MICROCHEMICAL REACTIONS OF THE COMMON ACIDS 417 



I. To a drop of the moderately concentrated aqueous solution of the unknown 

 apply a drop of concentrated solution of silver nitrate by Method /, page 299. 



A. No precipitate is produced and no crystalline deposit is ob- 

 tained until the drop concentrates through spontaneous evapo- 

 ration. See I. A, below. 



B. A colored precipitate is produced. See I. B, below. 



C. A white or colorless precipitate is produced. See page 418. 

 After a few seconds apply a small drop of nitric acid (i : 3) to 



the zone of precipitate. 



1. The precipitate dissolves in whole or in part. If only in 

 part, decant the solution and apply a fresh drop of nitric acid 

 to the residue, to ascertain if the unknown consists of a mixture 

 of both soluble and insoluble silver salts. 



2. The precipitate is unaffected. 



II. To another drop of the dilute aqueous solution add a drop of barium 

 chloride solution. See page 299. 



A. No precipitate results. See page 419. 



B. An amorphous, granular or crystalline precipitate is pro- 

 duced. See page 419. 



1 . The precipitate is soluble in whole or in part in nitric acid. 



2. The precipitate is insoluble in nitric acid. 



III. To a drop of the dilute aqueous solution of the unknown material add a 

 drop of nitric acid. A granular or amorphous precipitate results. See page 420. 



I. A. No Precipitate with Silver Nitrate. 



Chlorate. 



Fluoride; silicofluoride. 1 



Nitrate. 



Perchlorate. 1 



Sulphate. 1 



I. B. The Precipitate is Colored (by Reflected Light). 



Arsenate. Red, brown or thick crystals black. 



Arsenite. , Yellow. 



Chromate, bichromate. Red, brown or black. 



1 Crystals separate slowly from moderately concentrated solutions or even 

 from dilute solutions on long standing. 



