render reddened
litmus paper blue. This is likewise the case with the sulphides of the
alkalies. The neutral salts of the alkalies, formed with the strong
acids, do not change litmus paper, but the salts formed with the weak
acids, render the red litmus paper blue; for instance, the alkaline
salts with boracic acid. Fused with borax, soda, or microcosmic salt,
they give a clear bead. The alkalies and their salts melt at a low red
heat. The alkalies cannot be reduced to the metallic state before the
blowpipe. They are not volatile when red hot, except the alkali
ammonia, but they are volatile at a white heat.

(_a._) _Potassa._(KO).--It is not found free, but in combination with
inorganic and organic acids, as well in the animal as in the vegetable
organism, as in the mineral kingdom. In the pure, or anhydrous state,
or as the carbonate, potassa absorbs moisture, and becomes fluid, or
is deliquescent, as it is termed. By exposing potassa, or its easily
fusible salts (except the phosphate or borate), upon platinum wire, to
the point of the blue flame, there is communicated to the external
flame a violet color, in consequence of a reduction and reoxidation.
This color, though characteristic of all the potassa compounds, is
scarcely visible with the phosphate or borate salts of that alkali.
The admixture of a very little soda (1/300th) destroys the color
imparted by the potassa, while the flame assumes a yellow color,
characteristic of the soda. The presence of lithia changes the violet
color of the potash into red. The silicates of potassa must exist in
pretty large proportion before they can be detected by the violet
color of the flame, and those minerals must melt easily at the edges.
The presence of a little soda in these instances conceals the reaction
in the potassa entirely.

If alcohol is poured over potassa compounds which are powdered, and
then set on fire, the external flame appears violet-colored,
particularly when stirred with a glass rod, and when the alcohol is
really consumed. The presence of soda in lithia will, in this case
likewise, hide by their own characteristic color, that of the potassa.

The salts of potassa are absorbed when fused upon charcoal. The
sulphur, bromine, chlorine, and iodine compounds of potassa give a
white, but easily volatile sublimate upon the charcoal, around the
place where the fused substance reposed. This white sublimate
manifests itself only when the substance is melted an