these results we are justified in considering these gems as rubies, and
they have been placed in the collection named as such.
the Eussian Court at the London Exhibition of 1851 there was a
beautiful stone labelled Phenacite, which is a silicate of glucina, and
it is used in Eussia as a gem-stone. Experts' opinions differed as to
whether this was the correct name for the specimen. The owner's
permission was obtained, and the stone tested. On taking the specific
gravity it was found to be 3'5. The specific gravity of phenacite being
at the highest 3, it was at once proved not to be that mineral, and on
further tests being applied it was found to be a topaz.
As a large number of gems develop this property more or less, it is of some importance in their discrimination.
will develop electricity in the diamond and topaz most markedly. The
diamond displays positive electricity whether it be polished or in its
rough state. Other gems are positively electric in the polished state
only, and only have the power of developing negative electricity when
in their rough state.
development of electricity in a mineral may be seen by its power of
attracting or repelling a light pith pellet suspended by cotton, or
better, by a silken cord from a glass rod; or a small piece of cotton
wool suspended in the same manner will answer the purpose ; even a
piece of paper will be attracted in this way.
or that developed by heat, is very marked in some minerals ; tourmaline
especially, when heated to not more than 150° C, and suspended by a
silken thread, will behave like an electro-magnet, having