360 ELEMENTARY CHEMICAL MICROSCOPY 



This test is excellent when pure manganous salts are being 

 dealt with, but is seriously affected by much alkali and ammonium 

 salts or by the presence of those elements readily precipitated as 

 oxalate, for example, the elements of Group VIII of the Periodic 

 System, or those of Group II. 



Free mineral acids seriously interfere. 



With solutions highly concentrated with respect to manganese 

 no reaction will be obtained nor will satisfactory results follow 

 the use of too dilute test drops. 



Silver, lead, mercurous and stannous salts should be absent. 



EXPERIMENTS. 



a. Test as above MnSO 4 . Then try the addition of a drop of H 2 C 2 O 4 to a test 

 drop by Method /, page 251. 



b. Try effects of free acids upon the test. 



c. Test mixtures of MnSO 4 with members of Group VIII. 



B. By Means of Potassium Chr ornate. 



Apply reagent to test drop by Method ///, page 252. 



Sheaves of yellowish brown, acicular, strongly pleochroic 

 crystals separate from neutral or feebly acid solutions; but from 

 drops containing a trace of free nitric acid stout dendritic masses 

 and clusters of yellowish brown prisms are obtained. The test 

 drop should be moderately concentrated. 



Nitric acid greatly slows down the reaction and if present in 

 more than traces prevents the formation of crystals. The other 

 mineral acids behave in a similar fashion. 



With pure manganous salts this test is excellent, but is of 

 little value in the presence of silver, lead, mercury or in fact any 

 element forming a difficultly soluble chroma te. 



See Silver, Method JB, page 334; Mercury, Method B, page 

 321. 



Potassium bichromate applied as above gives no crystalline 

 precipitate. 



EXPERIMENTS. 



a. Test a drop of MnSO 4 with K 2 CrO 4 ; with K 2 Cr 2 O 7 . 



b. Repeat the test, previously acidifying with HNO 3 ; with HC1; with HC 2 H 3 O 2 . 



c. Repeat in the presence of Ag, of Pb. 



