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To the Editors of the Philosophical Magazine. 



ttFNTT itmfn The University, Birmingham. 



brENTLEMEN — ^ September, 1917. 



I THANK you for your courtesy in allowing me to reply 

 to Dr. Snorter's criticism of my paper. 

 Dr. Shorter seems to imply that I attempted to give a 

 rigid mathematical deduction of Raoult's law from my 

 general theory, whereas all I did was to indicate certain 

 conditions under which the law should hold good. These 

 conditions were explicitly stated as being that the addition 

 of the solute shall cause no change in the molecular volume 

 of the solvent (p. 433), and that the solution shall have no 

 heat of dilution (p. 437). Dr. Shorter overlooks these limi- 

 tations which I was careful to impose, and devotes undue 

 attention to the obviously extreme and indefensible numerical 

 illustration given on p. 434. I stated in the paper that this 

 illustration was extreme: unfortunately it was too extreme to 

 stand the general application which Dr. Shorter gives to it. 



The trend of Dr. Shorter's criticism and development of my 

 theory is scarcely valid since at the outset of his argument 

 he deliberately omits as of no account the heat of dilution, 

 which I myself was at pains to include, knowing that in 

 many cases it is by no means negligible. This omission of 

 Dr. Shorter's accounts for some ef his misunderstandings 

 of my paper. Had Dr. Shorter considered it more fully he 

 would have discovered that the heat of dilution is actually 

 a measure of the self-same vital factor which he says I have 

 omitted, viz. the effect on the \apour pressure of a change in 

 the intermolecular forces acting on the solvent molecules. 

 As is well known, the Dieterici work factor A of my paper is 

 determined almost entirely by the magnitude of these forces, 

 so that the heat of dilution, which is equal to the change which 

 A undergoes when the solution is formed (pp. 435-6 et seq.), 

 is also determined by the change in the intermolecular forces 

 caused by the addition of the solute. Under these circum- 

 stances Dr. Shorter is scarcely entitled to state categorically 

 that the theory breaks down because of the supposed omission 

 to consider the effect on the vapour pressure of changes in 

 the intrinsic pressure. The omission is in Dr. Shorter's 

 development of my general theory, and not in mine. 



The general expression for the lowering in the vapour 

 pressure to which my treatment leads is 



