56 ENERGY CHANGES INVOLVED IN DILUTION OF AMALGAMS. 



Absolutely no change of temperature was noted upon withdrawing" the 

 partition in either of two apparently perfect experiments on the dilution 

 of this 3 per cent cadmium amalgam. If the clockwork stirrer caused heat 

 enough to raise the temperature 0.001 , the dilution of the cadmium amal- 

 gam could not have had a cooling effect on dilution of much more than this. 

 Therefore, it seems probable that the total internal energy-change involved 

 in the dilution of a 3 per cent cadmium amalgam by pure mercury is neg- 

 ligibly small, not over 1.0 joule per gram atom; and it is further probable 

 that the dilution of cadmium amalgams of lower concentrations absorb even 

 less heat. 



Before accepting these results, a determination on pure mercury and on 

 each amalgam was made by another method. The clockwork was dispensed 

 with, and a second thermometer inserted so that one thermometer was im- 

 mersed in each of the liquids to be mixed. A hand stirrer whose shaft was 

 incased in a long glass tube projected into the calorimeter. The other feat- 

 ures of the process remained unchanged. After a long time at constant tem- 

 perature the partition was pulled out and hand stirring begun. As expected, 

 the vertical motion of a small circle of glass rod was far less satisfactory than 

 the automatic paddle which it replaced ; the rate of mixing, as inferred from 

 the movements of the thermometers, was slow, and the clumsy stirring was 

 attended by the evolution of much heat. The superposition of this effect 

 upon the true heat of dilution gave rise to ill-defined results. None of these, 

 however, threw doubt on the measurements obtained by the first method ; 

 hence the extremely small heat effect in the dilution of cadmium amalgams 

 was confirmed. 



It may here be stated that besides these calorimetric experiments, others 

 were instituted in order to determine the change of heat capacity of a metallic 

 system during amalgamation. 69 The heat capacity of both zinc and cad- 

 mium amalgams were studied, and were found to be slightly, but only 

 slightly, greater than some of the heat capacities of the mercury and other 

 metal before mixing. The difference was so slight that it is safe to assume 

 that the further dilution of either amalgam involves no appreciable change 

 of heat capacity. Hence these experiments need not be described in detail 

 here ; they will be recounted at length in another place. 



59 Richards, Henderson and Forbes, Proc. Am. Acad., 41, 8 (1905)- 



