Ixii Annual Report of the Council. 



of electrolytes, and suggested that in aqueous solutions these 

 were split up into ions, each of which behaved as a single 

 molecule in depressing the freezing point. The number of ions 

 could be calculated from the conductibility of the solution ; and 

 Arrhenius's theory has received experimental confirmation in 

 many cases, although there are still many results not in harmony 

 with it. It constitutes a first approximation to the truth. 



Raoult in his first paper on freezing points recalled the fact 

 that not only the depression of the freezing point but also the 

 fractional depre.'^sion of the vapour tension [(/-/')// where /is 

 the vapour tension of the pure solvent, /' that of the solution] 

 was proportional to the concentration in dilute solutions. This 

 was discovered by Wiillner, and Guldberg {see p. Ivi, above) had 

 indeed, in 1870, shewn that the one phenomenon could be 

 deduced from the other by thermodynamical reasoning. In 

 1886 van't Hoff shewed how the absolute value of both 

 depression of freezing point and fractional lowering of the 

 vapour tension could be deduced from the osmotic pressure of a 

 solution, and in 1887 Raoult published an experimental confirma- 

 tion of van't Hoff's formula for certam substances. It was the 

 first of a long series of researches on ' tonometry ' of solutions, 

 as elaborate and careful as those on their 'cryoscopy.' It is 

 by his work on these two subjects that he will be remembered. 

 He wrote nearly 60 memoirs dealing with them, in addition to 

 two excellent summaries, ' Tonomeirie,^ published in May, 

 1900, and ' Cryoscopie,' published posthumously, in 1901, in 

 the ' Scientia ' series. The most general expression for the 

 tonometric constant of a solution in terms of the other quantities 

 involved was given in a joint paper by M. Raoult, and M. 

 Recoura, Dean of the Faculty of Sciences of Dijon, Raoult's 

 son-in-law. 



' Ce grand savant, etait aussi le meilleur des hommes.' 

 Raoult was a man of remarkable simplicity of character, free 

 from any trace of affectation or conceit, and admirably courteous 

 and kind in manner. He was devoted to chemistry and to the 

 provincial university which he served for 34 years, and which he 



