( 205 ) 



branch é e^, while llic solid ])luiso lies naiuriillj on Ihe line GG . 



With a suitable volume llie thiee phases may now continue to 

 exist over the whole range of pressure and tenipei-ature indicated 

 by ^i' c', but then the vapour phase must have disappeared when 

 we have reached the point c', for in (he point c' the liciuid has the 

 same concentration as the solid combinalion. 



Beyond the maximum, respectively minimum in figs. 5 and 6 the 

 concentration of liquid and vapour is, of course, always different, 

 just as in lig. 4, and as the line for the combinalion iiever coincides 

 with this maximum, respectively minimum, when there is a maximum 

 or minimum, in the above mentioned case the two phases will 

 necessarily only get the same concentration, when two phases 

 coexist. 



At c', we leave the three phase region, which we had entered 

 at ^i' and coexistence of solid A B -^ licpiid at higher temperatures 

 can now only take place under higher j)ressurc. 



Van dkr Waat-s has called the temperature of the {)oint 6'/ the 

 maximum suhllmation temiieraiare and that of the |)oint c', the 

 minimum meltimf point temperature or the meltimj point proper of 

 the combinalion. 



Further it is worthy of note that as appears from the figs. 4, 5 and G, 

 the highest three i)hase temperature cannot be reached when we 

 start from pure AB, as this temperature corresponds with a total 

 concentration which contains more A than the combinalion. 



It is obvious from the foregoing, that (he distinguishing feature 

 between a non-dissociating and a dissociating substance is this, that 

 whereas for a non-dissociating substance the three [)hases can oidy 

 exist at one temperature, they can coexist for a dissociating substance 

 over a certain temperature range. We may express this also in this 

 way : a non-dissociating substance has only a three phase pointy 

 but a dissociating substance a three phase line. 



Before leaving tigs. 4. 5 and 6 I will point out, that the solubility- 

 isotherm at the maximum three phase temperature has a shape 

 which is indicated by the line f'C/\. This line touches the liquid 

 branch at 6' and has an horizontal tangent at the point whore it cuts 

 the line for the combination. At higher temperature the solubility 

 isotherm gets detached from the licpiid line and moves as a whole upward. 



5. U is obvious that the two three phase pressure lines ecs and 

 e^ Cj ^1 must coincide at the maximum three phase temi)erature, but 

 where the place of coincidence in the three phase regions must be 

 drawn is a point which calls for further elucidation fiom the sub- 

 joined ^>^projections. 



