296 ANALYSIS OF MATERIALS 



dryness, and the sulphates gently calcined until the 

 weight is constant; the mixture of sesquioxide of iron 

 and sulphate of manganese is then weighed, a little 

 water poured upon the sulphate, decanted and washed 

 upon a filter, which is ignited with the peroxide of 

 iron and weighed. This weight is the oxide of iron, 

 which, taken from the weight previously obtained, 

 gives that of the sulphate of manganese. By adding 

 the red oxide of manganese deducted from the weight 

 of the sulphate with the oxide of iron, the exact 

 total weight of manganese and iron is known, which 

 have been calculated by difference at the time when 

 the pure alumina was weighed. This verification 

 dispenses with the direct weight of the sulphate of 

 manganese. If, however, it is deemed desirable to 

 determine it, the sulphate from the washing should be 

 evaporated, and the manganese may be weighed in 

 this form. 



The preceding operations may be verified in the 

 following manner : 



1st. The alumina should be colored or slightly 

 tinged with gray ; it should be soluble in bisulphate 

 of potassa in large excess. 



2d. The oxide of iron, tested with the blowpipe with 

 carbonate of soda in the oxidizing flame, should give 

 no green color. 



3d. The sulphate of manganese, treated with the sul- 

 phate of ammonia, a little nitric acid and ammonia, 

 should give no precipitate. 



Analysis of the Materials soluble in Nitrate of Ammonia. 



They contain 1st, lime; 2d, magnesia, and sometimes 

 manganese; 3d, potassa, 4th, soda. 



The liquid contains at first a certain quantity of 

 lime, which has been introduced to decompose the 

 mineral. A quantity of pure crystallized oxalate of 



