DISCUSSION OF EVIDENCE. 195 



In the early days of the theory of electrolytic dissociation it was, 

 however, pointed out that we have a fairly satisfactory explanation 

 of why the simple gas laws do not hold for concentrated gases, this 

 being expressed in the equation of Van der Waals; while no analogous 

 explanation was offered in the case of solutions. That this point was 

 well taken is obvious. A theory of solution, to be of the greatest value, 

 must be applicable to all solutions, regardless of the nature of the sub- 

 stance, regardless of the nature of the solvent, and regardless of the 

 concentration of the solution. 



The explanation of these apparent exceptions to the theory of elec- 

 trolytic dissociation presented by concentrated solutions has been fur- 

 nished by the solvate theory. We now know that, for solutions in 

 general, a part of the solvent is combined with the dissolved substance. 

 While the amount of the solvent combined with any one ion is greater 

 the more dilute the solution, at least up to a certain point, the total 

 amount of the solvent in combination with the dissolved substance is 

 greater the more concentrated the solution. 



That the amount of combined solvent may become very great, even 

 relative to the total amount of solvent present, can be seen from the 

 following facts: In a normal solution of calcium chloride about two- 

 fifths of the total water present is combined with the dissolved sub- 

 stance. In a three-normal solution of calcium chloride about five- 

 sevenths of the total water is combined. 



In the case of a normal solution of aluminium chloride in water, 

 about five-eighths of the water present is combined with the dissolved 

 substance, while in a two-normal solution about five-sixths of the water 

 present is in a state of combination. 



What we suppose to be a normal solution of calcium chloride is, there- 

 fore, more than 1^ tunes normal, while what we suppose to be a three- 

 normal solution is in reality more than eight times normal. In the 

 case of aluminium chloride, what we suppose to be a normal solution 

 is more than twice normal, while what we prepare as a twice normal 

 solution is about twelve times normal. 



These few facts, taken from thousands of a similar character, show 

 that even fairly concentrated solutions are much more concentrated 

 than we would suppose from the method of their preparation; while 

 very concentrated solutions are many times more concentrated than, 

 without the facts of solvation, we should be led to expect. 



The general conclusion is that even fairly concentrated solutions 

 are much stronger than if no solvation occurred, and are much more 

 concentrated than we are accustomed to consider from the amount of 

 substance added to a given volume of the solution more or less of the 

 water present being in combination and only the remainder playing 

 the role of solvent. Without the theory of solvation, we have hitherto 

 regarded all of the water present as acting as solvent. 



