94 
Transactiom of the Royal Society of South Africa. 
For the 12 months , 
ending Jnne 30th. Carats, 
1902 ... 76 
1903 ... 61 
1904 . . . 54 
1905 ... 46 
1906 ... 41 
1907 . . .37 
1908 . . . 37 
1909 . . . 42 
1910 ... 38 
1911 ... 28 
1912 . . .31 
1913 ... 29 
Prior to the amalgamation of the various small companies working the 
De Beers and Kimberley Mines, the yield was considerably over 100 carats 
per 100 loads. Not only that, but many of the smaller diamonds used to 
be thrown away in the rough and ready methods of winning, leaving great 
heaps of tailings and debris well worth washing again in later years. Thus 
it would seem that the greatest wealth of these two mines was concentrated 
in the upper levels. On the other hand, only the richer areas were worked 
to any great extent in the earlier years, the poorer areas being left to spoil 
the averages of later times. 
The Dutoitspan yield for the four years 1911-14 averaged about 22 carats 
per 100 loads. 
18. Anomalous Behaviour of Diamonds on the Grease Tables. 
Diamond appears to have a curious affinity for lime. It was discovered 
some years ago that diamonds from the Wesselton yellow ground were not 
readily caught on the grease separators, while it was exceptional for a dia- 
mond from the blue ground to fail to be caught. Experiments showed that 
yellow ground diamonds cleaned in acid lost their non-adhesive property 
and behaved normally on the tables like blue ground diamonds, whereas 
blue ground diamonds immersed for a few days in a paste of soft magnesian 
limestone, or of yellow ground, or in water that had been shaken up with 
lime or with yellow ground and dried, would not stick to the grease. 
Evidently the diamonds had acquired a thin coating of lime, which, when 
wetted, lessened the surface tension between them and the grease, and so 
caused them to behave like the ordinary gravel of the heavy pulsator 
deposit. Yellow ground, by the way, contains a large admixture of lime, 
some specimens losing a good half of their weight after treatment with aqua 
regia. 
