168 
the influence of the acidity on the movability of our 
organisms the method was suitable, when at least we are 
content with the knowledge of the course of the changes. 
AIl my curves, except those for sodium acetate are 
obtained by means of this method. They can only be of 
service to examine the qualitative course of the phenomenon. 
Conclusions about the absolute value of the H-ion con- 
centrations, must be considered under a certain reserve. 
À method, which permits, to make reproducable solutions 
with small H-ion concentrations, is the using of so called 
buffer solutions. These are obtained by adding to solutions 
of salts of weak acids with strong bases and of strong 
acids with weak bases, the according free acid or free base. 
À well-known buffersolution is sodium acetate since 
the sodium acetate is split up hydrolytically, we must 
add to a solution it, rather much free acetic acid to cause 
a slight change in the H-ion concentration of the solution. 
The acetate makes go back for a great deal the dissocia- 
tion of the free acetic acid in H-ions and axions of the 
acid. This causes the effect of a buffer. In buffer-solutions 
the H-ion concentration can be easely stated electrometri- 
cally. The drawbacks of this method are, that te number 
of buffer-solutions is limited, and that, as a rule they can 
only be used for solutions of which the H-ion concen- 
tration lies in a rather limited region. Moreover there are 
always ions in the solutions, which can also have an 
influence on the phenomenon and of which the concen- 
tration is so high, that their influence cannot be entirely 
excluded. 
