20 ABSORPTION SPECTRA OF SOLUTIONS. 



We then see, from a study of this plate, that in A bands X4270, X5100, 

 X5200, and X5750 narrow with dilution, the amount of change being in the 

 order given; that is, least in X5100 and greatest in X5700. In B there is an 

 appreciable change in only X5750, while in C none of the bands are affected 

 by dilution. 



NEODYMIUM BROMIDE IN WATER. (See Plate 14.) 



The concentrations of the solutions used in making negative A, beginning 

 with the solution whose spectrum is farthest from the scale, were 1.66, 0.0166, 

 and 0.0033 normal; the corresponding depths of absorption layer being 0.5 

 cm., 50 cm., and 250 cm., respectively. 



The concentrations used in making B were half of those of A, and those of 

 C half those of B. The same range of cell depth was used in all three sec- 

 tions of this plate, viz, 0.5 cm., 50 cm., and 250 cm., respectively, beginning 

 with the strip farthest from the spark lines. In A , characteristic absorption 

 bands appear at X3400, X3525, X3800, X4275, X4450, X4700, X4750, X4800, 

 which are hardly affected by change in dilution, except for a slight increase 

 in the intensity of band X4275 in the most concentrated solution. 



The three bands, X5090, X5120, and X52 10, narrow uniformly with dilution, 

 the greatest change being between strips 2 and 3, where the change in dilu- 

 tion is the greatest. With the bromide, as is seen in plate 14, the effect of 

 dilution is most pronounced in band X5750. The shading is almost exclu- 

 sively towards the red, the violet edge remaining practically unchanged. 

 This edge shows no change between strips 1 and 2, yet the red edge is 

 widened as much as 30 a.u. 



In B, where the concentrations were 0.83, 0.0083, and 0.00166 normal, 

 respectively, the depths of absorbing layer were the same as used in A. 

 There is no measurable change in any of the absorption bands except the 

 band whose center is near X4800. This band shows the characteristic nar- 

 rowing with dilution, as the dilution is increased. The total change is not 

 greater than 20 a.u. Band X5200 is slightly more intense in the third strip. 



When we reach the dilution used in C, which is four times that of A, any 

 change due to dilution has disappeared except a narrowing of probably 10 

 a.u. between the third and second strips. 



Taking plate 14 as a whole we see, first, the narrowing due to increased 

 dilution is most marked in A, less in B, and least in C. This is seen to be 

 the same order as their respective concentrations. Considering an indi- 

 vidual section, we find the most pronounced narrowing where the change in 

 dilution is greatest that is, between strips 2 and 3. 



NEODYMIUM NITRATE IN WATER. (See Plate 15.) 



The concentrations of neodymium nitrate used in making negative A of 

 this plate, beginning with the strip farthest from the numbered scale, were 

 2.15, 0.0215, and 0.00430 normal, the corresponding depths of absorbing 

 layer being 0.5 cm., 50 cm., and 250 cm., respectively. 



