Chap. IV. ] 
PSIIiOMELANE. 
113 
In the second table (No. 15) I give the analyses of the same psilome- 
lanes arranged in terms of their oxides. On examining these analyses it 
will be seen that there is occasionally a small surplus of oxygen over 
that required for the conversion of all the manganese present into peroxide. 
This, of course, means that in these particular cases the aiiiOuiit oi 
manganese in the form of Mn03 in the manganates is in excess of the 
amount of manganese in the form of MnO in the base portion of the mole- 
cule, Mn2Mn05. I am not aware, however, that such an excess of oxygen 
over that required to convert all the manganese present in a mineral into 
peroxide has ever been recorded. Probably it is not to be expected 
except in the case of a mixture of two minerals, one of which in course 
of formation probably rejects oxygen from Mn02, taking only the MnO 
portion, and thus liberates a surplus of oxygen for the remaining mineral, 
the psilomelane. In this case the braunite perhaps acts in this way. 
It will be further seen from these analyses that these examples of 
psilomelane are very variable in composition, apart from the question of 
whether iron is shown as present or not, this being, as already explained, 
to a large extent due to whether the iron has been calculated into the 
braunite or the psilomelane of the original analysis. In several of the 
analyses the alkalies have not been determined, but cannot be large in 
amount in these cases, because in the original analyses the totals approxi- 
mated to 100 without them.i Only one of them shows an important 
amount of potash. This is the Sivarajpur specimen. The baryta is 
variable in amount, being in one case nil and in two of the Kajlidongri 
specimens as high as 10-66 and 13'22% respectively. The latter 
ugure is not surprising in view of the fact that the hoUandite of this 
locality contains 18% of this constituent. In several of the analyses 
cobalt, nickel, copper, and zinc, have not been looked for.^ But in those 
in which these constituents were tested for, namely the first and the last 
five, variable amounts of these constituents were found. Thus in one 
case, namely M.4 from Sontulai, which might perhaps be better included 
under the heading of wad than in this place, there is 1'52% of copper 
oxide, CuO. The nickel oxide, NiO, is as high as r23% in the same 
specimen, whilst in one of the Kajlidongri specimens there 's 0*90% 
of cobalt oxide, CoO. 
1 These have since been determined ; see footnote to table on page 112. 
^ The Co, Ni, and Cu, have since been determiued ; see footnote to tnble on page 112 
