82 



SCIENCE 



[N. S. Vol. LIII. No. 1361 



cation in tlie order Li > Na > K > Eb, where 

 Li with the smallest radius " attracts " the 

 negatively charged water most and lib with 

 the largest radius " attracts " the water least. 

 The monatomic monovalent anions " rejwl " 

 the negatively charged particles of water 

 directly in proportion with the radius of the 

 ion in the order I > Br > CI, where I with 

 the greatest radius "repels" the negatively 

 charged water most, and CI least. 



The relative " attractive " and " repelling " 

 action of the two oppositely charged ions of 

 an electrolyte for negatively charged water is 

 not the same in all concentrations. In the 

 lowest concentrations the attractive influence 

 of the cation for negatively charged water 

 increases more rapidly with increasing con- 

 centration than does the repelling action of 

 the anion; while beyond a certain concentra- 

 tion the repelling action of the anion on the 

 negatively charged water increases more 

 rapidly than the attractive action of the 

 cation. Finally a concentration is reached 

 where the electrical effects of the two oppo- 

 sitely charged ions balance each other more 

 or less and from then on the solution behaves 

 more like that of a non-electrolyte. 



VI 

 In the course of these experiments facts 

 were observed which indicate a chemical 

 source for the electrification of water when in 

 contact with a collodion membrane. We have 

 mentioned the fact that when a membrane 

 has been treated with a protein, the sign of 

 the electrification of water in contact with 

 the membrane can be reversed by acid. The 

 protein forms a fine film on the surface and 

 probably inside the pores of the collodion 

 merabrane. In an alkaline or neutral, and 

 often even a very faintly acid concentration 

 the water in contact with the protein film is 

 positively charged, but when the hydrogen ion 

 concentration exceeds a certain limit the 

 water assumes a negative charge. The writer 

 has measured the hydrogen ion concentration 

 at which this reversal occurs and has found 

 that it changes in a characteristic way with 

 a certain chemical constant of the protein 



which constitutes the film, namely its iso- 

 electric point. Proteins are amphoteric elec- 

 trolytes which behave differently on the two 

 sides of a hydrogen ion concentration which 

 is termed the isoelectric point. On the alka- 

 line side from the isoelectric point proteins 

 behave like a fatty acid, e.g., CHgCOOH, 

 forming metal proteinates with alkalies, e.g., 

 Na proteinate. On the acid side of the iso- 

 electric iM)int the proteins behave like NHj, 

 forming protein-acid salts, e.g., protein 

 chloride. We may imagine that proteins 

 exist in the form of two isomers, one on the 

 alkaline side of the isoelectric jxjint possess- 

 ing COOH as the active chemical group; the 

 other on the acid side of the isoelectric point 

 possessing NHj as the chemically active 

 group. The isoelectric point, i.e., the hydro- 

 gen ion concentration at which the reversal 

 of one type of protein salt to the other occurs, 

 is a characteristic constitutional property of 

 each protein. Its value is, according to L. 

 Michaelis, a hydrogen ion concentration of 

 10-*- ■'iV for gelatin and for casein, lQ-*-^N for 

 crystalline egg albumin, and 10"^- ^iV for oxy- 

 hemoglobin. 



The writer has been able to show that the 

 reversal of the sign of charge of water when 

 in contact with a collodion membrane pos- 

 sessing a protein film practically coincides 

 with the isoelectric point of the protein used, 

 lying slightly on the acid side of this point. 

 The method of determining the hydrogen ion 

 concentration at which the reversal in the 

 sign of electrification of water occurs is as 

 follows: We have shown that M/64: CaCl, or 

 M/256 LaClg " attract " negatively charged 

 water powerfully, while these two salts do not 

 " attract " positively charged water. On the 

 other hand, Ifa^SO^ " attracts " positively 

 charged water powerfully while it does not 

 " attract " negatively charged water. We fill 

 a series of collodion bags previously treated 

 with a protein each with a lf/64 CaCl, solu- 

 tion, and dip each collodion bag into a beaker 

 with distilled water. The ilf/64 OaCl, solu- 

 tion in each bag is brought to a different 

 hydrogen ion concentration by adding suit- 

 able quantities of HNO, or NaOH to the 



