harcoal, leaving the substance
intact upon its surface. If intumescence takes place, the presence of
either tartaric acid, molybdic acid, silicic, or tungstic acid, is
indicated. The silicic acid will fuse into a bead, which becomes clear
when it is cold. Titanic acid will fuse into the bead, but may be
easily distinguished from the silicic acid by the bead remaining
opaque when cold.

Strontia and baryta will flow into the charcoal, but lime will not.
The molybdic and tungstic acids combine with the soda, forming the
respective salts. These salts are absorbed by the charcoal. If too
great a quantity of soda is used, the bead will be quite likely to
become opaque upon cooling, while, if too small a quantity of soda is
used, a portion of the substance will remain undissolved. These can be
equally avoided by either the addition of soda, or the substance
experimented upon, as may be required.

As silica and titanic acid are the only two substances that produce a
clear bead, the student, if he gets a clear bead, may almost conclude
that he is experimenting with silica, titanic acid being a rare
substance. When soda is heated with silica, a slight effervescence
will be the first phenomenon noticed. This is the escape of the
carbonic acid of the carbonate of soda, while the silicic acid takes
its place, forming a glass with the soda. As titanic acid will not
act in the same manner as silica, it can be easily distinguished by
its bead not being perfectly pellucid. If the bead with which silica
is fused should be tinted of a hyacinth or yellow color, this may be
attributed to the presence of a small quantity of sulphur or a
sulphate, and this sometimes happens from the fact of the flux
containing sulphate of soda. The following metals, when exposed with
carbonate of soda to the reducing flame, are wholly or partially
reduced, viz. the oxides of all the noble metals, the oxides and acids
of tungsten, molybdenum, arsenic, antimony, mercury, copper,
tellurium, zinc, lead, bismuth, tin, cadmium, iron, nickel, and
cobalt. Mercury and arsenic, as soon as they are reduced, are
dissipated, while tellurium, bismuth, lead, antimony, cadmium, and
zinc, are only partially volatilized, and, therefore, form sublimates
on the charcoal. Those metals which are difficult of reduction should
be fused with oxalate of potassa, instead of the carbonate of soda.
The carbonic oxide formed from the combustion of the acid of this salt
is very efficie