Page:Outlines of Physical Chemistry - 1899.djvu/125

 or -r L ... r

��OF The

��MAGNETIC ROTATION

��"HttfEPorrY

��between the perforated magnet-poles (or perforated ai tures). After exciting the magnet, we find that a rotatory power has been developed, to the right or to the left, according to the direction of the current, and to a greater or less extent, depending on the intensity of the magnetic field and the nature of the liquid.

Fig. 26 shows the arrangement.

In order to obtain comparable results it is necessary to employ always the same light (monochromatic sodium

��light), and work at the same temperature (15°C.) in tubes of the same length (10 centimetres). The magnetic rotation of a substance is expressed by the formula

��aM

��a being the observed angle, m and d the molecular weight and density of the substance under investigation.

Water is chosen as standard of comparison, and Perhin

terms the quotient of -=- for any substance by the corre-

��ct

��a'M

��sponding value —^- for water, the molecular magnetic rota- tion of the substance. In the determination of the angles a and a', the same electric current must be used. That is, the magnetic molecular rotation is

aud f a' m' d'

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