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Appendix A - Discrimination of Precious Stones

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Appendix.
313
have lost weight, being, in fact, buoyed up by the water ; now add carefully more weights, till an equipoise is effected ; note the weight by which this is obtained, and divide the original weight of the stone by it, and the quotient will give the specific gravity required.
Example .ยท In weighing a white stone whose specific gravity we required, we found the weight of the stone to becarats. The weights effecting the equi-
poise,carats. We have, therefore,
orwhich is the specific gravity required. This
would indicate the specific gravity of a Diamond.
Jolly's spring-balance, an instrument made in Munich, is often now used by mineralogists on the Continent, and enables the specific gravity of small specimens to be determined with great rapidity. Another instrument much used is the Westphal balance, named from its inventor, and constructed on the principle of the familiar steel-yard.
There are various other methods for determining this physical constant, but the above will suffice for ordinary purposes. Care should always be taken to have the stone perfectly clean, and damped before operation, whilst all adherent air-bubbles must be most carefully removed. In the preceding pages the specific gravity of each stone has been given at the end of its chapter.
The Optical Properties of Gems.
The optical properties of Gems are of paramount importance. It is to these properties that the Diamond owes its superlative brilliancy and its flashing forth of " living fire ;" to these properties, too, the Ruby, owes its
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