180 PROCEEDINGS OP THE AMERICAN ACADEMY. 



Pulfrich * so that from the observed angle the index may read directly 

 from the table. 



In the following table giving the refractive power (the excess of the 

 index of refraction over unity), after the numbers representing the 

 refractive power of the distillates purified by a mixture of nitiic and 

 sulphuric acids, and with fuming sulphuric acid, the differences between 

 the refractive power before purification and afterwards are given. 



Pennsylvania. Ohio. Canada. 



163°. 



Ref. Power, Dif. Rcf. Power, Dif. Ref. Power, Dif. 



Unpurified distillate .4241 .4248 .4276 



After treatment with 



IINO3 and H2SO4 .4083 .0158 ,4123 .0125 .4133 .0143 



After treatment with 



H2S2O7 .4146 .0095 .4113 .0135 .4137 .0139 



173° .5 

 Uupurified distillate .4163 .4239 .4245 



After treatment with 



HNOsandHsSO^ .4118 .0045 .4134 .0105 .4149 .0096 



After treatment with 



H2S2O7 .4093 .0070 .4118 .0121 .4138 .0107 



196°. 

 Unpurified distillate .4214 .4251 .4309 



After treatment with 



HNO3 and H2SO4 .4158 .0056 .4214 .0037 .4219 .0090 



After treatment with 



H0S2O7 .4163 .0051 .4209 .0042 .4231 .0078 



216°. 

 Unpurified distillate .4249 .4280 .4289 



After treatment with 



HNOsandlLSOi .4209 .0040 .4244 .0036 .4219 .0070 



After treatment with 



H2S2O7 .4209 .0040 .4241 .0039 .4212 .0077 



Inspection of the columns in this table headed Kefractive Power shows 

 a gradual increase with the rise in boiling points, less regular in the un- 



* Zeit. fiir Instrunientenkunde, 1888, p. 47. 



