232 ANALYTICAL CHEMISTRY. 



Examination of compounds of manganese. The native manganese 

 dioxide invariably contains other mineral matter ; according to 

 the U. S. P., it should contain not less than 66 per cent, of the 

 dioxide, and has, consequently, to be examined by quantitative 

 analysis. 



A solution of manganese sulphate, acidulated with hydrochloric 

 acid, should give no precipitate with hydrosulphuric acid (ab- 

 sence of copper, etc.) ; the aqueous solution of the salt from 

 which the manganese has been precipitated by ammonium 

 sulphide, should leave no residue on evaporation and gentle 

 ignition (absence of magnesium, alkalies, etc.). 



Potassium permanganate is completely decolorized (deoxidized) 

 by oxalic acid and sulphuric acid. The colorless solution 

 should be tested with ferrous sulphate for nitric acid, and with 

 silver nitrate for hydrochloric acid. It should also be tested 

 quantitatively. 



Examination of compounds of chromium. Solution of potassium 

 dichromate and chromium trioxide, acidulated with nitric acid, 

 should not be precipitated by barium chloride, (absence of sul- 

 phuric acid) ; both substances, when neutralized with potassium 

 hydrate, should give an immediate red precipitate with silver 

 nitrate, a white precipitate indicating chlorides. 



Examination of compounds of lead. Solutions of compounds 

 of lead, when completely precipitated with either sulphuric 

 acid or with hydrosulphuric acid, should yield a filtrate which 

 leuves no residue on evaporation and gentle ignition (absence 

 of all other metals). 



Lead oxide (litharge) and lead carbonate should dissolve com- 

 pletely in nitric acid. 



Lead iodide should be tested for lead chromate by triturating 

 it with 2 parts of ammonium chloride and water, which dis- 

 solve the iodide, but not the chromate. 



Examination of compounds of copper. Solutions of cupric salts 

 (sulphate), when completely precipitated by hydrosulphuric acid, 

 should yield a filtrate which gives no precipitate with ammo- 

 nium hydrate, sulphide, or carbonate. Ammonium hydrate 



