504 



PROCEEDINGS OF THE NATIONAL MUSEUM. 



after repeated ignition with dry ammonium carbonate. Here the cal- 

 cium was only moderate in amount, but the cohimbium and tantalum 

 oxides seemed sufficiently high to attempt to determine the relative 

 amounts of the two. 



For this purpose the oxides were fused with potassium acid fluoride, 

 reprecipitated, and ignited as recommended by Foote and Langley ^ 

 and the specific gravity then determined. Although the impossi- 

 bility of duplicating the conditions exactly renders the result uncer- 

 tain, it is probably quite as dependable as that obtained by any of the 

 direct methods of determination. The 2.20 per cent of mixed oxides 

 obtained had a specific gravity of 7.02, corresponding to about 2/3 

 tantalum, so that tlie percentages of the two oxides are stated as tan- 

 talic oxide 1.50, columbic oxide 0.70. No tin or titanium could be 

 detected in either sample of wolframite. 



1. Wolframite, Cornwall, England. U. S. Geol. Surv.,Bull. 583, p. 27. 



2. Wolframite, Cave Creek, Arizona. Idem, p. 32. 



In calculating the approximate mineral composition of 1 it was assumed that the only free base was the 

 Iron oxide, that the iron manganese ratio was the same in thecolumbite-tantalite as in the wolframite, and 

 that equal proportions of eolumbium and tanfcilum were present. 



In calculating that of 2 it was again assumed that the iron and manganese were present in the columbitc- 

 tantalite in the same ratio as in the wolframite, and that the deficiency in the summation of the analysis 

 was due to the manganese being too low. 



A few words should be added concerning the nomenclature here 

 adopted.^ The names wolframite, scheeUte, columbite, and tanta- 

 lite are used as series names, that is, as referring to any and all inter- 

 mediate members of the isomorphous series, no matter what the 

 relative proportions of the bases are. For the theoretical end members, 

 chemical prefixes are applied to these roots.^ This method is pre- 



1 Amer. Journ. Sci., ser. 4, vol. 30, 1910, p. 393. 



2 Which represents an extension of that proposed in Science, vol. 39, 1914, p. 575. 



»The end members are described as theoretical because they can not be expected to occur In nature, 

 elements being apparently never found free from at least small amounts of their isomorphs. Their 

 chemical-prefixed names should therefore not be included in "lists of new mineral names." 



