RICHARDS. — CHANGING HEAT CAPACITY. 



297 



Factors in 

 Reaction. 



Heat Capacities of 

 MsOj+200H2O+JI'. 



Factors. 



Ni+CuSOi 



Fe+CuSO^ 



Zn+CuSO^ 



Mg+CuSOi 



Fe+NiSOi 



Zn+NiS04 



Mg+NiSOi 



Zn+FeSO^ 



Mg+FeS04 



Mg+ZnS04 



mayers. 

 14,907 



14,996 



14,996 



14,995 



14,967 



14,966 



14,966 



14,955 



14,955 



15,014 



Products. 



Loss of 



Heat 

 Capacity 



during 

 Reaction. 



mayers. 

 14,966 



14,955 



15,013 



14,889 



14,957 



15,016 



14,891 



15,015 



14,890 



14,890 



mayers. 



+ 31 

 + 41 



- 17 



+106 

 + 10 



- 50 

 + 75 



- 60 

 + 65 

 +124 



Electro- 



ffiotive 



Force. 



volts. 

 0.57 



0.69 



1.10 



1.81 



0.12 



0.53 



1.24 



0.41 



1.12 



0.71 



Electro- 

 motive 

 Energy. 



Observed 



Heat of 



Chemical 



Reaction 



«? I » 



C o j^ -ij 



K t, = .3 



kilojoules. 

 + 20 



+ 22 



- 3 

 +180 

 + 1 



- 22 

 +160 



- 22 

 +158 

 +181 



The data in this table are reduced as nearly as possible to the same 

 standards. The heat capacities and electromotive forces correspond to 

 solutions containing two hundred molecules of water to every molecule of 

 salt; the electromotive force scarcely changes with dilution. It is not 

 always easy to ascertain from Thomseu's statements the dilution corre- 

 sponding to the heat of reaction, but in every case the solutions were at 

 least as dilute as this, being sometimes of twice the dilution. Here also 

 such further dilution can cause but a negligible effect on the result. The 

 atomic weights used in Thomsen's work were unusually crude, even for 

 that day, and all his results have been recalculated to correspond to 

 more accurate values. For example, the values given by him for mag- 

 nesium correspond to the value 24. instead of 24.3G ; and accordingly 

 since magnesium itself was weighed, all his data for this element must 

 be raised by one and oue-half per cent.* The details of these and other 

 similar calculations may be omitted, since their outcome does not seri- 

 ously affect the conclusions attained. 



* In passing it may be pointed out tliat a complete recalculation of till heats of 

 reaction woiilil be deinanclftl if tlio stamlard of atomic \veiy;lit8 were changed 

 to. O = 15.879. 



