312 Appendix.
varieties
of Quartz, and Moonstone. On the other hand Garnet, Sapphire, Ruby,
Chrysoberyl, Spinel, Topaz, Diamond, and Chrysolite, from their
greater specific gravity, would sink.
Of
late years Sonstadt's solution has been replaced by other liquids of
even higher density. Thus, the boro-tungs-tate of cadmium is a salt
which gives a pale-yellow solution of the density of 3'28. This is
known, from its discoverer, as Klein's solution. Methylene iodide,
again, is a very convenient liquid, its specific gravity being about
3*3, or slightly higher. It is a yellow liquid, readily miscible with
benzene ; and its use was suggested by Dr. Brauns.
But
the densest of all liquids, as discovered by Dr. Retgers, is the fused
nitrate of thallium and silver, which has a specific gravity of about
5, and fuses at as low a temperature as 750 C, or 1670
Fah. Thus, at a temperature considerably less than that of boiling
water, the salt forms a liquid, which is clear and colourless, and may
be mixed in any proportion with water, whereby its density can be
reduced at will.
Another
method of taking specific gravities is by weighing the stone first in
air and then in water, and dividing the former weight by the difference
between the two weighings. A simple method, and one generally of
sufficient accuracy, is to employ a first-class pair of Diamond
scales, as follows : Drill a small hole in the bottom of one of the
scale pans, through which pass a double fibre of silk, so as to hang
say 4 inches below the pan ; tie a knot to prevent its slipping through
; suspend the stone in the silk by bending back the silk upon itself,
so as to form a double slip noose ; and weigh the stone very carefully
while hanging suspended in this position. Then immerse the stone, as it
hangs, in distilled water. It will appear to
