Just as we saw that the refractive power is very much influenced by the constitution of the molecule, so also is the magnetic rotation. A double linkage, for instance, very considerably increases the characteristic a, as may be gathered from the last figure of the first column of numbers in the table. But this increase is very far from constant ; the difference between the molecular magnetic rotations of vinyl- and ethyl-bromides is 0*869, whilst between their iodides it is 1*708.
The observations on magnetic rotation of carbon compounds have not led to anything like the same regu- larities as we have discovered for the refraction and atomic volumes.
It may be added that magnetic rotation observations have been carried out on inorganic substances ; but the interpretation of the rotatory powers of acids, bases, and salts in aqueous solution appears to offer great difficulty.
We cannot enter further into this exceedingly interest- ing subject, the practical work on which demands resources which are not at the disposal of every chemist.
Those specially interested in the subject would do well to consult Perkin's publications in the 'Journal of the Chemical Society/ and also John ('Wiedemann's Ann.' 43. 280), Wachsmuth (ibid. 44. 877), and Schonrock C Zeitschrift f. phys. Chem.' 11. 758).
��Solutions
Molecular Volume of Dissolved Substances
The density of a solution is determined in the same way as that of a homogeneous liquid, namely, by means of a pycnometer, or by Westphal's balance.
If we consider a quantity of a solution containing one gram-molecule of dissolved substance, it is evident that the volume occupied by the substance is equal to the volume
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