50 ABSORPTION SPECTRA OF SOLUTIONS. 



teenth solutions, the percentage of water increased from 12 to 40 per cent, 

 the absorption diminishing slightly; the limit of transmission in the six- 

 teenth solution is at X 6650. The shading, although still noticeable as 

 far down as X 6000, is much weaker than in the fourth solution. The point 

 to be specially noted is that the greatest change takes place at first, with 

 addition of water, the change in the total amount of absorption being 

 greater from the first to the second solution than from the second to the 

 third, and so on. The effect of the water may then be said to be two- 

 fold. First, it tends to make the edge of the band much more hazy, and 

 secondly, as more of it is added, it tends to narrow up the band somewhat. 



| COPPER CHLORIDE IN ETHYL ALCOHOL WITH WATER. (See Plate 36.) 



The concentration of copper chloride was constant throughout and 

 equal to 0.10 normal. The percentages of water in the solutions, begin- 

 ning with the one whose spectrum is adjacent to the numbered scale, 

 were 0, 4, 8, 12, 16, 20, 24, 28, 32, 36, 40, 44, 48, 52, 56, and 60, the strips 

 being all the same and equal to 4 per cent. 



With addition of water, the color of the solutions as seen in the bottles 

 changed from an olive-green to a light-blue. The common depth of cell 

 was 2.0 cm. Exposures to the light of the Nernst lamp and spark lasted, 

 respectively, 1 and 3 minutes, the slit having the usual width of 0.01 cm. 



The limit of transmission in the blue and violet region moves towards 

 shorter wave-lengths with addition of water, more rapidly at first, then more 

 and more slowly as the percentage of water is increased, giving the edge of 

 the band a curved form, the convex side being towards the region of shorter 

 wave-lengths. The limit of transmission for the solution containing no 

 water is X 4800, and for the one containing 60 per cent of water it is at 

 X 3400. The solution containing 40 per cent of water ceases to transmit at 

 X 3570, whereas for the methyl alcohol solution containing 40 per cent of 

 water it is at X 3750. When we consider that the limit of transmission for 

 the solution in pure ethyl alcohol is X 4800, while for that in pure methyl 

 alcohol it is at ^4500, we see how much more rapidly the absorption of the 

 ethyl alcohol solution decreases with addition of water. The difference is no 

 doubt to be accounted for by the smaller concentration of the metallic salt 

 in the case now under discussion, the change in the absorption apparently 

 being determined by the ratio of the amount of water to the amount of 

 dissolved salt, rather than by the actual percentage of water in the solvent. 



In the red the absorption decreases regularly with addition of water. 

 The limit of transmission for the first solution is at X 6400, the shading 

 extending to X 6000. For the sixteenth solution the absorption is complete 

 at X 6900, shading extending down to about X 6400. No trace of the effect 

 observed in the case of methyl alcohol solutions was found. 



COPPER CHLORIDE IN ACETONE WITH WATER. (See Plate 37.) 



The concentration of the copper salt was constant throughout and 

 equal to 0.014 normal. The percentages of water in the solutions, begin- 

 ning with the one whose spectrum is adjacent to the numbered scale, 

 were 0, 1, 2, 3, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 26, and 30. The depth 

 of cell throughout was 2.0 cm. 



