3 
Lime 0*0380 grm. 
On adding sodium phosphate to the filtrate a mere trace 
of magnesia, appearing only after the lapse of some hours, 
was found. 
The remaining constituent, namely water, was deter- 
mined by igniting the mineral in a stream of dry carbonic 
acid carefully freed from air, until the loss of weight 
appeared constant. 
1*1205 grm. substance lost 0*2311 grm. water. 
Calculated from the foregoing analysis, the composition 
of the mineral is as follows : — 
Lime 2*68 
Magnesia Traces 
Ferric Oxide 36*44 
Silica 40*30 
Water 20*98 
.100*40 
On subtracting the lime, which evidently may be 
regarded as an unessential constituent, the percentage com- 
position agrees very well with that required by the formula 
Fe 2 0 3 3 Si 0 2 + 5H 2 0. 
Found. 
Calculated. 
Ferric Oxide 
37*24 ., 
37*20 
Silica 
41*29 .. 
41*86 
Water 
21-47 .. 
..... 20*94 
100*00 
100*00 
Nontronite is evidently a product of the decomposition 
by weathering of some siliceous mineral rich in iron. It 
possesses a light green colour, which on the expulsion of 
water changes to a dark chesnut brown. It is perfectly 
opaque, and shows no evidence of crystallisation. Its frac- 
ture is uneven, and the lustre of its streak resinous. It is 
unctuous to the touch, and yields easily to the nail, and is 
somewhat harder than talc. 
