Chemical elements
  Potassium
    Isotopes
    Energy
    Preparation
    Physical Properties
    Chemical Properties
    PDB 1a3w-1dul
    PDB 1dz4-1j95
    PDB 1jbr-1lqp
    PDB 1lrt-1o07
    PDB 1o76-1qb9
    PDB 1qj5-1t86
    PDB 1t87-1vq9
    PDB 1vqk-1yj9
    PDB 1yjn-2aop
    PDB 2apo-2f4v
    PDB 2fbw-2hg9
    PDB 2hh1-2oij
    PDB 2oiy-2uxb
    PDB 2uxc-2x20
    PDB 2x21-3c0y
    PDB 3c0z-3dix
    PDB 3diy-3f5w
    PDB 3f7j-3hqo
    PDB 3hqp-3l01
    PDB 3l0u-3oi5
    PDB 3oia-3r9b
    PDB 3rde-4e6k
    PDB 4edj-8gep

Preparation of Potassium






The metal was first isolated by Davy by electrolysis of the hydroxide, and shortly afterwards Gay-Lussac and Thenard obtained it by the action of iron on the carbonate. Charcoal can be substituted for iron, one process consisting in the decomposition at low red heat of potassium hydrogen tartrate, with formation of a mixture of charcoal and potassium carbonate, the reduction to metal being subsequently effected at a higher temperature:

K2CO3 + 2C = 2K + 8CO.

If the temperature is too low, there is danger of the liberated potassium combining with carbon monoxide to form a highly explosive compound, potassium carbonyl, C6(OK)6. Another modification of the method consists in heating a mixture of tar and potassium carbonate or hydroxide at dull redness, and subsequently raising the temperature of small portions of the carbonaceous mass to bright redness, the molten metal being tapped off. The fused hydroxide can also be allowed to flow over heated charcoal, and the metal distilled off.

When equivalent weights of sodium and potassium hydroxide are mixed, and fused in absence of air, sodium monoxide is formed, hydrogen evolved, and potassium distils at a temperature of about 670° C. The metal can be condensed, and the process is claimed to be applicable to its manufacture.

Latterly the production of potassium by the electrolytic process has become of industrial importance, partly on account of the purity of the product, and partly because the attendant risk is much less than with the chemical methods. The ordinary Castner process for the isolation of sodium is inapplicable to potassium, Lorenz having shown that part of the potassium is dissolved in the molten state by the fused hydroxide, and part is vaporized and after condensation in minute drops is diffused throughout the liquid mass. The effect is that the liberated metal tends to combine with the anion at the anode. The difficulty is avoided by surrounding the iron-wire cathode with a cylinder of magnesite to prevent diffusion of the metal to the anode, by employing as low a temperature as possible, and by excluding air. An anode of sheet iron is immersed in the fused hydroxide outside the magnesite chamber. As substitutes for the hydroxide, potassium nitrate, and also potassium chloride with an admixture of fluoride to lower the melting-point, are employed. With the nitrate the cathode is an aluminium vessel.


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