scholarly journals THE RECIPROCAL RELATION BETWEEN THE OSMOTIC PRESSURE AND THE VISCOSITY OF GELATIN SOLUTIONS

1921 ◽  
Vol 4 (1) ◽  
pp. 97-112 ◽  
Author(s):  
Jacques Loeb
Keyword(s):  
Osmotic Pressure ◽  
Solid Particles ◽  
Protein Solutions ◽  
Reciprocal Relation ◽  
Gelatin Solution ◽  
Protein Solution ◽  
Donnan Equilibrium ◽  
Protein Ions ◽  
Protein Particles

1. These experiments confirm the conclusion that protein solutions are true solutions consisting of isolated ions and molecules, and that these solutions may or may not contain in addition solid submicroscopic particles capable of occluding water. 2. The typical influence of electrolytes on the osmotic pressure of protein solutions is due to the isolated protein ions since these alone are capable of causing a Donnan equilibrium across a membrane impermeable to the protein ions but permeable to most crystalloidal ions. 3. The similar influence of electrolytes on the viscosity of protein solutions is due to the submicroscopic solid protein particles capable of occluding water since the amount of water occluded by (or the amount of swelling of) these particles is regulated by the Donnan equilibrium. 4. These ideas are supported by the fact that the more the submicroscopic solid particles contained in a protein solution or suspension are transformed into isolated ions (e.g., by keeping gelatin solution for 1 hour or more at 45°C.) the more the viscosity of the solution is diminished while the osmotic pressure is increased, and vice versa.

scholarly journals VALENCY RULE AND ALLEGED HOFMEISTER SERIES IN THE COLLOIDAL BEHAVIOR OF PROTEINS

1923 ◽  
Vol 5 (5) ◽  
pp. 665-691 ◽  
Author(s):  
Jacques Loeb ◽  
M. Kunitz
Keyword(s):  
Osmotic Pressure ◽  
Chemical Nature ◽  
Membrane Potentials ◽  
Protein Solutions ◽  
Gelatin Solution ◽  
Protein Solution ◽  
Sulfosalicylic Acid ◽  
Protein Gel ◽  
Donnan Equilibrium ◽  
Lactic Acids

1. The action of a number of acids on four properties of gelatin (membrane potentials, osmotic pressure, swelling, and viscosity) was studied. The acids used can be divided into three groups; first, monobasic acids (HCl, HBr, HI, HNO3, acetic, propionic, and lactic acids); second, strong dibasic acids (H2SO4 and sulfosalicylic acid) which dissociate as dibasic acids in the range of pH between 4.7 and 2.5; and third, weak dibasic and tribasic acids (succinic, tartaric, citric) which dissociate as monobasic acids at pH 3.0 or below and dissociate increasingly as dibasic acids, according to their strength, with pH increasing above 3.0. 2. If the influence of these acids on the four above mentioned properties of gelatin is plotted as ordinates over the pH of the gelatin solution or gelatin gel as abscissæ, it is found that all the acids have the same effect where the anion is monovalent; this is true for the seven monobasic acids at all pH and for the weak dibasic and tribasic acids at pH below 3.0. The two strong dibasic acids (the anion of which is divalent in the whole range of pH of these experiments) have a much smaller effect than the acids with monovalent anion. The weak dibasic and tribasic acids act, at pH above 3.0, like acids the anion of which is chiefly monovalent but which contain also divalent anions increasing with pH and with the strength of the acid. 3. These experiments prove that only the valency but not the other properties of the anion of an acid influences the four properties of gelatin mentioned, thus absolutely contradicting the Hofmeister anion series in this case which were due to the failure of the earlier experimenters to measure properly the pH of their protein solutions or gels and to compare the effects of acids at the same pH of the protein solution or protein gel after equilibrium was established. 4. It is shown that the validity of the valency rule and the non-validity of the Hofmeister anion series for the four properties of proteins mentioned are consequences of the fact that the influence of acids on the membrane potentials, osmotic pressure, swelling, and viscosity of gelatin is due to the Donnan equilibrium between protein solutions or gels and the surrounding aqueous solution. This equilibrium depends only on the valency but not on any other property of the anion of an acid. 5. That the valency rule is determined by the Donnan equilibrium is strikingly illustrated by the ratio of the membrane potentials for divalent and monovalent anions of acids. Loeb has shown that the Donnan equilibrium demands that this ratio should be 0.66 and the actual measurements agree with this postulate of the theory within the limits of accuracy of the measurements. 6. The valency rule can be expected to hold for only such properties of proteins as depend upon the Donnan equilibrium. Properties of proteins not depending on the Donnan equilibrium may be affected not only by the valency but also by the chemical nature of the anion of an acid.

scholarly journals DONNAN EQUILIBRIUM AND THE PHYSICAL PROPERTIES OF PROTEINS

1921 ◽  
Vol 4 (1) ◽  
pp. 73-95 ◽  
Author(s):  
Jacques Loeb
Keyword(s):  
High Viscosity ◽  
Relative Volume ◽  
Solid Particles ◽  
Protein Solutions ◽  
Gelatin Solution ◽  
Hydrogen Ion Concentration ◽  
Egg Albumin ◽  
Donnan Equilibrium ◽  
Order Of Magnitude ◽  
Protein Particles

1. The proof is completed that the influence of electrolytes on the viscosity of suspensions of powdered particles of gelatin in water is similar to the influence of electrolytes on the viscosity of solutions of gelatin in water. 2. It has been suggested that the high viscosity of proteins is due to the existence of a different type of viscosity from that existing in crystalloids. It is shown that such an assumption is unnecessary and that the high viscosity of solutions of isoelectric gelatin can be accounted for quantitatively on the assumption that the relative volume of the gelatin in solution is comparatively high. 3. Since isoelectric gelatin is not ionized, the large volume cannot be due to a hydration of gelatin ions. It is suggested that this high volume of gelatin solutions is caused by the existence in the gelatin solution of submicroscopic pieces of solid gelatin occluding water, the relative quantity of which is regulated by the Donnan equilibrium. This would also explain why the influence of electrolytes on the viscosity of gelatin solutions is similar to the influence of electrolytes on the viscosity of suspensions of particles of gelatin. 4. This idea is supported by experiments on solutions and suspensions of casein chloride in which it is shown that their viscosity is chiefly due to the swelling of solid particles of casein, occluding quantities of water regulated by the Donnan equilibrium; and that the breaking up of these solid particles into smaller particles, no longer capable of swelling, diminishes the viscosity. 5. This leads to the idea that proteins form true solutions in water which in certain cases, however, contain, side by side with isolated ions and molecules, submicroscopic solid particles capable of occluding water whereby the relative volume and the viscosity of the solution is considerably increased. This accounts not only for the high order of magnitude of the viscosity of such protein solutions but also for the fact that the viscosity is influenced by electrolytes in a similar way as is the swelling of protein particles. 6. We therefore reach the conclusion that there are two sources for the viscosity of protein solutions; one due to the isolated protein ions and molecules, and the other to the submicroscopic solid particles contained in the solution. The viscosity due to the isolated molecules and ions of proteins we will call the general viscosity since it is of a similar low order of magnitude as that of crystalloids in solution; while the high viscosity due to the submicroscopic solid protein particles capable of occluding water and of swelling we will call the special viscosity of protein solutions. Under ordinary conditions of hydrogen ion concentration and temperature (and in not too high a concentration of the protein in solution) the general viscosity due to isolated ions and molecules prevails in solutions of crystalline egg albumin and in solutions of metal caseinates (where the metal is monovalent) while under the same conditions the second type of viscosity prevails in solutions of gelatin and in solutions of acid-salts of casein; and also in solutions of crystalline egg albumin at a pH below 1.0 and at higher temperatures. The special viscosity is higher in solutions of gelatin than of casein salts for the probable reason that the amount of water occluded by the submicroscopic solid gel particles in a gelatin solution is, as a rule, considerably higher than that occluded by the corresponding particles of casein.

scholarly journals ION SERIES AND THE PHYSICAL PROPERTIES OF PROTEINS

1921 ◽  
Vol 3 (3) ◽  
pp. 391-414 ◽  
Author(s):  
Jacques Loeb
Keyword(s):  
Physical Properties ◽  
Osmotic Pressure ◽  
Opposite Sign ◽  
Hydrogen Ion ◽  
Ion Concentration ◽  
Depressing Effect ◽  
Protein Solution ◽  
Hydrogen Ion Concentration ◽  
Specific Effects ◽  
Protein Ions

1. Ions with the opposite sign of charge as that of a protein ion diminish the swelling, osmotic pressure, and viscosity of the protein. Ions with the same sign of charge as the protein ion (with the exception of H and OH ions) seem to have no effect on these properties as long as the concentrations of electrolytes used are not too high. 2. The relative depressing effect of different ions on the physical properties of proteins is a function only of the valency and sign of charge of the ion, ions of the same sign of charge and the same valency having practically the same depressing effect on gelatin solutions of the same pH while the depressing effect increases rapidly with an increase in the valency of the ion. 3. The Hofmeister series of ions are the result of an error due to the failure to notice the influence of the addition of a salt upon the hydrogen ion concentration of the protein solution. As a consequence of this failure, effects caused by a variation in the hydrogen ion concentration of the solution were erroneously attributed to differences in the nature of the ions of the salts used. 4. It is not safe to draw conclusions concerning specific effects of ions on the swelling, osmotic pressure, or viscosity of gelatin when the concentration of electrolytes in the solution exceeds M/16, since at that concentration the values of these properties are near the minimum characteristic of the isoelectric point.

scholarly journals THE INFLUENCE OF ELECTROLYTES ON THE SOLUTION AND PRECIPITATION OF CASEIN AND GELATIN

1921 ◽  
Vol 4 (2) ◽  
pp. 187-211 ◽  
Author(s):  
Jacques Loeb ◽  
Robert F. Loeb
Keyword(s):  
Osmotic Pressure ◽  
Colloidal Particle ◽  
Opposite Sign ◽  
Salting Out ◽  
Donnan Equilibrium ◽  
Donnan Effect ◽  
Low Concentrations ◽  
Protein Ions ◽  
High Concentrations ◽  
The Stability

1. Colloids have been divided into two groups according to the ease with which their solutions or suspensions are precipitated by electrolytes. One group (hydrophilic colloids), e.g., solutions of gelatin or crystalline egg albumin in water, requires high concentrations of electrolytes for this purpose, while the other group (hydrophobic colloids) requires low concentrations. In the latter group the precipitating ion of the salt has the opposite sign of charge as the colloidal particle (Hardy's rule), while no such relation exists in the precipitation of colloids of the first group. 2. The influence of electrolytes on the solubility of solid Na caseinate, which belongs to the first group (hydrophilic colloids), and of solid casein chloride which belongs to the second group (hydrophobic colloids), was investigated and it was found that the forces determining the solution are entirely different in the two cases. The forces which cause the hydrophobic casein chloride to go into solution are forces regulated by the Donnan equilibrium; namely, the swelling of particles. As soon as the swelling of a solid particle of casein chloride exceeds a certain limit it is dissolved. The forces which cause the hydrophilic Na caseinate to go into solution are of a different character and may be those of residual valency. Swelling plays no rôle in this case, and the solubility of Na caseinate is not regulated by the Donnan equilibrium. 3. The stability of solutions of casein chloride (requiring low concentrations of electrolytes for precipitation) is due, first, to the osmotic pressure generated through the Donnan equilibrium between the casein ions tending to form an aggregate, whereby the protein ions of the nascent micellum are forced apart again; and second, to the potential difference between the surface of a micellum and the surrounding solution (also regulated by the Donnan equilibrium) which prevents the further coalescence of micella already formed. This latter consequence of the Donnan effect had already been suggested by J. A. Wilson. 4. The precipitation of this group of hydrophobic colloids by salts is due to the diminution or annihilation of the osmotic pressure and the P.D. just discussed. Since low concentrations of electrolytes suffice for the depression of the swelling and P.D. of the micella, it is clear why low concentrations of electrolytes suffice for the precipitation of hydrophobic colloids, such as casein chloride. 5. This also explains why only that ion of the precipitating salt is active in the precipitation of hydrophobic colloids which has the opposite sign of charge as the colloidal ion, since this is always the case in the Donnan effect. Hardy's rule is, therefore, at least in the precipitation of casein chloride, only a consequence of the Donnan effect. 6. For the salting out of hydrophilic colloids, like gelatin, from watery solution, sulfates are more efficient than chlorides regardless of the pH of the gelatin solution. Solution experiments lead to the result that while CaCl2 or NaCl increase the solubility of isoelectric gelatin in water, and the more, the higher the concentration of the salt, Na2SO4 increases the solubility of isoelectric gelatin in low concentrations, but when the concentration of Na2SO4 exceeds M/32 it diminishes the solubility of isoelectric gelatin the more, the higher the concentration. The reason for this difference in the action of the two salts is not yet clear. 7. There is neither any necessity nor any room for the assumption that the precipitation of proteins is due to the adsorption of the ions of the precipitating salt by the colloid.

scholarly journals ON THE INFLUENCE OF AGGREGATES ON THE MEMBRANE POTENTIALS AND THE OSMOTIC PRESSURE OF PROTEIN SOLUTIONS

1922 ◽  
Vol 4 (6) ◽  
pp. 769-776 ◽  
Author(s):  
Jacques Loeb
Keyword(s):  
Membrane Potential ◽  
Hydrostatic Pressure ◽  
Osmotic Pressure ◽  
Membrane Potentials ◽  
Hydrogen Ion ◽  
Ion Concentration ◽  
Gelatin Solution ◽  
True Solution ◽  
Hydrogen Ion Concentration ◽  
Donnan Equilibrium

1. It is shown that when part of the gelatin in a solution of gelatin chloride is replaced by particles of powdered gelatin (without change of pH) the membrane potential of the solution is influenced comparatively little. 2. A measurement of the hydrogen ion concentration of the gelatin chloride solution and the outside aqueous solution with which the gelatin solution is in osmotic equilibrium, shows that the membrane potential can be calculated from this difference of hydrogen ion concentration with an accuracy of half a millivolt. This proves that the membrane potential is due to the establishment of a membrane equilibrium and that the powdered particles participate in this membrane equilibrium. 3. It is shown that a Donnan equilibrium is established between powdered particles of gelatin chloride and not too strong a solution of gelatin chloride. This is due to the fact that the powdered gelatin particles may be considered as a solid solution of gelatin with a higher concentration than that of the weak gelatin solution in which they are suspended. It follows from the theory of membrane equilibria that this difference in concentration of protein ions must give rise to potential differences between the solid particles and the weaker gelatin solution. 4. The writer had shown previously that when the gelatin in a solution of gelatin chloride is replaced by powdered gelatin (without a change in pH), the osmotic pressure of the solution is lowered the more the more dissolved gelatin is replaced by powdered gelatin. It is therefore obvious that the powdered particles of gelatin do not participate in the osmotic pressure of the solution in spite of the fact that they participate in the establishment of the Donnan equilibrium and in the membrane potentials. 5. This paradoxical phenomenon finds its explanation in the fact that as a consequence of the participation of each particle in the Donnan equilibrium, a special osmotic pressure is set up in each individual particle of powdered gelatin which leads to a swelling of that particle, and this osmotic pressure is measured by the increase in the cohesion pressure of the powdered particles required to balance the osmotic pressure inside each particle. 6. In a mixture of protein in solution and powdered protein (or protein micellæ) we have therefore two kinds of osmotic pressure, the hydrostatic pressure of the protein which is in true solution, and the cohesion pressure of the aggregates. Since only the former is noticeable in the hydrostatic pressure which serves as a measure of the osmotic pressure of a solution, it is clear why the osmotic pressure of a protein solution must be diminished when part of the protein in true solution is replaced by aggregates.

scholarly journals The potential difference occurring in a Donnan Equilibrium and the theory of colloidal behaviour

1923 ◽  
Vol 102 (719) ◽  
pp. 705-710 ◽  
Keyword(s):  
Second Law Of Thermodynamics ◽  
Great Emphasis ◽  
Potential Difference ◽  
Protein Solutions ◽  
Hydrogen Ions ◽  
Protein Solution ◽  
Strong Argument ◽  
Donnan Equilibrium ◽  
Viii And Ix ◽  
The Difference

J. Loeb, in a recent and stimulating work (1), has given a convincing, if somewhat over-emphatic, study of the colloidal behaviour of proteins in solution, based largely upon the theory of the Membrane Equilibrium first suggested by Donnan (4). In one important particular, however, his argument is incorrect. Loeb observed, by certain means (2) devised by himself, the potential difference (P. D.) between a protein solution on one side of a semipermeable membrane and a solution of acid, or of acid and salt, on the other side. He found this P. D. to vary as the concentration of hydrogen ions, or of salt, was varied, in the same manner as did a number of other factors (osmotic pressure, viscosity and swelling). He found also that this P. D. could be “calculated” from the observed difference of ρ -H (or of ρ -Cl) in the two solutions, on the basis of the theory of the Donnan Equilibrium, and he concludes that the excellent agreement between calculated and observed is a strong argument in favour of his explanation of other colloidal phenomena by that theory. This conclusion is not correct: the equality found by Loeb of the observed P. D., to that calculated from the difference of ρ -H is a necessary consequence of any mechanism which does not offend the Second Law of Thermodynamics, and in itself offers no support to the theory that the Donnan Equilibrium underlies the colloidal behaviour of protein solutions. That theory may rest on other and stronger ground; since, however, Loeb appears, throughout his book (and especially in Chapters VIII and IX) and in other places (2), (3), to lay great emphasis on this agreement of the observed P. D. with that “calculated” from the observed ρ -H’s it is necessary to point out that this agreement proves no more than that the system investigated was in equilibrium, and that the observations were accurately made.

scholarly journals AMPHOTERIC COLLOIDS

1919 ◽  
Vol 1 (4) ◽  
pp. 483-504 ◽  
Author(s):  
Jacques Loeb
Keyword(s):  
Osmotic Pressure ◽  
Maximum Pressure ◽  
Gelatin Solution ◽  
Bivalent Metal ◽  
Degree Of Ionization ◽  
Bivalent Cation ◽  
Protein Ions ◽  
Close Proximity ◽  
Tentative Explanation ◽  
Previously Treated

1. A method is given by which the amount of equivalents of metal in combination with 1 gm. of a 1 per cent gelatin solution previously treated with an alkali can be ascertained when the excess of alkali is washed away and the pH is determined. The curves of metal equivalent in combination with 1 gm. of gelatin previously treated with different concentrations of LiOH, NaOH, KOH, NH4OH, Ca(OH)2, and Ba(OH)2 were ascertained and plotted as ordinates, with the pH of the solution as abscissæ, and were found to be identical. This proves that twice as many univalent as bivalent cations combine with the same mass of gelatin, as was to be expected. 2. The osmotic pressure of 1 per cent solutions of metal gelatinates with univalent and bivalent cation was measured. The curves for the osmotic pressure of 1 per cent solution of gelatin salts of Li, Na, K, and NH4 were found to be identical when plotted for pH as abscissæ, tending towards the same maximum of a pressure of about 325 mm. of the gelatin solution (for pH about 7.9). The corresponding curves for Ca and Ba gelatinate were also found to be identical but different from the preceding ones, tending towards a maximum pressure of about 125 mm. for pH about 7.0 or above. The ratio of maxi mal osmotic pressure for the two groups of gelatin salts is therefore about as 1:3 after the necessary corrections have been made. 3. When the conductivities of these solutions are plotted as ordinates against the pH as abscissæ, the curves for the conductivities of Li, Na, Ca, and Ba gelatinate are almost identical (for the same pH), while the curves for the conductivities of K and NH4 gelatinate are only little higher. 4. The curves for the viscosity and swelling of Ba (or Ca) and Na gelatinate are approximately parallel to those for osmotic pressure. 5. The practical identity or close proximity of the conductivities of metal gelatinates with univalent and bivalent metal excludes the possibility that the differences observed in the osmotic pressure, viscosity, and swelling between metal gelatinates with univalent and bivalent metal are determined by differences in the degree of ionization (and a possible hydratation of the protein ions). 6. Another, as yet tentative, explanation is suggested.

scholarly journals The thermodynamic analysis of the observed osmotic pressures of protein salts in solutions of finite concentration

1929 ◽  
Vol 126 (800) ◽  
pp. 16-24 ◽  
Keyword(s):  
Osmotic Pressure ◽  
Protein Solutions ◽  
Ideal Solution ◽  
Partial Pressures ◽  
Protein Ions ◽  
Finite Concentration ◽  
Simplifying Assumptions ◽  
Fundamental Equations ◽  
General Method ◽  
The Ideal

The application of Dalton’s law of partial pressures to the osmotic pressures of mixtures of protein salts and diffusible salts has been discussed in a previous communication. The observed osmotic pressures of protein salts, measured with membranes permeable by water and other crystalloids but impermeable by the protein, are difficult to interpret until they have been analysed in terms of the partial osmotic pressures of protein ions and of diffusible ions. The partial osmotic pressure of the protein ions, symbolised p p , may be calculated from the observed osmotic pressure p by the formula p = p p + P i , in which P i represents the “ion pressure difference,” or the pressure due to the excess of diffusible ions inside the membrane. The provisional estimates of these partial pressures, p p and p i , published in the paper referred to above, depend upon a number of simplifying assumptions concerning the deviations from the ideal solution laws in mixtures of protein salts and diffusible salts, and the range of application of the approximate formulæ employed is restricted to mixtures in which the equivalent concentration of the protein salt is relatively small. In order to confirm the provisional results and to interpret the osmotic pressures of concentrated protein solutions, a more general method, based on Gibb’s fundamental equations, is developed in this paper.

scholarly journals Sampling of interstitial fluid and measurement of colloid osmotic pressure (COPi) in pigs: evaluation of the wick method

1998 ◽  
Vol 32 (4) ◽  
pp. 439-445 ◽  
Author(s):  
J. K. Heltne ◽  
P. Husby ◽  
M.-E. Koller ◽  
T. Lund
Keyword(s):  
Osmotic Pressure ◽  
Interstitial Fluid ◽  
Acute Inflammation ◽  
Circulatory Arrest ◽  
Colloid Osmotic Pressure ◽  
Protein Solutions ◽  
Protein Solution ◽  
Young Pigs ◽  
In Series

The wick method for sampling of interstitial fluid from subcutis was applied in fluid balance studies in young pigs. Colloid osmotic pressure was measured in serum (COPs) and interstitial fluid (COPi) using a membrane colloid osmometer. Our aims were to determine the 'true' COPi, and to find the optimal duration of wick implantation. In series I ( n=6) a 'crossover' experiment was performed using wicks soaked in different priming solutions (nondiluted and diluted serum protein solutions or isotonic salt solution). Circulatory arrest was induced just before wick insertion in order to eliminate the vascular part of the acute inflammation. In series II ( n=6) wicks were removed in sequence after 60, 90, 120 and 180 min sampling time in anaesthetized pigs in vivo. COPs, COPi and haematocrit (HCT) together with haemoglobin (Hgb), serum albumin and total protein concentrations were determined in the same animals. In series I average COPs and COPi were 13.7 (1.4) and 7.2 (1.4) mmHg respectively (SD). In series II the optimal wick implantation times were estimated to be 60–90 min for wicks soaked in diluted protein solution, and 90–120 min for dry and saline-soaked wicks. COPs averaged 13.0 (0.7) mmHg, HCT 30.0 (1.6)%, Hgb 8.3 (0.9) g/dl, s-albumin 22.7 (0.6) g/l and s-protein 47.3 (2.3) g/l. Compared to commonly reported reference values, we found surprisingly low values for most of the measured variables. This may be related to the fact that we used immature pigs. An analysis of the validity of the wick method based on our own results and published reports is presented. We conclude that sampling of interstitial fluid with subcutaneous wicks is easy to perform in young pigs. However, the COP-values measured in wick fluid have to be carefully evaluated especially when sampling is performed in vivo.

scholarly journals VALENCY RULE AND ALLEGED HOFMEISTER SERIES IN THE COLLOIDAL BEHAVIOR OF PROTEINS

1923 ◽  
Vol 5 (5) ◽  
pp. 693-709 ◽  
Author(s):  
Jacques Loeb ◽  
M. Kunitz
Keyword(s):  
Chemical Nature ◽  
Hydrogen Ion ◽  
Ion Concentration ◽  
Protein Solutions ◽  
Hofmeister Series ◽  
Protein Solution ◽  
Hydrogen Ion Concentration ◽  
Protein Gel ◽  
Protein Particles ◽  
As Solubility

It is shown by the older experiments by Loeb and by the experiments reported in this paper that the effect of salts on the membrane potentials, osmotic pressure, swelling of gelatin chloride, and that type of viscosity which is due to the swelling of protein particles, depends only on the valency but not on the chemical nature of the anion of the salt, and that the cation of the salt has no effect on these properties, if the pH of the protein solution or protein gel is not altered by the salt. The so called Hofmeister series of salt effects on these four properties are purely fictitious and due to the failure of the former authors to measure the hydrogen ion concentration of their protein solutions or gels and to compare the effects of salts at the same pH of the protein solution or the protein gel. These results confirm the older experiments of Loeb and together they furnish a further proof for the correctness of the idea that the influence of electrolytes on the four properties of proteins is determined by membrane equilibria. Such properties of proteins which do not depend on membrane equilibria, such as solubility or cohesion, may be affected not only by the valency but also by the chemical nature of the ions of a salt.

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