78 COLLOID CHEMISTRY OF THE PROTEINS 



particularly instructive. It is well known that in high acid 

 concentrations albumin is precipitated with formation of a 

 coagulum, which is not dispersed again on dilution. If this 

 irreversible change is regarded as a secondary effect, one can 

 reasonably suppose that this precipitation is only effective on 

 the neutral particles, for only such can be deposited out of a 

 solution. 



It can further be supposed that neutral particles are more 

 soluble the more they are hydrated. The viscosity of the acid 

 proteins after the maximum has been passed is a measure of 

 the number of neutral particles, and therefore of their hydra- 

 tion ; consequently a relation between viscosity and precipi- 

 tation by acids is to be expected in the sense that low viscosity 

 and low precipitation will be coincident. This has actually 

 been found by Pauli and R. Wagner,* who measured the con- 

 centration of various acids required to precipitate a serum 

 albumin free from salts (Table 32). 



Table 32. 



The agreement in this table is very satisfactory, particularly 

 when one considers that the final products of the acid precipita- 

 tion exhibit considerable differences in properties (e.g., solubi- 

 lity in excess of acid) . The reaction of nitric acid with albumin 

 does not permit of viscosity measurements at 25 when more 

 than o-oi N acid is present. Even better agreement is obtained 

 when the series of hydrion concentrations, corresponding to the 



* " Anzeiger Akad. Wissensch. Wien." 1910. No. IX. Biochem. 

 Zeitsch., 1920, 104, 190. 



