The nature and origin of living matter.

  • Henry Charlton Bastian
Date:
1905
Catalogue details

Licence: In copyright

Credit: The nature and origin of living matter. Source: Wellcome Collection.

Provider: This material has been provided by Royal College of Physicians, London. The original may be consulted at Royal College of Physicians, London.

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    cases, the assumption or not of such a form is entirely dependent upon the conditions under which the separation takes place. Many substances which, in the chemist's laboratory, are only seen in the form of insoluble precipitates made up of amorphous granules, could have been procured in a crystaUine condition, if the same decomposition which had given rise to the amorphous precipitate had been allowed to take place more slowly. If instead of pouring a certain amount of a solution of sulphate of potassium into one of chloride of barium, we allow the mixture to take place gradually by means of dialysis, then crystals of sulphate of barium are formed rather than an amorphous precipitate. It has, in fact, been ascertained by Fremy' that insoluble compounds generally, which appear in the laboratory as a result of double decomposition in the form of amorphous precipitates, can almost invariably be obtained in a crystaUine condition when the chemical reaction is allowed to take place very slowly. This may be brought about by making the saline solutions mix after osmosis through membranes, wooden vessels, or porous porcelain. By one or other of these methods, he obtained many very insoluble salts in the crystalline condition—such as the sulphates of baryta, strontia, and lead, the carbonates of baryta and lead, oxalate of hme, chromate of baryta, and several sulphides. Variation in the ' conditions ' under which the crystallisation of any particular substance occurs, moreover, often gives rise to the most marked variation in its crystalline form. Thus, referring to the article ' Dimorphism' in Watts's Dictionary of Chemistry, we find the following statements :— Many substances, both simple and compound, crystallise in forms which belong to two or three different systems of crystallisation, or which, even if they belong to the same system, yet exhibit such differences in their corresponding angles as to render it quite impossible to reduce them to the same form : this was first shown by Mitscherlich, in 1823 (Ann. Ch. Phys. [2] xxiv. 264). Such bodies are said to be dimorphous and trimorphous. The difference of crystalline form which they exhibit is associated with difference of specific gravity, hardness, colour, and other properties. Whether a body shall crystalhse in one system or another seems to depend chiefly upon tempera- ture. . . . Sometimes the form of the crystal varies according to the solvent from which it separates: thus arsenious anhydride ' Compt. Rend. t. l.xiii. p. 714.