94 UNIVERSITY OF COLORADO STUDIES 



solved in dilute ammonia and added to the major portion previously 

 obtained, the whole being then evaporated to dryness, ignited, and 

 weighed as W0 3 . The iron nitrate was added to the filtrate from the 

 aqua regia decompositions, and allowed to stand for twenty-four hours. 

 Sometimes a slight precipitate of W0 3 , which had passed through the 

 filter, settled out. This was added to the tungstic acid solution obtained 

 after treatment with ammonia. These steps are necessary in order 

 to be sure of getting all the tungstic acid. 



The iron and aluminum were separated by the sodium acetate method, 

 the ignited precipitate fused with KHS0 4 , dissolved and reduced, 

 titrated with standard KMn0 4 , and the alumina obtained by difference. 

 The manganese was precipitated by ammonium sulphide, dissolved in 

 acid, precipitated by ammonia and bromine water and estimated as 

 Mn 3 4 . The calcium and magnesium were precipitated as oxalate 

 and phosphate respectively. The ores were examined for moisture by 

 Penfield's method, but in no case was an appreciable amount found. 



As will be seen from the following tables, the Nederland ore is mainly 

 tungstate of iron, the mineral ferberite. Most textbooks on mineralogy 

 give a very brief description of this mineral, classifying it as a rarity. 

 On account of its occurrence in such large quantity in Boulder County, 

 it would hardly come under this class. None of the Nederland speci- 

 mens showed even a trace of sulphur. Mr. Hugh F. Watts of Boulder, 

 who has made over two thousand assays of these ores, tells me that it is 

 not often that they show sulphur; in fact he has ceased making sulphur 

 analyses on the ores, unless for special reasons. These specimens show 

 only a fraction of a per cent, of manganese. The multitude of com- 

 mercial analyses of these ores shows that rarely does the amount of 

 manganese present run over one per cent. 



The ore from Ward, Colorado, is a wolframite, carrying pyrite. 

 The specimen showed the pyrite crystals very clearly. On this account 

 the mineral has not been mined profitably. 



The two ores from Silverton, Colorado, are hubnerite and a mixture 

 of hubnerite and wolframite respectively. The hubnerite specimen 

 was composed of light-brown bladed crystals, a single splinter being 

 almost transparent. The small amount of iron was shown to be in 



