CONTIUBUTIONS FROM THE CHEMICAL LABORATORY 

 OF HARVARD COLLEGE. 



ON THE DETERMINATION OF SULPHURIC ACID IN 



THE PRESENCE OF IRON; A NOTE 



UPON SOLID SOLUTIONS. 



By Thkodoue William Richards. 

 Keceived February 5, 1900. Presented February 14, 1900. 



Within the past year have appeared three interesting articles by 

 Kiister and Thiel * concerning several methods of precipitating bai'ic 

 sulphate free from iron when that element has been present in the solu- 

 tion. One of the methods which they have proposed is an excellent 

 addition to our always imperfect analytical repertory, and the chemical 

 world owes them a debt for the ingenious although exceedingly simple 

 suggestion. 



While not wishinor in the least to detract from the merit and interest 

 of this work, I feel that attention should be called to several omissions 

 in their paper, especially those which concern theoretical considerations 

 involved in previous work upon the subject. 



In their first paper, where the admirable analytical device is explained, 

 Kiister and Thiel ascribe the '' occlusion" of iron to the presence of the 

 ferric ion. It is interesting that this idea, which they themselves have 

 since shown to be false, should have led them to the desired goal. The 

 circumstance might be taken as an argument in favor of the proposition 

 that even an incorrect idea is better than none. In a reference to this 

 paper, Ostwald t points out that the occlusion is in all probability due 

 not to the ferric ion, but rather to a molecular complex ; and in their last 

 paper Kiister and Thiel describe experiments which prove beyond much 

 doubt the correctness of Ostwald's suggestion. Oddly enough, however, 

 they still cling, in their summing up of the matter, to the statement that 

 the ferric ion is the essential agent. 



* Kiister and Thiel, Z. anorg. Cliera., 19, 97 (1899); 21, 73 (1899); 22, 424 

 (1900). 



t Ostwald, Z. pbys. Chem , 29, 340 (1899). 



