358 Koenig and Hubbard — Powellite from a new Locality. 



produced just such a nearly colorless bead as the above residue. 

 Upon this proportion is based the percentage of WO, in 

 analysis (I). 



The results of analysis (II) are the most satisfactory of 

 several trials. The methods followed are those of H. Kose 

 and v. derPfortden — precipitation of MoS 3 in tartaric solution. 

 It was found that the MoS 3 after repeated solution and pre- 

 cipitation and final reduction to the metal would still leave a 

 residue upon volatilization, which reacted in microcosmic salt 

 like the one in (I).* The sulphides were weighed and aliquot 

 portions reduced to metal in a current of dry hydrogen, and 

 from these weights of the metals the figures are deduced. 



I. II. 



Mo0 3 65-74 67*84 



W0 3 . 4-50 1-65 



CaO 27-41 27-30 



MgO__ -16 



Fe 2 3 __. undet. -96 



Si0 2 .... 1-52 



Cu trace 



97*65 99-43 



The percentages of W0 3 in (I) and (II) may be taken as a 

 maximum and minimum respectively. Possibly the mean of 

 the two is near the true percentage. In order to form a normal 

 tungstate and molybdate we have 



for (I) Mo0 3 65-74 require 25*56 CaO 



WO, 4-50 require 1-09 +0"76 



26-65 



for (II) Mo0 3 67-84 require 26-38 CaO 



W0 3 1*65 require 0'40 



26-78 +0-52 



Analysis (II) with its plus of 0'52, and (I) with its plus of 

 0-76 of CaO are, neither of them, up to the theoretical require- 

 ment, but we do not know what role Si0 2 plays. The latter 

 must be present as a silicate decomposable by HC1 and ^H0 3 , 

 for these acids leave no residue when acting on the powder. 



It may be questioned whether Melville was justified in 

 speaking of his powellite as practically pure calcium molybdate, 

 it showing over 10 per cent W0 3 . This name would properly 

 go to the intermediate combinations of calcium tungstate and 

 calcium molybdate. The pure molybdate awaits discovery 

 and should then be given a new name. 



*This residue was found, by calculation, to contain an amount of W that 

 could not exceed - 984 per cent W0 3 . — L. L. H. 



