312 
Transactions of the Boyal Society of South Africa. 
6. Imitation Diamonds (p. 41). 
The author quotes the following from the ' Ao'astimata ' : " When a 
connoisseur believes that he recognises an artificial diamond, he should test 
it by means of acids or vinegar, or through the application of heat : if false 
it will lose colour ; if true it will double its lustre." Chinese authorities 
echo the same advice. 
Neither the acids known to the ancient Indian or Chinese chemists, nor 
heat, would be sufficient in every case to detect a false stone, especially if it be 
colourless. The colour of South African zircons is easily removed in the 
flame of a spirit lamp, and this test is decisive as regards fragments of 
zircon and diamond of the same yellowish-brownish colour, which are not 
easy to discriminate by the eye. In general the hardness and specific 
gravity will decide. Acids (and sometimes the flame), by removing coatings 
of foreign matter, improve the appearance of some rough diamonds amazingly. 
Parcels of South African diamonds are always cleaned in acid (hydro- 
fluoric or aqua regia) and spirits of wine before being, sorted for shipment 
to Europe. 
7. Stones of Nocturnal Luminosity (p. 55). Phosphorescence of 
Precious Stones (p. 63). 
The author inclines to the opinion that the various Greek and Chinese 
legends of night-shining gems do not necessarily prove that the phosphor- 
escence of the diamond was a recognised phenomenon: "Altogether we 
have to regard the traditions about gems luminous at night, not as the 
result of scientific effort, but as folk-lore connecting the Orient with the 
Occident." 
One would be inclined to doubt, in fact, whether, if the property of 
phosphorescence had not been established, anyone at all would have read 
into the accounts that have come down anything more than a mere fairyland 
exaggeration of the light-catching power of diamond. It is remarkable 
how strongly a cut diamond seems to catch stray feeble rays at night, even 
starlight, when other gems remain obscure. Some rough diamonds have 
the same property, though in a much less degree. 
Phosphorescence, contrary to belief,* is not a general property of 
diamonds. I have examined a hundred or more Kimberley diamonds (after 
having exposed them to sunlight) without detecting it. Le Bon exposed 
about a hundred diamonds, said to be one half Brazilian and the other half 
Cape, to the illumination produced by burning magnesium, and found that 
" nearly all the Brazilian and all those of the Bahia mine were, during the 
* " They say the proof of a true diamond is to glitter in the dark " (Dryden's 
' Amphitryon,' III). "E 9eo dit Phisologus que adamas ad vertut plus . . . pur 
nuit gete grant luur" (P. de Thaun). 
