162 GEOLOGICAL RECONNOISSANCE 
The above numbers are the direct result of analysis. In order to ascer- 
tain how much of the volatile matter, expelled by heat, is water, and 
how much oxygen, the pulverized mineral was heated in a platina capsule — 
over the smallest flame of a spirit-lamp with Argand burner, until the 
weight remained constant; the loss amounted to 1.82 per cent. The heat 
was then raised and kept for about half an hour, just below redness: the 
mineral did not suffer any further loss. Assuming the 1.82 per cent. of 
volatile matter, expelled below red-heat, to be water, we obtain for oxygen 
5.931—1.82—4.111 per cent. The 91.367 per cent. of manganoso-manga- 
nic oxide consist of 84.995 parts of protoxide of manganese with 6.372 
parts of oxygen; these, added to the above 4.111 per cent., give 10.483 
per cent. of free oxygen, and the composition of the mineral may, there- 
fore, be expressed thus: 
Protoxide of manganes€++serrsetereaceeeenucees 84.995 
Free OXYZEN+ seer t sce e eee ree eeerences eoseveee 10.483 
Silica +++ ccc er cc cee snc ceesene eo Bihee ere ales es lie i epee 2.845 
Baryta eee hea Breice oh . . . is fevefe Senate 0.512 
Lime oe eeesscececes a eC ar are eet ar a er ae aCe CY trace 
Water wa wees er ee tency eee seh Seca 1.820 
100.655 
As a controlling experiment, the amount of free oxygen was determined 
by Mohr’s method [v. “methods of analysis,” below], and found to be 10.510 
per cent. 
No. 21. Psilomelane, from same locality as No. 20. 
Massive; close-textured; color bluish steel-gray; hardness 5.5; fracture 
splintery and subconchoidal; brittle; strikes fire with steel; powder reddish- 
brown. 
Before the blowpipe, and to reagents, behaves like the preceding. 
Composition, dried at 250 deg. F: 
Manganoso-manganic Oxide+++++essereseeeeees 88.628 
Silene svawee«s Mrs eee a tre tee pr Nee 5.329 ” 
Barytaicecececcc cence eee esewcescverersreseee 0.282 
Lime: oc cee cecccccccscrereserevese Oe ee ee 1.178 
Magnesia: - sie teicnce ace: Cerrar are garter ie ere $585" Wiese areas trace: 
Water.and oxygen, expelled by heat.-.-++...+.. 4.483 
99.850 
The air-dried mineral lost 1.02 per cent. of moisture at 250 deg. F. 
