787 



the H-ioii concentration of the solution, a series of solutions was 

 prepared, which all contained 0.01 normal sodium acetate, but 

 varying quantities of free acetic acid or free sodium hydroxide. We 

 thus obtained seiies of solutions in which the concentration of 

 the acetate was constant, while that of the H-ions varied graduall3^ 

 The concentration of the other constituents of these solutions was 

 too small for them to have any significance. 



It was now found, that the reaction to gravity did not take |)lace 

 at all or took place badly in the most acid and in the most alkaline 

 solutions of the series. The H-ion concentration of the limiting 

 solutions was measured elect rometrically and was found to be for 

 acid solutions between [H] = 10-5'^ and [HJ = JO--'-'^ (the H-ion 

 concentration was expressed in gramions per litre), and for alkaline 

 solutions between [H] = 10— ^^-^ and [H] = 10— ii'-^. We may assume 

 that, in this case at least, the effect of acid and base is to be 

 attributed for the most part to the H-ion (or OH'-ion) content. 



The same experiment was repeated with solutions containing instead 

 of acetic acid and an acetate, malic acid and a malate (these solu- 

 tions always contained 0.01 grammolecules per litre of sodium 

 malate). F'or acid solutions the limit Avas here found to be between 

 ^^H'] = 10~^-^ and [H] =. 10"*^ and for alkaline solutions between 

 [H-] = 10-10-6 and [H- 1 = lO-ni. These results confirmed the con- 

 ception of the influence of the H--ions. The displacement of the 

 limits in acid malate solutions with respect to those of acid acetate 

 solutions showed, however, that even small concentrations of salt 

 also contribute to the effect. 



In order that enough observations could be made to give an idea of 

 the behaviour of the alga in solutions of a single salt, it was often 

 necessary to use a fresh culture. In that case the last determinations 

 with tie old culture were repeated with the new one. Often the 

 results were not completely identical, but the differences between 

 the two cultures were generally so small, than they could be ne- 

 glected. In the experiments with KCl, however, once a great displace- 

 ment of the limiting concentration was observed on using a fresh 

 culture Figure 3 shows how in solutions containing in addition to 

 KCl, 0.00065 normal KOH, the new ctdture showed a modified 

 behaviour. In consequence of this the curve consists of two discon- 

 tinuous pieces. It is probable that the new piece would indeed be 

 a continuation of the old, if we displace the new piece in a hori- 

 zontal as well as in a vertical direction. The dotted lines would 

 then probably unite the portions of the two pieces which correspond. 

 In using new cultures with sodium acetate a less pronounced dis- 



