Analysis of the Copper Ore of Franconia. 253 



Analysis of the Copper Ore of Franconia, New-Hampshire, 

 luith remarks on Pyritous Copper. By James Freeman 

 Dana, M. D. Professor of Chemistry in the University of 

 the State of New-York. Read April 2, 1827. 



The chemical constitution of pyritous copper, in common 

 with that of many other minerals, has been involved in great 

 obscurity. The ore is known to contain not only copper 

 and sulphur, but also iron, as a constant constituent and in 

 variable proportions ; the proportion of copper having been 

 stated from 35.5 to 40, of iron from 33 to 40, and sulphur 

 from 20 to 25, and the mineral has been regarded as a me- 

 chanical mixture of these bodies, rather than as an atomic 

 compound of sulphurets of copper, and sulphurets of iron. 

 " There does not," says Professor Cleveland, " appear to be 

 sufficient sulphur to produce two sulphurets."* A different 

 view of the subject, however, is embraced by Proust, and a 

 gleam of light has been thrown on the constitution of pyritous 

 copper, by the analysis of Mr. Rose. 



It appears to be established by the experiments of Thom- 

 son, to whom the atomic theory is so much indebted for its 

 elaborate experimental conr mation, that there are three dis- 

 tinct compounds of sulphur and iron,f viz. 



1. Protosulphuret of iron, containing 1 atom of iron -f- ! atom ofsulph. 



2. Sesquisulphuret of ;ron, do. I do. li do. 



3. Bisulphuret of iron, do. 1 do. 2 do. 



Two of these compounds, the first and the third under the 

 names of magnetic pyrites, and of sulphuret of iron, have 

 been long known to mineralogists ; and their composition was 



* Mineralogy, 2d ed. Vol. II. p. 55T. 

 + First Trine, pp 19). 192. Vol. II. 



