Atomistry » Potassium
Atomistry »
  Potassium »
    Isotopes »
    Energy »
    Preparation »
    Physical Properties »
    Chemical Properties »
    PDB 1a3w-1d7u »
    PDB 1d7v-1gmk »
    PDB 1gup-1k4c »
    PDB 1k4d-1m40 »
    PDB 1m5h-1o07 »
    PDB 1o76-1pqo »
    PDB 1pr9-1s61 »
    PDB 1s72-1u1f »
    PDB 1u1g-1w29 »
    PDB 1w2b-1yj9 »
    PDB 1yjn-2aaq »
    PDB 2adp-2c13 »
    PDB 2c44-2frz »
    PDB 2fxi-2hw8 »
    PDB 2hzv-2o84 »
    PDB 2o8l-2qxl »
    PDB 2qyo-2vxy »
    PDB 2w0f-2xo0 »
    PDB 2xo1-3atv »
    PDB 3ay9-3ccl »
    PDB 3ccm-3dke »
    PDB 3du0-3f2t »
    PDB 3f2y-3gvf »
    PDB 3gvx-3irp »
    PDB 3is7-3lut »
    PDB 3m62-3ow2 »
    PDB 3oyt-3q9b »
    PDB 3q9c-3rs8 »
    PDB 3rs9-3spj »
    PDB 3srd-3ugx »
    PDB 3ukm-3vrs »
    PDB 3vuw-3zns »
    PDB 3zq6-4bg9 »
    PDB 4bga-4cn0 »
    PDB 4cn5-4edj »
    PDB 4eei-4gx0 »
    PDB 4gx1-4ije »
    PDB 4ikr-4k8t »
    PDB 4k93-4l4b »
    PDB 4l4c-4mj3 »
    PDB 4mkk-4pdv »
    PDB 4pjo-4qne »
    PDB 4qrh-4tof »
    PDB 4tog-4wo3 »
    PDB 4wol-4xs1 »
    PDB 4xs4-4zqr »
    PDB 4zum-5avv »
    PDB 5avw-5cbw »
    PDB 5cc8-5dmj »
    PDB 5dou-5fcw »
    PDB 5ffz-5g1a »
    PDB 5g1b-5irg »
    PDB 5iuj-5kse »
    PDB 5kuk-5mrn »
    PDB 5mro-5t5i »
    PDB 5t5m-5urq »
    PDB 5urs-5wgk »
    PDB 5wgl-5yfv »
    PDB 5yfw-6ab2 »
    PDB 6ab8-6c3x »
    PDB 6c3y-6deq »
    PDB 6der-6dp6 »
    PDB 6dp7-6eng »
    PDB 6eo1-6gep »
    PDB 6gg4-6hsg »
    PDB 6hsh-6jpt »
    PDB 6jr2-6mo3 »
    PDB 6mpd-6nv8 »
    PDB 6nzg-6pye »
    PDB 6pyp-6r3i »
    PDB 6r3j-6t2g »
    PDB 6t3k-6uk3 »
    PDB 6ukn-6vwo »
    PDB 6vwp-6we6 »
    PDB 6wfl-6xu0 »
    PDB 6xup-6zkl »
    PDB 6zkm-7azk »
    PDB 7b02-7dif »
    PDB 7dmr-7kgu »
    PDB 7klb-7mky »
    PDB 7mtu-7pxg »
    PDB 7pxh-8gep »

Element Potassium K, Alkali Metal

About Potassium

While the knowledge of some of the potassium compounds can be followed back almost to the most remote monuments of culture, the characterisation of the potassium compounds as derivatives of a special element was first effected towards the end of the eighteenth century by Marggraf. On account of the preparation of potassium carbonate from cream of tartar, which is deposited in the barrels in the fermentation of wine, that compound received the name of vegetable alkali, in contradistinction to mineral alkali, sodium carbonate or soda. Although potassium hydroxide or caustic potash could not be decomposed, it was long felt that it was no simple substance; but the actual proof that a metallic element formed the basis of the potassium compounds was first given in 1807 by H. Davy, who decomposed potassium hydroxide by an electric current derived from a voltaic battery, which had just then been invented.

After it had been obtained in this way, the method of preparing it by purely chemical means was soon discovered, a method which was for long the only one employed. The most important of these reactions is the heating of potassium carbonate with charcoal; carbon monoxide and metallic potassium are formed, the latter of which volatilises and is condensed under rock oil - K2CO3 + 2C = 2K + 3CO. Quite recently the electrical method of preparing it has been again adopted, since the necessary electrical energy can now be cheaply generated in any desired amount.

Potassium is a silver-white metal which melts at 62°, and which, even at the room temperature, is so soft that it can be kneaded and easily cut with a knife. At 720° it volatilises; the vapour is blue- green in colour. The colour can be rendered visible by heating the metal in a glass tube which is filled with a gas or vapour free from oxygen; the phenomenon, however, is visible only for a moment, since the potassium vapour quickly attacks the glass, which thereby becomes covered with a black coating of liberated silicon.

Potassium combines with very great readiness with oxygen, so that it decomposes almost all substances which contain that element. In the air, therefore, under the joint action of the water vapour, it immediately becomes tarnished, owing to the formation of a layer of hydroxide, and its metallic lustre can be observed only immediately after a fresh surface has been made. If it is enclosed in a tube which is exhausted or filled with hydrogen, and then fused, the metallic surface can thus be rendered visible and permanently preserved.

On account of this property, potassium must be kept in such a way that oxygen has no access to it. In large quantities it is preserved in a soldered tin; smaller quantities are kept under rock oil, since this liquid does not contain oxygen. It, however, absorbs gaseous oxygen, and the potassium kept under rock oil soon becomes covered with a grey-brown crust which, however, only slowly becomes thicker and protects the metal fairly well.

It is very remarkable that in dry oxygen potassium is not (i.e. is only very slowly) oxidised, whereas the smallest amount of water immediately produces a rapid reaction. Such behaviour, however, in spite of its great generality, must not be regarded as universal, for instances of oxidation processes have been proved (e.g. the combination of nitric oxide with oxygen) where the reaction takes place with undiminished velocity, even between the very carefully dried substances.

Concerning the determination of the combining weight of potassium, the essential points have already been given under chlorine. It amounts to K = 39.15.

Potassium Occurrence

Potassium is present in many rocks in the form of silicates, such as orthoclase, K2O,Al2O3,6SiO2; mica, K2O,3Al2O3,4SiO2; and leucite, K2O,Al2O3,4SiO2. It is a constituent of the waters of mineral springs and of the ocean. The deposits at Stassfurt in North Germany, formed by evaporation of large volumes of land-locked sea-water, contain enormous quantities of carnallite, a double chloride of potassium and magnesium of the formula KCl,MgCl2,6H2O; kainite, a mixture of potassium and magnesium sulphates with potassium and sodium chlorides; and sylvine or potassium chloride. From these and other similar deposits in the same locality most of the potassium salts of commerce were obtained prior to August 1914. The outbreak of the great European War stopped the supply, and the ensuing dearth of potassium salts gave a valuable stimulus to research on their production from orthoclase, which contains about 2.4 per cent, of K2O. Potassium salts are a constituent of the soil, and are present in large quantities in plants. In these vegetable products the metal is usually combined with organic acids such as oxalic, tartaric, and malic.


Last articles

Zn in 7VD8
Zn in 7V1R
Zn in 7V1Q
Zn in 7VPF
Zn in 7T85
Zn in 7T5F
Zn in 7NF9
Zn in 7M4M
Zn in 7M4O
Zn in 7M4N
© Copyright 2008-2020 by
Home   |    Site Map   |    Copyright   |    Contact us   |    Privacy