)/^ 



Zlj^^^ 



THE BEGINNINGS OF LIFE. 



47 



^^^binatioi^ .■- solution ; when heat is applied to a solution ot lime. 



soluti 



nl 



ion is 



combi 



3 



n 



f other 

 ^sical 



atioi 



such 



t 



some of it becomes precipitated j whilst, when either 

 heat or cold is applied to a solution of sodic sulphate 

 already at a temperature of '>,'^' C, some of this salt 

 separates from the state of solution i. Here, as in 

 other cases of decomposition, the molecules of the dis- 

 solved substance and of the solvent, being themselves 



quality, 

 ■^te of soIutioD; 



nuiaity to ^\ diiFerent, are difFerently afFected by the influence of the 

 ^ be reduced t same change or disturbing influence^. And we must 



suppose the amount of difference induced to be so great 



* * 



:)mation whose as to weaken or wholly destroy the affinity which had 

 ical combinat previously held them together^ so that the molecules of 

 ren^th of the i' the water under the new conditions are no longer able 

 the solvent aoc to hold asunder the molecules of the substance with 



bilitv accordiiE ^^^^^ ^^1 were previously in combination. Or a 

 , ^g^g5 similar effect may be brought about by the addition of 



^ility of comp. 



of heat 

 ssible. ^ 



a considerable quantity of a substance more soluble 

 than that which is already in solution 3. Thus^ sodic 

 chloride crystallizes from its aqueous solution on the 



icrease 

 iger po 



)f alum or ' i ^^^ Sullivan considers ('Rep. of Brit. Assoc' 1859, P- 292) that the 



|-^j|J2e out ' solubility of very many salts (like that of sodic sulphate) attains a maxi- 



' " mum at some particular temperature, above or below which it diminishes. 



1: 



think, deny 



of salt in ^^'''' 

 of sail _ ^^^jj. 



jljjt K This temperature may frequently be above ioo"C; hence the common 



m 



belief that solubility always increases with rise of temperature, because 

 temperatures higher than ioo°C are rarely resorted to. Calcic sulphate 

 (gypsuin) is less soluble in boiling than in cold water, and is quite 



decreases 

 affinity i^ ''PL 



J insoluble in water at 140° C, 



vvn,3. 



chang 



ein 



,1 



# 



^ See vol. I. pp. 98-104. 



^ Even saturated solutions of certain substances, however, will permit 

 a solution of some other salts without occasioning a precipitation of those 



ny exp 



erio^^^^^'..: originally dissolved. 



opP 







¥.■ 



of *'=.'.>' 



salt 111 



dis 



