Page:Outlines of Physical Chemistry - 1899.djvu/119

 all states of aggregation, and crystalline rotatory power due to the arrangement of the molecules in the crystalline particle. In crystallised bodies possessed of both these causes of optical activity, the two effects, although absolutely independent of each other, would be found to combine.

3. H. Landolt has recently shown (' Berichte d. d. ch. G.' 1896) that finely pulverised sodium chlorate (in grains of diameter 0*004 to 0*012 millimetre) retains its rotatory power. This shows that the reduction to this state of division has not destroyed the crystalline structure,

4. Generally speaking, it may be asserted that, as yet, no organic substance endowed with rotatory power has been discovered which does not contain at least one asymmetric carbon atom. But substances are known which contain asymmetric carbon atoms and yet are optically inactive. This circumstance, however, is in no way in opposition to Le Bel and van't Hoff's theory, since the substances may belong to the inactive or racemic types. Most artificial substances, prepared either synthe- tically or by transformations of natural products at high temperatures, belong to the racemic type. The chief methods of resolving this type into the constituent dextro- and laevo- modifications are these :

a. Crystallisation of a salt. — Example : double tartrate of sodium and ammonium (must be crystallised below a certain temperature).

b. Crystallisation of a salt formed with an optically active acid or base. — Example : cinchonine malate in the preparation of dextro-malic acid.

c. The action of certain fungi (Penicillium Glaucum, Aspergillus Niger, yeast plants, &c). — Example: the decomposition of racemic (tartaric) acid by Penicillium ; the fungus feeds chiefly on the dextro-acid, and if the cultivation be stopped at the correct moment the laevoacid can be isolated.

The same fungus living at the expense of the racemic form of amyl alcohol destroys the dextro- modification first.

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