Januaet 28, 1921] 



SCIENCE 



83 



solution; and the distilled water in the beaker 

 is always brought to the same hydrogen ion 

 concentration as that of the il//64 CaOU 

 solution inside the collodion bag dipped into 

 the beaker. Similar experiments are made 

 with Na,SO^ brought to a different hydrogen 

 ion concentration. The result of these ex- 

 periments is striking. There is always one 

 definite hydrogen ion concentration at which 

 the "attraction" of both 1//64 OaCl^ (or 

 LaClJ as well as that of M/256 ISTa.SO^ for 

 water is almost zero. As soon as the hydro- 

 gen ion concentration rises, the attraction of 

 il//64 CaCU for water becomes noticeable and 

 increases with a further increase in the hy- 

 drogen ion concentration until it reaches a 

 maximum (at a hydrogen ion concentration 

 of about 10-3 JV). xhe attraction of 11/256 

 Na^SOj for water rises when the hydrogen 

 ion concentration falls below the point where 

 the attraction is zero. Jf/256 !N'a.,SO^ at- 

 tracts water when it is positively charged and 

 lf/64 CaCl^ does so when water is negatively 

 charged. Where neither solution " attracts " 

 water the latter is not electrified. (It should 

 be mentioned that the attraction of a cane 

 sugar solution of M/Q4: or below for water is 

 very slight and scarcely noticeable, and that 

 this is the reason that when water is not elec- 

 trified it is not noticeably attracted by ilf/64 

 CaCl, or M/256 Na,SO,.) Table II. shows the 

 close relation of this hydrogen ion concentra- 

 tion and that of the isoelectric point for differ- 

 ent proteins. Water begins to become nega- 

 tively charged in contact with a collodion 

 membrane as soon as the hydrogen ion con- 

 centration is slightly on the acid side of the 



isoelectric point of the protein forming a film 

 on the membrane. 



The quantitative agreement between the 

 isoelectric point of the protein forming the 



film on a collodion membrane and the point 

 of reversal of the sign of electrification of 

 water is such that it is difficult to question 

 the connection between the chemical constitu- 

 tion of the protein and the sign of electrifica- 

 tion of water. It is also obvious that the 

 density of the charge varies with the hydrogen 

 ion concentration. 



When the collodion membrane is not treated 

 with a protein the water is always positively 

 charged and no reversal in the sign of the 

 charge can be obtained by an increase in the 

 hydrogen ion concentration. This harmonizes 

 with the fact that collodion is not an ampho- 

 teric electrolyte. 



It is to be expected that in addition to the 

 chemical nature of the membrane the chem- 

 ical nature of the liquid in contact with the 

 water also infiuenees the sign (and density) 

 of the electrical charge at the boundary of 

 the two phases. Indications supporting this 

 view exist but they can not be discussed in 

 this connection. 



VII 



van't Hoff's theory of osmotic pressure con- 

 fronted the physiologists with the puzzling 

 fact that in the phenomena of secretion water 

 diffused often from places of higher to those 

 of lower osmotic pressure. In 1908 Girard 

 suggested that such cases of abnormal osmosis 

 as occur in organisms might be explained on 

 the assumption that the opposite sides of a 

 membrane separating pure water from an acid 

 or alkaline solution are oppositely charged, 

 and that therefore Perrin's experiments on 

 electrical endosmose furnish the explanation 

 of these phenomena. According to Girard, 

 only H or OH ions should produce such a 

 difference in charge and neutral solutions of 

 electrolytes should behave like solutions of 

 non-electrolytes which is, however, not cor- 

 rect. Bernstein, in 1910, also reached the 

 conclusion that electrical endosmose might be 

 utilized for the explanation of abnormal 

 osmosis as manifested in secretion and in 

 his book on " Electro-Biology " many specula- 

 tions in this direction are offered but un- 

 fortunately very few experiments. He also 

 assumes that the opposite sides of the mem- 



