ON SOME DOUBLE COMPOUNDS OF NICKEL AND COBALT. 20'J 



Report of the Committee, consisting of Mr. W. N. Hartley, F.R.S.E., 

 Mr. W. C. Roberts, F.R.S., and Mr. John M. Thomson, appointed 

 for the purpose of investigating some Double Compounds of Nickel 

 and Cobalt. By Mr. John M. Thomson. 



Part I. 



On attempting to form the conjugated sulphate of Nickel, Cobalt, and Po- 

 tassium, the existence of which is mentioned by Vohl (Ann. Chem. Pharm., 

 vol. lxv.), who assigns asits composition the formula NiCoK 4 (S0 4 ) 4 ,12H 2 0, 

 it was found that the several fractions of crystals deposited consecutively 

 from a solution containing molecular quantities of the simple potassic sul- 

 phates of the two metals were of different colours, and showed also to a re- 

 markable degree the property of dichroism. The operation being repeated 

 several times with a like result, it was determined to prepare a series of 

 fractions from a solution containing the two potassic sulphates 



NiK 2 (S0 4 ) a ,6H 2 and CoK 2 (S0 4 ) 2 ,6H 2 



in molecular proportions, to submit each fraction to analysis, and to examine 

 whether or not any regular replacement between the nickel and cobalt took 

 place. 



For this purpose 250 grammes of each potassic sulphate in the anhydrous 

 condition were accurately weighed, dissolved in a sufficient quantity of water,: 

 and evaporated gently over a water-bath, the temperature of the solution 

 never being allowed to rise above 80° C. The solution was thus fractionally 

 crystallized, the several fractions consecutively deposited constituting the 

 series of salts marked A i., n., in., rv., v. 



A second quantity, consisting of 250 grammes of each potassic sulphate 

 in the pure crystallized condition, having been crushed, pressed between 

 blotting-paper and finally air-dried, was dissolved in water and fractionally 

 crystallized at the same temperature as in the first instance. These fractions 

 constitute the series of salts marked Bi., n., iii.,iv., v., vi. In both these 

 cases care was taken to purify the salts before commencing the experiments. 



The crystals of the conjugated double sulphates are oblique rhombic prisms, 

 having a tendency to modification when allowed to grow to any great size. 

 The first fractions possess a greenish-grey colour when seen in the mass, 

 showing the preponderance in them of the nickel over the cobalt ; the latter 

 fractions, however, become more crimson in colour as the reverse action takes 

 place. The salts do not lose their water entirely till between 150° to 180° C, 

 and can be fused without decomposition. On heating the first fractions in 

 a crushed condition in the air-bath, the colour changes from a light grey to 

 purple, finally becoming pink when the water is entirely driven off ; if the 

 salts be heated in a porcelain or platinum capsule they fuse, the liquid mass 

 becoming of an intensely deep-blue colour, which fades on cooling, the mass 

 solidifying to the pink anhydrous salt. This deep-blue colour can be again 

 produced, however, by fusing the dried salt, and is evidently due to some 

 change not explained by loss of water. 



The following Tables give the details and results of the analyses of the two 

 series of salts marked A and P>. The replacement of the nickel and cobalt is 



1877. r 



