272 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1923 



flat bottom, and rests in a horizontal position. At its center there 

 is a vertical revolving shaft to which radiating arms are attached. 

 On these arms are metal teeth that revolve in the pan and thus 

 stir the diamond-bearing material that is fed into the pan. Dur- 

 ing this stirring the diamonds and associated heavy minerals gradu- 

 ally settle to the bottom of the pan, while the clay and other light 

 minerals rise to the surface and flow out of the pan near its center. 

 The concentrates thus obtained in the bottom of the pan are then 

 sized and next jigged. The jigged concentrates are carefully searched 

 for diamonds on metal-covered tables or are washed by water over a 

 table which is covered with a thick film of grease and which is 

 shaken rapidly from side to side by an eccentric. While the con- 

 centrates are washed across the table the grease sticks to the dia- 

 monds and holds them, whereas it does not stick to the other min- 

 erals, most of which are therefore washed off the table. The grease 

 and the diamonds and other minerals embedded in it are removed 

 from the tables from time to time. The diamonds are then freed 

 from the grease by converting it into soap or by putting it into 

 boiling water. 



