OF ARTS AND SCIENCES. 29 



The formula CoaCNHa)!^ (NO.,)^S.OJ, requires 



Calculated. Found. 



1 2 



Cobalt, 2 11-99 12-21 11-64 



Iodine, 4 51-60 49-90 49-96 



SO, 1 9-75 9-77 10-80 



Nitrogen, 12 17-07 16-63 



Salts 1 and 2 were from different preparations. 



The analyses do not correspond as closely to the formula as might 

 be wished, but it must be remembered that the salt cannot be recrys- 

 tallized without decomposition, and is probably not quite free from the 

 first described, or normal iodo-sulphate. The salt gives off iodine on 

 heating. The structural formulas of the two salts may be written as 

 follows : — 



Co„ 



fNH, — NO, fNHg — NO2 



NH, — NH, — I 



NH3 — NHI — 0.<.,0 — I 



NH„— nh;! — O^^^O— I 



NH3 — NH3 — I 



Nil, — NH„^^^ p^ 



NH3— nh;^^^^ ^""^ 

 NH3— NH3— I 



NH3 — NO., 



NH3 — NH3 — o- 

 NH., — NH3 



NH., — NO 



2 



This mode of writing the formulas, however, involves certain theoret- 

 ical, conclusions, which I shall examine in detail hereafter. I added 

 PtClgNaj to a solution of sulphate of xanthocobalt, hoping to obtain a 

 salt with the formula Co2(NH3)i„(N02)2(SO,)Clo(PtCg, analogous to 

 a platinum salt of roseocobalt, which 1 shall hereafter describe, and 

 which has the formula Co^ (NH3)io(SO,),PtCle. The beautiful crys- 

 talline precipitate formed proved to be only the salt Co2(NPI3)jq(NO^)2 

 ClaPtClfl + OH2, described in the first part of this memoir. 0-3882 gr. 

 gaveO-1612 gr. Co -|-Pt = 41-52. The formula requires 41-39 per cent. 

 Nitrite of Xanthocobalt. — When argentic nitrite is boiled with a 

 solution of chloride of purpureocobalt, the liquid soon loses its fine 

 violet color, and assumes the wine yellow tint of the salts of xanthoco- 

 balt. The filtrate from the argentic chloride gave, on careful evapora- 

 tion, two distinct salts, — a salt in beautiful scaly crystals, and one in 

 octahedral crystals. The two salts were separated by crystallization. 

 Of the scaly salt 



0-2854 gr. gave 0-2286 gr. SO.Co -}- SO.Agj = 79-97 per cent. 



The formula of the ammonia-cobalt-nitrite, Co2(NH3),(N02)8Ag2 re- 

 quires 80-75 per cent, and the salt was easily identified by its appear- 

 ance and properties, with the silver salt of Erdmann's series. As the 



