156 COLLOIDS IN BIOLOGY AND MEDICINE 



The conditions governing the action of neutral salts upon acid 

 albumin are not sufficiently understood to warrant proposing a simple 

 scheme. 1 



The optical rotation of albumin runs parallel with the changes 

 in its internal friction and coagulability (Wo. PAULi,* 5 M. SAMEC, 

 E. STRAUSS). In fact, the albumin ions rotate light more power- 

 fully than neutral albumin. 



Let us summarize briefly : neutral albumin has a low internal fric- 

 tion, coagulates easily and shows little optical rotation; ionized albumin 

 has high internal friction, coagulates with difficulty and rotates light 

 powerfully; neutral salts diminish ionization. 



This chemical point of view is additionally supported by the 

 investigations of P. PFEIFFER and J. W. MODELSKI as well as of P. 

 PFEIFFER and WITTKA. These authors have shown that amino acids 

 and polypeptids of known chemical structure form with neutral 

 salts of the alkalis and earth alkalis, crystalline addition compounds 

 constructed on simple stoichiometric principles. Some of these 

 molecular compounds are much more readily soluble in water than 

 the aminoacids or polypeptids and some much less soluble, so that, 

 as in the case of albuminous substances, it is possible to salt some of 

 them out (analogous to globulins). 



Albumin and Inorganic Hydrosols 



According to U. FRIEDEMANN*! electrolyte-free albumin is precipi- 

 tated both by positive and by negative inorganic hydrosols. Hydro- 

 phobe hydrosols such as As 2 S 3 , Au, etc., regularly form precipitates, 

 which, according to W. PAULI and HECKER, are not inhibited by an 

 excess either of hydrosol or of albumin. Neutral salts, acids and 

 alkalis exert a protective action, but nonelectrolytes, such as urea 

 and sugar, are inactive. 



In the case of positive hydrophik inorganic hydrosols such as 

 Fe(OH) 3 there is an optimum precipitation zone that lies somewhere 

 between one part by weight of Fe(OH)3 and three parts by weight 

 of the electrolyte-free albumin. With an excess of Fe(OH) 3 there is 

 increasing solution which is complete in about the proportion of two 

 to three; there is no complete solution with an excess of albumin. 

 Neutral salt exerts a protective action when albumin is in excess but 

 on the contrary favors precipitation when Fe(OH) 3 is in excess. 

 Acids inhibit precipitation; alkalis precipitate when Fe(OH) 3 is in 



1 From the formula it should not be assumed that only free terminal NH 2 

 groups are considered. As the result of the work of BLASEL and J. MATUTA on 

 deaminized glutin (glutin whose free NH2 groups are satisfied) it is more probable 

 that its interior NH groups are involved in the formation of salts with acids. 



