62 PRACTICAL AGRICULTURAL CHEMISTRY [.198-203 



NITRATE (N0 8 ).— Use potassium nitrate (KN0 3 ). 



198. Ferrous Sulphate (FeS0 4 ) Solution when 



carefully added to the above solution, previously 



mixed with its own volume of strong sulphuric 



acid and cooled, will form a brown ring where 



the two layers join (fig. 24). This brown colour 



is destroyed by heat ; hence the tube must be 



kept quite cold during this test. 



109. Copper Turnings (Cu) added, after 



acidifying with strong sulphuric acid (H 2 S0 4 ), 



gives off brown fumes either at once or on 



warming the tube. 



200. Heated with indigo and sulphuric acid 



the indigo is bleached. The most accurate 



method of applying this test is described in 



paragraph 87. 

 Fig. 24 r ° r 



CHLORIDE ('Cl).-Use sodium chloride (NaCl) solution. 



201. Silver Nitrate (AgN0 3 ) gives a pure white pre- 

 cipitate of silver chloride (AgCl), soluble in ammonium 

 hydrate (NH 4 OH), and insoluble in nitric acid (HN0 3 ). 



Filter off a little of the precipitate and expose the filter- 

 paper containing the precipitate near a window : it will be 

 darkened by the action of the light. 



202. Strong Sulphuric Acid (H 2 S0 4 ) warmed with 

 solid sodium chloride gives off copious fumes of hydro- 

 chloric acid (HC1), which redden blue litmus-paper. 



203. The solid mixed with manganese dioxide (Mn0 2 ) 

 and strong sulphuric acid gives off a green gas, chlorine (CI), 

 which bleaches moist red litmus-paper. 



