()77 



At low temperature tliey can all exiat at ordinary [)re.ssLire, but 

 the formation will be hampered by the afore-said reason that the 

 compoinid can put a stop to (he action of the two phases (gas and 

 solid) on each other by separation. 



It is worthy of notQ that evidently through the action of aromatic 

 amines on carbonic acids free acide are formed in contrast with 

 ammoniac and the aliphatic amines, which form salts. 



Of the said carbaminic acids a few salts are known. When it is 

 tried to obtain the free acids by double conversion with acid, they 

 split up into carbonic acid and the free amines; only at high 

 pressure or low temperature could the free carbaminic acids be 

 formed. Yet it is possible, and even piobable that these acids, though 

 they are durable at the ordinary temperature oidy under increased 

 pressure, occur in the liquids L.^. The assumption that for cei'tain 

 reactions the carbaminic acids can act as intermediate product, is 

 therefore certainly not to be deemed impossible. 



It appears from the P-T-diagrams that the quadruple point of 

 p-tolylcarbaminic acid lies higher than that of phenylcarbaminic acid. 

 Possibly the quadruple point of one of the xylylcarbaminic acids 

 lies at still higher temperature. Tlie as-o-xylidine certainly invites to 

 further investigation, the quadruple point will probably have shifted 

 here to higher temperature, as the melting-point lies higher than 

 that of p-toluidine. It is possible that for this system the quadruple 

 point has already disappeared ; we should then pass to another type 

 of l)inary systems; in this case the behaviour will become analogous 

 to that of sulphuretted hydrogen-ammoniac, the particulars of which 

 •1 described on an earlier occasion. ^) 



When we think the quadruple point gradually removed to higher 

 temperature, it will disappear when it coincides with the critical 

 end-point. A gradual change is not to be realized, as the change in 

 constitution takes place discontinnously. It is here, however, possible 

 that by suitable choice of the homologues the displacement takes 

 place in small leaps, and the transition of the type presented by 

 these systems into that of sulphuretted hydrogen-ammoniac appears 

 \"ery clearly. 



In his thesis for the doctorate Büchner already pointed out the 

 existence of such a transition for systems without compound. I shall 

 describe the phenomena which present themselves in these trans- 

 formations in a later treatise. 



Delft, August 30^11 1918. Technical University. 



1) Thesis for the Doctorate (1909). Zeitschr. physik. Chemie. 71. 214 and 671. 

 1910). 



