8ü7 



Fig. %i is a little more intricate, because here the binary com- 

 pound D^ is formed from the ternary compound D^ at higher tem- 

 perature. This gives rise to two new quintuple points CD^D,LG 

 and BD^D^LG. Now the temperature maxima of the four phase 

 lines CD^LG and BD^LG have disappeared, and instead of this 

 the four-phase line D^D^L(r Jiow possesses a temperature-maximum. 



Of the greatest importance, however, is the P-T tig. 4a, which 

 corresponds with fig. 4. 



In a binary system occur the critical endpoints ,S + (-^ = ^0> in 

 consequence of the three-phase line S ~{- L -\- G meeting the plait- 

 point curve L = G, just as for the system ether-anthraquinone. In 

 a ternary system the critical endpoints ,S'i + .S'^ + f L = 6*) occur, 

 which I have called douhle critical endpoints, when tlie four-phase 

 line /S', (S'j L <} meets the critical endpoint curves .S, -f- {L = G) and 

 S^ -{- {L = (t), which meeting must of course take place simulta- 

 neously. In fig. 4« tiie lines j'^iy^ and PJ{P„VP^, refer lo the 

 critical endpoint curves C-\-[L=zG) and 1)^ ~\- (L ^= G). 



Where the four-phase line (JD^LG meets these critical endpoint 

 curves, the double critical endpoints 6' -j- -D, -}- (L = ^r') occur, from 

 which it therefore follows that this meeting must take place in the 

 points of intersection of the critical endpoint curves mentioned. The 

 double critical endpoints l\ and P^ are connected by the critical 

 endpoint curve I\VI\ tiie oilier half of lliis curve is nielaslalile. 



As has been said it is very well possible thai Ihis case occurs 

 in the system H,0 — SiO, -K,t), but it is also possible that the critical 

 endpoint curves p^rq^ and P^RP^VP^ do not intersect, and in this 

 case the four-phase line CD,LG proceeds uiulistuibed tVdin one 

 quintuple |)oint to the other. 



Dr. Mokey's investigation will be able to decide this point. 



Aiion/diiic Cht'iiiicii/ 



Amsterdam, Oct. 28, 1915. Lnhnnituri/ of the Unirersitii. 



Chemistry. — " The Periodic Passlvltij of /raji." By Prof. A. Smits and 

 C. A. LoBRY DE Bruyn. (( 'omiuunicated by Prof, van dkr W,\.\ls). 



(Communicated in tlit' meeting of Ücluber 30, 191.")). 



1. The periodic /uisslvlti/ on mtodf pohinsation. 

 As was already communicated before ') the passive stale of iron 

 can be abolished by bringing the iron into contact with solutions 



') Chem. Weekblad 12, 678 (1915). 



52 

 Proceedings Royal Acad. Amsterdam. Vol. XVllI. 



