26o 
CHEMISTRY: E. J. COHN 
Proc. N. a. S. 
on the ionization constant of the acid or base and the amphoteric constants 
of the protein. The effect of a neutral salt upon such systems has recently- 
been exhaustively studied by Sorensen, Hoyrup, Hempel and Palitzsch.^ 
It is illustrated by the data in table I. These are in substantial agree- 
ment with those recently published by Sorensen and his collaborators. 
They moreover derived an equation from the mass law which enabled them 
to calculate the hydrogen ion concentration of any ampholyte in the pres- 
ence of an acid, and the salt of the acid and a strong base, if the dissocia- 
tion constants of ampholyte, acid, and salt, and the concentrations of the 
components of the systems were known. In this equation "the influence 
of the salt only appears by the fact that the values of" "the degree of 
dissociation of the acid" and "of the salt of the acid together with the am- 
pholyte" "vary with the concentration of the salt." (9, pp. 93 and 101.) 
In other words, the effect of a neutral salt with a common ion is to de- 
press the dissociation of the acid, and of the salt of the acid with the pro- 
tein. As a result the acid combining capacity of the protein is increased, 
and the hydrogen ion concentration decreased. If the protein is ionized 
as acid on the other side of its isoelectric point and is combined with base, 
the depression in the dissociation of the base, and of the salt of the protein 
and the base, causes the hydrogen ion concentration to increase. The 
effect of salt in depressing the dissociation of the protein compound, how- 
ever ionized, thus causes the hydrogen ion concentration of protein systems 
to converge upon the isoelectric point of the protein. As a result Sorensen 
has concluded: 
"at hydrogen-ion concentrations which are not situated at or in the 
neighborhood of the isoelectric point of the ampholyte the capacity to 
combine with acids 
"(a) is independent of the ampholyte concentration; 
"(6) increases with rising concentration of salt; 
'\c) is positive at hydrogen-ion concentrations superior to that corre- 
sponding with the isoelectric reaction of the amphol3rte, and 
'\d) is negative — that is, the ampholyte is combined with sm-plusbase — 
at hydrogen-ion concentrations inferior to that corresponding with the iso- 
electric point of the ampholyte. 
"At hydrogen-ion concentrations corresponding with or situated in the 
neighborhood of the isoelectric point of the ampholyte, the conditions are 
not easily discernible; the capacity to combine with acids is in this case 
not independent of the concentration of the ampholyte, but is the greater 
the smaller the latter is." (9, p. 161.) 
Whenever complicating colloidal phenomena do not interfere, therefore, 
the mass law demands that a neutral salt increase the hydrogen ion con- 
centration of systems containing protein when ionized as acid, and de- 
crease the hydrogen ion concentration when ionized as base. Salt should, 
accordingly, have least effect when the hydrogen ion concentration of the 
