OF ARTS AND SCIENCES. 43 



compares his results with the two formulas (old style), Co,,CljjON,^H^., 

 and Co,,CIj,O.^NjgH^g. I find that his analyses agree fairly well with 

 the formula, — 



Co,(XH3),.O.Cl,+NH,Cl. 



If we suppose that the black salt consists at least essentially of 

 Co.,(NH„)g.O.Cl^ the formation of Rose's dark green chloride of dichro- 

 cobalt is readily explained by the equation, — 



Co,(XH3),.O.Cl,+2 H CI = Co,(NH,),Cl,+OH„ 



The existence of such a double chloride as Co„(NH3)y.O.Cl^-[- 

 NH^Cl is in itself not very probable, nor is it easy to see how such a 

 salt could be dissolved in concentrated siil})huric acid, and precipitated 

 by chlorhydric acid without change. Farther investigations are re- 

 quired to determine the constitution of the salt definitively. 



Ten-eil * appears to have first shown that salts of the cobaltamines 

 are formed when powerful oxidizing agents are added to ammoniacal 

 solutions of eobaltic salts. Terrell employed hypermanganates and 

 hypochlorites ; Brauii.t the hyperoxides of lead and manganese ; 

 Mills, + iodine, bromine, and potassic dichromate ; Blomstrand, § 

 iodine and eobaltic sulphate. On repeating these processes, I find that 

 that of Mills with potassic dichromate is by far the best for preparing 

 nitrates of roseocobalt and purpureocobalt. Blomstrand's method is 

 inconvenient upon the large scale in consequence of the insolubility of 

 the sulphato-ioilide of luteocobalt, but answers well on the small scale, 

 and gives a fine lecture-table exjieriment. A good method of prepar- 

 ing the salts of luteocobalt in quantity is still wanting, as the chloride 

 and nitrate form valuable reagents in various analytical operations. 



* Zeitschrift fiir Anal Chemie, v. p. 114. t Comptes Rendus, Ixii. p. 139. 

 X Phil. Mag. (4) xxxt. p. 245. § Chemie der Jetztzelt, p. 295. 



