90 Transactions of the Royal Society of South Africa. 
In the acid the blue ground effervesced strongly, the yellow ground 
violently, the limestone scarcely at all. A sample of hard blue from 
De Beers Mine, tested at the same time, gave scarcely any effervescence, 
while some lumps of hard and soft limestone from Kenilworth effervesced 
violently, leaving no great proportion of insoluble residue, so that the 
effervescence of the blue ground may have arisen, at any rate in part, 
from an admixture of a foreign carbonate. Moreover, the substance 
(alluded to above) lining the matrices of sundry blue-ground diamonds 
effervesced very little. 
These rough tests seemed to supply a clue worth following towards a 
solution of the problem. There is more carbonate of lime in yellow ground 
than there is in blue ground, and the question is, Will it, when it is 
plentiful enough, spread itself on a diamond surface in a crust capable 
of being wetted ? Numerous experiments were accordingly made in the 
hope that premised feasible natural processes might to some extent be 
imitated in forming such a crust. Pastes were made of the blue ground, 
the yellow ground and the limestone, with hot and with cold water, in 
which small diamonds that had adhered normally to the first grease table 
were enclosed for some days. Sometimes these pastes were kept wet 
throughout, sometimes they were dried in gentle heat, and sometimes left 
to dry of themselves. Finally the enclosed diamonds were taken out and 
run over the grease tables at the pulsator. The results were only so far 
encouraging that neither the diamonds from the yellow paste nor those 
from the limestone paste showed any particularly marked inclination to 
stick to the grease. But, on the other hand, curiously enough, neither did 
the diamonds from the blue paste. Thus although all were originally 
normal first table captures, the act of putting them into the different pastes 
had for the most part destroyed their adhesive property. 
Of course, only a soft and easily removable crust, at the best, can be 
deposited on diamonds by enclosing them for short periods in pastes of this 
kind. One effort was made to deposit a harder crust on four first table 
diamonds of about six carats each by placing them in four separate vessels 
with some blue, yellow, and lime ground respectively, well stirred with 
plenty of water, and leaving the water to evaporate slowly. This is a 
lengthy process, and was only partially successful. Scarcely any blue 
ground appeared to have attached itself to the diamond surface, though the 
lime and yellow were deposited in patches with some freedom. Upon 
roughly testing these diamonds for surface tension in water, it was found 
that those from the lime and yellow grounds gave much higher values per 
unit area of surface than those from the blue ground did, albeit a single test 
of this kind cannot be regarded as of much consequence. These same 
diamonds were afterwards passed over the grease tables : three adhered, 
and one, which had a fair coating of lime, rolled away. 
