344 ME. W. S. TUCKEE ON HEATS OF 



It is evident that although the thermal capacity of the solution may change 

 rapidly with temperature the heat of dilution suffers very little change. 



(9) EXAMINATION OF THOMSEN'S KESUI/TS.* 



In most of THOMSEN'S experiments the ranges of concentration are not such as 

 make the results comparable with those quoted above. 



There are, however, a few substances such as sulphuric acid, nitric acid, and 

 hydrobromic acid, other than the above substances, in which a series of results are 

 obtained at high concentrations. 



THOMSEN finds a hyperbolic relation between total heats of dilution and con- 

 centration. With the first two acids named this relation is of the form 



Q = 



where a and b are constants and N number of molecules of water to one molecule 

 of acid.. 



The heat of dilution at any given concentration then becomes 



ab 



This form of relation cannot be applied to other substances such as hydrochloric 

 acid and sodium hydroxide. In the latter case the heat of dilution changes sign 

 when the solution is very dilute. The varying thermal changes observed at higher 

 dilutions for several substances, suggests that these solutions are more complex than 

 the stronger ones. 



^ Moreover experimental difficulties prevent the measurement of these quantities 

 with sufficient accuracy to warrant their use for deriving a general equation to 

 represent the thermal changes for all concentrations. 



An attempt is therefore made to analyse the results for stronger solutions only, and 

 it will be found that the relation Q = a log e N + Z>N + c holds well under these 

 conditions. 



(l) Sulphuric Acid. 

 From THOMSEN'S values of Q for N == I, N = 2 and N = 5 respectively, the equation 



IS 



Q = 4666 log, N-196 N + 6595. 

 ' Thermoehemische Untersuchungen." 



