( 93 ) 
to contain the nitrogen in the form of ammonia, the latter is expelled 
by heating with an alkali and estimated by titration. 
His conciusion is that this method gives trustworthy figures for 
the carbon but not always so for the nitrogen; or, as he states a 
little further on, it is only adapted for such substances which, according 
to DAFERT, may be safely analysed by Karerpaur’s nitrogen process, 
such as amides etc. 
But already the first amide which Miss van AKEN analysed in 
this manner, namely wrea, gave wrong figures for the nitrogen; 
only half the theoretical quantity was obtained. This not only 
caused the investigation of other amides but also and particularly 
the application of the process to many other kinds of urea derivatives. 
In the case of those substances which behaved abnormally a nitrogen 
determination was also made by the KsELDAHL method as modified 
by Guynine, which consists in the simple addition of a certain quan- 
tity of potassium sulphate, just to see in what cases the oxidising 
agent is the cause of the deficiency in nitrogen. A mutual compar- 
ison of those cases where a deficiency of nitrogen is found might 
then perhaps show why one amide gives good and another one 
bad results. 
The selection of the substances was guided by a number of ques- 
tions which at once presented themselves on considering the matter. 
1st. Is the result influenced by the hydrogen atoms of the urea? 
In order to solve this question substances were analysed in which 
they were replaced by methyl-groups namely symetric and asymetric 
dimethylurea, also tetramethylurea. 
All three only yielded half of their nitrogen in the form of ammo- 
nia, consequently behaved exactly like urea itself. Acetylurea in which 
a negative atom-group replaces an //-atom behaved similarly; the - 
H-atoms, therefore, exercise no influence. 
2nd, Is the result influenced by the oxygen of the urea? To an- 
swer this, thiourea, in which sulphur is substituted for oxygen, 
was analysed but this also yielded but half of the nitrogen as ammo- 
nia. The oxygen therefore, exercises no influence. 
3rd, What about cyclic urea derivatives? Of these rings with five 
and six polyvalent atoms were tested: viz. hydantoine, parabanic acid, 
dimethylparabanic acid, alloxan, alloxantin, methyluracil and malon- 
ureid which all yielded half their nitrogen as ammonia. Further, 
dicyclic urea derivatives, combinations of a 5 and a 6 ring namely 
uric acid and caffeine which, strange to say, yielded invariably more, 
although not much more than half the theoretical amount. Finally, 
isocyanuric acid, which may be considered as a eyclic urea deriva- 
