296 DEDUCTION FKOM THE GASEOUS THEORY OF SOLUTION. 



the experimeiita] data of Iliimsay and Young {Phil. Tranf!., 1.S8G). The 

 reason that ah-ohol was chosen is simi)ly that the data were convenient 

 to my hand. 



The two curves are strikingly similar in form and signilicance. In 

 Fig. 3 we see the specific volume of litjuid alcohol increasing slowly 

 with rise of temperature, while that of the saturated vai)or rather 

 rapidly decreases. In Fig. 2 we see the specific solution volume of the 

 aniline in the aniline layer slowly increasing, while that of the aniline 

 in the water layer decreases more rapidly, with rise of temperature* 

 In Fig. 3 we see that above the critical i)oint the existence of li(iuid 

 alcohol in i^resence of its vapor is imx)ossible. In Fig. 2 we see that 

 above the critical solution point the existence of an analine layer in 

 jn-esence of a water layer is impossible. In Fig. 3 we see an inclosed 

 area Avhich represents those temperatui'cs and spe(;ihc volumes which 

 are mutually incompatible. In Fig. 2 we see an inclosed area which 

 represents those temperatures and specific solution volumes which are 

 mutually incompatil^le. In Fig. 3 we see that any two points on the 

 curve Avhich correspond to equal temperature must also, from the na- 

 ture of the case, correspond to equal osmotic pressure. In Fig. 3 some 

 of the ])ressures are indicated, as this can be d(me from Ramsay and 

 Young's data. In Fig. 2 the value of the osmotic pressures can not be 

 given, as they have not been experimentally determined. In Fig. 3 

 any jjoint outside of the curve and to the right, as at a, corresi)onds 

 to the state of unsaturated alcohol vapor, whose tem})erature, specific 

 volume, and pressure are indicated — the last by the isobaric line 

 which passes through the point. In Fig. 2 any point outside the curve 

 and to the right, as at a, must correspond to the state of an unsatur- 

 ated aqueous solution of aniline, whose temperature and specific solu- 

 tion volume can be read, and whose osmotic pressure could be indi- 

 cated by an isobaric line, had we the data for plotting it. A little 

 thought makes it evident, too, that such isobaric lines would follow 

 the same general course as those shown in the alcohol diagram. 



Now, consider what must be the effect of gradually decreasing the 

 volume of the unsaturated vai>or in the one case and the solution 

 volume of the aniline in the unsaturated solution in the other, while 

 temperature is kei)t constant. In the case of the vapor (Fig. 3) the 

 point a will pass to the left across lines of increasing pressure until 

 the vapor becomes saturated at />. Then, if the diminution of volume 

 continue, a portion of the vapor will condense to the liquid state, or 

 be transferred to c, while the rest remains saturated vapor at b. With 

 continued decrease of volume, the proportion condensed will con- 

 stantly increase, but there can be no alteration of pressure till all is 

 condensed; and after that nothing but a very slight diminution of 

 volume is possible without a lowering of temperature. Well, how are 

 we to diminish the solution volume of the anihne in the unsaturated 

 aqueous solution ? Clearly by depriving the solution of some of its 



