i8 
CHEMISTRY: NO YES AND MacINNES Proc. N. A. S. 
aided by the loading of heavier calcareous and ferruginous deep-sea de- 
posits. Since the principal elevation and erosion of the continental border 
strips fronting the Atlantic took place during the Palaeozoic, it is suggested 
that the present conformation of the Atlantic bottom dates back in part 
at least to that era. 
THE IONIZATION AND ACTIVITY OF LARGELY IONIZED 
SUBSTANCES 
By Ajithur A. Noyks and Duncan A. MacInnes 
Research Laboratory op Physicai. Chemistry, Massachusetts Institute 
OF TeCHNOIvOGY 
Read before the Academy, November 10, 1919 
In applications of the ionic theory of solutions it is customary to em- 
ploy, in accordance with the original hypothesis of Arrhenius, as a measure 
of the degree of ionization of salts, acids, and bases, the ratio of the equiva- 
lent conductance of the substance at any given concentration to the limit- 
ing value of the equivalent conductance as the concentration approaches 
zero, where the ionization may be assumed to be complete. 
This assumption, however, is not a necessary conclusion from the 
fundamental theory of ionic conduction. According to this theory, 
the equivalent conductance A (which is by definition the quantity of elec- 
tricity which under a potential-difference of one volt passes per second 
between electrodes of indefinite extent 1 cm. apart, between which is 
placed that quantity of solution which contains one equivalent weight 
of the ionizing substance) is for a uniunivalent substance given by the 
expression A = 7F(u+ + u~), in which y is the fraction of the substance 
ionized (equal in this case to the number of equivalents of each ion present 
in the solution), F the quantity of electricity (96,500 coulombs) associated 
with each equivalent of ion, and u+ and u~ the mobilities of the positive 
and negative ions (that is, their velocities through the solution under a 
potential-gradient of one volt per centimeter). For the equivalent con- 
ductance Ao at zero concentration, where the ionization becomes com- 
plete, we have the corresponding expression Ao = f(Uo+ + Uo"). Com- 
bining these two equations we get 
A_ u+ + u~ 
Ao ^ Uo+ + Uo~* 
From this equation it is evident that A/Ao is equal to the ionization only 
when the mobilities of the ions can be assumed constant up to the concen- 
tration under consideration. That they should remain constant so long 
as the solution does not differ appreciably from water as a viscous medium, 
may seem reasonable; but, in view of possible electrical effects resulting 
from the large electric charges on the ions, it is by no means certain. 
