64 



ENERGY CHANGES INVOLVED IN DILUTION OF AMALGAMS. 



splitting up of chemical union among the atoms ; it might also be referred to 

 a less definite attraction, one similar to that causing the Joule-Thomson effect 

 in gases. In mercurial solutions this attraction would be the difference be- 

 tween two affinities, but for our purposes it can be treated as a single quan- 

 tity. Now, in the free expansion of carbonic acid from ten atmospheres to 

 normal pressure, a cooling effect of 1.4 C. occurs; if the molecular heat 

 is taken as 40 mayers, 56 joules are absorbed by each gram molecule. 

 When a gram-atom of zinc, in the calorimeter, expands from 44 to 20 atmos- 

 pheres osmotic pressure, without doing outside work, 52 joules are absorbed. 

 Clearly it would be possible to account for the cooling effect alone without 

 assuming chemical dissociation. 



In the next place, Tammann M found that zinc even in amalgams as weak 

 as 0.2 per cent lowers the freezing point of the mercury by a deficient amount, 

 not exceeding nine-tenths of the theoretical value which indicates that the 

 normal fully dissociated condition had not been attained. 



Again, Ramsay found an atomic weight of dissolved zinc even at 260 , 

 which was certainly not less than the true value (the average of three de- 

 terminations was 65.9). 



Finally, further evidence showing that zinc is more inclined to double its 

 atoms in mercurial solution than cadmium may be obtained by comparing 

 the volume changes occurring when a gram-atom of zinc or of cadmium is 

 dissolved in varying amounts of mercury. These changes are easily found 

 from the data given on page 14 as follows : 



(1) Zinc Amalgams. 



(2) Cadmium Amalgams. 



Zeit. Phys. Chem., 3, 441 (1889). 



