OF ARTS AND SCIRNCRS. 45 



tho Other six by clilorine, &.c. Upon this view cliloi-idi^ of i)iir|)iirco- 

 col);ilt becomes (IONII3) = Coj 1 Cl^, and diloiidc <»f hilcoi-olcilt 

 (12XIIjj)= Co^, I Cl,j. In this manner the old theory of coii|tlft.s or 

 (•onjii<jjate ammonias may be rationalized and brought into liannoiiy 

 with modern ideas. Two strong object ions may be uri^ed a<,Minst tiio 

 tlieory here proposed. The first is that it recpiires us to eon^^ider au 

 atom of cobalt as hexatomie, while it exhibits in no other compcMunl 

 an atomieity higher than f.mr. The other objection has, I think, 

 mnch greater weight. To explain upon this view the cases of isomer- 

 ism, to which I have myself directed attention, it becomes necessary to 

 assume that there are at least three allotropic forms of col)alt. — an 

 assumption wholly unsupporced by any other and independent evi- 

 dence. On mature consideration I have therefore rejected this theory. 

 The objection which I have urged against my own view, that it re- 

 quires us to consider cobalt as hexatomie, with the atomic weiglit 59, 

 may be avoided by considering the metal as tetratomic, and regarding 

 the two atoms as united by 6, 8, 10, or 12 atoms of ammonia, so that 

 the general formula of a normal cobaltamine chloride will be — 



CI CI 



I I 



CI — Co — (nNH,,) _ Co — CI 

 I " I 



CI CI 



since n atoms of ammonia will always form a diatomic whole. The 

 other objection, that the theory obliges us to assume the existence of 

 several allotropic forms of cobalt, will, however, still remain. 



The view which T now adopt is in substance that of Blomstrand, 

 which affords, as I think, the simplest and most satisfactory explana- 

 tion of the whole series of ammonia-metallic compounds at present 

 known, and which, while not free from theoretic ditficiilties, is yet iu 

 harmony with all the facts. 



According to this view, two atoms of tetratomic cobalt are asso- 

 ciated to form a hexatomie molecule, the six units of affinity being, in 

 all the cases at present known, in combination with four or six atoms 

 of ammonia, regarded as a diatomic. Six units of affinity remain, and 

 may be incompletely saturated by other atoms of ammonia or com- 

 pletely by chlorous elements or residues. Thus, on Blomstrand's view, 

 the .chlorides of purjiureocobalt or roseocobalt and luteocobalt have 

 respectively the formulas, — 



