﻿Constitution of Aqueous Solutions. 15 



values of ar from specific heats, and of r from densities, 

 stand as follow for the chief positive ions : — 



H. Na. K. NH 4 . Mg. Ca. Sr. Ba. Pb. 



ar 23 31 40 34 41 40 44 44 21 



lOOr 183 196 207 12'J 238 235 245 243 217 



Although the values of ar are not in a strictly constant ratio 

 to those of t, there is a close enough correspondence between 

 the two sets to show that the theory advanced for the com- 

 plicated specific heat of solutions is in substantial agreement 

 with the facts and theory of the contraction of volume on 

 solution. 



Concerning the coefficient be for different compounds I 

 have noticed that it shows a remarkable rough proportionality 

 to the square of the heat of formation of the compound from 

 its elements. If H is the heat of formation of a gramme 

 equivalent in kilocalories, 



be = 0'01 1 R 2 , approximately, . . . (19) 



as the following table shows. 



Table IV. 



NaCl. NaBr. NaT. NaNO s . Na.SO,. NaOH. .KCl. KBr. EI. 



H 98 86 69 111 164 102 104 95 80 



beoale.... 96 74 48 123 269 104 108 90 64 



be 99 56 51 124 125 122 91 36 43 



K 2 S0 4 . NH 4 C1. MgCl 2 . CaCl. SrCl. BaCl. MgS0 4 . Pb(XO a \,. 



H 172 76 75 85 92 97 151 53 



be calc... 295 58 56 72 85 94 228 23 



be 104 57 55 64 79 112 105 43 



The calculated values of be for the three sulphates are about 

 double the actual values. The bromides are exceptional, and 

 the calculated values for K compounds are larger than the 

 calculated for the Na compounds, while the relation of the 

 actual values is the reverse. Nevertheless, although other 

 physical properties of the ions seem to influence the values 

 of be, the chief phenomenon is the connexion of be with the 

 square of the heat of formation. The following is a brief 

 theoretical account of the reason for such a relation. In 

 Section 2 we treated the positive and negative ions as too far 

 apart to affect one another's action in unmaking and making 

 (H 2 0) 3 . We considered only the field of electric force at the 

 surface of an ion as an isolated unit. But there is another 

 type of electrical action, namely that of a positive and a 



