OF ARTS AND SCIENCES. 25 



Cobalticyanide, Co2( NH8)ioCye+Co2Cyu-(-30H2 



Platino-chloride, Co2(NH3)ioCls4-2PtCl,+50H2 



Auro-chloride, Co2(NH3)j„Cl,+2AuCl3-|-20H2 



Hydrargo-chloride, Co2(NH3),„CI,+ GHoCl^-h40H2 



Sulphato-hydrargo-chloride,* Co2(NHg)^(,(SOJoCL^-)-2HgCl2 



Sulphato-chloro-platiuate §, y, Co.^(NHg)^^{SO^).fi\.^-\-FtCl^ 



Sulphato-chloro-aurate /3, y, Co.^(N'H.^)^Q{SO^).fi\^-\-'i:OB.2 



Oxalo-chlorplatinate, Co2(NH3)io(C20J2C1.3+PtCl^ 



Cerous double sulphate Co",(NH3)i„(SOJ3+SCeSO,-j-OH2 



(Wing), 



Ceric double sulphate (Wing), Co2(NH3)io(SOj3+Ce2(SOj3-f OH^ 



Chloro-nitro-platino-chloride,* Co2(NH3)jo(N03)2Cl,+2PtCl, 

 Chloro-nitro-hydrargo-chloride,*Co2(NH3)io(N03)3Cl3-f3HgCl2. 



"With the data given above before us, we may now compare the 

 purpureo- and roseo- series more advantageously than has hitherto 

 been possible. Genth and I at an early period in our investigation 

 recognized the distinction between these two classes of salts, — a dis- 

 tinction which has been admitted by some chemists, strongly supported 

 by Mills t find F. Rose, and summarily rejected by Blomstraud J and 

 others. I shall omit from the discussion those salts which in the 

 present' state of our knowledge might be classed with either series. 

 As a basis for the distinction which I uphold, I present the following 

 facts : — 



1. Chloride of purpureocobalt, Co2(NH3)j(,Clg, cannot be converted 



into chloride of roseocobalt, Co2(NH3),oCl,;-l-20H25 by recrystal- 

 lization from water. In other words, it does not unite directly 

 with water to form a hydrate, the combination always taking 

 place indirectly, as, for instance, when chloride of purpureocobalt 

 is dissolved in ammonia water, and the solution poured into 

 strong cold chlorhydric acid. The same argument applies in 

 the case of the nitrate of purpureocobalt, which behaves in a 

 precisely similar manner. Chemistry presents, so far as I have 

 been able to discover, no single case in which similar relations 

 exist between a salt and its hydrate. 



2. Chloride of roseocobalt, in either concentrated or dilute solution, 



loses two atoms of water, and is converted into chloride of pur- 



* Krok, loc. cit. 



t L. & E. Phil. Mag. (4) xxxv. 245. 



t Chemie der Jetztzeit. p. 294, note. 



