354 The National Geographic Magazine 



The Old Method of Separating the Diamonds — Picking them out of the 



gravel by hand. 



ion of diamond mining and winning 

 which seemed beyond the application of 

 blind and unconscious machinery. But 

 men today are not inclined to admit that 

 anything greatly worth doing is impos- 

 sible. 



A series of experiments was initiated 

 by me with the object of separating the 

 diamonds from the heavy valueless con- 

 centrates with which they are associated. 

 An ordinary shaking or percussion table 

 was constructed, and every known means 

 of separation was tried without success. 

 One of the employees of De Beers, Mr 

 Fred Kirsten, was in charge of the ex- 

 perimenting, under the supervision of the 

 late Mr George Lab ram, the manager of 

 the large crushing plant and afterward 

 mechanical engineer to the company. 

 Xotwithstanding the fact that the specific 

 gravity of the diamond (3.52) was less 

 than that of several of the minerals as- 

 sociated with it, so that its separation 

 would seem a simple matter, it was 

 found in practice to be impossible, owing 



to the slippery nature of the diamond. 

 The heavy concentrates carried diamonds, 

 and diamonds flowed away from the per- 

 cussion tables with the tailings. When it 

 seemed that every resource to do away 

 with the head sorting had been ex- 

 hausted, Kirsten asked to be allowed to 

 try to catch the diamonds by placing a 

 coat of thick grease on the surface of the 

 percussion table with which the other ex- 

 periments had been made. Kirsten had 

 noticed that oily substances, such as axle 

 grease and white or red lead, adhered to 

 diamonds when they chanced to come 

 into contact, and he argued to himself, if 

 these substances adhered to diamonds 

 and not to the other minerals in the con- 

 centrates, why should not diamonds ad- 

 here to grease on the table, and other 

 minerals flow away? In this way the re- 

 markable discovery was made that dia- 

 monds alone of all minerals contained in 

 the blue ground will adhere to grease, 

 and that all others flow away as tailings 

 over the end of the percussion table with 



