104 OUTLINES OF PHYSICAL CHEMISTRY
attempts have been made to explain these by stereo-chemical considerations. Here we shall only mention the aldoximes and the ketoximes, hydroxamic acids and certain analogous compounds. We know, for example, two benzaldoximes to which Bechmann assigns the formulae
C 6 H 5 — CH=NOH and C 6 H 5 — CH NH
\ / *
H. Goldschmidt has studied the compounds of these
substances with phenyl isocyanate and concludes that the
a and j3 modifications of benzaldoxime have the same
structural formula. Werner and Hantzsch have proposed
the following stereo-chemical formulae :
CeH 5 — CH C 6 H 6 — CH
��HON NOH
Anti-benzaldoxime Syn-benzaldoxime
This theory is, however, not quite definitely established, and Beckmann, amongst others, has furnished fresh experi- mental evidence in support of his view. According to the late V. Meyer \ the cause of this isomerism is to be found in the constitution of hydroxy lamine (' Berichte,' 23. 2407).
But it is now time to leave the domain of pure chemistry and pass on to subjects more in harmony with the title of this book.
Magnetic Rotation
Some substances, which themselves are possessed of no optical activity, may acquire a rotatory power when placed under the influence of a powerful electro-magnet. This very interesting phenomenon was discovered by Faraday (in 1845), and its development from the chemical point of view is due almost entirely to W. U. Perkin, sen.
Perkin's method of examination is, to place a polari- meter tube containing the liquid or solution, axially
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