﻿8 BULLETIN 18, U. S. DEPAETMENT OF AGEICULTUEE. 



the upper end as the cylinder revolves. A 2-inch stream of water 

 under a pressure of 60 pounds to the square inch is played upon the 

 phosphate material from the upper end of the cylinder. This 

 washes the sand, clay, and finely divided phosphate down to the lower 

 end of the cylinder where it escapes through the screen and then flows 

 out through a trough to the wash heap, which is usually located at 

 some distance from the plant. The washed rock falls from the upper 

 end of the cylinder upon a rubber-coated belt 26 to 30 inches in width, 

 along which it is carried to the wet bins. Pickers are stationed along 

 this belt for the purpose of removing clay balls, marl, and any other 

 foreign material which may be mixed with the phosphate. From 

 the wet bins the rock is drawn into cars and sent to the drying sheds, 

 where it is burned on ricks of wood. About 6 cords of wood are re- 

 quired to dry 100 tons of phosphate from a moisture content of 15 per 

 cent down to a moisture content of 0.5 per cent. 



COST OF PRODUCTION. 



Unfortunately for the South Carolina phosphate industry, the cost 

 of production has increased without a corresponding advance in the 

 price of phosphate rock. Indeed, the price of this material is now sO 

 low that the smaller operators in these fields have entirely ceased 

 mining. 



The increased cost of mining is largely due to the practical exhaus- 

 tion of the more accessible deposits. It is now frequently necessary 

 to remove an overburden of 15 to 20 feet in order to uncover the 

 phosphate stratum, where formerly there were hundreds of acres of 

 rock lying practically at the surface or covered by only a foot or two 

 of soil. 



The price of labor has also advanced from 30 to 50 per cent, and 

 frequently it is so difficult to obtain hands that the output of rock 

 is seriously curtailed. The equipment of a modern phosphate plant 

 is both elaborate and costly. Steam shovels for excavation, grab 

 buckets and hoists for taking out the rock, many miles of steel rails, 

 locomotives and flat cars for haulage purposes, heavy machinery for 

 washing the rock, and large sheds for drying and storing the product 

 are essential parts of the present mining system. (PL III, figs. 1 

 and 2.) 



On account of the topography of the South Carolina coast, weather 

 and tide conditions affect the output of phosphate rock. In rainy 

 weather or when the tide is very high the trenches are continually 

 filling with water, the banks caving in, and the continual use of 

 pumps is necessary to make mining possible. The output of rock 

 under such conditions is often cut in half, thus practically doubling 

 the cost of mining per ton. 



