88 
Transactions of the Royal Society of South Africa. 
parcel of diamonds from the Wesselton Mine yellow ground was handed 
to me for examination. Some concentrates from the yellow ground had 
been passed over the grease tables with the following result : 
Third table, and final dry sorting of rejected concentrates 146 . 30-61 
That is to say, instead of a loss of between one-tenth and one-third per 
cent, (the values quoted above), only about a half of the diamonds were 
caught on the first table — a result scarcely better than an electrostatic 
separator would give. Clearly it was lucky that the grease tables were 
not thought of in the early days of Kimberley when nothing but yellow 
ground was being worked, for, had they been tried then, that excellent 
invention would probably have passed stillborn into oblivion. 
In the matter of the anomalous behaviour of the yellow-ground 
diamonds the problem to be solved was unique inasmuch as there was 
no outside analogy for a guide. To begin with, there was nothing to show 
whether the surface of yellow-ground diamond was essentially different 
from that of blue-ground diamond, or whether the anomaly arose from 
some disturbing factor in the matrix. As to the former alternative, there 
was a prevalent belief that [the surfaces of diamonds found in the early 
days of Kimberley were on the whole more brilliant than those obtained 
later, in the deep workings. As to the latter alternative, it appears that 
the soapy-feeling substance lining the blue-ground matrix of diamond has 
not quite the same constitution as adjacent blue-ground has. This point 
will be referred to again. 
The first step in the attempt to solve the problem was made by 
screening the diamonds caught on the three different tables into series of 
sizes. From the results it was ascertained that, generally speaking, the 
larger diamonds tended to adhere to the grease on the first table better 
than the smaller ones did, those caught on the third table not often 
exceeding a quarter of a carat each. There was, moreover, a marked 
difference in the behaviour of the smaller diamonds with respect to the 
tables, for while those caught on the third table, or dry sorted afterwards, 
were largely of good shape with no specially great proportion of cleavages 
and splinters, those caught on the first table were mostly irregular or 
broken pieces. Hence it seems that a still larger quantity would have 
been lost by the first table if the normally great percentage of Wesselton 
cleavage were less. Two possibilities were thus suggested : 
(1) The larger diamonds stick better than the smaller ones do because 
First table 
Second table 
Per 
cent. 
50-52 
18-87 
477 
100-00 
