166 



GEOLOGICAL RECONNOISSANCE 



free oxygen which they contain, that is: the quantity of oxygen more than 

 sufficient to form with the whole of the metallic manganese the lowest 

 degree of oxidation, the protoxide; for the purpose of the glass manufac- 

 turer, they ought also to be as free from iron as possible. Of the various 

 compounds of manganese, the ore containing the largest proportion of 

 free oxygen is the peroxide, commonly known as "black oxide of manga- 

 nese," a compound which occurs native as a mineral, called " pyrolusite;" 

 it contains 18.36 per cent, of free oxygen. 



In order to ascertain, as near as possible, the market value of the Ar- 

 kansas ores, I procured from a New York firm a sample of what is sold 

 in that city as " black oxide of manganese " at the rate of three and a 

 half cents per pound, by the hundred weight, in the ground state; on 

 analysis, I fou d this sample to contain 9.246 per cent, of free oxygen, 

 corresponding to 50.35 per cent, of pure peroxide of manganese; it contained 

 a large proportion of silica, a circumstance which probably makes the 

 ore very difficult to grind. In the Hartz mountains, a famous European 

 locality for the ores of manganese, three qualities of the ore are sold, the 

 price varying with the amount of free oxygen; the 



First quality contains 12.60 per cent, of free oxygen. 



Second " " 10.00 " " " " 



Third " " 7.36 " " " 



(See Bruno Kerl, in Chem. Cenlralblatt for 1853.) 



The ores of Arkansas contain 



NUMBER OF SPECIMEN. 



100 parts of ore| 

 Per cent, of free correspond to pure. Peroxide of iron, 

 oxvu-en. Mn 02 



No. 20 



No. 21 



No. 22, crude 



No. 22, freed from gangue* 



No. 23 



No. 24 



Ore from New York 



10.483 

 10.002 



7.820 

 11.460 



7.979 

 11.700 



9.246 



57.24 

 54.47 

 42.59 

 62.42 

 43.46 

 63.72 

 50.35 



none 

 none 

 trace 



3.523 



? 



The ores Nos. 20, 21, 24, and 22 when freed from its gangue, are, as 

 seen by the table, superior to the ore procured from New York, and ought 

 to command, therefore, a higher price; they contain, on the average 10.911 

 per cent, of free oxygen, which places them intermediate between the 1st 

 and 2d quality of the German ore. 



