656 EEPOKT — 1887. 



The author further shows that if we take two salts, say chlorides, in one of 

 which the heat of combination is greater than in the other, we find that the differ- 

 ence appears in the increased heat of solution of the latter, modified by the difference 

 of affinities of the metals for ; as for example : — 



Difference of Heats of Combination Difference of Heats of Solution 



[KSCP] -[Li-,C1=] =23600 [Li%C12]-[K^CP] = 25760 



[Li-,0,Aq]-[K-,0,Aq] 1900 



25560 25760 



Also in comparing chlorides with bromides it is found that the excess of heat 

 of combination of the two salts over that of their respective acids varies inversely 

 as the heat of sokition of the two salts ; thus — 



Difference of Heats of Combination Difference of Heats of Sohition 



[Ba,Cl=]-[H-,Cr-,Aq] 116110 [Ba,Br=] [Ba.Cl-] 2910 



[Ba,r.r-] - [H-,Br-,Aq] 113200 



2910 2910 



Finally, by taking pairs of any salts every consideration but heats of combinatiou 

 on the one side and heats of solution on the other can be eliminated ; and it is evi- 

 dent the heats of solntion just vary inversely with the heats of combination ; as, 

 for instance — 



Difference of Heats of Combination Difference of Heats of Solution 



[Mg,S,0<]-[JIo-,Cl-] 151300 -15640 



[Zn,S,0^] -[Zn,Cl=] 132860 + 2800 



+ 18440 -18440 



In considering how the absolute amount of heat of solution arises, the author 

 shows that it seems to be due to a balancing of affinities among the constituent 

 elements, and that when, for instance, [M,Cr-] — {[M,OAq] + Neutr.} is equal to 

 [IP,G1-, Aq] — [H'-,0] there is no heat of solution, and the salt is insoluble. Several 

 examples of chlorides and other salts are given. It would appear also that when 

 an oxide is neutralised by an acid solution and the salt remains in solution the 

 operation is not complete; either the oxide and the acid are not completely decom- 

 posed when we have positive heat of solution, or, on the other hand, the salt and 

 water resulting from the double decomposition are not completely formed when we 

 have negative heat of solution. When both parts are complete we have insolubility. 

 Several examples are given to show this. It is also pointed out in this paper that 

 in the case of the sulpbates when the heat of combination of the oxide with sul- 

 phuric anhydride is equal to the heat of combination of the metal with sulphur 

 there is no solubility, but when the former is less than the latter, solution imme- 

 diately appears ; thus — 



[SrO.SO^] =99220 [Sr,S] =99220 . . . salt insoluble 

 [CaO.SO^] =84200 [Ca,S] =92000 . . . salt slightly soluble 

 [JlgO.SO^] = 53070 [Mg,S] = 79000 . . . .salt very soluble 



The author finally draws attention to the fact that solution is probably a 

 periodic function of tiie elements. 



5. On the Thermal Plienomenn, of Neutralisation and their bearing on the 

 Nature of Solution.^ Bij W. W. J. Xicol, M.A., D.Sc, F.R.S.E. 



The author examines the thermal equation 



M,R, Aq - M',R,Aq = M,Il', Aq - M',E,',Aq, 

 expressing the general relationship existing between the heats of formation of 



' Chemical ^'c lis, 1887. 



