(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 and absorbed within the charcoal, and ceases to be visible as soon as it is submitted to the reducing flame, while the external flame is colored violet; sulphate of potassa, for instance, is reduced by the glowing charcoal into the sulphide.  This latter is somewhat volatile, but by passing through the oxidation flame, it is again oxidized into the sulphate.  This, being less volatile, sublimes upon the charcoal, but by exposing it again to the flame of reduction, it is reduced and carried off to be again oxidized by its passage through the oxidation flame.

Potassa and its compounds give, with soda, borax or microcosmic salt, as well when hot as cold, colorless beads, unless the acid associated with the alkali should itself produce a color.  When borax is fused with some pure boracic acid, and sufficient of the oxide of nickel is added, so that the beads appear of a brown color after being cooled, and then the bead thus produced fused with the substance suspected to contain potassa, in the oxidation flame, the brown color is changed to blue.  The presence of the other alkalies does not prevent this reaction.  As it is not possible to detect potassa compounds with unerring certainty by the blowpipe flame, the the wet method should be resorted to for the purpose of confirming it.