OF ARTS AND SCIENCES. 31 



appeared to contain different amounts of water of crystallization. In 

 one preparation in fine crystals : — 



1-3713 gr. gave 0-5952 gr. Cr.fl^ = Ql-Q2% Cr.O^. 



The formula Co2(NH3)j2(Cr20-)34-50H2 requires 61-17%. 



METAMERIC SALTS. 



I have already stated that roseocobalt and xanthocobalt give beauti- 

 ful crystalline salts with the electro-negative or chlorous radical of 

 Ei'dmanu's remarkable series. The formula of the octamin salt may 

 be written, — 



^Co,(NH3),(NO,)j"^Co,(NH3),(NO,),^"orCo,(NH3),(NO,),+ 



Co,(NH3),(NO,)„ 



while that of the xanthocobalt salt is, — 



^Co,(NH3),o(NOJ,nCo,(x\H3),(NO,),f, or Co,(NH3),„(NO,),-f 



2(Co,(NH3),(NO,),). 



It will readily be seen that, as already shown, the croceocobalt salt is 

 empirically 



2. Co,(NH3)„(NO^„ 



and the xanthocobalt salt 



3. Co,(NH3),(NO,)„ 



and consequently that both are metameric with the hexamin nitrite 

 of Erdmann Co2(NH3)y(NO^)^. I will now show that there are two 

 other compounds also metameric with Erdmann's salt, and yet per- 

 fectly distinct in chemical structure and properties. 



When potassic nitrite is added to a solution of cobalt containing a 

 little free acid, a yellow crystalline substance is gradually precipitated, 

 which is the well-known salt first described by Fischer. The investi- 

 gations of Professor Sadtler first definitively proved that this salt is 

 essentially Co.,(N02)ioKg, the number of atoms of water of crystalliza- 

 tion varying with the circumstances under which the salt is firmed. 

 Professor Sadtler has also described and analyzed the corresponding 

 sodic and ammonic salts. The sodic salt is not immediately precipi- 

 tated when sodic nitrite is added to an acid solution of cobalt, but in 

 presence of an excess of the alkaline nitrite remains in solution, giving 

 a deep orange-colored liquid. I found that this solution gave beauti- 

 ful crystalline precipitates with salts of luteocobalt and roseocobalt. 



