RICHARDS AND BONNET. — DISSOLVED CHROMIC SULPHATE. 21 



(1.88 parts) if the salt were normal. The discrepancy indicated only 1.6 

 atoms of the sulphur for every 2 atoms of chromium, a proportion as 

 nearly as possible identical with that obtained by the analysis of the pure 

 ultra-basic solution. 



Any conclusions based upon these figures must be somewhat insecure, 

 because the data are only the somewhat variable differences between large 

 quantities, and because traces of other groups besides the complex sul- 

 phate are probably occluded by the baric sulphate. Nevertheless it seems 

 safe to say that the chief occluded body causing the green color of the 

 impure precipitate is basic, and that nearly half of the sulphuric acid 

 which should be combined with the chromium may be replaced by hy- 

 droxyl. There is nothing in the results to prove that there are not 

 several soluble green basic salts, of different degrees of hydrolytic decom- 

 position ; but even the least basic of these, obtained in a strongly acid 

 solution, seems to be more basic than that represented by the formula of 

 Recoura. 



Having thus determined in various ways the existence of a basic com- 

 plex, it seems highly desirable to discover whether or not an acid com- 

 plex containing chromium also exists, according to the possible equation, 



a:Cr 2 (S0 4 ) s + H 2 = Cr^OHCSO*)^ + HCr(S0 4 ) a . 

 This matter forms the subject of the following section. 



Migration Experiments. 



Whitney showed in 1809 that the method of Lodge* for observing 

 electrolytic migration afforded proof of the presence of ionized hydrogen 

 in the green solution. We were desirous to carry this matter further, in 

 order to discover whether or not there was any observable migration of a 

 green complex anion, concerning whose possible existence Whitney was 

 not anxious. In a number of experiments according to Lodge's method 

 we obtained inconclusive results, which were found to be due to the fact 

 that the green solution coagulates the gelatine and leaves free passages 

 for convection in the expelled solution. Gelatine thus coagulated by the 

 green chromium solution cannot be melted by warming, hence it is evi- 

 dent that a compound must be formed. On this account we rejected 

 gelatine, and continued the migration experiments with the help of an 

 apparatus similar to Ilittorf's. 



The. diagram illustrates this arrangement. The glass cups or cells 



* O. Lodge, H. A. Reports, 396 ( 1880). See also Whetham, Phil. Mag. [5], 38, 

 392 ( 1894) ; Orme Masson, Zeit pliys. Chem., 29, 501 (1899). 



