110 



Mr. D. Forbes on the Chemical Composition 



Cobalt . . . 



. . 1592 



Nickel . . . 



. . 5-17 



Iron . . . 



. . 2-62 



Silver . . 



. . 2-06 



Arsenic . . 



. . 74-02 



Sulphur . . 



. . 0-21 



10000 



These results indicate at a glance the composition of sraaltine, 

 differing in no respect from the mineral usually met with, except 

 in being somewhat more argentiferous. Notwithstanding the 

 impurity of this mineral mixture, there can be no doubt as to 

 the existence of one or more true compounds of silver with 

 arsenic; and, as before stated, the formulae Ag 6 As and Ag 3 As, 

 which represent the compounds here described, very probably are 

 definite mineral species, which on further search may be obtained 

 in a purer condition. 



Sulphide of Lead and Zinc, 



This mineral is found in a mine at Ingahuas in the depart- 

 ment of Huasco, where it occurs in the form of rather large 

 lumps or nodules. It is lighter in colour, and possesses less 

 lustre than galena, which mineral it in most points resembles, 

 except in its peculiarly compacted and homogeneous saccharoidal 

 structure, which, even when examined by a magnifier, discloses 

 no intermixture of any other mineral, nor trace whatever of 

 zincblende. 



Its composition, according to Domeyko, is 



Lead 48-6 



Zinc 25-6 



Sulphur .... 19-2 



Gangue and loss . . 66 



100-0 



Calculating the percentage of lead, sulphur, and zinc, after 

 deducting the amount of gangue and loss, we have the composi- 

 tion of the pure mineral shown as follows : — 



Lead 52'03 



Zinc 27-41 



Sulphur 20-56 



100-00 

 which numbers approximate very closely to 2 equivalents lead, 

 3 zinc, and 5 sulphur, which require a percentage composi- 

 tion of 



