Algoclonite and some artificial copper-arsenides. 445 



2. Stibio-domeyMte. 



With this name I propose to designate the domeykite from 

 the Mohawk mine, Keweenaw Co., and any other locality 

 where mineral of similar composition will be found. In 

 physical properties it is undistingnishable from the domeykite 

 of the Houghton Co. mines. It is remarkable for the massive- 

 ness of its occurrence, the freedom from admixtures. It has a 

 decided subconchoidal fracture and takes on a brass tarnish 

 very soon, which, however, ultimately turns into bluish purple. 

 It is very brittle but not as friable as the Mohawkite. Its 

 hardness is very near 4, a little below. 



Specific gravity at 21° C.= 7-902 (made with 4*5595 grams) 

 B. B. In the open tube after heating the molten globule for 

 five minutes one observes the forming of yellow spots near the 

 globule and a slight ring or patches farther on, which turn 

 yellow on applying higher heat and volatilize in part. Farther 

 on there is a copious sublimate of arsenic trioxide. If now one 

 washes out the tube in a jet of water and passes H 2 S into the 

 tube one observes the above ring and patches turn red, whilst 

 the arsenic oxide turns gold-yellow. I was astonished myself 

 to find that one could demonstrate thus the presence of O'l per 

 cent antimony in the mineral. On charcoal blow the point of 

 the oxidizing flame upon the melting mineral for two minutes, 

 then drive off the white arsenic with a gentle flame, the anti- 

 mony trioxide remains. The open tube reaction is preferable 

 and certain. Concentrated nitric acid does not dissolve the 

 mineral completely; a white cloudiness or a white sediment 

 will be left. When fused oh charcoal alongside of a borax 

 bead, the latter colors greenish after several minutes' action 

 (cobalt and nickel cannot be thus found, though present in 

 small amount). 



The analysis gave (type specimen) : 



Cu 72-48 



(Fe,Ni,Co) 0-24 



As 26-45 



Sb 0-78 



99-95 



This is evidently a typical domeykite, and one would 

 expect likewise that the percentage of antimony is variable. 

 In order to ascertain this I took twelve pieces, all over one 

 pound each, and treated one gram of each with 10 co of con- 

 centrated nitric acid, boiling until the color was blue, then 

 added 15 cc of water to each and stood the beaker glasses in a 

 row. (The type specimen with its 0*78 antimony was among 

 the lot.) It appeared that all contained antimony, but no two 



