THE EFFECT OF HEAVY SALTS ON ALBUMINS 



307 



soluble in an excess of both the heavy metal and the albumin, Galeotti 

 has spoken of such compounds as reversible ones, but Pauli points out 

 rightly that the term ' reversible ' should only be used for the com- 

 pounds which, on dilution with water or on dialysis, are reconverted 

 into the initial unaltered albumin. Reversible coagulates are thus 

 only formed by the neutral salts of the alkalies and of magnesium. 

 According to Pauli 1 the essential difference between the salts of the 

 alkaline earths and those of the heavy metals is shortly this : In the 

 alkaline earths both kat-ions and an-ions play a part in producing 

 coagulation, although the effect produced by the an-ions is subsidiary. 

 In the salts of the heavy metals the only coagulating factor is the 

 kat-ion, the an-ions being negligible. 



* Concentration of ZnS0 4 



Pauli has experimented on egg-white with ZnS0 4 , CuS0 4 , and 

 3 . He distinguishes the following three types of phenomena. 



1 . In the case of ZnS0 4 , starting with very dilute concentrations of 

 tiis salt O'OOOS to O'OOl normal in I'lO egg-white, a coagulum is 

 btained, which on dilution is not reversible ; in concentrations of 

 5 to 4 normal, ZnS0 4 does not cause coagulation ; beyond 4 normal 

 oncentrations a precipitate is formed, which, on diluting the solution 

 ip to 4 and 0'5 normal, dissolves again, while, if the dilution be 

 arried beyond 0'5 normal, an irreversible coagulum is formed. The 

 reater the concentration of the albumin, the more does the indifferent 

 one become narrowed down, as is seen from the figure given by Pauli, 

 n which L, II., and III. represent increasing strengths of albumin. 



From this figure it also follows that in the region of the second 

 recipitation the albumin will be precipitated by diminishing not only 

 he albumin + salt-content, but also the salt percentage alone. 



1 W. Pauli, ffofmeister's Beitrage, 6. 233 (1905). 



