HARD ROCK PHOSPHATE ORE DRESSING 47 



log, which is driven by gear-wheels, works the ore 

 towards the head of the box and discharges it into 

 the second washer which is a single log. Water 

 is introduced at the upper end of the box, while the 

 ore is fed at the lower end; the clean water thus 

 meets the ore and when it becomes dirty it flows 

 out at the lower end, carrying with it the clay in 

 suspension. There is no general standard for these 

 log washers. The box is about four feet deep at 

 one end and two feet at the other, according to the 

 length of the logs, which vary from sixteen feet 

 to thirty feet and are pitched at an angle sufficient 

 to give a rise of one and one-quarter inches to the 

 foot. The dirty water from the washers generally 

 flows away in sluices, but where the fall is not 

 sufficient a centrifugal pump of some type is used 

 to assist in its removal. 



After the log washers have removed most of the 

 clayey matter, the ore passes through a chute into 

 a trommel with an internal spray, which eliminates 

 the remaining clay and the smaller portions of the 

 sand from the ore. These screens have jackets 

 ranging from one-eighth inch to one-sixteenth inch, 

 and are commonly known as "rinsers. " The ore 

 after passing through the "rinser, " falls through a 

 chute on to a slowly revolving table, known as a 

 " picking-table, " where boys and old men pick out 

 the "sand rock" and other foreign matter not re- 

 moved by the log washers and screens. The ore 

 after hand-sorting is automatically pushed through 

 the center of the table by a large brush or scraper 



