Abstract
1. Our results show clearly that the Hofmeister series is not the correct expression of the relative effect of ions on the swelling of gelatin, and that it is not true that chlorides, bromides, and nitrates have "hydrating," and acetates, tartrates, citrates, and phosphates "dehydrating," effects. If the pH of the gelatin is taken into considertion, it is found that for the same pH the effect on swelling is the same for gelatin chloride, nitrate, trichloracetate, tartrate, succinate, oxalate, citrate, and phosphate, while the swelling is considerably less for gelatin sulfate. This is exactly what we should expect on the basis of the combining ratios of the corresponding acids with gelatin since the weak dibasic and tribasic acids combine with gelatin in molecular proportions while the strong dibasic acid H(2)SO(4) combines with gelatin in equivalent proportions. In the case of the weak dibasic acids he anion in combination with gelatin is therefore monovalent and in the case of the strong H(2)SO(4) it is bivalent. Hence it is only the valency and not the nature of the ion in combination with gelatin which affects the degree of swelling. 2. This is corroborated in the experiments with alkalies which show that LiOH, NaOH, KOH, and NH(4)OH cause the same degree of swelling at the same pH of the gelatin solution and that this swelling is considerably higher than that caused by Ca(OH)(2) and Ba(OH)(2) for the same pH. This agrees with the results of the titration experiments which prove that Ca(OH)(2) and Ba(OH)(2) combine with gelatin in equivalent proportions and that hence the cation in combination with the gelatin salt with these two latter bases is bivalent. 3. The fact that proteins combine with acids and alkalies on the basis of the forces of primary valency is therefore not only in full agreement with the influence of ions on the physical properties of proteins but allows us to predict this influence qualitatively and quantitatively. 4. What has been stated in regard to the influence of ions on the swelling of the different gelatin salts is also true in regard to the influence of ions on the relative solubility of gelatin in alcohol-water mixtures. 5. Conductivity measurements of solutions of gelatin salts do not support the theory that the drop in the curves for swelling, osmotic pressure, or viscosity, which occurs at a pH 3.3 or a little less, is due to a drop in the concentration of ionized protein in the solution; nor do they suggest that the difference between the physical properties of gelatin sulfate and gelatin chloride is due to differences in the degree of ionization of these two salts.
Highlights
The second row gives the pH of these supernatant HC1 solutions after 1 hour, and the third row gives the pH of the gelatin solutions after the supernatant HC1 solution had been drained off and after the remaining mass of gelatin had been melted and brought to a volume of 100 cc. by adding enough distilled water of pH 5.6. It will be noticed: first, that the pH of the supernatant HC1 solution after 1 hour is higher than the pH of the original HC1 solution owing to the fact that some acid combined with the gelatin; and, second, that the pH of the gelatin solution is considerably higher than that of the supernatant solution owing to the Donnan equilibrium, according to which the concentration of free acid outside the gelatin must be greater than inside
It is obvious that the pH of the supernatant solution is higher than that of the gelatin solution, as we should expect from the Donnan equilibrium
We may say that gelatin chloride becomes soluble in an alcohol-water mixture containing more than 75 per cent alcohol as soon as its p H is ~ 4.45
Summary
Follow this and additional works at: https://digitalcommons.rockefeller.edu/collection-of-reprints-loeb. In this paper we will continue the demonstration of the relation between the combining ratios of acids and bases with proteins and the effect of ions on the physical properties of proteins This demonstration completes the proof that the purely chemical forces of primary valency determine the reactions of proteins with other compounds. It is generally stated in colloidal literature that gelatin swells more in chlorides, bromides, or nitrates than in water and that it swells less in citrates, acetates, tartrates, phosphates, and sulfates than in water. As far as the writer can determine from tire literature the discrimination between "hydrating" and "dehydrating" ions originated from these experiments
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