Rotatory Polarization of Liquids* 411 



effect itself must be admitted to be less energetic when the tem- 

 perature is higher. With certain liquids, such as alcohol espe- 

 cially, the direct influence of the temperature is almost insensible, 

 which is probably owing to the great dilatability of that liquid 

 rendering preponderant the influence of the decrease of density. 



§ 4. Determination of the Magneto-rotatory Power of the Mixture 

 of Two Liquids. 



I began by mixing equal volumes of distilled water and rec- 

 tified alcohol of sp. gr. 0*804. The magneto-rotatory power of 

 the mixture was obtained by means of two series of experiments, 

 made at two different periods, and which gave the following 

 numbers : — 



Mixture. Water. Ratio. 



11° 40' 12° 0-972 



The magneto-rotatory power calculated as the mean of those 

 of water and alcohol is 0*938, that of water being 1*000, and 

 that of alcohol 0*876. The actual density of the mixture was 

 found to be 0*935 • the density calculated as the mean of those 

 of alcohol and water would be 0*902. Now the ratio of the 

 real rotatory power to the calculated is 1*0362 ; and the ratio 

 between the actual and the calculated densities is 1*0365. Thus, 

 in a mixture of equal volumes of water and alcohol,, which is ac- 

 companied by a sensible contraction (proved by the increase of 

 density), the magneto-rotatory power augments in exactly the 

 same proportion as the density — which proves that the molecular 

 magneto-rotatory power does not change. We have seen, in the 

 preceding Section, that it is the same with alcohol with respect 

 to the changes of density proceeding from variations of tempe- 

 rature. In taking a mixture of equal volumes of water and 

 alcohol, I chose that in which the change in volume is the 

 greatest ; it is evident, then, that with mixtures in other propor- 

 tions the same result would be found. 



The mixtures of water and sulphuric acid in different propor- 

 tions gave very interesting results, which I think deserving of 

 detailed exposition. This kind of experiments present some 

 difficulties, especially with concentrated solutions, on account of 

 the rapidity with which they attract humidity from the air, which 

 changes their identity; nevertheless this inconvenience may be 

 avoided by taking precautions. In fact we have seen that mo- 

 nohydrated sulphuric acid having a rotatory power of 0*750 

 acquires one of 0*757 after one or two removals from one vessel 

 to another in the air, andone equal to 0*768 after a greater number. 



My first experiments were made with the Paris sulphuric acid, 

 of which the rotatory power is 0*800, and the density (taken 



2E2 



