320 MR. W. S. TUCKER ON HEATS OF 



remembered that only the final specific heat of the solution need be known in order 

 to measure the heat generated. 



This process of largely diluting a solution, i.e., in all cases using a larger bulk of 

 solvent than solution, has been employed also by BERTHELOT,* STEIN WEHR,t and 

 BISHOP.} 



Very few experimenters quote results sufficiently numerous to establish any 

 relation between heat of dilution and concentration. THOMSEN, from results on 

 solutions of nitric acid and sulphuric acid, deduces a hyperbolic relation between the 

 total heat of dilution and the final concentration N in molecules of water per 



N 

 molecule of solute. It is of the form Q = ^ - where a and It are arbitrary 



constants. The equations admit of no simple interpretation. 



For hydrochloric acid solutions, lie employs the different type of equation 



THOMSEN obtained a large number of readings for sodium hydroxide solutions. At 

 low concentrations the heat of dilution changes sign, and no attempt was made to 

 give a relation between Q and N. 



Acetic acid also changes the sign of its heat of dilution. It is negative for strong 

 solutions and positive for weak ones. A great number of results were published by 

 THOMSEN for many salts, but not sufficient in any one case for the purpose of 

 deducing a Q and N relation. 



RuMELIN has more recently found heats of dilution for phosphoric acid solutions, 

 but only for four concentrations. LEMOJNE|| also examined lithium chloride 

 solutions, but quoted results in which no high order of accuracy was suggested. 

 These methods differ from those previously quoted, for here the diluting was done in 

 stages. 



Summing up all the results and the conclusions derived from them by the 

 various authors, there seems to be no simple law which can be applied to all 

 satisfactorily. 



The author in previous work with concentrated solutions^ has obtained evidence 

 in certain cases of those solutions being simpler in character than weaker ones. The 

 present paper deals almost entirely with the thermal effects in what may be called 

 concentrated solutions, and a sufficient number of observations are taken to get a 

 good concentration relation with heat of dilution. Heats of dilution were found for 



* ' Annales de Chimie et de Physique,' vol. IV., p. 468, 1875. 



t ' Zeitschr. fur Phys. Chem.,' vol. 38, p. 185, 1901. 



I ' Physical Review,' vol. 26, p. 169, 1908. 



' Zeitschr. fur Phys. Chem.,' vol. 58, p. 458, 1907. 



|| ' Comptes Rendus,' vol. 125, p. 604, 1907. 



U 'Proceedings of the Physical Society,' vol. XXV., Part II., p. 111. 



