164 
tration. Within the series of constant salt concentration 
we find two, one for acid and one for alkaline solutions 
(hydrion concentration large, hydrion concentration small). 
That in one case we find one, and in the other case two 
critical concentrations will be understood, when we con- 
sider the proportion of the concentrations of the various 
ions in a solution. 
In a solution of a salt (with univalent anion and 
univalent cation) the number of negative is as great as the 
number of positive ions. Às regards the salt we have to 
do with the combined influence of an equal number of 
anions and cations. In a series of solutions, where the 
H-ion concentration changes, we always have the com- 
bined influence of H-ions and OH-ions. The mutual 
relation of these ions is now such, that the concentrations 
of it give a constant product, when we work by a con- 
stant temperature. Àre the concentrations expressed in 
gram-ions per liter, then the constant product, by 18° C. 
issabout A0 
Now we can find the case, that the H-ion concentra- 
tion is great and the OH-ion concentration is small. 
Under those circumstances it is especially the influence 
of the H-ions, which will act a part. Is the number 
of OH-ions great as regards the concentration of the 
H-ions, we chiefly see the influence of the OH-ions. 
The rather complicated connection between the H-ions 
and the OH-ions gives us an opportunity to examine 
the influence of every ion separately. Hence that we 
find two critical concentrations for the H-ions in a 
series with constant salt concentration. The constant 
product of H-ions and OH-ions causes that the con- 
centration of the hydroxylion can be found from the 
concentration of the hydrions. Às, moreover of a solution 
the H-ion concentration can be measured immediately, 
and the OH-ion concentration not, it has become a habit 
