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BULLETIN 18, U. S. DEPARTMENT OF AGRICULTURE. 



After calcining, the rock becomes more brittle and can be readily and 

 cheaply ground. 



Although the South Carolina phosphate is considerably lower in 

 grade than that from many other sources, it makes an acid phosphate 

 of excellent quality and good mechanical condition for mixing pur- 

 poses. Some farmers prefer this material to the higher grade prod- 

 uct made from Florida or Tennessee phosphate. 



The rock now marketed contains on the average about 61 per cent 

 of bone phosphate of lime, though individual nodules and fragments 

 are sometimes found which contain as much as 75 per cent. The 

 following table, compiled by Chazal from analyses made by Shepard, 

 gives the composition of South Carolina phosphate from different 

 localities. The samples from which these analyses were made were 

 collected during the early development of the South Carolina phos- 

 phate industry and are of somewhat lower grade than the rock which 

 is now obtained from some of the same localities. 



Table II. — Phosphate content of South Carolina phosphate 



rock from various sources. 



Location. 



Description. 



Moisture. 



P 2 6 , 

 undried 



basis. 



Ca 3 (P0<) 2 , 



undried 



basis. 



Ca 3 (P04) 2 , 

 dried 

 basis. 







Per cent. 

 3.68 



Per cent. 

 25.61 

 20.68 

 25.70 

 27.01 

 27.11 

 27.26 

 25.14 

 27.26 

 26.78 



Per cent. 

 55.91 

 58.24 

 56.21 

 58.95 

 59.18 

 59.51 

 54.88 

 59.51 

 58.46 



Per cent. 

 58.04 



Do 







Do 



Large bowlder 



Hot air-dried cargo sample. . 



1.50 

 .00 

 10.07 

 .84 

 .79 

 .57 

 .66 



57.07 



Ashley River, land deposit 



58.95 





Hot air-dried cargo sample. . 

 do 



60.00 





55.32 





do 



59.85 



Do 



do 



58.85 









METHODS OF MINING. 



For many years the mining of South Carolina phosphate was car- 

 ried on by hand labor. For a short time even the washing of the 

 phosphate was done by hand. The product, therefore, was at first 

 regarded rather unfavorably, as it was not clean and produced an acid 

 phosphate of poor quality. The early methods of mining and hand- 

 ling the rock have been largely supplanted by modern and more 

 efficient methods, which turn out a clean, dry product well fitted for 

 the manufacture of acid phosphate. Hand mining is still economi- 

 cally practiced where the overburden is sufficiently light and of such 

 a character as to render the steam shovel unnecessary, but washing 

 by hand has been entirely supplanted by the modern washer plant 

 capable of turning out from 150 to 600 tons of clean rock every day. 

 Hand mining (see PI. I, figs. 1 and 2) is carried out as follows: 



After thorough prospecting to determine the extent and value of the 

 phosphate property, a ditch is dug through or alongside the tract to 

 be mined and below the level of the phosphate stratum. Laterals 



