RICHARDS. 



CHANGING HEAT CAPACITY. 



297 



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 Thomsen'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 24.36 ; and accordingly 

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

 be raised by one and one-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 that a complete recalculation of all heats of 

 reaction would be demanded if the standard of atomic weights were changed 

 to O = 15.879. 



