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concentrations, the critical concentrations and the high 
limiting concentrations cut twice the ordinate-axis and 
once the abscissa-axis. The points of intersection of the 
ordinate-axis agree with the limiting concentrations and 
the critical concentrations of solutions, which contain only 
acid or base; the point of intersection with the abscissa- 
axis agree with the limiting concentration and the critical 
concentration of solutions, which contain only salt. Between 
the lines connecting the limiting concentrations, we find 
a region, containing all the points, which represent tran- 
sition concentrations. The region between the curves for 
the low limiting concentrations denotes all the solutions 
in which the Alga is so movable, that during the experiment 
they clearly show the reaction to gravity. Outside of the 
curves for the high limiting concentrations we find all 
solutions of the salt, in which the algae do not show the 
reaction to gravity. 
$ 6. The preparation of the solutions. 
The preparation of the solutions requires a nearer 
discussion. We can be short, as regards the obtaining of 
the desired concentrations of the neutral salt. To this 
purpose we make normal solutions (is that not possible, 
solutions with the normality !/,). The concentrations of 
the successive solutions of a series differed, as a rule, 
0,01 normal. Thus were prepared solutions of 0,01 normal 
to 0,20 normal, by taking with a pipette 1—20 cM". of 
the normal fluid and adding to this quantity distilled water 
up to 100 cM*. Properly speaking, it would be necessary, 
in stead of denoting the concentration in the normality, 
to define the concentration of the ions. For the various 
neutral salts the ionisation however is equally strong for 
every definite concentration. This holds for the small 
