786 



acid, it was possible to ensure lliat in each series the H-ion concen- 

 ti'ation remained approximately constant, while for the various series 

 the H-ion concentration varied in a regular manner. Of' the solntions 

 containing the limiting- concentrations of sodium acetate, Ihe H-ion 

 concentration was now determined electrometrically. 



Mixtures of sodium acetate and acetic acid have a H-ion concen- 

 tration' which in practice is well detined, can be calculated in advance 

 and can moreover be readily determined electrometrically. These 

 mixtures are "buffer solutions". 



The experiments were carried out at room temperature. The 

 literature indicated that in so far as the influence of temperature 

 on chemotaxis has been investigated at all, it is insignificant. Nor 

 has a great influence of teujperature on ceitain phenomena of 

 colloidal chemistry, e.g. on the stability of suspensoids, been i-ecorded. 



For a series of solutions of cart)onic acid in tap waler the limiting 

 concentiations weie determined at 25'^ C and at about 0° C. P'or 

 both temperatures the same result was obtained. Nevertheless the 

 temperature was always noted. 



We always worked in diffuse daylight. An altempt to carry out 

 the experiments in the dark was unsuccessful, as it yielded very 

 irregular results. 



The limiting concentrations observed and the ciitical concentiations 

 calculated from them were plotted graphically for each of the salts 

 investigated. 



On the abscissa-axis of a biaxial system of rectangular coordinates 

 the concentration of the salt was {)lofted, and on the ordinate axis 

 on one side of the origin the concentration of the acid, on the 

 other side that of the base. For mixtures of sodium acetate and 

 acetic acid the acidity was indicated by plotting the H-ion concen- 

 tration on the axis of ordinates. 



The hmiting concenlration at which tlje reaction to gravity still 

 just occurred was indicated by, the limit at which no reaction was 

 visible by °. The points found for the critical transitional concentration 

 by calculation, were connected by a curve, which was regarded 

 as the boundary between the region containing all concentrations 

 of salt and base, and of salt and acid, at which the gravitational 

 reaction took place, and the region of concentrations, in which no 

 clear reaction occurred. 



Figures 1, 2, 3, and 4 reproduce the curves for K,SO,, sodium 

 acetate, KNO, and KOI, at least in so far as they have been 

 determined. 



In order to prove that the effect of acid and base was due to 



