. 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. 14 GENERAL CHARACTERS OF PRECIOUS STONES the scale-pan of the balance, leaving the latter quite free to move. The thread or wire with the attachment for can-ying the stone is fastened to the hook on the upper part of the right-hand scale-pan. Obviously the water-containing vessel must not be so large as to interfere with the movement of the balance
. 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. 14 GENERAL CHARACTERS OF PRECIOUS STONES the scale-pan of the balance, leaving the latter quite free to move. The thread or wire with the attachment for can-ying the stone is fastened to the hook on the upper part of the right-hand scale-pan. Obviously the water-containing vessel must not be so large as to interfere with the movement of the balance, and the length of the wire must be such that. Fig. 3. Oi-dinary balance with arrangement for hydrostatic weighing. the stone it carries will not touch the bottom of the vessel nor rise partly out of the water when the balance is swinging. In the determination of a specific gravity with such a balance the best mode of pro- cedure is as follows : A fragment of a mineral or metal or any object, the weight of which is greater than that of the stone whose specific gravity is to be determined, is placed in the left-hand scale-pan. This acts as a counterpoise, and must remain throughout the whole operation. It has been pointed out above, that the wire with its carrying attachment must I'emain immersed in water till the completion of the operation. Weights are then placed in the right-hand scale-pan so as to balance the counterpoise; let the weight required be m. These weights are then replaced by the stone ; equilibrium is restored by adding a weight, /, in the right-hand scale-pan. The weight of the stone will therefore he m — I = ff say. The stone is then attached to the end of the wire and immersed in water, care being taken that it hangs freely without touching the sides and bottom of the vessel. By adding more weights to the right-hand scale-pan the balance is again brought into equilibrium. If the total weight is now t, then, the loss in weight of the stone, when weighed inw
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