W. T. Schaller — Notes on Powellite and Molybdite. 75 



by direct weighing. It was found that the water given off at 

 110° by heating the mineral in a glass tube in a toluene bath 

 while a current of dry air was passed over the mineral and 

 collecting and weighing the water (shown in a below), was con- 

 siderably greater than the amount given off at 110° by heating 

 the mineral in a crucible in a toluene bath, and determining 

 the water by loss in weight (shown in h below). The results are 

 shown below : 



Amt. given 

 off at 110° ' at 200° total 



a 13-77 2-23 16-00 



b 11-39 4'34 15-73 



In the previous paper on the composition of molybdic ocher, 

 the writer determined the water given off at 110° by loss in 

 weight to be six molecules of the total 1\. From the results 

 given above, it seems probable that this is not necessarily the 

 correct amount and that the temperature at which different 

 parts of the entire water content are given off still remains to 

 be determined. 



The density of the powdered sample was determined with a 

 pycnometer, using 3 grams of material. The value obtained 

 is 3*026. This is corrected on the following basis, the sample 

 being composed of 



Molybdenite density 4*7 = 5-50 

 Silica " 2-65 = 16-51 



Molybdite = 77-99 



100-00 



The corrected value becomes 2*99, in which, however, no 

 allowance is made for the extraneous moisture. 



An experiment was made to determine approximately the 

 solubility of molybdite in water. About 3 grams of the min- 

 eral were stirred in a beaker for a day with 760 cc distilled 

 water at room temp, (about 25°), and then filtered repeatedly. 

 The final filtrate showed a very faint cloudiness. It was 

 evaporated down in platinum, the residue dissolved in HC1 

 and the iron precipitated as hydroxide with ammonia and 

 weighed. The 760 OC of water contained -0051 gram of Fe 2 3 . 

 On the assumption that this all came from the mineral, it is cal- 

 culated that the solubility of molybdite in water is approxi- 

 mately 1 to 33,000, so that the mineral is rather insoluble. 



Continued attempts to form the crystallized mineral 

 Fe 2 3 .3Mo0 3 .7^H 2 0, by heating the amorphous precipitated 

 ferric molybdate in a closed tube at a high temperature have 

 so far been completely unsuccessful, and the writer does not, at 

 present, intend to continue the attempts to prepare this mineral 

 artificially in a crystallized condition. 



