igoS.i KELLER— NOTES ON CHILEAN COPPER MINERALS 83 



nated through a silicions rock, and partly as an incrustation upon 

 quartz. On account of its physical characters, as well as the strong 

 reaction its solution gave with barium chloride, I was first inclined 

 to regard it as a typical brochantite. This impression was confirmed 

 by rough estimations of the copper and sulphur trioxide, but as these 

 tests had been made on impure material, I decided to attempt the 

 analysis of a carefully prepared sample. To obtain about .5 grm. 

 of the substance, I found it necessary to sacrifice the best specimens 

 in my possession, and my patience was put to a severe test in picking 

 the minute crystals under the lens. They were sorted over and over 

 until the microscope showed only a few remaining specks of quartz 

 adhering to the larger crystals of the copper mineral. 



The quartzy material from which this sample had been picked 

 still contained considerable quantities of the copper mineral, and it 

 occurred to me that it might serve for a qualitative, and, perhaps, 

 a preliminary quantitative analysis. Accordingly the material was 

 extracted with hydrochloric acid, and the resulting green solution 

 divided into equal parts. When the copper had been precipitated 

 with hydrogen sulphide, it was noticed that yellow flakes began to 

 form, and after the liquid saturated with the gas had been allowed 

 to stand in a warm place over night, a considerable amount of the 

 yellow precipitate had settled on the black copper sulphide. There 

 could be no doubt, then, that arsenic was present in the form of 

 arsenic acid. The sulphides were separated and worked up in the 

 usual manner, and the filtrate was searched for other metallic ions. 

 It yielded only traces of iron oxide and alumina. The other half 

 of the original solution was used for the determination of the 

 sulphur trioxide and the arsenic acid. The results of the determi- 

 nations, calculated for the entire amount of copper mineral dissolved, 

 gave : 



Copper 5068 grms. 



Sulphur trioxide 0783 grms. 



Arsenic anhydride 1309 grms. 



The question now arose as to whether the very large proportion 

 of arsenic acid found really constituted an integral part of the sup- 

 posed brochantite, or whether it did not belong to another mineral 

 contained in the rock. The test previously made seemed to preclude 

 such an arsenic content of the mineral under examination. 



