138 DicA'son — Platinum in the Nickel- Copper Ores. 



the experiments here described give additional weight to his 

 conclusion. 



With the object of settling the point, if possible, the present 

 writer began a number of experiments about a year ago, on 

 various samples of ore from the Sudbury District, but without 

 arriving at any conclusive results. Then the discovery of Pro- 

 fessors Wells and Penfield,* that the platinum in the copper 

 ores from the Rambler mine, Wyo., was present as sperrylite, 

 led to some further experiments, one of which proved notably 

 successful. As Walker had shown that the platinum was 

 associated with the chalcopyrite, this mineral was selected as 

 the object of special investigation. A number of samples from 

 different localities were freed from pyrrhotite and other foreign 

 minerals as well as possible, and were used for the tests. The 

 only one, however, which gave satisfactory results was some 

 massive and almost pure chalcopyrite from the Victoria mine, 

 about twenty miles west of Sudbury. Seventy-five grams 

 of the coarsely crushed mineral were treated a number of times 

 with hot nitric acid, till all the sulphides were decomposed. 

 The sulphur which separated was removed by means of carbon 

 bisulphide, and the residue treated several times with sulphuric 

 and hydrofluoric acids, to remove the quartz and silicates. The 

 final residue consisted of quite a large number of small and 

 very brilliant tin-white crystals and fragments, resembling 

 sperrylite. On a qualitative examination the mineral proved 

 beyond doubt to be the arsenide of platinum. It yielded a 

 crystalline sublimate of As 2 3 in the open tube. On long con- 

 tinued treatment with hot concentrated aqua regia some of it 

 was dissolved, and on the addition of ammonium chloride gave 

 the well known yellow crystalline precipitate of ammonium- 

 platinic chloride. The test of dropping some of the fragments 

 on a piece of hot platinum foil was also tried. The mineral 

 melted, sprouted, and gave off white fumes, so there can be no 

 doubt as to its nature, chemically. 



Some of the crystals were very well developed, and fifteen 

 or twenty of them ranged between 0'5-l mm in diameter. A 

 number also presented interesting and complicated combina- 

 tions of forms, and in order to prove the crystallography of the 

 mineral, and to compare it with that from the locality of the 

 original discovery, some of the angles were measured. Nearly 

 all the crystals are more or less distorted ; a modified, elongated 

 cube being perhaps the commonest. The largest and most per- 

 fect crystal (an elongated cube) had the following faces : cube 

 (001), octahedron (111), pyritohedron (210), and trapezohedron 

 (211), besides some smaller indefinite faces which could not be 

 accurately determined. 



The measurements are as follows : — 



* This Journal (4), xiii, 95, 1902. 



