1Q2 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 aplatina 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 percent, 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 manganese 84.995 



Free oxygen 10.483 



Silica 2.845 



Baryta 0.512 



Lime trace 



Water 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. Tsilomelane, from same locality as No. 20. 



jMassive; 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 88.628 



Silica 5.329 



Baryta 0.282 



Lime 1.178 



Magnesia trace 



Water and oxygen, expelled by heat 4.433 



99.850 

 The air-dried mineral lost 1.02 per cent, of moisture at 250 deg. F. 



