before they lose it forms a valuable mark of distinction amongst them.
The Indians have for a long time been aware of this property peculiar to gems.
The celebrated Hauy speaks of it at great length, while describing many instruments used by him to certify the phenomenon.
FUSION AND SOLUTION.
The facility or difficulty experienced in melting or dissolving a gem serves to indicate the elements of which it is composed.
The diamond alone will not dissolve, although it is combustible.
All
the corundums can be dissolved by means of borax, but with great
difficulty; the emerald, the jar-goon, and the spinel more easily.
Caloric
produces very different effects on other gems; , some change colour,
others swell and crackle, and many others burn—are changed into
vitreous globules, into a kind of cement, into a powder; and in some
others phosphorescence is produced.
Many
other precious stones, besides the diamond, are incapable of injury by
acids; amongst these are the corundum and the spinel.
Not a few change colour in acids, as, for example, the German agate.
