CUPRIC CHLORIDE. 101 



all of the shortest waves of light. Also the successive increments of absorp- 

 tion become less and less as the concentrations of the solutions increase. 



o 



For example, the seventh photographic strip ends about 200 Angstrom units 

 farther along than the fifth strip, the twelfth 90 units beyond the eleventh, 

 and the sixteenth 55 units beyond the fifteenth. The region of transmission 

 for the mother-solution extended from about 0.483/ ( to 0.574/z. 



The negative for plate 3 (6) was obtained with a Cramer trichromatic 

 plate. The exposure for each of the five most concentrated solutions was 

 two minutes in length. The depth of the cell was 0.67cm., as before. This 

 spectrogram shows correctly the limits of transmission not only at the blue 

 side, but also towards the red ; since the photographic plate would have been 

 made deep black as far as its very ends, if the light had not passed through 

 the absorbing layers of liquid. The limits of the region of transmission for 

 the solution whose concentration was 2.073 were 0.460/( and 0.593/t, while 

 the corresponding numbers for the mother -solution were 0.4S5/* and 0.5S3/. 

 Therefore, the rate of increase for absorption is greater at the more refrangi- 

 ble end of this region than at the less refrangible end. In fact, the middle 

 of the transparent region shifted towards the red by about 75 A. U. as the 

 concentration increased from 2.073 to 3.976. 



Plate 4 (a) was taken with the wedge-cell set at an angle of 19.5' and starting 

 with nearly zero depth. Times of exposure were ninety seconds and eighty 

 seconds with the Nernst filament and spark, respectively. The thinnest layer 

 transmitted a trace of the cadmium line at 3133.3. The boundary of the 

 ultra-violet region of absorption then curved around as is shown by plate 4 (a) , 

 and reached about 0.400;*, corresponding to the thickest part of the wedge. 

 The great intensity of the ultra-violet absorption is worthy of note. 



Eye observations fully confirm the results obtained by the photographic 

 method. For the most dilute solution, transmission began at about 0.727 ft, 

 i. e., in the bright red. As more and more concentrated solutions were 

 observed, the absorption at the red end of the spectrum extended gradually 

 to shorter and shorter wave-lengths. The following numbers were recorded 

 as the wave-lengths of the extreme limits of visual transmission for the first, 

 fourth, seventh, tenth, twelfth, fourteenth, and sixteenth solutions, named 

 in the order of increasing concentration, viz., 0.727/t, 0.677/ ( , 0.646^, 0.634/, 

 0.624u, 0.616/, and 0.660, respectively. The reasons why the eye obser- 

 vations agree qualitatively, but not quantitatively, with the photographic 

 results scarcely need explanation. The limits of the more refrangible ends 

 of the regions of transmission of the solutions, as obtained with the spec- 

 troscope, are not as satisfactory as the results gotten photographically, for 

 the reason that the absorption fades away very gradually in the part of 

 the spectrum under consideration. Therefore, no more wave-lengths will 

 be given for the simple solutions of copper chloride in water. 



