>84 



NA TURB 



[September 2, 1909 



of non-electrolytes, if only a small amount of the solvent 

 be withdrawn by combination with the solute, the altera- 

 tions may be regarded as almost entirely due to the 

 " mechanical " interference of the substance introduced, 

 opportunity being given for the simpler, more attractive 

 molecules of the solvent to exist in greater proportion 

 because of the diminution of the chance of reuniting which 

 is conditioned by the presence of practically inert molecules 

 of another kind ; if a more or less considerable amount of 

 the solvent become associated with the solute the conditions 

 become more complex, but similar considerations apply. 

 From such a point of view a liquid is rendered more active 

 by the addition of any soluble substance. Its vapour pres- 

 sure is therefore diminished; the internal "osmotic" 

 stresses are raised ; its freezing-point is lowered. 



Although it is generally admitted that water is not a 

 uniform substance but a mixture of units of different 

 degrees of molecular complexity, the degree of complexity 

 and the variety of forms is probably underestimated and 

 little or no attention has been paid to the extent to which 

 alterations produced by dissolving substances in it may be 

 the outcome and expression of changes in the water itself. 

 The attempt to extend the " laws " which are applicable to 

 the gaseous state to liquids has led us away from the 

 truth by narrowing our conceptions. If the contention be 

 justifiable that the alterations attending dissolution are 

 very largely alterations in the character of the water, atten- 

 tion has been directed of late far too exclusively to the 

 dissolved substance. 



To give emphasis to the view, I have advocated ' the 

 restriction of the name laaXer to the liquid mixture and 

 have proposed that the simple molecule represented by the 

 symbol OH. bo termed Hydrone. The generalised expres- 

 sion 



(HoO)^ =: .vOH., 



may be considered to be representative of the state of 

 equilibrium in water — that is to say, of the character of 

 the change which it undergoes when the conditions are 

 varied either physically or by dissolving substances in it — 

 in the sense that it pictures the resolution of the more 

 complex into simpler forms and vice versa, without taking 

 into account the variety of molecular forms (.v, x\ x' , . . .) 

 which are present. 



It is probable that the agreement between " theory " and 

 practice on which reliance has been placed, particularly in 

 interpreting osmotic phenomena, is more often than not 

 only apparent and fictitious, and but the outcome of 

 counterbalancing effects which have been left out of 

 account. We are too prone to believe in constants ; we 

 need to remember that, except perhaps in the case of the 

 perfectly gaseous state, constants are dependent variables. 

 To take an example, it is assumed that glucose and cane 

 sugar produce like osmotic effects when used in equivalent 

 proportions ; indeed, it has been the fashion of late years 

 to treat non-electrolytes as harmless neutrals : in point of 

 fact they differ as much in behaviour as do electrolytes, 

 and such a conclusion must be viewed with the gravest 

 suspicion. Recently Dr. Eyre and I have been able to show 

 that three substances so similar as methylic, ethylic and 

 propylic alcohols produce effects in precipitating salts from 

 solution which are markedly different, propylic alcohol being 

 the most effective although the least soluble. It is clear 

 that the precipitant does not act mainly by itself combining 

 with and withdrawing water in direct competition with the 

 salt ; but that it promotes the dissociation of water by the 

 mechanical interposition of its molecules ; in fact, that the 

 " dehydrating " powers of the water are enhanced owing 

 to the increase in the proportion of simple molecules in the 

 liquid conditioned by the presence of the solute. 



The same effect is obvious when the reduction of the 

 electric conductivity of a salt, such as potassium chloride, 

 by equivalent quantities of the three alcohols is considered. 

 This amounts to about 6 per cent, in the case of methylic, 

 12 in that of ethylic, and 17 in that of propylic alcohol ; 

 the reduction effected by glucose, however, amounts to 

 about 27, and that effected by cane sugar to no less than 

 42 per cent. In these two latter cases the amount of 

 water actually withdrawn from the solution by the sugar is 

 probably considerable, and the " mechanical effect " of the 



^ Roy. Soc. Proc. 1908, 



, 80 ; Science Ptogress, January', 1909. 



NO. 2079, VOL. Si] 



solute is therefore exercised in a more concentrated solu- 

 tion — more concentrated, that is to say, than those in vihich 

 the alcohols act. If, therefore, solutions of glucose and 

 cane sugar of equivalent strength produce like osmotic 

 effects, it is because unperceived compensating factors are 

 at work in the solutions which in algebraic sum have the 

 same aggregate influence. 



To explain the effect produced by substances which give 

 rise to conducting solutions when dissolved in water (acids, 

 alkalies, and salts), it is necessary to consider the special 

 nature of the changes which may be supposed to attend 

 dissolution in such cases. Why, it may be asked, is an 

 aqueous solution of hydrogen chloride a conductor, whilst 

 that of alcohol is a non-conductor? I believe the answer 

 to be that it is because, in the former case alone, the two 

 components of the solution hre reciprocally distributed ; that 

 it is because two correlative systems — 



H H 



HCl/ and H„0 



OH "CI 



are produced which interact under the influence of the 

 electric stress.^ In the case of alcohol no such inter- 

 change takes place. It may be that the alcohol is hydro- 

 lated to some slight extent, but the hydrol must be less 

 basic than hydronol ; probably, like ammonia, alcohol exists 

 in solution for the most part in the hvdronated state : — 

 .H /H 



H.,0< EtHO.^ EtHO=OH., 



\OH ^OH 



Hydronol. Ethanol-hydrol. Ethanol-hydrone. 



Much more must be learnt of the properties of solutions 

 before definite decisions can be arrived at with regard to 

 such delicate and refined issues. 



I would apply the interpretation here given of the nature 

 of conducting solutions generally to the explanation of all 

 cases of chemical change : in other words, I assume that 

 in all cases correlative systems are present which are 

 formed by the reciprocal distribution of the interacting sub- 

 stances. From this point of view the solvent is no mere 

 medium but an active participant in the series of inter- 

 changes of which, as a rule, only the final product is 

 noticeable. 



The solution thus offered of the complex problem dis- 

 cussed vcrv fully in mv .Address in 1885, which has ever 

 since occupied my thoughts, will, I trust, be found to bi- 

 helpful, although by no means complete in all its details. 



In effect, the doctrine makes no demand which tht* 

 chemist should not be able to grant forthwith, as it i.s 

 generally supposed that hydrols are easily formed — to giv<' 

 an example, in the case of the conversion of 

 chloral, CCl,.COH, into chloraldehydrol (chloral-hydrate), 

 CCl,.CH(OH),. The novelty of the conception lies in sup- 

 posing that the occurrence of electrolysis involves the inter- 

 action of the hydrol and its correlative and the explanation 

 which it affords of the difference between electrolytes and 

 non-electrolytes. 



It is essentially an association theory, although it involves 

 the dissociation of the interacting substances but never the 

 production of separated ions. In the case of aqueous 

 solutions the amount of the distributed substances may be 

 taken as the measure of the activity — of the degree of 

 ionisation, so-called. A wrong view prevails that the so- 

 called molecular conductivities are measures of activity : 

 they are in reality only measures of the relative activities 

 under corresponding conditions of the substances to which 

 they refer. The molecular conductivity of an acid is at a 

 maximum in its weakest solutions : presumably it is then 

 present to the maximum extent in its simplest state and 

 in the active hydrolated state ; but as a hydrolytic agent 

 its activity is at a maximum near to the opposite end of 

 the scale. In other words, the hydrolytic activities of a 

 series of acids are in the order of their molecular con- 

 ductivities in solutions of comparable strength, but mole- 

 cular-hydrolytic and molecular-electrolytic activity run in 

 opposite directions ; the maximum electrolytic conductivity 

 of an acid solution, which is manifest at a particular 



^ I would repeat the plea I put forward in 1885 that the use of the term 

 hydrochloric acid as applied to hydrogen chloride is undesirable if not un- 

 j-ustifiable ; the solution of the gas may be said to contain chtorhydric acid, 

 HCl(0H2)-r. From my point of view, oxygen is a constituent of all acids. 



