80 HYDRATES IN AQUEOUS SOLUTION. 



Nickel chloride shows a minimum in the molecular lowering of the freezing- 

 point in the neighborhood of 0.5 normal. The nitrate of nickel shows the 

 freezing-point minimum at about the same concentration. The sulphate 

 of nickel, like the sulphate of manganese, does not show the freezing-point 

 minimum until a much greater concentration is reached than that at which 

 it appeared with the chloride and nitrate. The positions of the minima 

 in the case of the three salts of nickel can be seen at once by referring to 

 fig. 34. This also shows the actual values of the molecular lowerings 

 produced by the three salts. The chloride gives a molecular lowering of 

 6.12 at 0.743 normal; the nitrate at this concentration giving a molecular 

 lowering of only about 5.6. The most concentrated solution of the nitrate 

 investigated 1.522 normal gave, however, a molecular lowering as great 

 as 7.15. 



The molecular lowering of nickel sulphate, in addition to showing a 

 minimum, presents another point of special interest. The molecular lower- 

 ing produced by nickel sulphate is very small, and in the most concen- 

 trated solutions studied is less than the constant for water. This means 

 that in such solutions the nickel sulphate is polymerized, and to an extent 

 that more than overcomes any electrolytic dissociation that may have taken 

 place. Consequently, the molecular lowering is less than would be produced 

 by a completely undissociated, non-polymerized substance. The molecular 

 conductivities of all three of the nickel compounds increase regularly with 

 the dilution, from the most concentrated to the most dilute solution that 

 was employed. This is seen from the results, and is represented graphi- 

 cally in fig. 35. 



The refractivity data for the three salts of nickel are given. The index of 

 refraction in each case increases regularly with the dilution, and when the 

 index of refraction is plotted as one ordinate and the concentration as 

 the other, the resulting curve is practically a straight line for all three 

 compounds (see fig. 36). 



SALTS OF COBALT. 



The data for the three compounds of cobalt that were studied are given, 

 and the results are plotted as curves, figs. 37 to 39. 



COBALT CHLORIDE. 



Only a very small number of the results for cobalt chloride had been 

 obtained by Jones and Get man.* This applies also to the freezing-point 

 lowerings, since only those produced by dilute solutions had been measured. 

 The same holds for the conductivity measurements, and all of the specific 



*Amer. Chem. Journ., 31, 322 (1904). 



