Algodonite and some artificial copper-arsenides. 443 



Cu = 61-67 X 8-96 = 5'5256 



Ni = 7 03 X 9-5 = 0-6678 



Co = 2-02 X 8-96 = 0-1809 



As = 2385 X 5-63 == 1-6242 



7-9985 

 8-0650 found 



+ 0-0665 difference 



This is quite a satisfactory agreement. Yet it occurred to 

 me at this stage of the investigation to verify the relations 

 between specific gravity and composition by artificial com- 

 pounds and also to see in how far domeykite might be obtained 

 in crystals. 



A combustion tube was closed at one end over the lamp. 

 Resublimed arsenic, roughly powdered, was placed into the 

 bottom to the amount of 79 grams. On top of this was 

 poured 2O0 grs. of copper filings. The latter had been the 

 end product in a determination of oxygen in refined copper. 

 Total non-copper in this material 0*07 per cent, consisting of 

 arsenic and iron. An asbestos plug was put over the copper 

 and the tube placed in horizontal position into an Erlenmeyer 

 combustion furnace. The copper was first heated to a dull 

 cherry redness and then the arsenic was heated to the sublima- 

 tion temperature. The heating was kept up for two hours, the 

 open end of the tube being provided with a mercury valve to 

 prevent any air currents from entering the tube. The copper 

 absorbed the arsenic with avidity. One could see that only 

 the part nearest the vapors changed in color and 30 minutes 

 from the beginning this front portion began to melt off. After 

 all the arsenic had become volatilized and a considerable part of 

 the liquid compound had been formed the temperature of this 

 liquid was raised to bright redness and kept so until the end of 

 the experiment ; it being 6 o'clock p. m. The tube was 

 inclined so that the liquid covered the solid portion and left to 

 cool slowly. In the morning three distinct substances were 

 found. A dark colored fused mass, then a porous gray part 

 and then the apparently unaltered copper filings, merely 

 slightly caked together, (a) The dark, fused portion. On the 

 fracture blue-gray color ; strongly developed radial structure 

 and, in fact, so closely resembling chalcocite that one could not 

 tell by the eye one from the other. The weight of all three 

 parts was 27*27 grams. The weight of the unaltered (appar- 

 ently) part was 9 - 65 grams ; hence in the altered part there 

 must be approximately 10*35 of copper and 7*2 grams of 

 arsenic, giving an atomic ratio of 9*6 : 16*4. Now if the quanti- 

 ties taken of copper and arsenic were in the ratio of 3 : 1 it is 



