Rotatory Polarization of Liquids. 407 



in the tube a bubble of air (which was not in the path of the 

 polarized ray), in order to allow the liquid to dilate freely. The 

 heating did not sensibly augment the volume of the tube ; so 

 that it effected no change in the length of the liquid column, but 

 solely a diminution of its density. To avoid all chance of error, 

 I operated both by heating the water and by letting it cool after 

 heating. 



Rectified Alcohol. 

 Temperature. Rotation. 



7C. 



9 10 



33 „ 



8 55 



40 „ 



8 52 



60 „ 



8 40 



70 „ 



8 30 



This Table exhibits the means of the results obtained on arri- 

 ving at the temperatures indicated either by heating or cooling. 

 From it are deduced the following ratios between the density of 

 the liquid and its corresponding magneto-rotatory power. 



Temperatures. **> bet ^ eeu * atl ° ^ tween 



o L o the densities. the rotations. 



7 and 33 1-028 1*028 



7 „ 40 1-037 1-035 



7 „ 60 1-062 1-058 



7 „ 70 1-079 1-078 



33 „ 60 1-031 1-029 



33 „ 70 1-050 1-050 



40 „ 60 1-025 1023 



40 „ 70 1042 1043 



60 „ 70 1-017 1-019 



Thus, by raising the temperature of alcohol, its magneto-rota- 

 tory coefficient is diminished in nearly the same ratio as its den- 

 sity. In fact it must not be forgotten that in the experiments 

 the length of the column passed through by the polarized ray 

 remains constant, and that it is the density that changes ; there- 

 fore the ratio of the volume at 33° to the volume at 7° gives the 

 ratio of the density at 7° to the density at 33°, and the same 

 for the other differences of temperature; and it was by taking 

 the ratios between the volumes at different temperatures, as given 

 in the Tables of dilatation, that I determined the ratios between 

 the densities. 



I pass now to my experiments upon iodide of ethyle and amy- 

 lic alcohol, in which I used the same process as in those on 

 rectified alcohol. 



