1820.] extracted from Fyrites at Fahlun. 25 



This great loss must be partly attributed to the carbonic acid 

 xinited to the hme. in a great measure to the selenium which it is 

 diflticult to separate completely, and pardy to the unavoidable 

 loss in this kind of experiment. 



The 38-93 parts of silver combine with 2-86 oxygen. The 

 23-05 of copper require to form the protoxide 2-91 parts of oxy- 

 gen ; and the 26 parts of selenium in order to be acidified 

 require 10-5 parts. We see from this that the two metals absorb _ 

 an equal quantity of oxygen, and that the selenium absorbs 

 twice as much ; that is to say, that they are combined in the 

 same proportion as in the neutral seleniate of silver and the pro- 

 toseleniate of copper. Hence the chemical composition of this 

 mineral may be expressed by the foUov/ing symbol ; 2 Cu Se 

 + Ag Se''. It may be requisite to recall to the attention of 

 the reader another mineral recently described by MM. Hauss- 

 man and Stromeyer,* to which they have given the name of 

 silber-hipfcr glans, and the composition of vv'hich, according to 

 their analysis, is 2 Cu S + Ag S^ ; so that there exists native 

 a doable sulphuret analogous to the double seleniuret, which. 

 I have just described. These two minerals, therefore, ought 

 to be placed beside each other in the mineralogical system. 



As this mineral requires a name not derived from its composi- 

 tion, for the sake of shortness, I have called it eukairite (from 

 ivitdipo;, opportiimis) ; because I consider the accidental discovery 

 of selenium in the mineral kingdom just at the time that I had 

 finished my experiments on this interesting body, as a peculiarly 

 fortunate circumstance. 



I could not at first discover whence this pretended ore of 

 tellurium caine ; but having consulted M. Hisinger, to vvhom 

 Swedish mineralogy lies under such obligations, he immediately 

 knew that the mineral came from an old abandoned copper mine 

 at Skrickerum, in the parish of Tryserum, in Smoland, and that 

 specimens of it were occasionally observed in old collections 

 under the name of native bismuth of Skrickerum. I examined 

 afterwards the specimens from that mine found in the collectioii 

 of the College of Mines at Stockholm, and had the satisfaction 

 to find a very good specimen of eukairite. It is surrounded by a 

 serpentine of a black or dark-green colour, which, at the point 

 of contact with the eukairite, is penetrated by seleniuret of 

 copper, in which only traces of silver can be observed. This 

 seleniceferous serj)entine is found here and there in the mass of 

 the eukairite, as I remarked above. The quantity of seleniuret 

 of copper in the serpentine diminishes in proportion as its dis- 

 tance from the eukairite increases. In its neighbourhood, it 

 becomes metallic when rubbed with a hard body ; but this does 

 not happen at a distance from the eukairite ; and when the interval 

 amounts to a line and a half, all trace of selenium disappears. 



• Gilbert's Annalender Phyeik, 1816, vol. x. p. Ill, 



