300 Messrs, W. and R. Phillips on [April, 



ted hydrogen; it was, therefore, probably oxide of lead. An- 

 other portion of solution saturated with nitric acid gave a preci- 

 pitate with nitrate of lead, after all the sulphuric acid had been 

 tlirown down by nitrate of barytes. It is evident, therefore, that 

 some arsenic acid was present. 



Crystallized yellow copper ore appears, therefore, to consist of 



Sulphur 35-16 



Iron 32-20 - 



Copper 30-00 



Earthy matter 0*50 



97-86 

 Lead, arsenic, and loss 2-14 



100-00 



If we neglect the small quantity of lead, arsenic, and earthy 

 matter, as extraneous, it will appear that my analysis of the crys- 

 tallized ore agrees so nearly with Gueniveau's statement of the 

 composition of the amorphous variety, that they may be consi- 

 dered as differing only in form. 



The mamellated variety was next submitted to analysis : this 

 is much less common than the other varieties, and I am not sure 

 whether it occurs in any other place than Cornwall. It is thus 

 described by Count Bournon, in the Philosophical Transactions 

 for 1801, under the name of yellow hematitic copper ore : **This 

 kind of copper ore is sometimes of a deep yellow colour, which 

 inclines the more to green, as it is destitute of brilliancy. It is 

 very compact, and, when broken, the fracture appears smooth, 

 sometimes a little conchoidal ; its surface, however, has a very 

 fine grain, which, when viewed with a powerful lens, resembles 

 the aggregation of a very close compact mass of the finest sand." 

 It is afterwards stated that it occurs mamillated, botryoidal, and 

 in the form of small cylinders ; and by the decomposition of the 

 surface, it acquires violet, blue, and green colours. 



In the same volume of the Transactions, Mr. Chenevix has 

 given an analysis of this ore, according to which it consists of 



Sulphur 12 



Copper 30 



Oxide of iron 53 



Silica 5 



Too 



The first observation which occurs with respect to this ana- 

 lysis is, that there docs not exist, as far as I recollect, any mineral 

 which consists of a sulphuretted metal in combination with an 

 oxide. Added to this, it is to be observed that the sulphur 

 exceeds by 4*5 the quantity required to form a protosulphuret 

 with the copper, and is deficient 3 to form a persulphuret. 



