PRECIPITATION 279 



Practical application has been made of this phenomenon 

 for separating the various types of protein. Thus, for example, 

 if an aqueous solution containing an albumen and a globulin 

 be mixed with an equal volume of saturated ammonium sul- 

 phate solution, the globulin, being insoluble in the resulting half- 

 saturated ammonium sulphate, is precipitated ; after filtering 

 off the globulin, the albumen may be precipitated from the 

 mother liquor by saturating it with ammonium sulphate. 



The precipitated albumen and globulin are chemically un- 

 changed and can be redissolved if desired. 



PauH,* in studying the precipitation of albumen by various 

 salts, came to the conclusion that the precipitating power of 

 a salt was an additive property which depended on the 

 constituent ions. 



Rations, as a rule, act as precipitants for albumen, while 

 anions tend to keep it in solution.f 



The precipitating power of the kations increases in the 

 following order: Mg, NH4-, K, Na, Li, while the inhibiting 

 or solvent action of the anion increases in the following 

 order : -C2H302,-Cl,-N03,-Br,-I,-CNS. 



According as the precipitating power of the kation or the 

 inhibiting power of the anion predominates the resulting salt 

 will either precipitate or not precipitate albumen. 



The observations are given below in tabular form. As 

 shown by the arrows, the kations and the anions are arranged 

 in ascending order of precipitating and inhibiting power 

 respectively. The symbols + and - respectively signify that 

 the salt does or does not precipitate albumen, the blank spaces 

 meaning that the salt has not been investigated. 



Rations _> Mg NH4 K Na Li 



Anions 



I 



Fluoride + + + 



Sulphate + + + + + 



Phosphate + + + 



Citrate + + + 



Tartrate + + + 



Acetate - - + + 



Chloride - - + + + 



Nitrate - - - + + 



Chlorate - - + 



Bromide _ _ _ _ 4. 



Iodide _ _ _ 



Sulphocyanide _ _ _ _ 



* Pauli : " Beitr. z. chem. Phys. u. Path.," 1902, 3, 225 ; 1903, 5, 30. 

 t See p. 300. 



