8 ABSORPTION SPECTRA OF SOLUTIONS 



The neodymium oxide, being heavy and very slightly soluble in water, 

 settles to the bottom of the cell, and the solution clears up. In this way 

 it is evident that the solution becomes slightly more dilute as the tempera- 

 ture is raised ; but this would lessen the number of absorbers in the path of 

 the beam of light, and thereby produce a narrowing of the bands and could 

 only decrease the effect indicated on the plates. This antagonistic influence 

 could certainly not cause a widening of the absorption bands, with rise in 

 temperature. 



NEODYMIUM CHLORIDE IN WATER. (See Plate 1.) 



The solution whose spectrum is given in section A was saturated, the 

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

 the strip nearest the numbered scale, were 20, 45, 70, 95, 115, 140, and 

 165, respectively. Absorption bands which are unchanged by the range of 

 temperature from 20 to 200 appear at X3800, X4025, X4200, X4325, X4440, 

 X4600, X4690, X4750 and X4820. The double band from X5050 to X5270 is 

 only slightly affected, if at all. 



The two most interesting absorption bands are those whose centers are 

 near X4275 and X5800. The former of these in strip 1 is very sharp and 

 intense, though only a few a. it. wide. Both edges were well defined. As 

 the temperature is raised the violet edge remains very sharp, while a rapid 

 shading off of the red edge takes place. At a glance the band appears to be 

 less intense in the higher temperature strips, but on close examination it is 

 seen to be more diffuse, the red edge diffusing over a range of about 20 a.u. 

 at the highest temperature. This is exactly in accord with what Jones and 

 Anderson 1 had found. They showed that when the number of molecules 

 in the path of light was kept constant, this band remained practically con- 

 stant ; while it has been shown by Jones and Anderson and by ourselves that 

 this band changes with dilution, being more intense in the most concen- 

 trated solution. 



The X5800 band is affected most by temperature as well as by dilution. 

 In strip 1 this band is about 200 a.u. wide, the width increasing regularly 

 as the temperature is raised, until at the highest temperature it is over 

 250 a.u., or there is a total widening of 50 a.u. The violet edge remains 

 perfectly sharp, while the shading is toward the red end of the spectrum. 



It occurred to us that whatever effect might be produeed by a rise in 

 temperature, if it was a true temperature effect, the reverse should happen 

 when the solution was allowed to cool. 



With this in view B was made. The concentration of the solution and 

 the depth of layer photographed in section B were exactly the same as in A. 

 In fact, the same solution was used. As soon as the film A had been exposed 

 with rising temperature, it was removed from the camera and developed. 

 Without even allowing the cell to cool, another film was placed in the camera 



2 Carn. Inst. Wash. Pub. 110. 



