36 
Moreover, the stimulating action of neutral salts on the catalytic 
activity of hydrogen-ions has long since been attributed to a raising 
of the dissociation constants of acids by salts. 
Another instance of such an effect has recently been supplied by 
Ko.tHorr '), who showed, that the dissociation-constants of indicators 
are increased by the addition of neutral salts. 
Mannitol showed the same behaviour as potassinm chloride. 
In 8°/, phosphate solutions the following values for py were 
determined : 
without mannitol 6.89 (29 
with 5 °/, mannitol 6.84 7.24 
difference 0.05 0.05 
Hence again a constant decrease of py, that is an increase of 
the dissociation-constant of water. 
In ammonium carbonate solution 5°/, mannitol produced a small 
decrease of urease activity (m decreased from 0.0029 to 0.00275), 
from which it is to be inferred, that the dissociation-constants of 
urease are increased by this neutral substance also. 
Figure 9. 
5°, Mannitol. 5 0/, Glucose. 
40 80 120 160 200 240 40 80 120 160 200 240 
minutes. 
Glucose, added to the amount of 5°/, to ammonium-carbonate 
1) Chem. Weekblad 1918, 394. 
