416 Wright and Kr eider — Relation between 



Art. XLIII. — The Relation between Structural and Magneto- 

 optic Rotation ; by A. W. Wright and D. A. Kreider. 



The fact that any transparent, simply refracting, optically 

 inactive substance when placed in a powerful magnetic field 

 instantly acquires the property of rotating the plane of polar- 

 ized light, and that the effect thereon is apparently of the same 

 nature as that characteristic of certain specific atomic group- 

 ings in molecules, as, for example, those containing the asymme- 

 tric carbon atom, or of a particular molecular aggregation in 

 certain crystalline units, such as sodium chlorate, naturally 

 raises the question of relation between the two causes. Upon 

 this subject literature furnishes no decisive records. Verdet's 

 admirable researches have brought to light many interesting 

 facts in regard to the two rotations, but none upon the subject 

 here proposed. 



It is known that when an optically active substance is placed 

 in a magnetic field the two rotations are superposed, so that 

 the resultant optical activity is the algebraic sum of the struc- 

 tural and magnetic rotations. An interesting result is Yerdet's 

 observation upon the behavior of iron and some other magnetic 

 substances, to the effect that these, contrary to the general 

 rule, rotate the plane in a direction opposite to that of the 

 electric current or magnetic whirl. 



It seemed worth submitting to an experimental investiga- 

 tion whether, if the optically active molecular structure or 

 aggregation were effected in a magnetic field, it would be 

 influenced thereby to an extent sufficient to show in its final 

 optical properties, which would seem probable providing the 

 interatomic or intramolecular forces are electrodynamic. 



Experiments on Tartaric Acid. 



Tartaric acid, three of the four isomeric forms of which are 

 optically different, seemed applicable in this investigation, and 

 upon it the first experiments were made. 



Ordinary dextrotartaric acid, when heated to 175° C. in the 

 presence of water in sealed tubes, is gradually converted into 

 equal amounts of the racemic and the inactive forms.* If 

 the atomic arrangement in this molecule is subject to the 

 influence of magnetic force, it might be expected that by 

 effecting the above change in a magnetic field, the resulting 

 product should differ from that ordinarily obtained. For 

 instance, if the molecules or their factors possess polarity, the 

 magnetic field should exert upon them a directive action, and it 



* Jungfleisch, Jahresb., 1872, 515. 



