74 W. T. Sch oiler— Notes on Powellite and Molyhclitr. 



Allowing- for impurities, the value is raised to 4-24, which, 

 like the preceding case, is dependent on certain assumptions. 



As powellite and scheelite are doubtless isomorphous we may 

 be justified in assuming that they have nearly the same molec- 

 ular volume. Considering the molecular volumes as identical 

 and taking the gravity of scheelite as 6*14, the density of pow- 

 ellite then becomes as calculated by Melville,* 4-267. 



As all previous analyses of powellite showed the presence of 

 tungstic oxide, the densities given are all too high for the pure 

 calcium molybdate. The two values obtained by the writer, 

 though uncertain as they are based on some assumptions made 

 in applying the corrections, agree so well not alone with each 

 other, but also with the calculated value, that the average of 

 the three values (4-24, 4*23, 4 - 27), namely 4*25, may be taken 

 as being very close to the true density of the pure calcium 

 molybdate, CaMo0 4 . 



4. Molybdite from, a new locality. — A sample of molybdite 

 from Hortense, Colorado, was received through the kindness of 

 Mr. F. L. Hess. The yellow mineral occurs in lumps, several 

 of which have a diameter of over 2 cm . With the molybdite 

 are associated molybdenite, quartz and a mica. The sample 

 looks earthy, but under the microscope is seen to be well crys- 

 tallized and shows the characteristic optical properties of 

 molybdite as described in a previous paper. A sample was 

 selected as pure as possible, but which was found on analysis 

 to still contain a large amount of insoluble matter. The pow- 

 dered specimen caked together in the sample tube and proba- 

 bly contained some extraneous water. The analysis also 

 showed too high a water content for molybdite. Below are 

 given (I) the analysis ; (II) the same with the insoluble matter 

 deducted and the analysis recalculated to 100 per cent ; and 

 (III) the percentage calculated for Fe 2 3 .3Mo0 3 .7iH 2 0. 



I II in 



H 2 15-87 20-19 18-57 



Fe 2 O s 15-95 20-30 22-01 



Mo0 3 46-77 59.51 59-42 



MoS 2 5-50 



SiO„ 16-51 



100-60 100-00 100-00 



The residue, insoluble in HC1, was roasted in an open cruci- 

 ble to change the MoS 2 into Mo0 3 and then weighed. The 

 oxide of molybdenum was then dissolved by HC1, leaving the 

 silica, which was tested with HF for its purity. The determi- 

 nation of water was made in two ways, by loss in weight and 

 * This Journal, xli, 138, 1891. 



