When this double salt is heated, the water and the ammonia escape,
while the incombustible residue has a composition similar to borax,
viz., a free acid and an easily fusible salt. The effect of it is,
therefore, similar to the borax. The free phosphoric acid expels,
likewise, most other acids from their combinations, and combines with
metallic oxides.

For supports, the platinum wire may be used, but the hook must be
smaller than when borax is used, or the bead will not adhere. As for
all the other experiments with this salt, the microscosmic salt is
used the same as borax.


9. _Nitrate of Cobalt._--(CoO, NO^{5}).--This salt can be prepared by
dissolving pure oxide of cobalt in diluted nitric acid, and
evaporating to dryness with a low heat. The dry residue should be
dissolved in ten parts of water, and filtered. The filtrate is now
ready for use, and should be kept in a bottle with a glass stopper. If
the pure oxide of cobalt cannot be procured, then it may be prepared
by mixing two parts of finely powdered _glance of cobalt_ with four
parts of saltpetre, and one part of dry carbonate of potassa with one
part of water free from carbonate of soda. This mixture should be
added in successive portions into a red-hot Hessian crucible, and the
heat continued until the mass is fused, or at least greatly diminished
in volume. The cooled mass must be triturated with hot water, and then
heated with hydrochloric acid until it is dissolved and forms a dark
green solution, which generally presents a gelatinous appearance,
occasioned by separated silica. The solution is to be evaporated to
dryness, the dry residue moistened with hydrochloric acid, boiled with