248 VALUATION OF MANGANESE ORES. 



which may be known by the alkaline reaction of the 

 solution after adding an excess of chloride of barium, 

 the following modification of the process is necessary : 



2.41 grms. of the anhydrous sample are mixed with 

 about 8 parts of pure quartz-sand, and about J part of 

 powdered carbonate of ammonia; the mixture is moist- 

 ened with water, and, after some time, gently heated 

 till all water and ammonia are expelled. The dry 

 residue is then treated, as usual, in the above appa- 

 ratus. 



In order to prevent any inaccuracy arising from the 

 presence of sulphide of sodium or hyposulphite of soda 

 in the specimen, a solution of chromate of potassa is 

 added previously to the evolution of carbonic acid, in 

 order to oxidize these impurities. 



122. VALUATION OF MANGANESE ORES. 



Good manganese ore, which consists almost entirely 

 of binoxide of manganese, is crystalline, yields a black 

 powder, and, after being dried at a gentle heat, gives 

 no water, or only traces, when heated to redness. Man- 

 ganese ore, however, generally contains foreign mine- 

 rals, especially the hydratedsesquioxide of manganese. 

 In order to determine the amount of binoxide, or, in 

 other words, of available oxygen, several methods may 

 be employed. 



I. A weighed quantity of the manganese ore, pow- 

 dered as finely as possible, is introduced into the appa- 

 ratus employed for the quantitative estimation of car- 

 bonic acid (Fig. 34), where it is brought in contact with 

 sulphuric acid and a solution of oxalic acid, when sul- 

 phate of protoxide of manganese is produced, since all 

 the available oxygen, which may be regarded as in 



