4 Prof. J. Joly on the 



In my former paper I remarked with reference to group III.. 

 of the Table that, owing to the results then obtained being 

 mainly confined to iron, nickel, and cobalt compounds, wo 

 were not in a position to examine into the possible influence 

 of the atomic weight of the stable element present, and I drew 

 attention to the rather anomalous indication of domykite. In 

 the present list it will be seen that two other copper arsenides 

 support the position of domykite. It is to be remarked that 

 the somewhat higher decomposition point of whitneyite is 

 probably in part due to the coarser grain of the powder used ;. 

 the ductile nature of this substance rendering pulverization 

 impossible. It can only be powdered by abrasion. From 

 these results it would appear as if the stable element present 

 was not without some effect on the temperature of sublimation. 



Some analyses carried out on the apophorometer, bearing 

 upon the formula? to be ascribed to some of the minerals 

 examined, may now be given. 



Primarily there is the question, which I raised in my 

 former paper, as to where arsenides of the composition RAs 2 

 should be placed in the Table. A smaltite of Schneeberg was 

 carefully examined : — 



Analysis 1. Smaltite ; Schneeberg, Saxony. Weight 

 taken 13*6 mgrms. Total As 2 3 up to white heat 

 13'0 — 9*8 mgrms. As. Residue 4*5 mgrms. 



The Schneeberg mineral, according to Hintze, is mainly a 

 nickel chloanthite with As = 77 ; Co = 3 ; Ni = 12 ; S = l or 

 less. The residue in the present experiment gave a vivid 

 blue bead with borax, but it does not much matter for the 

 purpose of the experiment whether we calculate it as NiO, 

 Co 3 4 , or Fe 2 3 . Tke first gives 3'6 Ni ; the second 34 Co;. 

 the third 3-7^Fe. I take 3'6 (Ni, Co, Fe). This makes the 

 added weights 13'4. The deficit is about 1*5 per cent, and 

 is probably S. 



Hence, As = 72'0 ; (Ni, Co, Fe) = 26'5 ; S = l/5. And 

 the relative number of atoms — As 96 ; (Ni, Co, Fe) 45 

 (about) — leaves little doubt that the formula is essentially 

 (Ni, Co, Fe) As 2 . 



Now in the experiment the As 2 3 was evolved as 

 follows : — 



0-5 mgrms. at 230- 320. Group II. 



9-4 „ „ 420- 540. „ III. 



1-0 „ „ 660- 760. 



0-5 „ „ 920-1450 (?) 



1*6 „ ., full white heat. 



