TRANSACTIONS OF SECTION B. 619 



between the two men have teen misrepresented. The author has shown else- 

 where ' how this misrepresentation has arisen. Proust was unable to furnish the 

 experimental distinction between compounds and mixtures which Berthollet 

 demanded again and again ; nor until lately has it been possible to establish one. 

 It is possible that such a one may be based on the recent work of Raoult, who has 

 shown that the melting-point of a pure compound is always lowered and its 

 boiling-point raised by the ad'dition of a small quantity of some dissimilar sub- 

 stance. But it is important to realise that a satisfactory experimental distinction 

 is still a desideratum, and that the only definition that we can give of a compound 

 to distinguish it from a mixture is a theoretical one based on the consideration of 

 molecules. 



9. The Atomic Weight of Carbon.- By Professor J. A. Wanklyn. 



Members of this Section who, like myself, a third of a century ago were at 

 that time charged with the responsibility of teaching chemistry to the students of a 

 University will have a lively recollection of the incidents attendant on the change 

 of notation at that period. The controversies of that day evolved, as will be 

 remembered, a short and easy method of arriving at the molecular weight of a 

 chemical substance, and likewise a short and easy method of finding the atomic 

 weight of an element. 



In Kekule's words, very slightly modified, these methods were as follows : — 



' Defining standard volume (or, as it was called, the standard two volumes) as 

 that vobime which is occupied by two grammes of hydrogen at a given suitable 

 temperature and pressure, we were told that, if we would know the molecular 

 weight of any chemical substance, we must ascertain how many grammes of the 

 substance were required to fill the standard volume with the vapour of the sub- 

 stance, and that that number was the molecular weight. And the atomic weight 

 of an element was to be foimd by observing what was the very least quantity of 

 that element ever entering into the standard volume tilled with a compound 

 of that element.' 



Having laid down the law much in that style, advocates of the new notation 

 forthwith proceeded to make the practical application by noting that the least 

 number of grammes of carbon ever occurring in the standard volume of any 

 carbon compound was 12 — w^o, the atomic weight of carbon is 12. 



It was at the same time incidentally noted that in all those cases where more 

 than 12 grammes of carbon was found in the standard volume, the number was 

 either 24 or 36, or some other multiple of 12. And so the matter has rested until 

 the present day. 



I have now to announce that, as the result of most laborious investigation 

 carried on conjointly with my friend and colleague, Mr. Cooper, there exists a 

 multitude of carbon compounds wherein the quantity of carbon in the standard 

 volume is not a multiple of 12, but is a multiple of G. And the consequence 

 follows that the atomic weight of carbon is 6, as was commonly believed by 

 chemists a third of a century ago. 



10, Popular Method for the Estimation of Carbon Dioxide in the Air. 

 By J. B. Cohen, Ph.D., and G. Appleyard, Yorkshire College. 



The method consists in determining the time required to precipitate the lime in 

 dilute lime water containing an insulficient quantity of lime to unite with all the 

 COj present. 



Phenolphthalein is used as indicator, and the end of the reaction is determined 

 by noting the point at which the liquid becomes decolourised. 



A 22-ounce stoppered bottle is used with 10 c.c. of lime water made from 

 saturated lime water, diluted 100 times with distilled water. One-third of a c.c. 



' Nature, June 14, 1894. 



= See Phil. Mag., May 1894, p. 495. 



