412 SCIENCE PROGRESS 



oxalates, citrates, and tartrates should be in the region of the 

 sulphate curve. 



Similar results are obtained with the alkalis ; the curve 

 for the weak base ammonium hydroxide is the same as that for 

 the strong bases, lithium, sodium, and potassium hydroxides, 

 when plotted with pH as abscisscC, whilst the curve for calcium 

 and barium hydroxides are considerably lower. 



Salts such as sodium acetate, which give an alkaline 

 solution in water, owing to hydrolysis, have an abnormal 

 effect on the swelling, etc., of gelatin, when compared with, 

 say, sodium chloride. Loeb has shown that this is due to the 

 alteration of the pH of the gelatin solutions when the salt is 

 added ; when compared at the same pH, sodium chloride and 

 sodium acetate have the same effect. 



The above results, and many others, indicate the necessity 

 of knowing the pH when investigations are carried out, and 

 show that when comparisons are made under the proper 

 conditions the Hofmeister series, with their anomalies, disappear. 



The increased swelling, viscosity, etc., which take place on 

 either side of the isoelectric point, and reach a maximum ^ at 

 pH's of about 3'5 and 8'5 respectively, are attributed by Pauli 

 to the greater hydration of the gelatin ions formed, as compared 

 with that of the neutral molecule, but Loeb is not in agree- 

 ment with this. The latter postulates the existence in any 

 protein solution of molecularly dispersed particles, floating 

 side by side with submicroscopic particles occluding water, 

 the amount being regulated by the Donnan equilibrium 

 (Procter was the first to apply the Donnan equilibrium to the 

 study of gelatin solutions). The osmotic effects are determined 

 by the molecular particles, the viscosity effects by the sub- 

 microscopic particles. Any influence in the solution, e.g., 

 change in the hydrion concentration, by which the molecular 

 dispersion is increased at the expense of the solid particles, 

 will result in an increase in the osmotic pressure and a decrease 

 in viscosity, and the opposite conditions will result in the 

 reverse of these effects. 



The structure of gels has been a bone of contention for a 

 long time. Bogue {Journ Amer. Chem. Soc, 1922, 44, 1343) 

 has given a summary of the various views which have been 

 held, which may be stated briefly as follows : Nageli assumed 

 that gels were two-phased, and that the solid phase was 

 crystalline, but Sherrer has not found any indication of crys- 

 talline structure in gelatin, when examined by the X-ray 

 method. Biitschli and van Bemmelen have advocated a cell- 



^ Pauli and Loeb give different explanations of the maximum, but these 

 will not be entered into now. 



