348 MR. W. S. TUCKER ON HEATS OF 



THOMSEN must have experienced great difficulty in measuring accurately such small 

 quantities of heat, and the variation of the calculated from the experimental values 

 are well within the limits of his possible experimental errors. 



The limiting concentration is in this case well within the range over which the 

 linear relation holds. Thus the heat of dilution 



dN \N 63'49/ 



The second term within the brackets has very nearly the value f and corresponds 

 2CH 3 . COOH . 3HA or CH 3 . COOH . 1'5H 2 O. 



Values ofdQ/JN are obtained from concentration 0'5H 2 O to 8H 2 0. The negative 

 values are obtained while there is excess of acid added to the critical hydrate 

 2CH 3 . COOH . 3H 2 0, and the positive values when there is excess of water. 



DUNNINGTON AND HOGGARD's RESULTS.* 



A series of determinations of heats of dilution for different strong solutions, were 

 made by the above investigators. They made saturated solutions of various salts, and 

 then added water until some whole number of molecules of water was associated with 

 each molecule of the salt. Then one or two molecules of water were further added, 

 and the heat generated or absorbed quoted. 



A solution of ammonium acetate was taken in three molecules of water. Heat was 

 generated throughout the process of dilution. The results quoted show a distinct 

 break in continuity between solutions containing from six to eight molecules of 

 water. 



Lithium chloride is the only other solution which generates heat to any extent on 

 dilution. These results have already been compared with those obtained above. 



One solution only is given with values extending over a range of concentrated 

 solutions, in which heat is absorbed. This is ammonium nitrate solution. The initial 

 and final concentrations are quoted in columns I. and II. in the subjoined table, 

 expressed in molecules of water (N) to one molecule of solution. The heat generated 

 was quoted as in column III., using the same type of relation as that previously 

 adopted for this heat. 



Values of a and 6 are thus formed for the range of solutions between N = 3 and 

 N = 12. They are 



a = -1172 I = +4877. 



* ' Amer. Chem. Journal,' vol. 22, p. 211. 



