356 TRANSACTIONS OF SECTION B. 



salt that is truly abnormal, the theoretical result is to be expected. Suppose 

 that the ions do behave normally in the ionisation, then they must also act with 

 normal active mass with reference to the solid, with which they may be regarded 

 as in direct equilibrium according to the closed scheme referred to above. A 

 change, then, in the concentration of any one of the ions, brought about by the 

 addition of a foreign salt with that ion, will necessarily bring about the change 

 in solubility of the salt calculated from the mass-action law, so far at least as 

 experiment can tell us, for any variation from theory is caused by the change in 

 the nature of the solvent due to the addition of the foreign substance. Wo 

 ought, then, on the assumption that the ions behave normally, to expect that the 

 principle of the constant solubility product would yield results of the same 

 degree of accuracy in dilute solutions whether the electrolytes considered were 

 normal or abnormal. This, as I have said, is actually the case. 



To put the whole matter briefly, in the equilibrium between electrolytes agree- 

 ment will be obtained between theory and experiment whether we use the mass- 

 action law, or an empirical law such as van't Hoff's dilution formula, provided 

 only that we attribute the abnormality to the non-ionised portion of the electro- 

 lyte. Thus we can deduce the ordinary formula? for hydrolysis or for isohydric 

 solutions as readily for abnormal as for normal electrolytes, and find the most 

 satisfactory agreement with experiment in both cases. 



By this one simple assumption, then, for which I have offered some direct 

 justification, it is possible to find a basis for calculation with abnormal electro- 

 lytes. The problem of why certain electrolytes should be normal and others 

 abnormal is, of course, in no way touched by this assumption. That is a matter 

 for further investigation and research. 



Another great desideratum of the theory of solutions is to find a general 

 basis for the calculation of hydrates. The present position of the theory of 

 hydrates in solution may perhaps most aptly be compared with the theory of 

 electrolytic dissociation for solvents other than water. That hydrates exist in 

 some aqueous solutions is undoubted, but no general rule or method exists for 

 determining what the hydrates are and in what proportions they exist. Similarly 

 the theory of electrolytic dissociation applied to other than aqueous solutions 

 affords no general means of determining what the ions are and how great is the 

 degree of ionisation. It is only for aqueous solutions that Arrhenius was able to 

 give a practically realisable definition of degree of ionisation, and it is on this 

 definition that the whole effective work on aqueous electrolytes is based; and 

 until some general practically applicable principle of a similar character is 

 attained for hydrates, the work done on that subject, however interesting and 

 important it may be in itself, must necessarily be of an isolated character. 



Arrhenius did not originate the doctrine of electrolytic dissociation or free 

 ions : that was enunciated in 1857 by Clausius, and remained relatively barren. 

 What he did was to introduce measurable quantities into the doctrine, and to 

 show its simple quantitative applicability to aqueous solutions ; immediately it 

 became fertile. And as soon as a simple quantitative principle is developed for 

 hydrates in solution, that doctrine will become fertile also. 



It is surely now time that all the irrelevant and intemperate things that have 

 been said and written by supporters of the osmotic pressure and electrolytic dis- 

 sociation theories on the one hand, and by those of the hydrate theory on the 

 other, should be forgotten. Far from being irreconcilable, the theories are com- 

 plementary, and workers may, each according to his proclivity, pursue a useful 

 course in following either. One type of mind finds satisfaction in using a handy 

 tool to obtain practical results ; another delights only in probing the ultimate 

 nature of the material with which he works. For the progress of science both 

 types are necessary — the man who determines exact atomic weights as well as 

 the man who speculates upon the nature of the atoms. That the lack of know- 

 ledge as to what the exact nature and mechanism of osmotic pressure is, should 

 prevent accurate experimental work being done on it, or interfere with its use 

 in theoretical reasoning, is equally ridiculous with the proposition that because 

 in the theory of osmotic pressure we have a good quantitative tool for the inves- 

 tigation of solutions, therefore we should abandon altogether the problem of its 

 nature. 



The fundamental ideas of a science are the gift to that science of the few 



