1 64 Dr. J. II. Gladstone on the Specific Refraction 



These numbers are as close as two different specimens of the 

 same salt, even if they were in the same condition, are likely 

 to be. It did not seem worth while to obtain additional proof 

 of a law which has already been established by many cases ; 

 not only by my previous observations, but also by those of 

 Topsoe, Bedson, and Kanonnikoff. 



Do these figures confirm the law that the refraction- 

 equivalent of a compound body is the sum of the refraction- 

 equivalents of its components? 



The alums may be regarded as a compound of the sulphates 

 of two metals of different kinds w r ith 24 molecules of water. 

 Now water in the uncombined state has the refraction-equi- 

 valent of 5*926 ; and in regard to the sulphates we have the 

 following data : — 



Ammonium sulphate, (NH 4 ) 2 S0 4 , 39*3. The mean of five 

 determinations made by myself gives 39*35 * : Kanonnikoff 

 gives 39-27 f. 



Sodium sulphate, Na 2 S0 4 , 26*6. Kanonnikoff gives 26*02. 

 Methylamine sulphate, (NCH 6 ) 2 S0 4 , 54*5 ; i. e. ammonium 

 sulphate with the addition of 2CH 2 , or 15*2. 



Potassium sulphate, K 2 S0 4 , 32*4. The mean of five deter- 

 minations gave me 32*6 : Kanonnikoff gives 32*22. It may 

 be estimated at 32*3 from Topsoe and Christiansen's determi- 

 nations of the crystallized salt. 



Rubidium sulphate, Rb 2 S0 4 , 41*3. This is KanonnikofTs 

 determination, which I prefer to my own made in 1869. 

 Caesium sulphate, Cs 2 S0 4 , 55*3. Also KanonnikofTs. 

 Being not content with my old observations on the sul- 

 phates of the trivalent metals, I have recently determined 

 them afresh, with the following results : — 

 Aluminium sulphate, A1 2 (S0 4 ) 3 , 70*5. 



Chromium sulphate, Cr 2 (S0 4 ) 3 , 82*5 ; the result of old and 

 new observations. 



Ferric sulphate, Fe 2 (S0 4 ) 3 , 89*1 ; the mean of old and new 

 observations. 



It is evident that on adding together 



Ammonium sulphate . . 39*3 

 Aluminium sulphate . . 70*5 

 24 Water 142*2 



We obtain .... 252*0 



In this way the second column of the following table has 

 been calculated : — 



* Four of these are given in my paper in the Phil. Trans. 1860, p. 9. 

 t Journal of the Russian Physico-Chemical Society, 1884, p. 119. 



