94) Transactions of the Royal Society of South Africa. 
Alum, Epsom salts, sal ammoniac, common salt, saltpetre. Saturated 
solutions of the following increased the tension somewhat : Chloride of 
lime, borax, hyposulphite of soda. On the other hand, a solution of caustic 
soda wetted the diamond thoroughly. But of all the substances tried 
carbonate of soda proved by far the most effective, A diamond (crystal or 
bort) dipped into a saturated solution of carbonate of soda comes out wet 
and dries with a thick deposit of the substance. Even here, however, the 
wetting tends to be to a certain extent selective. The deposit as a rule 
dries thicker on the faces of the octahedron than it does on the edges ; and, 
by the same token, thicker on the edges of the rhombic dodecahedron than 
it does on the faces. Some octahedra dry with their faces thickly coated 
(saving where deep triangular indentations interfere) and their edges 
scarcely dimmed, and some dodecahedra dry with their edges sharply out- 
lined in white. This result may arise from faulty manipulation, or it may 
have been accidental to the limited number of stones treated ; but it is 
curious that the observer occasionally comes across a diamond naturally 
coated on its octahedron faces with a black adamantine incrustation, while 
its edges are so clear that the colourless interior can be seen through them. 
On the other hand a bort incrustation favours the dodecahedron faces of 
Wesselton " black " (nearly opaque) diamond. 
One other, minor, point : If a diamond be placed in a solution of car- 
bonate of soda contained in a glass vessel, the soda, in spite of its affinity 
for the diamond, will crystallise out, as the water evaporates, by preference 
on the sides of the vessel above the water surface, while the diamond 
remains uncovered in the solution. But in a solution of cane-sugar 
crystallisation will begin on the diamond alone, and the latter after a time 
will appear as if enveloped in an extensive cloudy condensation. The reasons 
need not detain us. 
Coated Diamonds : Some Observations and Inferences. 
Diamonds with a black incrustation are common, especially at Wesselton. 
In the mines of the Kimberley area this incrustation is usually very thin, 
and under magnification is seen to consist of minute dull black specks more 
or less uniformly streaked over a somewhat rough and pitted surface — so 
thin indeed as to make the diamond look slaty-grey by reflected light and 
smoky-brown by transmitted light. Not improbably this coating is allied 
to the frequent black spots included in the body of spotted stones. Whether, 
so far as the Kimberley mines are concerned, it represents the remains of a 
thicker coating Avhich has been lost either naturally or in the process of 
mining and winning is doubtful. Mr. P. Ross Frames, however, has 
obtained, at the Premier Mine, Pretoria, a small diamond from the midst 
of a lump of graphite, and at this mine diamonds with quite a thick, soft 
