42 ABSORPTION SPECTRA OF SOLUTIONS. 



at X 4320, and that there is a slight return to transparency at / 3000 to 

 X 3100, then complete absorption to X 2200 or the end of the spectrum. 

 The X 3960 band narrows regularly with curved edges as the concentrations 

 of the calcium salt decrease, its limits in the eighth strip being x* 4150 and 

 x 3750. The increase of transparency beyond the band is also very marked. 



The first strip of B shows that transmission in the violet ceases at 

 X 4370, and that there is no return to transparency in the ultra-violet. 

 The red edge of the x" 3960 band moves towards the region of shorter wave- 

 length, rapidly in the first four strips, then more slowly till the eighth 

 strip is reached, where the limit of transmission is X 4150 as in A. No 

 transmission in the ultra-violet region beyond the band is visible in the 

 first three strips. In the fourth strip there is a slight amount of transmis- 

 sion from X 2800 to X 3400, which increases rapidly as the amount of alu- 

 minium chloride is further diminished. 



The red end of A shows that, although the limit of transmission moves 

 slightly towards the region of longer wave-lengths with decrease in the 

 amount of calcium chloride, the absorption in the region X 6000 to X 6500 

 increases rapidly, thus showing that on the whole the absorption in the 

 red is decreased very much by adding the calcium salt. 



With the addition of aluminium chloride the absorption in the region 

 X 6000 to X 6500 decreases slightly, while in the region X 6800 to X 7100 it 

 increases considerably; on the whole, therefore, the red absorption is per- 

 haps somewhat increased. 



The first three solutions show three rather narrow absorption bands, 

 whose wave-lengths are X 6110, X 6250, and X 6440. Of these the first and 

 last are rather faint, the one at X 6250 fairly intense. They could not be 

 seen in a layer of the mother-solution of aluminium chloride 20 cm. deep, 

 and hence are not to be ascribed to the aluminium salt. A careful exami- 

 nation of the first strip on the negative for A reveals faint traces of the 

 three bands, having here about the same intensity as they have in the 

 second strip of B. The bands are hence to be ascribed to the nickel salt. 

 A more concentrated solution of the nickel salt with large quantities of 

 the dehydrating agents would undoubtedly have brought out these bands 

 very much better. 



NICKEL SULPHATE IN WATER BEER'S LAW. (See Plate 28.) 



The concentrations of the solutions used in making the negative for 

 A, beginning with the one whose spectrum is adjacent to the numbered 

 scale, were 2.1, 1.7, 1.32, 1.05, 0.80, 0.65, and 0.53; the corresponding 

 depths of absorbing layer being 6, 7.5, 9.5, 12, 15, 19, and 24 mm. The 

 concentrations for set B were 0.80, 0.64, 0.50, 0.40, 0.32, 0.25, and 0.20; 

 the depths of cell were the same as in A. The exposures to the Nernst 

 lamp and spark lasted 1 and 2 minutes, respectively, the slit having a 

 width of 0.01 cm. 



The spectrogram shows that the solutions were quite transparent in 

 the ultra-violet. That there is a slight amount of general absorption 

 beyond the X 3960 band may, however, be inferred from the fact that 

 although the exposure for the narrow comparison strip was only about 



