. 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. SPECIFIC GRAVITY 15 this is also the weight of the water displaced, that is, the weight of a volume of water equal to the volume of the stone. Hence the specific gravity of the stone is, as. before. To take a numerical example. If the weight first added to balance the counterpoise be m = 10-784. grams (or other unit), and the weights which, togethe
. 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. SPECIFIC GRAVITY 15 this is also the weight of the water displaced, that is, the weight of a volume of water equal to the volume of the stone. Hence the specific gravity of the stone is, as. before. To take a numerical example. If the weight first added to balance the counterpoise be m = 10-784. grams (or other unit), and the weights which, together with the stone, balance the counterpoise be I = 4-803 grams, then the weight of the stone is ^ = ??j - Z = 10-784 - 4-803 = 5-981 grams. Let the weight added when the stone is immersed in the water be t = 7-060. Then the loss of weight of the stone will be ^ - Z = 7-060 - 4-803 - 2-257 , g 5-891 grams, and a — J~_^i = g.^gy = 2-65. This is the specific gravity of rock-crystal (quartz). Other conditions being equal, the more delicate and sensitive the balance the more accurate will be the specific gravity determination. Under favourable conditions and with careful weighing the determination should be correct to the third place of Fig. 4. Bench for use in hydrostatic weighing with an ordinary balance. Certain precautions, however, must be attended ito. In the first place, all parts immersed in water must be quite free from adhering air-bubbles; these may often be dislodged with the help of a clean platinum wire, but frequently it is advisable to bring the water almost to the boiling-point while the stone and wire are immersed in it. For this pui-pose the wire must be detached from the balance; but before replacing the vessel of water on the balance it should be allowed to cool, which process may be hastened by immersing the vessel, still of course containing the wire and stone, in a bath of cold water. Should the stone and wire be at all greasy through being handle
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