EVOLUTION OF COLLOIDS 135 



Here, then, is conclusive proof as to these 

 molecular affinities and valencies. The chlor- 

 ide has no measurable affinity, and separates 

 without water, the bromide and iodide have 

 specific and different affinities, and a molecular 

 valency double that of the water molecule. 



This is not an isolated case ; the majority 

 of inorganic crystalline substances show the 

 same effect, and exhibit specific variations in 

 molecular affinity and molecular valency. 

 Here are a few examples from the wealth of 

 them in the literature : — Calcium nitrate, 

 four molecules of water, 112 K ; manganous 

 sulphate, five molecules, 138 K ; nickel chlor- 

 ide, six molecules, 203 K ; magnesium sul- 

 phate, seven molecules, 241 K ; barium 

 hydrate, eight molecules, 254 K ; sodium 

 carbonate, ten molecules, 217 K ; alkaline 

 sodium phosphate, twelve molecules, 284 K. 



These examples prove both varying molecu- 

 lar valency from, substance to substance, and 

 also varying molecular affinity, and the basis 

 of proof is exactly that admitted for the 

 atomic analogues. 



Common experience proves the same thing, 

 when almost any crystalline body is dissolved 

 in water, the solution is cooled thereby. 

 The cause of the cooling is that the dissolved 

 substance produces a pressure in the solution 



