144 RE-EXAMINATION OF AMERICAN MINERALS. 



examination of the minerals obtained by Lieut. Gilliss, of the 

 U. S. Chili Expedition, has afforded an opportunity of analyzing 

 certain minerals that it was well to investigate, and amoDg these 

 were one or two fine specimens of iodide of silver. A re-exam- 

 ination of this mineral is especially interesting, from the fact 

 that its composition is still in doubt, owing to the discrepancy 

 between the original analysis of Vauquelin on the mineral from 

 Zacatecas in Mexico and that of Domeyko on the mineral from 

 Chanarcillo in Chili. TT ^ 



Vauquelm. Domeyko. 



Iodine 22.6 A 2T 46.89 A T 



Silver 77.4 A ^ L 54.25 A ^ L 



The constitution of the native chlorides and bromides of 

 silver would lead to the supposition that Domeyko's analysis 

 was the correct one, and this is strengthened by its resem- 

 blance to the artificial iodide of silver. 



The specific gravity was found to be 5.366, being a little 

 lower than that given by M. Domeyko. The analysis of an 

 exceedingly pure specimen gave me 



1 2 



Iodine. 52.934 53.109 



Silver 46.521 46.380 



Chlorine trace trace 



Copper trace trace 



1)9.455 99.489 



clearly showing its constitution to be Ag. I = Iodine 53.85 

 Silver 46.15 = 100, leaving no doubt of its perfect analogy to 

 the natural chloride and bromide of silver. The other prop- 

 erties of this mineral are not mentioned, as they are all fully 

 stated in all works on mineralogy. 



38. Copiapite. 



This mineral was also furnished me by Lieut. Grilliss, it 

 having been brought from Chili. It consists of most beautiful 

 silky fibers or fibrous masses of a pearly luster. Its color is 

 white, with a very fine tinge of yellow. From the specimens 

 in my possession there was no difficulty in picking out a por- 

 tion in a state of great purity. Its specific gravity is 1.84. 

 Examined under the microscope its form appears to be a hex- 

 agonal prism. Cold water has but little action on it, merely 

 causing the crystals to separate and the mass to swell out to a 

 very much increased bulk. If the water be boiled, decom- 



