EFFECT OF DILUTION ON ABSORPTION OF LIGHT. 21 



111 discussing the absorption bands of this, as well as other plates through- 

 out this paper, we do not attempt to give the exact position of the band in 

 question, as has previously been done by many workers; but we simply indi- 

 cate the position of the band by selecting a wave-length near its center. 

 For instance, in speaking of band X5800, we mean that broad band extending 

 from X5700 to X5850. This is not confusing and saves space and time in 

 the description of any plate. 



This is probably the best plate we have illustrating the effect caused by 

 dilution. Bands which are hardly affected over the range of dilution given 

 in A are located at X3525, X3820, X4440, X4620, X4750, X4830. In strip 3 

 the well-defined band X4275 is more diffuse, though probably not so intense. 

 This is in keeping with the behavior of this same band as shown by other 

 salts of neodymium, though probably a little more marked. There is faint 

 transmission at X5100 for about 10 a.u. In strip 3, representing the most 

 concentrated solution, the bands X5090 and X5125 have so broadened that 

 they coalesce. The X5220 band widens uniformly towards the red and 

 violet as the solution becomes more concentrated. 



Band X5800, which is most affected by dilution, shows a total change of 

 probably as much as 70 a.u., the shading being largely towards the red. 

 In strips 1 and 2 the violet edge is hardly changed, while in strip 3 it is prob- 

 ably shifted 20 a.u. On the original film these three strips show abso- 

 lutely the same development, hence are directly comparable. 



Section B represents the absorption of neodymium nitrate. Beginning 

 with the strip farthest from the numbered scale, the concentrations are 

 1.075, 0.01075, and 0.00215 normal, the corresponding depths of cell being 

 the same as in A. In this section only a few bands need be discussed. 

 Bands X5090 and X5125, which appear as distinct bands in strips 1 and 2, 

 have slightly broadened so as to form a single hazy band whose center is 

 near X5120. The X5750 band narrows as much as 40 a.u., almost the entire 

 change being between strips 2 and 3. 



In C, the X5750 band alone is noticeably changed, narrowing about 20 

 a.u. from strip 3 to strip 2, but is not changed in the last dilution, i. e., from 

 strips 2 to 1. 



NEODYMIUM SULPHATE IN WATER. (See Plate 16.) 



A gives the absorption spectra of a solution of neodymium acetate. The 

 concentrations of the solutions used, beginning with the strip farthest 

 removed from the numbered scale, were 0.5, 0.01, and 0.002 normal. The 

 corresponding depths of cell were 1, 50, and 250 cm. 



This additional plate of neodymium acetate was made to study the effect 

 of exposure on the apparent widening of the bands with concentration. 

 Strip 2 was more exposed than strip 1, and strip 3 had a longer exposure 

 than strip 2. Nevertheless the X5800 band has widened as much as 50 a.u. 

 between the first and third exposures. In view of the unequal exposures of 

 these strips, it is not thought advisable to discuss the other bands. These 



