368 
PHYSICS: T. LYMAN 
general solutes may be treated as normal or 'perfect* solutes is much 
more persistent. 
The magnitude of the deviation of the strong electrolyte from the 
normal behavior depends greatly upon the terms in which this devia- 
tion is expressed. The equilibrium expression C] I increases with 
the concentration. Thus for potassium chloride it increases from 0.026 
at 0.001 normal to 0.55 at 0.1 normal, an increase of 21 fold. The 
results given in the table show that this behavior is accounted for by a 
deviation of 3.3% in the osmotic pressure of the ions and of 37% in 
that of the undissociated molecules. The percentage deviation when 
expressed as here in terms of osmotic pressure is smaller than when it 
is expressed, as Lewis^ has done, in terms of activity; this follows from 
the logarithmic relation between the two. 
A more thorough study of these topics is appearing in The Journal 
of the American Chemical Society. 
1 E. W. Washburn, /. Amer. Chetn. Soc, 32, 484-5 (1910). 
2 S. J. Bates, /. Amer. Chem. Soc, 35, 519 (1913). 
3 The data have been taken in great measure from the compilation of A. A. Noyes and 
K. G. Falk, /. Amer. Chem. Soc, 32, 1011 (1910). This has been supplemented by the 
recent measurements of F. Fliigel, Zs. physik. Chem., 79, 577 (1912), of W. A. Roth, Ibid., 
79, 599 (1912), of E. W. Washburn and D. A. Mclnnes,/. Amer. Chem. Soc, 33, 1686 (1911) 
and of L. H. Adams, Ibid., 37, 481 (1915). 
'Zs. physik. Chem., 33, 545 (1900). 
^J. Amer. Chem. Soc, 34, 1631 (1912). 
THE EXTENSION OF THE SPECTRUM BEYOND THE 
SCHUMANN REGION 
By Theodore Lyman 
JEFFERSON PHYSICAL LABORATORY. HARVARD UNIVERSITY 
Presented to the Academy, May 22, 1915 
The violet limit of the spectrum determined by direct eye observation 
lies in the neighborhood of 4000 angstrom units; with a glass prism and 
lenses the spectrum may be followed photographically to wave length 
3000 or thereabout; with a quartz system or with a reflecting grating, 
the limit may be pushed to wave length 1850. Victor Schumann showed 
that the absorption of the air and of the gelatine of the photographic 
plate were responsible for the abrupt termination of the spectrum. 
By employing a vacuum spectroscope and a special photographic plate 
whose emulsion was very poor in gelatine, he was able to push his ob- 
servations to wave length 1230. At this point he was stopped by the 
opacity of the fluorite of which his lenses were made. 
