46 UNIVERSITY OF COLORADO 



acid, adding a few drops of a solution of neutral potassium 

 chromate, and continuing the addition of the silver solution until 

 the red tint due to the formation of silver chromate remains perma- 

 nent. If cyanide only be present, the volume of silver solution now 

 required will be exactly equal to that previously employed to 

 obtain a permanent turbidity, whereas any excess over this amount 

 represents the silver solution corresponding to the chlorides 

 present. 



Formates, if present, will cause the salt to blacken on ignition. 

 They may be detected more certainly by precipitating the cold 

 dilute solution of the sample with excess of silver nitrate solution, 

 filtering cold and heating the clear liquid. In presence of a 

 formate, metallic silver will be precipitated. The filtrate from the 

 precipitate produced by silver nitrate will also give a red color 

 with ferric nitrate or sulphate if a formate be present. 



Carbonates will remain insoluble on treating the sample with 

 hot alcohol of 0.849 specific gravity. 



Silicates can be detected and estimated in the ordinary way by 

 evaporation to dryness with hydrochloric acid, the residue insolu- 

 ble in acidulated water being silica. 



Sulphates are detected by the formation of a white precipitate 

 on adding barium chloride to a solution of the sample previously 

 acidulated by hydrochloric acid. 



Sulphides will give a black precipitate with mercuric chloride, 

 and a yellow precipitate with a solution of cadmium. They can be 

 separated by agitating the solution with lead carbonate. 



Free ammonia can be recognized by the smell, and determined 

 by treating the solution with an alkaline solution of sodium hypo- 

 bromite and measuring the nitrogen gas evolved. 



