of Edinburgh, Session 1885-86. 783 
Compound. 
Heat of 
Formation. 
Compound. 
Heat of 
Formation. 
Difference = 
Heat of 
Solution. 
Zn,0, Aq 
82680 
Zn,S0 4 
230070 
H 2 ,SO, Aq 
210770 
h 2 ,o 
68360 
Neutr. 
28416 
316860 
- 
298430 
= 18430 
Ba,0. Aq 
158760 
Ba,S0 4 
338070 
H 2 ,S0 4 , Aq 
210770 
h 2 0 
48360 
Neutr. 
36800 
406430 
- 
406430 
0 
K 2 ,0,Aq 
164560 
k 2 ,so 4 
344640 
h 2 ,so 4 
210770 
h 2 ,o 
48360 
Neutr. 
31288 
406618 
- 
413000 
= - 6382] 
We thus see that on solution the salt and water are virtually 
though not actually decomposed, and built up again into another 
system in which all the affinities of the constituent elements take 
part. When there is no balance of affinities on either side there is 
no heat of solution, and the salt is insoluble. 'When the sum of 
the heats of formation of the salt and of the water is greater than 
the sum of the heats of formation of the oxide, the acid and of 
neutralisation, then the heat of solution of the salt is minus — that 
is, there is absorption of heat, and the temperature is lowered. 
The above conditions hold good whether the oxide is insoluble or 
not, and indeed when both oxide and salt are insoluble. 
4. On the Fructification of some Ferns from the Carboni- 
ferous Formation. By B. Kidston, F.G.S. Communi- 
cated by Dr Traquair. 
PRIVATE BUSINESS. 
The Lord Rayleigh was balloted for, and declared duly elected a 
British Honorary Fellow of the Society. 
Messrs Alphonse Milne Edwards, of the Institute of France; 
H. A. Newton, Yale College, U.S. ; l’Abbe Renard, Louvain; and 
Tobias Robert Thalen, Upsala, were balloted for, and declared duly 
elected Foreign Honorary Fellows of the Society. 
