18 ABSORPTION SPECTRA OF SOLUTIONS. 



for both A and B the slit was adjusted to a width of 0.01 cm. and the expo- 

 sures to the Nernst lamp and spark were 1J and 3 minutes, respectively. 



The spectrogram shows a region of absorption in the extreme ultra- 

 violet, which narrows regularly with dilution; the limits of transmission 

 for the strips corresponding to the most concentrated and most dilute 

 solutions of set A being, respectively, A 2670, and X 2630, while for set B 

 they are I 2580 and X 2550. 



The negative for set A also shows two absorption bands in the ultra- 

 violet, having their centers roughly at X 3100 and X 3600. These bands 

 are undoubtedly identical with those already noted in the same region 

 for the solutions in methyl alcohol. One difference, however, is to be 

 pointed out. The bands in the ethyl alcohol solutions are somewhat more 

 intense, in spite of the fact that the concentration of the colored salt is 

 smaller, and they also disappear much more slowly with dilution. 



The absorption in the green is very much fainter in ethyl alcohol than 

 in methyl alcohol; and measurement of the position of the center of the 

 band indicates that it is located a trifle nearer the red in the former case. 

 The position of the center was found to be at X 5280. The band remains 

 constant in width and position with dilution; A shows a region of intense 

 absorption in the yellow, orange, and red, which narrows somewhat with 

 decrease in concentration; the limits of transmission for the most concen- 

 trated solution being X 5500 and X 7170, and for the most dilute X 5500 

 and X 7060. 



In B the absorption in this region of the spectrum is less intense, espe- 

 cially for the more dilute solutions, which show faint transmission through- 

 out the band. The red edge of the band for the most concentrated solution 

 is at X 6970, while for the most dilute solution it is at X 6800, the wave- 

 lengths given corresponding to the limits of transmission as indicated by 

 the photographic blackening of the negative. The strips corresponding to 

 the more dilute solutions of set B show faint traces of bands, which appear 

 to correspond roughly in position to the bands noted in the description of 

 Plate 4. The bands at X 5910 and X 6050 only show faintly, and they both 

 appear much less clearly defined than in the methyl alcohol solutions. 



COBALT CHLORIDE IN ACETONE BEER'S LAW. (See Plate 6.) 



The concentrations of the solutions used in the negative for A were 

 0.0154, 0.0129, 0.0107, 0.0088, 0.0073, 0.0060, and 0.0051; the corre- 

 sponding depths of cell were 8, 9.5, 11.5, 14, 17, 20, and 24 mm., respec- 

 tively. For set B the concentrations were 0.0073, 0.0061, 0.0051, 0.0042, 

 0.0034, 0.0029, and 0.0024; the depths of cell were the same as in A. The 

 solutions were all blue, the color merely changing from a dark to a rather 

 light blue with dilution. 



The spectrogram shows two regions of absorption, one in the ultra- 

 violet and one in the red. The faint absorption indicated in the green 

 is due to the diminished sensibility of the Seed film in this region. 



The absorption in the ultra-violet is due entirely to the solvent, w r hich 

 may be inferred from the fact that it is the same in A and B, and also 

 from the fact that it increases with dilution. This, of course, is due to the 



