606 



PROCEEDINGS OF THE NATIONAL MUSEUM. 



especially selenium, and a Avhite ring of volatile crystals of selenous 

 oxide, which is faintly red in its lower portion from the presence of 

 unoxidized selenium. The silver remaining behind is quite pure and 

 hence is difficultly fusible. 



CHEMICAL PROPERTIES. 



The mineral is insoluble in hot concentrated or dilute hydrochloric 

 or sulphuric acids, but dissolves readily in hot concentrated nitric 

 acid. Samples free from the clay gangue could not be obtained, 

 as the mineral is too malleable to admit of pulverization. It was 

 thus necessary to estimate the amount of clayey impurity in the 

 sample analyzed from the amount of insoluble residue (ignited) 

 obtained from the mineral. A preliminary examination of the 

 purest and whitest clay which could be scraped from the crust 

 gave the following results: 



Insoluble matter (ignited) 87.70 



Silver 1. 14 



Selenium and sulphur (calculated) .34 



Water plus loss (by difference) 10.82 



100.00 



In the analyses the amount of insoluble material found, after 

 ignition, was multiplied by the factor 1.1234 and deducted from the 

 weight of the sample taken. After this deduction the analysis gave 

 the results given in column 1 below. Since the sample contained 

 some marcasite, the amount of iron found is deducted, togetlier 

 Math sulphur to form FeSj, leaving the results given in column 3 

 of the following table. In column 3 the figures are recalculated to 

 show the composition of the naumannite, free from marcasite. in 

 terms of 100 per cent. 



Analysis of naumannite from Idaho. 



