. Precious stones, a popular account of their characters, occurrence and applications, with an introduction to their determination, for mineralogists, lapidaries, jewellers, etc. With an appendix on pearls and coral. Precious stones; Pearls; Corals. 12 GENERAL CHARACTERS OF PRECIOUS STONES exception, perhaps, of the optical characters, no other feature is as important as a means of determination. Every dealer in jewels should therefore be able to make a rapid determination of the specific gravity of any given gem with sufficient accuracy for practical purposes. The time expended in acquiring t
. Precious stones, a popular account of their characters, occurrence and applications, with an introduction to their determination, for mineralogists, lapidaries, jewellers, etc. With an appendix on pearls and coral. Precious stones; Pearls; Corals. 12 GENERAL CHARACTERS OF PRECIOUS STONES exception, perhaps, of the optical characters, no other feature is as important as a means of determination. Every dealer in jewels should therefore be able to make a rapid determination of the specific gravity of any given gem with sufficient accuracy for practical purposes. The time expended in acquiring the necessary manipulation and the cost oi the apparatus will be amply rewarded. It is proposed to give here a detailed account of the methods in use for the determination of specific gravity, not only for those conspicuous for the accuracy of the results they furnish, but also such as would be chosen when rapidity andeaseof manipulation rather than extreme accuracy are needed. It will be noticed that the value of the specific gravity of any given mineral, as quoted in text-books or works of reference, varies between certain narrow limits. This is due, firstly, to small errors in determination ; and, secondly, to the impossibility of obtaining two absolutely identical specimens of the same mineral, since there may be, in certain cases, small or even considerable variations in chemical composition (isomorphous replacement); and, again, crystals frequently contain as enclosures various amounts of difl^erent impurities. Methods for the Determination of Specific Gravity. 1. Method with the Pycnometer.âThis is perhaps the most accurate of the several methods available for the determination of specific gravity. The pycnometer or specific gravity bottle (Fig. 1) is a small vessel of thin glass with a wide neck, into which fits a ground-glass stopper. The stopper is per- forated longitudinally by a very fine canal. To find the specific gravity of a stone its weight g is first observed.
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Keywords: ., bookcentury1900, bookdecade1900, booksubjectpreciousstones, booky
