CHEMISTRY: J. H. ELLIS 
83 
uncertainty, with the values which hold between the same metals at 
ordinary temperatures. 
So far then as experiment has thus far gone, Einstein^s equation seems 
to be an exact statement of the energies of emission of corpuscles under 
the influence of light waves. 
Nevertheless the physical theory which gave rise to it seems to me 
to be wholly untenable . Be this as it may, however, the photo-electric 
results herewith presented constitute the best evidence thus far found 
for the correctness of the fundamental assumption of quantum theory, 
namely, the discontinuous or explosive emission of energy by electronic 
oscillators. They furnish the most direct and most tangible evidence 
which we yet have for the actual physical reaHty of Planck's h. 
1 R. A. Millikan, Physic. Rev.. Ser. 2, 4, 73 (1914); Ibid., 6, 55 (1915). 
2 Einstein, Ann. Physik., Ser. 4, 17, 132 (1905) and 20, 199 (1906). 
^Ramsauer, Ann. Physik., 45, 1120 (1914), also 45, 961. 
^Millikan and Winchester, Physic. Rev., 24, 16 (1906), and Phil. Mag., Ser. 6, 14,188 
(1907). 
6 Millikan, Physic. Rev. 2, 143 (1913). 
s Schottky, Ann. Physik., 44, 1011 (1914). 
THE CHEMICAL ACTIVITY OF THE IONS OF HYDROCHLORIC 
ACID DETERMINED BY ELECTROMOTIVE FORCE 
MEASUREMENTS 
By James H. Ellis 
RESEARCH LABORATORY OF PHYSICAL CHEMISTRY. 
MASSACHUSETTS INSTITUTE OF TECHNOLOGY 
Received by the Academy, January 22, 1916 
The fact that the laws of perfect solutions which are conformed to 
by unionized or slightly ionized substances in dilute aqueous solutions 
are subject to large deviations in the case of largely ionized substances 
(salts, strong acids and bases) even at small concentrations makes it 
necessary, in the absence of any theoretical explanation of the deviations, 
to treat dilute solutions of these substances hke concentrated solutions 
of other substances, namely, to determine experimentally the behavior 
of the separate substances, with the hope that this empirical study may 
then lead to generalizations. Now the most important characteristic 
of ionizing substances is the chemical activity which results from their 
ionization, or more specifically the (mass-action) effect which their 
ions exercise in determining chemical equilibria. This effect in the case 
of theoretically perfect solutes is proportional to the concentration of 
the ions; but in the case of deviating solutes there must be substituted 
