44: UNIVERSITY OF COLORADO 



fere with the final steps of reducing the ferri-cyanide to ferro- 

 cyanide, and the titration of the latter with KMn0 4 in acid solution. 



Estimations can be made in 15 minutes, and concordant results 

 are obtained in different operators' hands. 



The solutions required are: 



25^ caustic alkali. 



20<£ H 2 S0 4 pure. 



Saturated solution of KMn0 4 , approximate strength only. 



Saturated solution of FeS0 4 , approximate strength only. 



N/10KMnO 4 . 1 cc.=.156 grams total CN, or more convenient 

 strength, 1 cc.=.100 total CN. 



The solution is standardized with K 4 Fe(ON) 6 +3Aq. 3 grams are 

 dissolved in 300 cc. H 2 and 15 cc. of the 20^ acid are added. 



880x3 



Value CN in grams per cc. 



157.9xcc. consumed 



Method. — Ten grams of the cyanide are weighed into a litre 

 flask and about 200 cc. water used to dissolve it, add 2 cc. of the 

 alkali solution and a quantity of the FeS0 4 solution equal to 12 

 grams FeS0 4 +7Aq. Add the latter 5 cc. at a time and shake well. 



6KCN and FeS0 4 +alkali=K 4 Fe<CN) 6 ^K 2 S0 4 +alkali. 



The reaction is immediate. Add H 2 S0 4 and Prussian blue is 

 formed. Then 15 cc. H 2 S0 4 and saturated solution of permanganate 

 until the color remains persistent; the color can be seen through 

 the edges. 1 or 2 cc. or more in excess does not matter. The above 

 quantity of acid is enough for each gram of KMn0 4 added, but if 

 more than 1 gram KMn0 4 is used acid must be added in the same 

 proportion, viz.: 15 cc. to each gram of KMn0 4 used. If much 

 sulpho-cyanide is present, allow to stand 15 minutes, and if neces- 

 sary, a further addition of KMn0 4 may be required. The reac- 

 tion is: 



5K 4 Fe(CN) 6 +4H 2 SO 4 +KMnO 4 =5K 3 Fe(CN) +3K 2 SO 4 +MnSO 4 +4H 2 O 



Next add FeS0 4 solution in quantity equal to 15 grams and 

 immediately 15 cc. alkali solution. The solution must be strongly 

 alkaline. Shake thoroughly and make up to the mark, again mix- 

 ing thoroughlv. 



