290 C. F. Roberts — Standardization of 



Potassium 3-47 



Ferrous iron 4-31 



Ferric iron 1236 



Bromine 73*15 



Water O^l* 







Calculated for 





KBr. 



FeBr 2 



.2FeBr 3 . 3H,>0, 



3-92 







3-98 



4-26 







5-71 



11-70 







11-42 



73-09 







73-39 

 5-50 



100-00 100-00 



These salts are dark green in color and quite opaque like 

 the double ferric bromides described above. The crystalliza- 

 tion of the rubidium salt is apparently rhombohedral, that of 

 the potassium cubical. 



In conclusion the author wishes to express his sincere thanks 

 to Prof. H. L. Wells, under whose direction the work has been 

 carried on, for his kindly aid and many valuable suggestions. 



Sheffield Scientific School, New Haven, Conn., July, 1894. 



Akt. XL. — The Standardization of Potassium permanganate 

 in Iron Analysis ; by Charlotte F. Koberts. 



[Contributions from the Kent Chemical Laboratory of Yale College — XXXV.] 



For practical work in iron analysis, the standardization of 

 the potassium permanganate is naturally a very important 

 problem. The best authorities agree in considering that it 

 should be finally standardized on ferric chloride, but the diffi- 

 culty consists in determining with accuracy the amount of iron 

 in this solution. Though the purest iron which can be obtained 

 commercially is used as the basis, the resulting ferric chloride 

 still contains some silica and phosphorus, which must be elimi- 

 nated or the amount determined gravimetrically. The process 

 of determining the amount of iron in the ferric chloride solu- 

 tion, upon which the potassium permanganate is finally stand- 

 ardized, thus becomes long and tedious. To obviate this, the 

 following experiments were undertaken in the hope of obtain- 

 ing the same result by a shorter and more convenient method. 



If the potassium permanganate could first be compared with 

 a solution containing a known weight of iron which is finally 

 brought into the same condition as the ferric chloride solution, 

 and then this same potassium permanganate directly titrated 

 with the ferric chloride itself, the necessary accuracy could be 

 obtained without the gravimetric work on the ferric chloride 

 recommended. f Since electrolytic iron is undoubtedly the 



* Water by difference. 



f Blair: The Chemical Analysis of Iron, pp. 212-216. 



