Copy 1, Volume 1

Hand-book of chemistry / Translated by Henry Watts.

  • Gmelin, Leopold, 1788-1853
Date:
1848-1872
Catalogue details

Licence: Public Domain Mark

Credit: Hand-book of chemistry / Translated by Henry Watts. Source: Wellcome Collection.

    58/562 (page 34)
    Ot ee 34 AFFINITY. similar substances contained in the compound are its Components or - Elements; and of these if one be fluid and the other solid, the former is called the Solvent or Menstruum, the latter the Dissolved body or Solutum, The sphere of action of chemical affinity has by some chemists been too much enlarged, by others too much contracted. An instance of the former of these errors has already been given in speaking of the mixture of gases (page 21). The following views on the contrary appear to restrict the idea of a chemical compound between too narrow limits. : 1. Many combinations of liquids with gases in which the latter lose | their gaseous condition are by Dalton and others regarded as mechanical (vid. Water). 2, All mixtures of liquids one with another, and all solutions of solids in liquids, are by Berzelius, Mitscherlich, Dumas, and others of the most distinguished modern chemists, regarded as not chemical, unless they take place in definite proportions: ¢.g., mixtures of water and alcohol, alcohol and volatile oil; solutions of acids, alkalies and salts in water, alcohol, &c. Mitscherlich attributes such combinations to adhesion, Berzelius to a modification of affinity,—while, according to his view, chemical combina- nations properly so called result not from affinity but from electrical: attraction. Dumas ascribes them to a solvent power which he supposes to hold a middle place between cohesion and affinity: inasmuch as the former causes the union of bodies of the same nature, the latter that of bodies of very opposite natures, producing compounds possessed of new and peculiar properties; while the solvent power causes the combination of bodies of very similar nature, as of metals with metals, acids, alkalies and salts with water, resin and fat with alcohol, &c. These views lead to no satisfactory definition of Affinity (for objections to them, vid. Gehler’s Phys. Worterbuch. Ausg. 2, 9, 1862). They are nevertheless true in this respect that a distinction must be made between strong and weak affinities, the former producing compounds of definite constitution and characterised by distinct and remarkable properties, while the latter gives rise to products of less definite composition and differing less in their properties from the bodies of which they are formed: on this ground Berthollet, in an earlier state of the science, distinguished the more intimate combinations as Compounds (Combinaisons) and the less intimate as Solutions (Dissolutions), though the two classes merge into one another by imperceptible gradations and admit of no determinate separation, | II]. Ranae or AFFINITY. Every simple, 7.¢., hitherto undecomposed body, is capable of entering into chemical combination with others, but generally speaking not with all. It is possible that every simple substance may have affinity for every other; but many compounds of these substances may not have been obtained hitherto, because the components have not been placed under the particular conditions in which their affinity can exert itself; others it may be impossible to form because the affinity between their components is overcome by the force of gravitation, cohesion, or elasticity. For exam- ple, the fact of carbon not combining with mercury may perhaps be explained partly by the great cohesion of carbon, the tendency of its particles to remain combined amongst themselves being possibly greater than their inclination to unite with those of mercury; partly from the greater specific gravity of mercury, by which that substance is prevented from diffusing itself through so comparatively light a body as carbon. ¢ G P