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ment both solutions were cooled to 0°; then they were mixed while 
being well stirred. So in 0.5 L. are present one millimol of amine, 
one millimol of NaNO, and about 6 millimol HCl. 
After different periods 5 c.c. samples were drawn with a pipette, 
which had been cooled to O° and coupled with 5 c¢.c. of a ScHAFFER’s 
salt solution (8 gr. of ScHArrer’s salt + 3 gr. of NaOH per L.); 
then an excess of alkali is present, so that the diazo reaction is 
brought to a stand-still. We executed the coupling reaction at 0° in 
order to evade every decomposition of diazonium compound. 
From determinations performed in the laboratory for Physical 
Chemistry of the Technical High School here at Delft, we knew, 
that at O°, even after 6 hours, we need not fear decomposition of 
the diazonium-compounds; this disturbance appears only at 20°. 
Below we cite some affinity-constants for these reactions, in which 
N, is split off: 
For aniline K3oe = 0.0064 K350= 0.0124 Kie = 0.0248 
te p. nitraniline Kase — 0.000869 Kige — 0.00136 
»  Sulphanilie acid Kygge= 0.0083  K51.7= 0.0078 Ks57= 0.0108 
From the coloured solutions, thus obtained after coupling, again 
5 ee. were measured and diluted to 500 ee. (with higher concen- 
trations Beer’s law did not hold good). Assuming the last sample 
taken after about 6 hours to represent 100°/,, we compared this 
standard solution in a colorimeter with the colours obtained from 
the samples after 2, 4, 6, 10 ete. minutes. In this way we could 
directly read the percentage of inverted amine. 
Finally it should be observed that we used distilled water for all 
our experiments, as water from the main possessed too much colour 
of its own. 
Below we give same numerical data. 
