785 



salr, not only varied in a regnlar manner as regards ooiicenlration 

 of the salt, but the degree of aridity was also varied regularly. 

 The hydrions are the cause of the effect which small quantities of 

 acids exert on Cklmnydomonas. The effect of small quantities of 

 basis is due to hydioxyl ions. 



The product of the H-ions and the OH'-ions is constant in 

 aqueous solution at any given temperature. Hence the strength of 

 an alkaline solution can be expressed by the H-ion concentration. 



We flow proceeded as follows. First the critical concentration was 

 determined for solutions of a given salt in distilled water. Then the 

 same was done for solutions of the salt containing 0.00005 n. acid, 

 and next for those containing 0.00010 n. acid, etc. Finally small 

 quantities of base were added to the salt solutions in order to 

 determine in the same way the limiting concentrations and the critical 

 concentration for series of solutions which were feebly basic instead 

 of feebly acidic. 



Since the effect of electrolytes is due to^the ions, it was necessary 

 to ensure that a regular variation of ionic concentration was indeed 

 obtained by the procedure outlined. With regard to the ions of salts 

 there need be no doubt, but for the hydrions (his was not self- 

 evident. 



The hydrion concentration of 0.00005 n. sulphuric acid for instance, 

 is in practice not always equally great. It was possible, by adding 

 small quantities of acid or base, to obtain regularly increasing or 

 decreasing H'-ion concentrations by following the following directions. 

 The solutions of a salt were made acid or alkaline by addition of 

 the acid or the base, which had an anion or a cation in common 

 with the salt (a sulphate was therefoi-e acidified with sulphuric acid, 

 a potassium salt was made alkaline with potassium hydroxide). All 

 acid solutions of a salt were prepared with the same solution of an 

 acid and likewise all alkaline solutions with the same solution of 

 a base. Newly distilled water was always used. 



Although a regular variation of H--ion-concen( ration was thus obtained, 

 its absolute value was unknown. Nor was it possible to compare 

 mutually the H-ion concentration, and therefore the degree of acidity, 

 of solutions acidified with hydrochloric and sulphuric acids. 



For solutions of sodiura acetate at different H-ion concentrations 

 the absolute value was determined electrometrically. These solutions 

 contained sodium acetate and acetic acid. The solutions were again 

 employed in series, and in each series the concentration of the 

 sodium acetate varied in a regular manner. By paying attention to 

 the relation of the acetate concentration to that of the free acetic 



