out over a 

 wider space it flows with an ever decreasing velocity. 



By the time the water has reached the end of the troughing 

 nearly all the coarse grains have been dropped and the water is 

 ready to be led into the settling vats, but as a farther and necessary 

 precaution it is discharged on a screen of 100 meshes to the linear 

 inch, with the object of removing any coarse particles that might 

 remain, and also eliminating sticks and other bits of floating dirt. 



Two kinds of screens can be used, the first stationary, the second 

 revolving. The stationary screen is simply a frame covered with 

 a copper cloth and set at a slight angle. The water and suspended 



