Overgvotvths on Diamond. 
91 
The experiments were repeated witli three good samples of virgin blue, 
yellow, and real limestone crust, obtained from the Kamfersdam Mine. In 
acid the blue gave no effervescence to speak of, while the yellow effervesced 
strongly, losing 20 per cent, of its weight, and the lime crust violently, 
losing fully 60 per cent. Pastes were now made as before of the virgin 
blue and of the lime crust in equal quantities, and ten first table diamonds, 
weighing on an average about a carat a-piece, were placed in each paste. 
The two lots of diamonds were chosen so as to be as nearly alike as possible. 
After the pastes had become quite dry they were broken, the diamonds were 
carefully extracted, soaked in water, and passed over the grease tables. 
Every diamond from the limestone paste rolled off as fast as the water could 
carry it ; whereas nearly all the diamonds from the blue were caught. 
Lastly, some third table and dry sorted diamonds, i. e., diamonds which 
originally were not easily caught, or even not caught at all, by the grease, 
adhered quite well after having been cleaned in acid. 
Reasoning from the above results, the following conclusions, ye/iio rogatum, 
would seem to be justifiable : 
Yellow ground contains more calcite than blue ground does. 
Calcic carbonate in suspension, or solution, deposits itself readily in thin 
layers on a diamond surface, causing that surface to approximate to the 
consistency of the common minerals in the pulsator concentrates. 
This deposit being more easily wetted than a bare diamond surface is, 
the surface tension in water is increased, and that in grease decreased 
accordingly. Hence the coated diamond behaves like an equal mass of 
limestone on the grease tables. 
The above account is drawn with no material alteration from my report 
made at the time some years ago. This report had been put away and the 
details half forgotten, although the conclusions were alluded to in a recently 
published paper. But during the last few months the results appear to 
have received some extraneous confirmation perhaps sufficiently important 
to warrant the publication of them. This latter development will now be 
briefly described. 
Now, it is to be noted that if calcite, or limestone, can be made to form 
a crust on a diamond by artificial means, it ought to do the same naturally, 
in propitious circumstances. So far as the Wesselton yellow-ground 
diamonds are concerned, since they do not always adhere readily to the 
grease tables, this would appear to have been proved, or at least made 
probable, by the experiments described above. But since calcite occurs in 
fair abundance in some specimens of blue ground, there ought to be cases 
here and there in which blue-ground diamonds had acquired a calcite coating. 
The chances would be, however, that even so it would not follow that the 
coating would survive the rough treatment of mining and winning to the 
