DEDUCTION FROM TllE GASEOUS THEORY OF SOLUTION. 20.3 



Alcxccirs exiKMiineiits iii)i»('ar to iiic to be ol' the \ <m y lii^licst 

 iin]K)rt;ui('(', and to iiieiit the closest attention in any iii(|niry into the 

 luitni'e of solntion. As alieady stated, tliey ail'ord the stroniicst snp 

 port to the hy}>otli('sis which I have been discnssing: indeed, had it 

 not been for this support, 1 shouhl liardly haA'c ventured to discuss it 

 at all. They refer to solutions in water, below and al)ove 100"^, of 

 ])hen(>l, salicylic acid, benzoic acid, aniline phenylate, and aniline, and 

 to solutions in molten stdphur of chlorobenzene, benzene, t(duene, 

 aniline, and nuistard (»il. All these afford instances of reciprocal i)ar- 

 tial solution throughout a considerable range of temperature, leading 

 eventually at a detinite temperature to intinite solubility. Several of 

 them afford instances also of solid substances with solution melting- 

 points below their true melting-points. 



Alexeeff experimentally determined the tem])eratures at which dif 

 terent mixtures of the same two liquids are just converted into clear 

 soluticuis; or, in other words, he ascertained the strengths of the satu- 

 rated solutions corresponding to different temperatures. For each 

 ])air of li(|uids he found that when a particular strength of mixtnre is 

 reached, the temperature of saturation is lowered by furthei- addition 

 of either liquid. Thus a mixture of about 37 parts aniline to (m parts 

 water requires a temperature of 1640-5 to convert it into a homoge- 

 necais solution: but one of 21 of aniline to 79 of w^ater assumes this 

 c<»iidition at l.ldo. j^^jd oneof 74:Of * 

 aniliiM' to ")() of water does so at 5 

 157^*r). He ])1otted his results in | 

 the foim of curves, with tempera- istf 

 tare an<l i»ercentage sticngth as 

 the two coordinates. The curve 

 for aniline aiul water is showMi in '20° 

 Fig. 1, and this may l)e taken as 

 a fair re])resenta.tive, the geneial 

 form of all being similar. It is 8o° 

 at once apparent that Ibr vvevy 

 temperature u]) to a certain limit 

 there are two iK)ssible saturated ^o" 

 solntions. one of water in aniline 

 and one of aniline in water. The 

 limiting tejnperature at whi<*li °°^7 



tlK're is but one l)OSsible satnrated ''"'■ l-— IVrccntagc. of imilinein its saturated aqno- 

 . ' oils soliitiou (Alcxucll). 



solution, and above which satu- 

 ration becomes imi)ossible, is called by Alexeelf the .Mischungs Tem- 

 I)eratur. It is what I ha\e called the critical solution temi)erature. It 

 is in the case of aniline and water about 107°, as nearly as one can 

 Judge from the curve without a greater number of experimcmtal points 

 than we have in this i)art; and the corresponding satrnation strength 

 is about 50 per cent. It is hardix lUM-essary to say that this equality 



