378 ELEMENTARY CHEMICAL MICROSCOPY 



FERROCYANIDES. 



a. Give a Blue Precipitate with Salts of Iron and a brown one 

 with salts of copper in acetic acid solution. 



b. With Quinoline Hydrochloride yield upon warming cubical 

 crystals. 



IODIDES. 



a. To a drop of solution add dilute sulphuric acid, a little 

 potato starch and a tiny fragment of ammonium persulphate. 

 The starch is turned blue or violet in the cold. See Bromides, 

 page 375- 



b. The silver nitrate precipitate is insoluble in ammonium 

 hydroxide; distinction from chloride and bromide. 



c. Yield characteristic hexagonal plates with lead nitrate. 

 See Lead, page 323. 



IODATES. 



a. Dissolve in water, add a very tiny drop of dilute sulphuric 

 acid, a little potato starch and finally a crystal fragment of 

 morphine sulphate. Iodine is set free and the starch granules 

 turn blue or violet. 



Iodides do not give this reaction; nor will iodates give reaction 

 a under iodides. 



NITRATES. 



a. With Nitron Sulphate in Acetic Acid Solution. Apply the 

 reagent by Method /, page 251. 



There is immediately formed a heavy precipitate, consisting of 

 masses of exceedingly minute needles. In a few seconds sheaves 

 of acicular prisms appear and later there are formed long thin 

 prisms with square ends, giving polarization colors and parallel 

 extinction. Nitron nitrate has a very low solubility even in 

 warm water, hence the reaction is a delicate one. The sheaves 

 of white crystals, appearing brownish by reflected light, are 

 characteristic. 



In dilute solutions none of the salts of the common acids inter- 



