14 ABSORPTION SPECTRA OF SOLUTIONS 



the concentrated solutions, while in the dilute solutions the bands remain 

 unchanged. In a word, rise in temperature and decrease in dilution produce 

 the same effect upon solutions of praseodymium nitrate. 



URANYL NITRATE IN WATER. (See Plate 10.) 



The concentration of the solution used in making A was 0.2 normal, the 

 depth of layer being 1 cm. The temperatures, beginning with the strip 

 nearest the spark spectrum, were 20, 40, 60, 80, 100, and 120, respec- 

 tively. In every strip the exposure to the entire spectrum was made for 30 

 seconds, a screen cutting off all wave-lengths beyond X4500 was inserted, 

 and the ultra-violet end exposed an additional 8 minutes. 



Since all the uranyl bands occur in the violet and ultra-violet end of the 

 spectrum, where general absorption is greatest, due to precipitates formed 

 by heating the solutions, etc., it was found very difficult to obtain satis- 

 factory results. So far as this plate shows, there is no decided change in any 

 particular band. The entire series seems to widen as the temperature is 

 raised, and at the same time the center of the band is slightly shifted toward 

 the red end of the spectrum. The general absorption, ending near X3500 in 

 strip 1, advances rapidly towards the red as the temperature is raised. The 

 broad diffuse edges of all the bands shade uniformly into each other, until 

 at the highest temperature they appear as one broad, hazy absorption band, 

 extending from X3800 to X4300. At least a part of this is due to general 

 absorption. 



In section B is given the absorption of a 0.02 normal solution of uranyl 

 nitrate, the depth of absorbing layer being 10 cm. The red end of the spec- 

 trum, beyond X4500, was exposed 8 seconds, while the ultra-violet below 

 X4500 had an exposure of 3^ minutes to the same source of light. The tem- 

 peratures, beginning with the strip nearest the numbered scale, were 20, 

 45, 70, 95, 115, 140, and 165, respectively. Eleven bands occur between 

 X3500 and X4600. As the temperature is raised, all the bands become more 

 diffuse and broader; the band whose center is near X4180 seems to be most 

 affected. The red edge of the band shades towards the red end of the spec- 

 trum as much as 25 a.u. The effect produced on this band by elevated tem- 

 peratures is more marked than in any of the other bands. There is very 

 broad and hazy absorption around X5100, X5600, and X6200. This increases 

 with rise in temperature. 



It has been found very difficult to give an exact description of what takes 

 place in any uranyl band as the temperature is raised, since the edges of the 

 bands are so hazy and the general absorption so marked in the region of the 

 spectrum at which these bands occur. Only the general statement can be 

 made that all uranyl bands become more diffuse with rise in temperature, 

 and in the band X4165 there is a decided shading on the red edge. 

 URANYL SULPHATE IN WATER. (See Plate 11.) 



The concentration of the solution used in making A was 0.166 normal and 

 the depth of cell 1 cm. The respective temperatures, beginning with the 

 strip nearest the numbered scale, were 20, 45, 70, 90, 115, 135, 155, 



