Schaller — Chemical Composition of Molybdic Ocher. 299 



into the combined ammoniacal filtrates until the characteristic 

 red color was produced. The solution was then acidified with 

 H„S0 4 and after heating on the steam bath, to allow the 

 molybdenum sulphide to settle, it was filtered through a Gooch 

 crucible. This was then dried, and the sulphide changed into 

 the trioxide at a low heat and weighed to constant weight. 

 The filtrate from the molybdenum sulphide was made alka- 

 line with ammonia, hydrogen sulphide again passed into the 

 solution, which was then re-acidified with fl 2 S0 4 and a small 

 amount of molybdenum which had escaped precipitation in the 

 first case recovered. The filtrate, on testing, showed no more 

 molybdenum. Neither was any residue found on evaporating 

 it to dryness and tests that were made showed the absence of 

 calcium and magnesium. The weighed iron oxide was fused 

 with sodium bisulphate and determined volu metrically with a 

 result that agreed with the gravimetric determination. The 

 results obtained are as follows : 



' 



1 



2 



3 



Av. 



Eatio 





H.O— . 



16-98 



17-95 



17-93 



17-62 



7-43 



1 2 



Pe 1 1 ... 



2T08 



21-07 







21-08 



1-00 



1 



Mo0 3 ... 



57-02 



57-49 



58-55 



57-69 



3-04 



3 



Insol. 



4-66 











4-66 







101-05 



Analysis 



Calculated 



18-28 



18-57 



21-87 



22-01 



59-85 



5942 



The average analysis, with the insoluble matter deducted and 

 reduced to 100 per cent, is compared with the figures calcu- 

 lated for Fe a 3 .3MoO,.7£H 9 0. 



H 2 



Fe 2 3 



MoO, 



100-00 100-00 



Partial water determinations were made on two samples as 

 follows, the amount of water being represented by the loss in 

 weight, the crucible being heated at the temperature given till 

 six hours further heating produced no difference in weight. 



Total loss up to 110° = 14-04$ 



" " " " 125° = 15-50 



" " " " 185° = 17-64 



" " " " 200° = 17-93 



This shows that of the total seven and a half parts of water, 

 5-92, or six parts, are given off at a little above 100°, while a 

 higher temperature is required to drive off the remainder. 



