Browning and Palmer — Estimation of Cerium. 83 



Art. IX. — On ih% Estimation of Cerium in the Presence 

 of the other Rare Earths by the action of Potassium 

 Ferricyanide ; by Philip E. Browning and Howard E. 

 Palmer. 



[Contributions from the Kent Chemical Laboratory of Yale Univ. — clxxvii.] 



The work to be described was undertaken to determine how 

 completely the oxidation of cerium from the cerous to the 

 eerie condition may be effected by potassium ferricyanide in 

 alkaline solution, and how completely the measure of the oxi- 

 dation can be registered in the amount of potassium ferrocy- 

 anide formed, according to the following equation : 



2K,FeC a N B + Ce.O, + 2KOH = 2K 4 FeC,N 6 + H 2 + 2Ce0 2 . 

 For this work a solution of pure cerous sulphate was made 

 and standardized by precipitating measured and weighed por- 

 tions with a definite amount of a standard solution of sodium 

 oxalate, filtering, igniting the cerium oxalate, and weighing 

 the eerie oxide obtained. As a check on this method, the 

 excess of the sodium oxalate over the amount used for the 

 precipitate was determined in the filtrate by titration with 

 potassium permanganate, and this amount was subtracted 

 from the whole amount of sodium oxalate used. From this 

 result the cerium present can be readily estimated, the amount 

 of sodium oxalate used in the precipitation being known.* 



The ferricyanide solution used was made by dissolving 2 

 grams of carefully selected crystals of potassium ferricyanide 

 in 100 cm3 of water. About 20 cm3 of this solution were used 

 in each determination. 



The procedure was as follows : To measured and weighed 

 portions of the cerous sulphate solution 20 cm3 of- the ferricy- 

 anide solution were added, and potassium hydroxide in solu- 

 tion to complete precipitation. 



The precipitated hydroxide was filtered off and the filtrate 

 and washings, amounting in volume to from 200 cm3 to 250 cm3 , 

 after being made distinctly acid with dilute sulphuric acid, 

 were titrated with a standard solution of potassium perman- 

 ganate until the presence of the permanganate color showed 

 the oxidation of the ferrocyanide to the ferricyanide,f accord- 

 ing to the equation : 



5K 4 FeC 6 N 6 -f- KMn0 4 + 4H 2 S0 4 = 5K 3 FeC 6 N 6 + 3K 2 S0 4 + 

 MnS0 4 + 4H 2 0. 

 By this equation and the preceding one the amount of cerium 

 present can be readily calculated. 



Each day before the ferricyanide was used a portion of 20 cm3 

 of the solution was acidified and titrated with the permanganate 

 to color, and the amount necessary, generally from one to 

 three drops, was subtracted from the amount of the perman- 



* Browning and Lynch, this Journal [4], viii, 457, 1899. 

 f Sutton's Volumetric Analysis, IX edition, page 209. 



