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, 1 found 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. Inthe 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 “ 6 10.00 “ « ef « 
Third ef " 7.36 “  %& sé #8 
(See Bruno Kerl, in Chem. Centralblatt for 1853.) 
The ores of Arkansas contain 
100 parts of ore 
NUMBER OF SPECIMEN. Per cent. of free correspond to pure| Peroxide of iron. 
oxygen. Mn O02 
DC. | 10.483 57.24 none 
No. Sheree cece cece cece ences 10.002 54.47 none 
No. 22, crude: +s seer eeeeeeeas 7.820 42.59 trace 
No. 22, freed from gangue:-.-- 11.460 62.42 
No, 2B sec ceev cree vcenscone 7979 43.46 3.523 
ING Ks Aha taisias Se esitesg 0) eta eaearece ates 11.700 63.72 ? 
Ore from New York.-+-+++++ 9.246 50.35 ? 
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 Ist 
and 2d quality of the German ore. 
