555 



(C,H,.NH,),„.(HCI),, = D,o.,. 

 C^H^ . NH, . HCl = ü;.i . 

 At 35° : 



(C«H, . NHJ, . (HCl), = D4.5 

 (C«H, .NH,),„.(HCD„ = Dio.ii 

 C.H^.NH, .HCl^Du 

 (C,H, . NH,), . HCl = D2., 

 (C,H, . NH3)3 . HCl = D3.1 . 



The eontimiatiori of this work will liave to solve the question, 

 whether mixed-ci\ystals may also perhaps make their appearance in 

 this system. 



Leiden, Inorganic-chemical Laboratory. 



Chemistry. — "Concerning combinations of urea loith acids." By 

 D. F. DU ToiT. (Communicated by Prof. F. A. H.Schkeinem akers). 



In all textbooks of organic chemistry it is usually stated as well- 

 known facts : 



1. that one molecule of urea forms an additive product with one 

 molecule of a monobasic acid, 



2. that urea can easily be demonstrated by making use of the 

 small solubility of its nitrate, CON^H^ . HNO3. or of its oxalate, 

 2 . CONjH^ . (COOH)^ in the solutions of the corresponding acids. 



Consequently it appeared interesting to find out how urea would 

 behave with respect to other acids (mono- as well as poly-basicj, 

 what the real solubility of the two above-mentioned salts is, and 

 whether urea is not capable of forming additive products with more 

 than one molecule of an acid. For this purpose certain isotherms 

 were determined in the ternary systems relative to this purpose, 

 and with the help of the "rests-method" the compositions of the 

 solid phases were deduced. 



We will consider the solid substances only, which are in equi- 

 librium with the solutions. 



Urea-Oxalic acid-Water. 



This system was determined at 20° and at 30°. In addition to 

 urea and (COOH J . 2 H,0, the compound (CON,H;;, . (COOH), was 

 found. 



8t> 



Proceedings Royal Acad. Amsterdam. Vol. XVI. 



