PROTEINS AS COLLOIDS 319 



ally neutral albumen, is explained by assuming that albumen 

 exerts some selective action on the ions, and is more permeable 

 to positively charged hydrogen ions than it is to the negative 

 chlorine ions. Pauli has further shown that his electrically 

 neutral albumen, unlike ordinary albumen, is not precipitated 

 from solution by the addition of salts of copper, iron, zinc, 

 lead or mercury. The fact that neutral albumen is, however, 

 precipitated by alcohol, although both substances are electric- 

 ally neutral, must not be taken as evidence against the view 

 that precipitation is produced as a result of the neutralization 

 of the charges borne by colloidal particles ; the explanation of 

 the precipitation in this case lies in the complete insolubility 

 of albumen in alcohol. 



These facts throw some light on the electrical behaviour of 

 native albumen in the living organism, for inasmuch as salts 

 of the metals at once precipitate such albumen, whereas they 

 refuse to precipitate neutral albumen, it follows that native 

 albumen must bear a negative charge. This negative charge 

 is most probably produced by the hydroxyl ions* liberated 

 from the salts in contact with it, a view which receives support 

 from the fact that on adding sodium bicarbonate to a fresh 

 solution of neutral albumen, the latter at once assumes a 

 negative charge. 



As a consequence of this negative charge, it follows that 

 the greater the electro-positive nature of an element, the 

 greater will be its tendency to precipitate native albumen ; on 

 the other hand, the electro-negative acid radicles will tend to 

 prevent precipitation, a tendency which is found to increase 

 in the following order sulphate acetate, chloride, nitrate, 

 bromide, iodide and sulphocyanide. 



The antagonistic action of electro-positive and electro- 

 negative radicles accounts for the fact that sodium in the 

 form of sodium sulphate is a precipitant, whereas in the form 

 of sodium bromide it is not ; in the case of sodium iodide and 

 sulphocyanide, the influence of the electro-negative radicle 

 entirely outweighs that of the electro-positive sodium, with the 

 result that these salts not merely do not precipitate albumen 

 themselves, but actually interfere with the precipitation of 

 albumen by other salts. 



* Pauli : " Hofmeister's Beitrage," 1906, 7, 531. 



