18 



Transactions of the Society. 



carry out with the small amount of material at our disposal, are 

 given below: — 



Grm. 



Weight of boat + osmium compound before experiment = 3 - 18265 



after „ = 3-16766 



Weight of boat alone = 3-14585 



Loss of weight of substance . . . . = 0-01499 



Weight of residual osmium . . . . . . = 0-02188 



Weight of P^Oj tube before experiment . . . = 22 • 27879 



„ " after „ . . . = 22-29508 



Weight of water derived from substance = 0-01629 — 



0-00081 . / = 0-01548 



Let p = weight of water contained in substance, and q = weight 

 of oxygen contained in substance. Then 2^ -{- q = 0-01499, and 



p -i-lq = 0-01518. Hence, p = 0-01107 and q = 0-00392. 



o 



From these ligures, and the weight of the osmium, the following 

 ratios are found : — 



These figures indicate that the black substance is a hydrated 

 form of osmium dioxide, OsOjAq. They would point to an 

 approximate formula OsOaSHaO. Such a substance has been 

 described, but we are not sufficiently convinced that the amount of 

 water contained in the solid was that corresponding with a definite 

 hydrate ; the degree of desiccation of the material was too arbitraiy 

 to allow of any such conclusion being drawn. If the small amount 

 of material be taken into account, we believe, on the other hand, 

 that the results are definitely in favour of the dioxide, and in any 

 case they definitely negative the hypothesis that the black material 

 is metallic osmium. 



The properties of osmium dioxide have recently been described 

 by 0. Euff and H. Eathsburg (S), but the material dealt- with by 

 these experimenters does not appear to have had properties at all like 

 those of our substance. They state that a colloidal solution is 

 formed, but the precipitated substance passed again into solution 

 on washing. Two solid forms are described, one pyrophoric — or 

 even spontaneously explosive when dry — and a second stable form, 

 OsOa, 2H2O, reduced almost explosively by hydrogen, and oxidized 

 rapidly by oxygen. The older experiments of Berzelius (4) pointed 

 to a substance of much greater stability, and we are inclined to 

 think that the material used by Ruff and Eathsburg may have 



