68 ENERGY CHANGES INVOLVED IN DILUTION OF AMALGAMS. 



SUMMARY. 



The main points of the present research may be summarized as follows : 



i. The potentials between various liquid amalgams were investigated 



at 23 C. Extraordinary precautions were taken against experimental errors, 



and the misuse of absolute units. The results are reliable within 0.00001 volt. 



2. Zinc amalgams gave potentials lower than those calculated from the 

 gas law ; and cadmium amalgams gave potentials higher than those calcu- 

 lated from the gas law. The regular and symmetrical curves thus con- 

 structed show the close approach of these deviations to zero as the dilution is 

 increased. 



3. In the most dilute amalgams investigated the closest approach to the 

 gas law ever noted in the study of solutions was found. 



4. The temperature-coefficient of the potential of the cadmium amalgam 

 cell was shown to be almost exactly identical with the tension increments of 

 a perfect gas, and that of the concentrated zinc amalgam cell about 3 per 

 cent greater. 



5. The heats of dilution of the amalgams were measured directly by a 

 new and accurate calorimetric process, and the results, taken in connection 

 with the temperature-coefficient of the potential, afford a striking verification 

 of the Helmholtz equation. 



6. On the other hand, the formula of Cady is found to be inadequate to 

 explain exactly the deviations from the gas law. In no case does the cor- 

 rection indicated by this formula account for more than a small part of the 

 deviations of potential. Therefore, Cady's equation is incomplete. The 

 uncertainty is shown to consist probably in the method of evaluating the 

 volumes to be used in the calculation. 



7. The densities of liquid zinc and cadmium amalgams were carefully 

 measured, and the extent of the contraction which takes place on mixing was 

 computed in each case. 



8. The constitution of zinc and cadmium amalgams is discussed from 

 chemical and kinetic standpoints. The irregularities of zinc cells are traced 

 primarily to partial polymerization, those of cadmium cells mainly to abnor- 

 mal osmotic pressures. The situation is shown to be too complex for the 

 complete quantitative treatment of these different tendencies until further 

 results upon osmotic pressure have been obtained. 



The Chemical Laboratory of Harvard College, 

 October, 1903, to June, 1906. 



