400 



On the Expansion of Salt-Solutions. 



At low temperatures, 20°-30° and 30°-40, the behaviour 

 of all the salts is the same ; they all expand more than is due 

 to the 100 H 2 contained in the solutions, and as the strength 

 increases the amount of expansion increases. Ascending the 

 temperature-scale, we come to points at which the expansion 

 per 10° is the same as that of water in the case of NaCl and 

 KC1, as pointed out above. Then at high temperatures NaCl and 

 KC1 solutions expand less the more concentrated the solution. 

 With NaN0 3 and KN0 3 this not the case ; though even here 

 there is a close agreement observable in the expansion of the 

 stronger solutions between 90°-100°, as compared with the 

 marked difference between 20° and 30°. 



The different behaviour of these four salts, which separates 

 them into two classes, NaCl and KC1, as compared with 

 NaN0 3 and KN"0 3 , lies entirely in the effect of temperature 

 on their solubility. According to Mulder*, the' solubility at 

 different temperatures is as follows : — 





20°. 



60°. 



100°. 



NaOl 



36-0 

 111 



373 

 11-5 



39-8 

 123 



Molecules 



KOI 



34-7 



8-4 



45-5 

 110 



56-6 

 137 



Molecules 



NaN0 3 



87-5 

 18-5 



122-0 

 25-9 



180-0 

 38-1 



Molecules 



KN0 3 



31-2 

 5-0 



1110 

 198 



247-0 

 440 



Molecules 



Thus, while NaCl increases in solubility between 20° and 

 100° in the ratio 1 : I'll, KC1 increases as 1 : 1*16, NaN0 3 

 1 : 2-06, KN0 3 1 : 7*92. It thus follows that a solution of 

 NaCl or KC1 is almost as nearly saturated at 100° as at 20° ; 

 while NaN0 3 solutions become on heating, so to speak, rapidly 

 more dilute ; and this is even more markedly the case with 

 KN0 3 solutions. 



It is therefore not to be expected that these salts should all 

 behave in precisely the same way ; but they do resemble one 

 another in this, that the volume-line is straighter than that of 

 water when merely equal volumes are considered. When mo- 

 lecular volumes are compared this similarity disappears ; and it 

 remains now to ascertain why in some cases the expansion of a 

 solution is actually less than that of the water it contains ; 



* Bijdragen tot de Geschiedenis van het scheikundig gebonden Water 

 (Rotterdam, 1864). 



