( 574 ) 



on tlie />-.('-plaiie ; further the sohihility isotherms corresponding with 

 the temperatures of the points /; and q are indicated, from which 

 the phenomenon of retrograde solidilication ap{)ears clearly. 



3. In the case discussed the situation of the points p and q 

 depends on different properties of the compound and its components. 

 In special cases it will, therefore, depend on this, on what part of 

 the three phase line of the compound the point q lies. Undoubtedly 

 there will be many cases where this point falls below the melting 

 point. Probably this case will occur the sooner the more the volatility 

 of the two components differs. In this paper, however, I continue to 

 assume, that a vapour of the composition of the compound may exist. 



In this different cases may present themselves, which each call for 

 a separate discussion. So highly remarkable phenomena make e. g. 

 their apj)earance, when the plaitpoint curve cuts the three phase line 

 of the compound between the melting point and the maximum subli- 

 mation point. I shall, however, discuss this case and some others in 

 another paper, and restrict myself now to the phenomena, which 

 occur, when the point of intersection q, as has been drawn in Fig. 2, 

 lies not onl}' below the melting point of the compound, but also 

 below the maximum sublimation point. Also in this case the possi- 

 biJity is excluded that the coinpound melts, and the only may in which 

 the solid compound can vanish, is by eva/wration. 



The line for solid A,„ B„ -)- G, which would touch the three phase 

 line Am B„ -f- L -j- G in the maximum sublimation point, if this 

 point existed, runs on uninterruptedly to inlijuty, at least when no 

 further complications appear. 



The T-X-projection occurring in tig. 2 may contribute te elucidate 

 some i)oints. As is to 'be seen there, the two phase region E\ qE' 

 coexisting with the solid compound, does not possess any liquid 

 or \apour of the com[)oyition of the compound, which is in harmony 

 with the supposition, that the points F and F' are wanting. 



In fig. '2a I have traced the projection of the two phase regions 

 coexisting with solid substance, and of the plaitpoint curve on' the 

 ^j-a;-plane. Further there are some solubility isotherms in this dia- 

 gram, which re(|uire a few words of explanation, 



The curve fGecf' denotes the solubility isotherm for a temperature 

 somewhat below that of the point q. If we now consider the tem- 

 perature of the point q, we get a solubility isotherm which touches 

 in f/' '^ii*' which has two more points iif inflection, as is indicated 

 l)y tiie curve /, G,q,gf'. At a higher temperature we get a solu- 

 bility isotherm, which does not touch any more, and from which 

 tiic two points uf inflection may disappear. 



