CYANIDE PROCESS 



i 

 DAILY WORK 



1. Titration of Cyanide Solutions. — This is invariably made 

 by Liebig's well-known method, depending on the fact that when a 

 solution of nitrate of silver is added, drop by drop, to the solution 

 to be tested, each drop of the silver solution forms a white cloud 

 of silver cyanide, which disappears on agitation so long as the 

 free cyanide is in excess, the reactions being as follows: 



(a). AgN0 3 +KCN=AgCN+KN0 3 . 



(b). AgCN+KCN=KAg(CN) 2 . 



The completion of the reaction is shown by the permanence of 

 a white turbidity or opalescence. As soon as the whole of the free 

 cyanide has been converted into the double silver salt, a further 

 drop of silver nitrate in excess gives a ppt. of silver cyanide which 

 does not redissolve on agitation. 



(c). AgN0 3 +KAg(CN) 2 =2AgCN+KN0 3 . 



From these reactions it is evident that 169.55 parts of AgN0 3 

 are equivalent to 130.04 parts of KCN. 



Standard Solution. — Dissolve 6.519 grams of AgN0 3 in 1 litre 

 of water. Every cc. of this solution is equivalent to .01 grams KCN. 

 Hence, if we take 50 cc. of the liquid to be tested, every cc. of the 

 standard AgNO s added will represent .01$ KCN. 



From the solution to be tested take, by means of a pipette, 

 50 cc, place in a beaker, dilute with 50 cc. H 2 0; add 5 cc. of a 1$ 

 neutral solution of KI,* and titrate with the standard solution. 



It is advisable to place about 9 inches of rubber tubing over the 

 end of the pipette, as a safeguard against drawing cyanide solution 

 into the mouth. When the pipette is blown out, fill it with an 

 equal volume of water and add to the cyanide solution in the 

 beaker or flask. The pipette is thus washed out and ready for 



* The addition of KI corrects the slight errors due to the presence of caustic alkalies, ammo- 

 nia, alkaline carbonates, chlorides, ferro-cyanides, thio-cyanates, thio-sulphates, and 

 perhaps some other salts. 



