THE PHYSICAL PROPERTIES OF THE PROTEINS 15 



As an example of a combined method of fractional precipitation 

 by both alcohol and a salt, the following, for the separation of five 

 constituents of Witte's peptone according to Haslam, may be quoted. 

 To a 2 per cent, solution of Witte's peptone add an equal volume of 

 alcohol and allow the mixture to stand overnight, or at least for 

 some hours. Filter, collect the precipitate and swim it out on water. 

 The insoluble portion is crude hetero-proteose and may be filtered 

 off or obtained by decantation. The soluble portion contains a- 

 proto- and a-deutero-proteose ; on half-saturation of the aqueous 

 solution of the mixture with ammonium sulphate the former can 

 be precipitated ; the latter comes down from the filtrate on complete 

 saturation. The /3-proto- and /3-deutero-proteose remain in the first 

 alcoholic filtrate. If the alcohol be evaporated off at a low tempera- 

 ture and the solution made up to its original volume, and the liquid 

 thus obtained be half-saturated with ammonium sulphate, /2-proto- 

 proteose is precipitated ; by completely saturating the filtrate the 

 /3-deutero-proteose can be obtained. By performing the precipita- 

 tions twice purer products can be obtained. 



SECTION II. THE DEGREE OF SOLUBILITY OF PROTEINS IN 

 SALT SOLUTIONS. 



In experiments on " salting out," the precipitation limits have 

 almost always been determined in solutions containing but a small 

 amount of protein ; even when so much salt has been added that no 

 further precipitation takes place, the solution may still contain a 

 certain amount of protein, owing to the fact that the latter is not 

 absolutely insoluble. But little work has been done so far in the 

 determination of this degree of solubility ; the most instructive is 

 that, perhaps, of Osborne and Harris on the solubility of plant 

 globulins in salts of various concentrations ; in this case the results 

 are of interest owing to the fact that the protein itself is insoluble in 

 pure water. These investigators found that there were two classes 

 of globulin solvents, viz. : (i) those in which a relatively considerable 

 quantity of salt must be present before notable quantities of globulin 

 commence to dissolve, and from which it is precipitated by dilution 

 with much water, or by the addition of small quantities of strong 

 acids, and (ii) those in which solution is brought about by low 

 concentrations of salt from which the protein is not precipitated 

 by dilution with water or by acids. The first class includes solutions 

 of the salts of strong bases with strong acids, the second the solution 

 of salts of weak bases. 



The degree of solution is considerably influenced in the case 

 of the globulin edestin by the presence of small quantities of 

 acids and bases ; this subject will, however, be discussed in greater 

 detail later in considering the action of acids and bases on pro- 

 teins. The behaviour of edestin towards acetate solutions is ano- 

 malous. Although it is insoluble in solutions of potassium, sodium 

 and ammonium acetate, it is soluble in the acetates of barium, 

 strontium, calcium and magnesium ; the solubility in these ace- 

 tates is in the order of their molecular weights. In solutions of 

 silver, copper and lead acetates it is nearly as soluble as in solutions 

 of free acids of corresponding concentration ; the positive ion enters 



