RESULTS CONCERNING HEAT OF DILUTION. 



55 



Cooling Effect on Diluting Zinc Amalgam. 



In the first case the stirrer probably ceased to revolve after a few revolu- 

 tions ; in the second case it worked efficiently. The mean fall of temperature 

 in this cooling effect is 0.022 ; corrected for the heat of stirring it becomes 

 0.023 . 



The total energy change of dilution is equal to the product of the heat 

 capacity and the temperature increment, 0.023 . The heat capacity is found 

 as follows : 



Heat capacity, 

 in mayers. 



2,300 grams of mercury 317 



2,300 grams of amalgam M 320 



130 grams of iron 60 



5 grams of grease and cement (estimated) 16 



Thermometer (estimated) 13 



Total heat capacity 720 



Therefore the energy-change was 720 X 0.023 = 16.6 joules. 



The 2,300 grams of amalgam contained 2 3 X 0.0091 mo j s Q f z j nc 



65.4 

 Hence the total energy-change involved in the same dilution of a gram- 

 atom of zinc is : 



_ 16.6 X ^ = 52 joules. 



2300 X 0.0091 



The further dilution of a zinc amalgam containing less than 1 per cent of 

 zinc thus causes a very appreciable cooling effect. 



The cadmium used to make amalgams for the investigation of heats of 

 dilution was the commercial " pure " article, but of course its purity was not 

 above suspicion. Inasmuch as the dilution of the small amount of impurity 

 which it might contain could not cause an appreciable heat effect, its use 

 was justifiable for these measurements. Even 2 per cent of zinc could cause 

 at the most a temperature change of only 0.001 . 



88 This value was found in a special series of determinations to be described else- 

 where. 





 LiklBRARYJaBi 



