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PRECIOUS STONES.
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The diamond is a non-conductor of electricity, while graphite and charcoal, substances identical in chemical constituents
with this gem, are very active conductors. Both in a natural and polished condition, it acquires positive electricity by friction, while, on the contrary, most precious stones are negative in the rough, and positive only when polished. It does not possess double refraction ; neither does it polarize light, as do some other gems. But it is the exceptional one that exhibits phosphorescence in a natural state, and then only in the case of certain stones, though this property is said to be generated by steeping in hot water. During the last century, it was shown that double refraction never occurs in non-crystallized substances, nor in crystals of the cubic system, to which the diamond is allied.
Haiiy confirmed this opinion, and maintained the converse, that all crystals not of the cubic system were doublerefracting. No solvents, not even acids, have the slightest influence in
decomposing the diamond — a fact which enhances its value as an ornamental stone. Until the middle of the seventeenth century, it was believed to be incapable of injury from heat, but Sir Isaac Newton believed it was combustible, before it was submitted to the operation of burning, on account of its refracting power. The relative density of quartz and diamond are as three to four, while their refractive powers are as three to eight. The experiment of publicly burning the diamond was successfully made at Florence in 1694, by means of a burningglass,* when some of the most celebrated scientists attended
as witnesses of the important ceremony. The stone, on ex- * MM. Dumas and Strass, it is said, burned this gem by means of the voltaic
battery, an experiment often repeated in modern laboratories. |
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