Schaller — Chemical Composition of Molybdic Ocher. 301 



Deducting the insoluble matter and reducing the analyses to 

 100 per cent, we obtain : 







No. 1 



No. 2 



No. 3 



Calc. 



H 





16-8 



19-5 

 20-0 

 60-5 



17-5 

 19-6 

 62-9 



18-6 



Fe 





20-2 



22-0 



■*" ^2 3 



Mo0 3 





63-0 



59-4 





100-0 



100-0 



100-0 



100-0 



The ratios 



give : 



Fe o 0, 



: H o 



: Mo0 3 . 





Anal. 



1, 



1-0 



: 7-3 



: 3-4 





Anal. 



9 



1-0 



: 8-6 



: 3-3 





Anal. 



3, 



1-0 



: 7-8 



: 3-5 





The analyses agree sufficiently well to show that the mineral 

 is uniform in composition and the analysis of the material from 

 !STew Hampshire serves to establish its formula. 



In considering the mode of formation of the hydrous ferric 

 molybdate, it may be well to call attention to the fact that the 

 interaction of molybdic acid, H 2 Mo0 4 . H 2 0, on limonite may 

 be written so as to yield a product with a formula that is iden- 

 tical with the new formula and exactly balances the equation : 

 2Fe a 3 .3H a O + 6(H a Mo0 4 .H 2 0) = 2(Fe a O s .3MoO,.7£H 9 0). 



Pyrognostic Properties. — On heating the mineral in a closed 

 tube abundant water is easily given off and the mineral be- 

 comes a dark olive color which on further heating again 

 becomes lighter in color. On heating the mineral in a crucible, 

 the color changes are very marked. At first, the yellow 

 mineral darkens and becomes a dark gray, appearing almost 

 black and with a slight olive tint, then it becomes a light yellow 

 again, and on further heating changes to a deep orange color. 

 If the mineral now be allowed to cool, the orange changes to 

 yellow and back to orange agam on reheating. If the dark 

 colored material be allowed to cool, it retains its dark gray color 

 and on reheating passes through yellow to the orange. On 

 heating for some time at a higher temperature, the mineral, 

 on cooling, becomes a permanent bright green. By further 

 heating all of the molybdenum is volatilized and the dark red 

 ferric oxide remains. The mineral is readily soluble in 

 hydrochloric acid, and dissolves slowly in ammonia, taking on 

 a brown color (probably due to the separating ferric hydrox- 

 ide). After a while, all the molybdenum of the mineral 

 goes into solution, leaving the insoluble ferric hydroxide. 



Artificial ferric molybdate.— Chemical dictionaries mention 

 but two hydrous ferric molybdates, neither of which is crystal- 

 line, and which approximate in formula to Fe 2 3 .4Mo0 3 .7H 2 0, 

 and Fe 2 3 .5Mo0 3 .16H 2 0. On adding a solution of ammonium 



