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OYEEaROWTHS ON DIAMOND. 
By J. E. Sutton. 
The Affinity between Diamond and Carbonate of Lime. 
"Formerly the diamonds were picked out from the concentrates by 
means of the keen eyes of skilled natives, but the process has been vastly 
simplified ... by the remarkable discovery made in 1897 by 
F. Kirs ten of the De Beers Company, that of all the heavy constituents 
of the blue ground, diamond alone, with the exception of an occasional 
corundum and zircon, which are easily sorted out afterwards, adheres to 
grease more readily than to water. In this ingenious machine . . . the 
concentrates are washed over a series of galvanised-iron trays, which are 
covered with a thick coat of grease. The trays are slightly inclined 
downwards, and are kept by machinery in constant sideways motion 
backwards and forwards. So accurate is the working of this device that 
few diamonds succeed in getting beyond the first tray, and none progress 
as far as the third." 
This account, which contains nearly all that is necessary by way of 
preface, is extracted from Gr. Herbert Smith's charming ' Gem Stones,' 1912, 
p. 148. Evidently the secret of the process, as Lawn has said, is surface 
tension. Common minerals can easily be wetted, whereas diamond cannot 
be ; and because of the wetting the grease cannot touch the mineral surface, 
whereas it can touch the dry diamond. 
According to Gr. F. Williams " only about one-third of 1 per cent, of 
diamonds is lost by the first table, and these are recovered almost to a 
stone when the concentrates are passed over the second table." The 
Diamond Mines of South Africa,' 1902, p. 380.) 
J. Stewart reports further that for the six months July to December, 
1909, out of 1,211,552 carats of diamonds recovered at the De Beers 
Company's pulsator all but 1,249 carats were caught on the first tables — 
an efficiency of 99*9 per cent. 
But it is a curious fact that while diamonds of all kinds, including bort, 
from the blue ground adhere readily to the grease tables, those from the 
surface yellow ground are much less easily caught. Some years ago a 
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