80 solution of the M/192 66 attraction" of Na,SO, for water had to have a concentration of about or over M/4. If the gas pressure effect alone determined the relative attraction of the two solutions for water the concentration of the sugar solutions required to osmotically balance the M/192 solution of Na2SO, should have been M/64 (or slightly less). Hence the sugar solution balancing osmotically a M/192 Na,SO, solution was found to be 16 times more concentrated than the theory of van't Hoff demands. This high concentration of cane sugar was needed to attractive" influence overcome the powerful of the anions of a M/192 solution of Na2SO for the positively charged particles of water. Table I. shows the results of a few such experiments. The solution of the electrolyte was in these experiments always theoretically isosmotic with a M/64 cane sugar solution (on the assumption of complete electrolytic dissociation). The data contained in Table I. have only a qualitative value since no attempt at an exact determination of the concentration of the balancing sugar solutions was made. The data show, however, that the "attraction" of M/128 KCl for positively charged particles of water is eight times as great, that of K2SO, sixteen times as great, and that of M/256 K, citrate almost forty-eight times as great as that of M/64 cane sugar; while the "attraction" of a M/192 solution of a salt with a bivalent cation and monovalent anion, like MgCl2, for water is not greater than that of a M/64 solution of cane sugar. These experiments then prove that the rate of diffusion of water from the side of pure water through a collodion membrane into a solution of an electrolyte increases with the valency of the anion and diminishes with the valency of the cation. They give also a rough idea of the relative influence of these ions upon the rate of diffusion of positively charged water through the pores of the collodion membrane from the side of pure water to the side of the solution. A second fact brought out in these experiments was that the relative influence of the oppositely charged ions of an electrolyte in solution upon the rate of diffusion of ence. We have already mentioned the fa the valency of the ion is not the only tity which determines its influence rate of diffusion of water through a co membrane. In addition to the valer the number of electrical charges) a quantity of the ion enters which designated provisionally as the influe the radius of the ion. In the case of valent and monatomic cations the re influence on the rate of diffusion of po charged particles of water through th dion membrane from the side of pur into a solution increases inversely w radius of the ion, namely in the Li > Na > K > Rb, where the retardin is greatest in the case of Li and leas case of Rb; while in the case of mo monovalent anions the accelerating upon the rate of diffusion of p charged particles of water from the pure water through the membrane i solution increases directly with the radius of the ion I > Br > Cl; where I has the greatest and Cl the smallest attractive action. This might be intelligible if the action of the ions on the particles of water were electrostatic, since in this case the action of the anion depends on the negative charge in its outermost shell of electrons and the electrostatic effect should be the greater the farther the shell is removed from the positive nucleus of the ion; while the electrostatic effect of the cation is due to the positive charge of the nucleus and this should be the greater the smaller the distance between nucleus and the outermost layer of electrons, i.e., the closer the positive nucleus can approach the water particles or the membrane particles on which the ion is to act. IV We have alluded to the fact that collodion membranes are not strictly semipermeable and that crystalline solutes diffuse out from the collodion flasks in our experiments. It might be argued that the differences in the flow of water measured in the preceding chapter are due to differences in the rate of diffusion of electrolytes from the side of the solution to the side of pure water through the collodion membrane. This assumption is, however, not tenable since it can be shown that the diffusion of the solutes into the pure water through the collodion membrane seems to follow Fick's diffusion law according to which the rate of diffusion of a solute is directly proportional to its concentration and this seems to hold equally in the case of electrolytes and non-electrolytes. The specific influence of solutions of electrolytes on the rate of diffusion of water from pure water through collodion membranes into solutions can therefore not be due to any difference in the rate of diffusion of electrolytes and nonelectrolytes through the membrane into the pure water, but must be ascribed to a difference in the behavior of water towards these two types of solutes. We have thus far mentioned only the influence of electrolytes on the rate of diffusion of positively charged particles of water. Perrin found in his experiments on electrical endosmose that in certain cases the water migrated to the positive electrode, namely when the solution had an acid reaction, while it migrated to the negative electrode when the solution had an alkaline reaction. No such reversal in the sign of electrification of water can be produced in the case of pure collodion membranes, since in this case the water is always positively charged no matter whether the solution is acid, neutral, or alkaline. When, however, we deposit a film of a protein on the inside (or on both sides) of the collodion membrane the latter becomes amphoteric. When the solution is sufficiently acid, the water migrates through the membrane as if its particles were negatively charged, while when the hydrogen ion concentration is lower, i.e., when the solution is only very faintly acid or neutral or alkaline, the water particles move through the protein film of the membrane as if they were positively charged. When we separate an acid solution of a salt by a collodion membrane possessing a protein film, from a solution of a pure acid of the same hydrogen ion concentration as that of the salt solution, the hydrogen ion concentration being equal to or above 10-4 N, the water migrates through the pores of the membrane as if its particles were negatively charged and as if they were "attracted by the cation and "repelled" by the anion of the electrolyte in solution with a force increasing with the valency of the ion. In this case, water is "attracted" more powerfully by salts with trivalent cation, e.g., AICI, or LaCl,, than by salts with bivalent cation e.g., MgCl2 or CaCl2; and it is "attracted" more powerfully by the latter than by salts with monovalent cation, e.g., NaCl or KC1; while negatively charged water is not "attracted" by salts with bivalent or trivalent anions, e.g., Na, SO, or Na oxalate or Na,Fe(CN),, etc. In the case of salts with monatomic and monovalent cations the "attraction of" the salt for negatively charged water seems to increase inversely with the radius of the 82 SCIENCE cation in the order Li > Na > K > Rb, where VI more 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 membrane. 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 a certain limit the concentration exceeds 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 e.g., which constitutes the film, namely The writer has been able to show solution; and the distilled water in the beaker is always brought to the same hydrogen ion concentration as that of the M/64 CaCl2 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 experiments is striking. There is always one definite hydrogen ion concentration at which the "attraction" of both M/64 CaCl2 (or LaCl) as well as that of M/256 Na,SO, for water is almost zero. As soon as the hydrogen ion concentration rises, the attraction of M/64 CaCl, for water becomes noticeable and increases with a further increase in the hydrogen ion concentration until it reaches a maximum (at a hydrogen ion concentration of about 10-N). The attraction of M/256 Na,SO, for water rises when the hydrogen ion concentration falls below the point where the attraction is zero. M/256 Na,SO, attracts water when it is positively charged and M/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/64 or below for water is very slight and scarcely noticeable, and that this is the reason that when water is not electrified it is not noticeably attracted by M/64 CaCl, or M/256 Na,SO,.) Table II. shows the close relation of this hydrogen ion concentration and that of the isoelectric point for different proteins. Water begins to become negatively charged in contact with a collodion membrane as soon as the hydrogen ion concentration is slightly on the acid side of the Nature of Protein Film on the Membrane Gelatin.... Casein Egg albumin TABLE II Hydrogen Ion Concentration where Water is Un charged 4 Isoelectric Point of Protein Oxyhemoglobin.. About 10-6.0 and 10-7.0N 10-47N 10-4-8N 10-6.8N 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 constitution of the protein and the sign of electrification 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 amphoteric electrolyte. It is to be expected that in addition to the chemical nature of the membrane the chemical nature of the liquid in contact with the water also influences 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 confronted 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 Hor 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 correct. 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 speculations in this direction are offered but unfortunately very few experiments. He also assumes that the opposite sides of the mem 84 brane of a gland are oppositely charged. Under such circumstances positively charged water particles will be driven in the direction from the positive to the negative side of the membrane. As soon as the positively charged water particle reaches the negative side of the membrane it gives off its charge. This enables other positively charged water particles to follow. Ideas similar to those offered by Girard and by Bernstein have been expressed by way of of abnormal explanation of other osmosis by Bartell and his collaborators, and by Freundlich. cases Whatever the ultimate theory of the driving force in these cases may be, we have a right to state that the electrification of the particles of water migrating through a membrane is a fact; that the sign of this electrification seems to depend on the chemical nature of the membrane in contact with water; that the rate of migration of these charged particles of water through the membrane from the side of pure water to the side of the solution is accelerated by the ions of the opposite sign of charge and retarded by the ions with the same sign of charge as that of the water with a force increasing with the valency of the ion; and that the relative acceleration and retarding effects of the two oppositely charged ions on the rate of diffusion of electrified water are not the same for all concentrations, that in lower concentrations of electrolytes the accelerating action of the oppositely Association in Winnipeg in the summe I was walking with him one day th one of the busy streets of Winnipeg wh asked if I would not step into a shop wit while he bought a little memento for Bumstead, a "bad habit" which he said h formed on trips away from home. I mention these two trivial incidents be they reveal the soul and heart of the man what, after all, is either science or art in parison? When in 1917 the important and di post of scientific attaché in London wa ated, Bumstead was the only man consi for no scientist in this country had hi his judgment, his knowledge of Englan his ability to assist in bringing about wh then, and what is now, the most importan of the modern world, namely, the coope and mutual understanding of the two branches of the Anglo-Saxon race. Bumstead's success in London was ordinary. The British liked and truste Admiral Sims and our own War Depa charged ion increases at first more rapidly placed large responsibilities upon him, a than the retarding effect of the other ion; while for higher concentrations the reverse is the case, until finally a concentration of the electrolyte is reached where the effects of the oppositely charged ions more nearly balance each other. THE ROCKEFELLER INSTITUTE FOR MEDICAL RESEARCH, NEW YORK, N. Y. JACQUES LOEB HENRY ANDREWS BUMSTEAD office became the center of a very acti |