Palmer — Potassium Ferricyanide in Alkaline Solution. 143 



obtaining an exact end point in the titration of large amounts 

 of ferrocyanide, owing to the formation of a precipitate of 

 K^MnFeCoNj during the titration, as was first pointed out by 

 Griitzner.* This modification consisted in adding an excess of 

 permanganate to the solution and, after the precipitate had 



cleared up, titrating back the excess of permanganate with — ■ 



potassium ferrocyanide in the presence of a trace of a ferric 

 salt, the formation of a permanent green coloration due to the 

 ferric ferrocyanide indicating the end point. 



In experiments carried on in confirmation of this method a 

 solution of potassium chromate was used, whose standard had 

 been determined by precipitating definite portions as mercurous 

 chromate and weighing as Cr„03 after ignition ; and also by 

 precipitating as chromium hydroxide by ammonia, after reduc- 

 tion with hydrochloric acid and alcohol, and weighing as Cr^Og. 



The determinations were made as follows : Portions of the 

 standardized solution were made slightly acid with hydrochlo- 

 ric acid, and a current of sulphur dioxide was passed through 

 the solutioTi until the clear green color indicated complete 

 reduction of the chromiiim to the condition of Cr.Oj. The 

 sulphur dioxide was then expelled by boiling in a current of 

 carbon, dioxide. To the cooled solution potassium ferricyanide 

 and potassium hydroxide were added in solution and the pro- 

 cedure given by Bollenbach and Luchmann, as outlined above, 

 was followed. 



However, using the amounts of ferricyanide and potassium 

 hydroxide given by Bollenbach and Luchmann as sufiicient to 

 completely oxidize the chromium, the low results of Table II 

 were obtained, indicating that the oxidation of the chromium 

 was incomplete ; but by using about 15 times the theoretical 

 amount of potassium ferricyanide and a rather strong solution 

 of potassium hydroxide, with the total volume of the solution 

 about 100 or 125 cubic centimeters, as in the experiments 

 recorded in Table III, results were obtained which were in 

 accordance with the theoretical. 



As in the previous work, a correction had to be applied to 

 the determinations for the amount of permanganate taken up 

 by the ferricyanide alone. 







Table II, 









CrOa 



EsFeCsNc 



KOH 



CrOa 







taken 



used 



used 



found 



Error 





grrn. 



grin. 



grrn. 



grrn. 



grrn. 



(1) 



0-1010 



6 



12 



0-0979 



— 0-0031 



(2) 



0-1010 



8 



16 



0-0981 



— 0-0029 



(3) 



0-1010 



8 



16 



0-0989 



-0-0021 



(4) 



0-1010 



8 



12 • 



00997 



— 0-0013 





* 



Chem. Zentralblatt. 1902, i, 



500. 





