164 GEOLOGICAL RECONNOISSANCE 
The air-dried mineral lost 2.1 per cent. of moisture at 220 deg. F. 
The amount of free oxygen was ascertained by Mohr’s method to be 
7.82 per cent. Taking into consideration the quantity of free oxygen 
contained in the manganoso-manganic oxide, we obtain for water expelled 
at a red heat 10.653 per cent.; hence, the composition of the mineral may 
be thus expressed: 
Protoxide of manganese:-++++++++++e5- 47,781 
Free OXYZEN+ ++ seers Be task hE RUNS Te Oe, 7.820 
Silica + ack cate Weise Can teas ekeeeae 96.990 
Alumina, with trace of irons ..+.+eeeees 6.245 
Oxide of cobalt... cc ec ee ee ener e ences 0.104 
Baryta- Sarasa Raves a eel enelees ene eae susie 1.875 
DS TATU E6855 Sicb 5S TES ate: Sara be Ghia eaten a arce trace 
Water: ss eccccccverons ee a ee eC 10.653 
100.708 
Subtracting silica and alumina, as adventitious intermixtures, and cal- 
culating the remaining constituents for 100 parts, we obtain for the wad 
the following composition: 
Protoxide of manganese +++++ssesseees 70.03 
Free OXYZEN+ +s see ee Tee cee ee ee eee 11.46 
Oxide of cobalt... sees eeecee er eeeeeee 0.15 
Baryta Dem ee ee mer er eee eer ee neerene 2.75 
LAG #8 oo ear ORE Pe ewe ae trace 
Waterssseeevecees eect e re ee Tee eee eS 15.61 
100.00 
No. 23. Braunite (?), from Poke bayou, Marion county. 
Massive; texture finely granular; lustre submetallic; color dark steel 
gray; hardness 5.5; strikes fire with steel; powder grayish-black; much 
more easily reduced to powder, than the two preceding minerals; wea- 
thered surface shows brown spots of hydrate of peroxide of iron. 
Before the blowpipe, infusible; on charcoal in reduction flame, becomes 
pale reddish-gray at the point of contact with the charcoal; in a matrass, 
yields a little water; with fluxes, gives the manganese reactions. 
Dissolves in hydrochloric acid with evolution of chlorine, leaving a 
residue of silica. 
Composition dried at 220 deg. F: 
Protoxide of manganese -++++++-eeseee+ 75.886 
Free oxygen vsrseeeeeesseeeveeeeeeeee 7,979 
