CONTRIBUTIONS FROM THE CHEMICAL LABORATORY 

 OF HARVARD COLLEGE. 



THE CHANGEABLE HYDROLYTIC EQUILIBRIUM OF 

 DISSOLVED CHROMIC SULPHATE.* 



By Theodore William Richards and Frederic Bonnet, Jr. 



Presented May 13, 1903. Received May 9, 1903. > 



Introduction. 



Many eminent chemists have attempted to solve definitely the riddle 

 involved in the dual nature of chromium solutions ; but some doubt still 

 remains concerning the precise interpretation of the facts. A complete 

 review of earlier work would require far too much space at present ; 

 instead of such a review, there is given at the end of this paper a 

 chronological bibliography of the subject, which will be referred to 

 throughout the discussion by simply naming the appropriate date. The 

 most satisfactory interpretation, based chiefly upon the work of Kriiger 

 (1844), Siewert (1863), Recoura (1887, 1890, 1895, 1899), Doyer van 

 Cleef (1881), and Whitney (1896, 1899), seems to point to the following 

 situation. The violet solution may be inferred to contain the chromic 

 salt in a state comparable to that of other normal salts, while the green 

 solution modified by heating appears to be hydrolyzed into acid and basic 

 substances.! The hydrolysis seems in many cases to proceed to such an 

 extent that about a gram atom of ionized hydrogen is developed for every 

 two of chromium present, but the results are too conflicting to prove 

 whether this is the indication of a nearly completed reaction or merely 



* A part of this paper formed a portion of a thesis presented by F. Bonnet, Jr., 

 for the degree of Ph.D. at Harvard University. 



t Recoura has' pointed out sharply tlie difference between the solutions thus 

 modified and those obtained from salts which have been heated in the dry state. 

 He names the two respectively " modified " and " green " chromic salts. The 

 present paper has to do only with the former. 



