A text-book of inorganic chemistry / by George Senter.

  • Senter, George, 1874-
Date:
1913
Catalogue details

Licence: In copyright

Credit: A text-book of inorganic chemistry / by George Senter. Source: Wellcome Collection.

    404/678 (page 390)
    certain important generalizations may be made. The electro-positive character (and also the electro-negative character) is most pronounced for univalent elements (e.g. the alkali metals, the halogens); but polyvalent elements may also show great affinity for electricity, e.g. aluminium. On the other hand, univalent elements are mostly strongly basic or acidic, and the oxides of polyvalent elements are often both weakly basic and weakly acidic {e.g. aluminium). When the same element forms both basic and acidic oxides, the higher oxides (that is, those containing the higher proportion of oxygen) are most acidic. Methods of Preparing Metals from their Compounds —The methods will be described in connexion with the metals them- selves, but a brief outline of the processes will prove useful at the present stage. The compounds chiefly employed are the oxides and the halides, and the method used in any particular case depends mainly on the volatility of the metal and on its chemical affinity for other elements. Provided the oxide is not too stable, it can be reduced by heating with carbon (examples: zinc, tin, iron, etc.) or with finely divided aluminium (examples : chromium, manganese, etc.). If the metal has so great an affinity for oxygen that this method cannot be applied, recourse is often had to the electrolysis of a fused salt, for example the fused chloride, the metal separating at the negative pole. Potassium, sodium, lithium, magnesium, alumi- nium and other metals are now obtained commercially in this way. In applying these general methods the naturally occurring com- pound of the metal has first to be converted into the oxide or chloiide, and purification may also be necessary. The methods used depend largely on the nature of the ore. Sulphides, for example, are con- verted into oxides by roasting, the sulphur being burned away as sulphur dioxide. Methods of Preparing Salts—The more important methods of preparing salts have already been described in connexion with the individual acids. If one or more of the reacting substances are used in solution, the method to be employed in any particular case depends greatly on whether the salt is or is not insoluble in water. If it is only slightly soluble the general method of preparation is by double decomposition between a solution containing the basic and one containing the acidic constituent, e.g.: BaCl2+H2S04->BaS04 +2HCI Pb(N03)2 + 2KI->PbI2 | +2KNO3. If, on the other hand, the salt is soluble in water, it may usually be