282 CHEMISTRY OF THE PROTEIDS CHAP. 



Spiro l regards the salting-out process in the light of the laws 

 regulating the coefficiency of distribution. This is fully discussed by 

 the author in his Physiological Histology? who there points out that 

 to say a substance distributes itself between two other substances, as 

 does, for example, an organic acid between ether and water, is not to 

 give an explanation at all, but amounts simply to a recapitulation of 

 the fact. For an explanation we must know ' why ' any given 

 substance distributes itself by preference in one of two substances, and 

 such an explanation must have a chemical basis. 



From the table on p. 281 showing the effect of saturated salt 

 solutions on albuminous substances, it is evident that solutions 

 behave quite differently according to the nature of the salt. If we 

 multiply the solubility by the molecular weight we find ammonium 

 sulphate, potassium acetate, and magnesium sulphate agree in giving 

 high figures as compared with sodium chloride, but potassium sulphate 

 does not coagulate although it gives a higher figure than does sodium 

 sulphate. 3 



Posternak published in 1901 4 an extensive series of experiments 

 on coagulation, but this work escaped the author in the summary of 

 colloids in his Physiological Histology. Posternak believes colloids to be 

 characterised by being in the form of micellae, a term which was first 

 used by v. Nageli. 5 A. micella is defined by Posternak as the 

 smallest quantity of a colloid, possessing the physical properties of 

 the colloid taken as a whole, and formed by the association of 

 molecules of large size. A micella is, however, not of invariable size, 

 for it may be diminished more or less according to the number and 

 the mobility of ions present in the solution. The ions diminish the 

 size of the micellae by imparting to them an electrical charge, the 

 diminution in the size of the micellar magnitude being proportional 

 to the charge or to the electrifying power of the ions, and therefore 

 an insoluble colloid cannot dissolve in distilled water. While according 

 to Posternak's view ions have the tendency to produce a solution of 

 the colloidal micellae, non-dissociated salt molecules are believed to 

 have the opposite effect, i.e. to produce precipitation. A struggle is 

 believed to go on continuously between the ions and the non-dissociated 

 molecules, and the greater the mobility of the ions the less protected 

 will a micella be. Thus if sodium chloride and potassium chloride 



1 K. Spiro, Hofmeisters Beitrage, 4. 300 (1903). 



2 Mann, Physiological Histology, 1902, pp. 328, 331, 311. 

 :>> Manu, Physiological Histology, 1902, p. 31. 



4 Swigel Posternak, Ann. de VInst. Pasteur, 15. pp. 85, 169, 451, 570 (1901). 



5 C. v. Nageli, Mechanisch-physiologische Theorie d. Abstammungslehre, Miinchen 

 and Leipzig, 1884. 



