76 Transactions Tennessee Academy of Science. 



For ten or twelve years after the discovery of the deposits only 

 this lump or plate rock was mined. In most cases everything be- 

 low one inch in diameter was thrown away. This included the 

 material lying between the plates, which differed in composition 

 from the plates themselves only by containing from, say, 5 to 

 25 per cent less phosphate of lime, and a considerably larger pro- 

 portion of sand and clay. The latter, together with the iron con- 

 tent in all clays or loams, was not, for the purpose of manufac- 

 ture, an inert material, but was decidedly objectionable, causing 

 the manufactured material, the so-called acid phosphate, to dry 

 out slightly, and to contain less of the valuable soluble phosphate. 

 There were two methods of cleaning this plate rock, namely, dry- 

 ing in the sun, and screening and washing in a crude way with 

 water. In the latter process settling ponds were, of course, neces- 

 sary to prevent stream polution by the waste materials. It was 

 recognized some years since that the waste in this process was 

 enormous, and that if the phosphatic material in the waste prod- 

 ucts could be saved, it formed not only a certain source of profit, 

 but the material itself was fairly close to the condition of fineness 

 to which the rock was afterwards reduced by the manufacturer, 

 thus necessitating only one manufacturing operation. 



About five years ago most of the miners in the field began to 

 depart from the old crude methods of mining, and to save this ma- 

 terial by utilizing well-known principles of settling in water for 

 the purpose of settling the phosphatic sands, as they are called, 

 from the siliceous or argillaceous components of the raw ma- 

 terial. It is obvious further that if a phosphate deposit consists 

 wholly of such comminuted material (as indeed many of them do), 

 the same process is applicable to its utilization, when under the old 

 methods it must be left alone. The problem involved, while not 

 specially difficult, presents certain questions of its own. Ore sepa- 

 ration by means of water is dependent chiefly upon two factors, 

 namely, the specific gravity of the material handled, and the size 

 and shape of the particles. The clay, sand and phosphate do not 

 differ greatly in specific gravity, and a certain important portion 

 of the phosphate material does not differ greatly in size from the 

 clay particles. It is obvious, therefore, that the dift'erences in 

 specific gravity do not admit of separation, and that advantage 

 must 1)C' (akfii as far as ])MssiI)lc of Ihc differences in the size and 



