( 573 ) 



representation for a first investigation of these prohlems. Foi' the sake 

 of clearness I mnst draw attention to the lai-t, that in the T-X-pro- 

 jection the lines nE, Ej), yFK' ami V/r are (lie solubility enrves, 

 whereas r/E,. Ei//. q¥'E/ am! E^'c represent the vaponr lines. In 

 the P-T-pi'ojection. however, we get one M/vv plin.se liiw for each 

 jiair of two ('orn'spondiiiu lines for the lii|iii(l and gas phases coexist- 

 inii' with solid sulislaiice. These three phase lines are indicated 

 U\ A + L-|-(;, A„, H„ +!> + <; and ll + L-fO in the P-T-prqjection. 



Tiie tirst meeting of a soliiliility curve with the plaitpoint cnrve 

 takes place in p and the second in 7. Ai-coi-ding to van dek Waals" 

 theory a continuous transition from the solubility curve into the 

 coexisting vapour curve takes place in these two points. If we take once 

 moie the system C'< ), — ('aO as an example, p indicates the critical 

 |ioiiil of the saturated solution of CaCO, in Huid carbonic acid, and 

 (/ the ciiiical point of anotlier solution saturated with C'aCO, with a 

 much larger concentration of CaCO,. 



Between these points p and (/ a Huid phase may occur alone or 

 by the siile of solid A,„ 1!„ (CaCO,), and in the neighbourhood of 

 these points the jdienomenon of retrograde solidification must present 

 itself. 1 will further emphatically [)oint out here, that it is assumed, 

 as is easily seen in the T-X-projeclion, that near the melting i»oint 

 the difference of liie \olalility of the comjionents is not so 

 large as to prevent the occiwrence of a \apour of the comiKJsition 

 of the compound. The point F', where the composition of' the \apour 

 is the same as that of the compound, is tiie ))uuiinu)ii-sid>/ii)i(itio)i. 

 pi'iiit and the point F, where the concentration of the liquid is the 

 same as thai of llie couipound, is the minimum meltimj puiiif, oi- \\>q 

 melting [loint under the three i)hase pressure '). What I did not vet 

 show in my ju-evi()us jiaper is this that two lines stai't from the 

 points F ami F', which pass continuously into each other at K. 

 The.se lines form the continuous bounding curve of the two sheets 

 of the PTX-siu'fa<-e for the composition of the compound. The con- 

 tinuous bounding curve touches the plaitpoint curve in K, so that 

 K denotes the critical point of the dissociating compound. That this 

 point K does not constitute a special point of the continuous [dait- 

 |ioini curve is duetto the fact that when the compound is assumed 

 to dissociate, the critical |)oiut of the licjuid compound does not 

 essentially differ from that of the licpuds with oilier compositions. 



In fig. Ill the projection of the two phase regions coexisting with 

 solid substance is I'cpresented, and also that of the plaitpoint curve 



1) These Proc, June 1005, p. 20U. 



