Tennessee Phosphate Industry. 77 



shape of the particles. The latter point, namely, the shape of 

 the particles, is of prime importance. The clay usually exists in 

 flakes, the phosphate in more or less rounded or concretionary 

 shapes, often almost microscopic. The latter, therefore, forms a 

 true sand, and does not have the same properties of suspension in 

 water that the clay has. A further complication is the presence 

 of lumps of pure clay in the phosphate desposits, which must be 

 disintegrated by super-mechanical means. The following- briefly 

 stated principles have been enunciated by Mr. J. A. Barr for the 

 theoretically perfect phosphate-sand washer: First, the velocity 

 of the water should not be more than 4-100 of a foot per second; 

 second, the clay must be thoroughly disintegrated, and should 

 travel in one direction by reason of fineness, shape and properties 

 of suspension in water, the sand settling out or traveling in an 

 opposite direction by reason of its greater settling power. To ef- 

 fect a perfect separation of clay and phosphate-sand the clayey 

 water must be washed from the phosphate-sand by the repeated 

 addition of clean water. 



Practically all the companies in the field utilize these principles 

 in their plants. It must be borne in mind that in the Mount Pleas- 

 ant district the lump or flake rock and the sand are dumped into 

 a hopper, and a stream of water from a large hydraulic nozzle 

 played upon it. Fed gradually from the hopper to a flight con- 

 veyor, run over a screen of inch and a half mesh, the large ma- 

 terial is carried up an incline, passing under sprays from per- 

 forated pipes, which carry the fine material through the screen. 

 The large lump is then separated from the smaller lump by pas- 

 sage over a grill. From both sizes of lump the clay balls are re- 

 moved by passing across a picker belt, from whence the clay is 

 picked out by hand. The fine material which has passed through 

 this inch and a half screen is crushed through rolls, and goes to a 

 collecting tank; thence it is carried up by pulsometer pumps to 

 washing bins, holding about sixty tons of dry material. While 

 these bins are being flooded and emptied the flow of dirty water 

 therefrom is regulated by gates in the side of the bin, which are 

 so handled that about five feet of water is kept on top of the sand 

 deposit and at the gate. In this way the clay and very fine par- 

 ticles of silica sand and phosphate-sand are in a large part re- 

 moved. When the tank is filled a few minutes are allowed for 



