10 ABSORPTION SPECTRA OF SOLUTIONS 



about 30 a.u. wide. The X4425 band shows a widening of about 15 a.u. 

 over the range shown in this plate. 



The broad bands with the centers near X5125 and X5800 show most marked 

 changes. In each case the most marked change is almost entirely toward 

 the red end of the spectrum, the violet edge of the band remaining almost 

 unchanged. This is the case especially with the X5800 band. 



The concentration of the solution used in B, plate 3, was one-tenth satu- 

 rated, the depth of the cell being 10 cm. The temperatures, beginning 

 next to the numbered scale, were 20, 45, 70, 95, 120, and 145. 



Although the total number of absorbers in B are the same as in A, yet it is 

 seen that the change in the bands is far greater m A,i. e., where the concen- 

 tration is greatest. Only the X5800 band shows appreciable change in B, 

 and even this does not widen more than 40 a.u. 



The concentration of the solution used in making the negatives of A, 

 plate 4, was one-tenth of saturation, the depth of absorbing layer 10 cm. 

 The temperatures, beginning with the strip nearest the numbered scale, 

 were 20, 45, 70, 95, 115, 140, 165, and 190. 



Aside from the slight tendency of all the absorption bands to become a 

 little more diffuse at the higher temperatures, though not more intense, 

 there is no marked change in any band except X4275 and X5800. The former 

 of these, as we go toward the higher temperatures, remains perfectly sharp 

 and constant on its violet edge, while there is a regular shading toward the 

 red end of the spectrum. Again, the greatest change takes place in band 

 X5800, the violet end remaining fixed and the red edge widening between the 

 first and last strips to the extent of about 50 a.u. All the exposures of this 

 plate were made as the temperature of the cell was raised. 



The identical solution used in A was photographed in B, plate 4, the cell, 

 intensity of light-source, and all of the apparatus remaining unchanged, 

 the only difference being that the exposures of B were made at regular 

 intervals as the temperature of the cell was lowered. The temperatures of 

 the successive strips in B were, beginning with the strip nearest the num- 

 bered scale, 190, 165, 140, 115, 95, 70, 45, 20. 



The original films shGw A and B to be exactly the reverse of each other. 

 Just those changes produced in A by a rise in temperature are reversed by 

 the corresponding fall of temperature in B. Of course this is only qualita- 

 tive, since we can establish no definite quantitative relations from the photo- 

 graphic plates. In order to do this, energy measurements must be made, 

 not only on each band, but on different parts of the same band. Such work 

 is now in progress. This would be very difficult to do with a narrow 

 band like X4275, but should be comparatively simple with band X5800. 



Band X4275, which in strip 1 appears broad and hazy on its red edge, 

 gradually acquires the characteristic sharp intense edges as the temperature 

 falls, until in strip 8 it is only about 8 a.u. wide. The total change in band 

 X5800 is a narrowing of about 60 a.u. There is no sudden or decided change 

 between any two successive strips, but, on the contrary, so far as the photo- 

 graphic plate is able to show, the change is a gradual one. 



