OF ARTS AN- 1) SCIENCES. 35 



salt, Co2(XII.,)^(NO^,)^A<.f._, ; it also gives, though soincwli it slii-iizi-hly, 

 the characteristic reactions of salts #f luteocobalt. Tiir analyst's and 

 reactions leave no iloubt as to the true constitution of the salt. Its 

 relations to the other bodies metauieric with it may be s-een fioni the 

 expression, — 



lCo,(\II,),, nCo,(NH3),(NO,),V, = 4 Co,(NII,)„(NO,)«. 

 It has the same molecular weight as the octamin salt : — 



In the metameric series to which I have directed attention, at least 

 two other members are theoretically possible. Thus we shoulil cer- 

 tainly expect the reactions and products indicated ijy the eipia- 

 tions : — 



3.Co,(NH3),o(NO,),Cl,+2.Co,(NO,)„Na, = \ Co.^{^ll,),,U 

 |Co,(NO,),J,+12NaCl. 



3.Co,(NH3)3(NO,),Cl,+Co,(NO,)„Na„ = \ Co,{^U,),(NO,\U 

 |Co2(N02)„f+6NaCI. 



The first or xanthocobalt salt would be empirically, 5.Co2(X.Il,)g 

 (XOo)^, v.'hile the second or croceocobalt salt would be 4.Co.,(NH3)g 

 (N02)g. I have more than once been fully confident that I had ob- 

 tained both these salts ; but in the final revision of my work I did not 

 succeed in obtaining either for analysis, and their existence must 

 therefore, for the present, remain doubtful. The difficulty in pi-epar- 

 ing the salts of the Co2(N02)]2 series depends mainly upon the fact 

 that it is iiidispensable to avoid an excess of sodic nitrite in preparing 

 the solution of Co2(N02),2Nag in that salt, as the sodic nitrite acts 

 readily on the new salts formed. The jwssible existence of the aidiy- 

 drous xanthocobalt salt of the Co2(N02),2 series is, however, shown by 

 the existence of the compound 



lCo2(NIL)„(NO2)2|3lCo2(NO2),2^,+0OIl2, 



which I have described with the salts of purpureocobalt, but which, as 

 already stated, belongs, as its reactions show, to the xanthocobalt sei-ies. 

 The metameric compounds, the existence of which may be con>id- 

 ered as fully established, are as follows, denoting ammonia by A, and 

 NOg by X, for brevity : — 



