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THE BOOK OF DIAMONDS
state.
The diamond in the rough is most unattractive, and would be thrown away
by a casual observer as a worthless pebble; its perfections are hidden
under a hard crust, which can be removed by its own dust. The deep
velvety blue of the sapphire, the glowing brilliant red of the ruby,
the soft clear green of the emerald, and the delicate strata of the
onyx, alike only display themselves in their true character after the
lapidary has exhausted his skill in cutting them into facets and
polishing them.
Most
precious stones are infusible or fusible with great difficulty by means
of fluxes such as borax or sodium carbonate. The ruby, sapphire and
all corundums, emerald and spinel are fusible but with great
difficulty. Spinel and corundum are not affected by any acid.
Various
tests can be made for diamonds. One of these is their hardness. No
chemicals will react with diamonds. The density of diamonds can be
determined with methylene iodide and thalium lead acetate. In the
former it will sink and in the latter float. An index of refraction and
the burning of diamonds in the presence of oxygen with a temperature
of 800°C. are also very good tests for diamonds.
Various
attempts have been made to measure the intensity of the iridescence of
diamonds by photographic means, but solar light has always proved too
diffused for accurate results. M. Malaval, of Paris, a chemist, has
invented a method to test the quality of diamonds. He has obtained
perfect results with ultraviolet light rays passed through a screen.
The purest white stones give the clearest picture, yellow stones
showing darker, while imitation diamonds
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