797 



GTcn^ \ 



Fig. 4. 



i)s the least volatile; D« less volatile than B and C; 



B more volatile than C ; A very volatile. 



Besides a combination with lig. 3 can occur, but tiiis case too 

 follows so easily from the preceding ones tiiat this does not call 

 for a separate discussion either. 



Thus it will also be clear that in the last case the two eiidpoint 

 curves coming from the sides AC and AB, which refer to the 

 coexistence of a critical phase with solid C resp. with solid B, 

 can come in contact with each other, as was drawn by me already 

 before, (fig. 5 in communication II), and then this case can occur 

 e.g. combined with case 7 or 8. 



What is, however, of more importance at the moment is the fact 

 that Dr. Morey in his study of the system H^O — SiO^ — K,0. found 

 phenomena which point to this that this system as far as its main 

 points are concerned, must be probably classed with fig. 4, when 

 we namely put that A = H^O, C =; SiO^ and B = K^O. The system 

 H.jO — SiO^ givfes two critical endpoints; further Dr. Morey has found 

 that in this sj'Stem a ternary compound KHSi,C\ occurs, which 

 probably also shows two critical endpoints, the former lying at 

 + 365°, the latter at + 500°. He has further found that this 

 ternary compound splits up at higher temperatures into the binary 

 compound K.^Si505, and a solution rich in SiO^. Of course the 

 critical endpoint curve of the compound need not come in 

 contact with that of SiOj,; this is however probably the case, and 



