40 ABSORPTION SPECTRA OF SOLUTIONS. 



A shows three regions of absorption, one in the extreme ultra-violet, 

 a band in the end of the visible violet, and a band cutting off the extreme 

 red. Besides this there is a rather strong general absorption in the entire 

 ultra-violet, beyond the absorption band in the end of the violet. 



The extreme ultra-violet absorption perhaps narrows slightly with 

 dilution, although from the second strip to the seventh the limit of trans- 

 mission seems to remain almost fixed at X 2550. The first solution, how- 

 ever, shows much more absorption in the whole ultra-violet region, includ- 

 ing the band at X 3960. 



The band at X 3960 narrows from the first to the third strips (counting 

 from the scale) and then remains of constant width, the limits of trans- 

 mission being approximately X 3700 and X 4230. The scale in the repro- 

 duction is shifted towards the red by nearly 50 A.U., due to the fact that 

 in making the prints this was adjusted with reference to the narrow com- 

 parison strip seen at the top of the spectrogram. This strip is displaced, as 

 may be seen by comparing the spark lines in the ultra-violet. The scale 

 for the red end of the plate is, however, correctly placed, so there is a slight 

 discrepancy at the point where the two prints were joined together. 



The absorption in the red shades off very gradually through a range 

 of wave-lengths of about 1000 A.U., being quite noticeable on the nega- 

 tive at X 6100 in the strip corresponding to the most concentrated solution, 

 and at X 6200 in the strip corresponding to the most dilute solution. The 

 limits of transmission for the two strips are at ^7150 and X 7250, respec- 

 tively. These measurements indicate a slight narrowing of the absorp- 

 tion band with dilution, but it must be remembered that photographic 

 registering of the spectra is not the best method for studying such very 

 hazy absorption bands, since a very slight change in the length of expos- 

 ure, or intensity of the source of light used, may apparently shift the band 

 very markedly. The only satisfactory method for studying such cases of 

 hazy absorption is a spectrophotometric determination of the absorption 

 coefficient for a number of wave-lengths in the region. 



In B the absorption in the extreme ultra-violet- has disappeared, the 

 last lines in the spark showing as well in the strips taken through the solu- 

 tions as in the narrow comparison strip with nothing but air in the path 

 of the beam of light. 



The band at X 3960 has become faint, but still shows distinctly on the 

 negative. It remains unchanged in intensity in the seven strips on the 

 spectrogram. 



The absorption in the red, although present as shown by the green 

 color of the solutions in their bottles, was of too diffuse a character to be 

 registered on the photographic plate, which, hence, shows complete trans- 

 mission to beyond X 7400. On the whole, except for the most concentrated 

 solution, Beer's law seems to hold quite accurately for nickel chloride. 



NICKEL CHLORIDE IN WATER IONS CONSTANT. (See Plate 47 A.) 



The concentrations, beginning with the solution corresponding to the 

 strip nearest the numbered scale, were 2.66, 0.93, 0.51, 0.305, 0.200, 0.135, 

 0.095; the depths of cell were 3, 4, 6, 9, 13, 18, and 24 mm. The exposures 



