Rotatory Polarization of Liquids. 419 



markable : thus, although denser and more refracting than water, 

 its magneto-rotatory power is only f of that of water (0*750); 

 while liquified sulphurous acid, much less dense, has a higher 

 magneto-rotatory power (1*240). The chemical nature of the 

 substance therefore exerts a preponderant influence : in fact, 

 as we have just seen, one equivalent more of oxygen in its com- 

 bination with sulphur is sufficient to reduce nearly one half the 

 magneto-rotatory power of the compound ; on the contrary, 

 bromine and, especially, iodine, on entering into a combination, 

 contribute remarkably to the greatness of its magneto-rotatory 

 power. To be assured of this, one has only to compare in this 

 respect the three compounds of ethyle. The presence of nitro- 

 gen in a compound also tends to increase the magneto -rotatory 

 power; this follows from the observations made upon amylamine 

 and isoamylamine, in which nitrogen replaces the oxygen in 

 amylic alcohol and hydrate of amylene, the composition of 

 which, excepting this substitution, is almost identical with that 

 of the two former substances. In general, the greater the pro- 

 portion of oxygen in a compound, the less is its magneto-rotatory 

 power. 



It is probable, however, that the mode of combination, and 

 particularly the mode of grouping of the atoms, consequently the 

 atomic volume, has, independently even of the nature of the 

 atoms, a great influence upon the intensity of the magneto-rota- 

 tory power. This follows especially from the differences in that 

 respect presented by isomeric substances. 



2. Rise of temperature diminishes, in all liquids, the magneto- 

 rotatory power, first by lessening their density and consequently 

 diminishing in a given volume the number of the particles which 

 act upon the polarized ray, and then by a direct effect indepen- 

 dent of the dilatation, an effect most perceptible in those liquids, 

 such as water, which are but little dilatable*. 



3. A mixture of two liquids, when its preparation is not ac- 

 companied by strong chemical action, has a rotatory power which 

 is the mean of the powers of the ingredients of which it is com- 

 posed. The example of the sulphuric-acid solutions seems to 

 prove that, when the solution contains less than two tenth parts 

 of one or the other component, the rotatory power of the mixture 



* Various physicists, and specially M. Wulner (Poggendorff's Annalen, 

 vol. cxxxiii. pp. 1-53), have stated that the refractive power of a liquid di- 

 minishes with the rise of temperature in the same ratio as the density ; but, 

 as M. Bertin (Ann. de Chim. et de Phys. S. 4. vol. xiv. p. 499) rightly re- 

 marks, the experiments were made with variations of temperature so small 

 that it is impossible to prove from them a general law ; I am convinced 

 that the above is only an approximative one, as in the case of the magneto- 

 rotatory powers. 



