1 8 THE VEGETABLE PROTEINS 



rate under these conditions in a crystalline form can usually be ob- 

 tained as a crystalline deposit by dialysing their saline solutions 

 into water, and this method, which was first employed by the writer 

 (301) for the production of crystalline preparations of proteins, is one 

 which presents many advantages and yields products of great purky. 

 Other salts than sodium chloride may be employed for extracting the 

 globulins but these have not been frequently used. Thus Griibler 

 (143) obtained crystalline preparations from solutions of the chlorides 

 of sodium, ammonium, barium, and calcium, of the bromides and 

 iodides of potassium, of magnesium sulphate, ammonium oxalate, and 

 potassium ferrocyanide. 



Preparations of seed globulins frequently contain more or less of an 

 alteration product which is insoluble in neutral saline solutions. (Com- 

 pare Chapter VII., p. 38.) This product, which forms in acid solutions, 

 greatly interferes with the subsequent purification of the globulin, as, 

 owing to the fact that it cannot be restored to its original condition, it. 

 is lost for further purification and study. The proportion of such in- 

 soluble derivatives of the globulin can usually be greatly diminished if 

 the amount of free acid in the extract is kept at a minimum. It is, 

 therefore, usually advisable to add to the saline solution, used in 

 making the extract, a sufficient quantity of baryta to make the extract 

 neutral to litmus. A larger proportion of baryta should be avoided, 

 for if more than enough is added to make the extract neutral to sensitive 

 litmus paper, the yield on dialysis may be greatly diminished. 



C. Extraction with Alkaline Solutions. 



Alkaline solutions were extensively used by Ritthausen and, during 

 the earlier years of his work, were almost exclusively employed by him 

 for isolating the proteins which he studied. Owing to the danger of 

 alteration in the protein which might result from the action on it of 

 the alkali, the results which Ritthausen obtained were regarded with 

 suspicion by most physiological chemists. Consequently the use of 

 alkalies has for many years past been abandoned except in those cases 

 where it is not possible to isolate the protein by any other means. It 

 is probable that the alterations which result in the protein during ex- 

 traction with sufficiently diluted alkalies have been greatly exaggerated, 

 and that such solvents often yield preparations of the unchanged 

 protein. In fact, experience has shown that evident alterations in the 

 protein molecule result far more quickly and extensively under the 

 influence of minute quantities of acid than they do under the influence 

 of equivalent quantities of alkali. Ritthausen showed that many of 



