250 HYDRATES IN AQUEOUS SOLUTION. 



the red, an absorption band extending from 0.495/< to 0.555/<. The density 

 of the negative was greater in the region of the blue and violet for the solu- 

 tion in rmthyl alcohol th in for the one in ethyl alcohol. Also the maxima 

 of transmission as given by the negative for the solutions in acetone and in 

 methyl alcohol were, respectively, near 0.470/< and 0.442/. The strip for the 

 aqueous solution showed the trace of the line at 2502.1, but the continuous 

 background faded away near 0.288j. The band of absorption in the green 

 comprised the region from 0.452/< to 0.551,". 



The contrasts of the regions of absorption and of transmission of the four 

 solutions under consideration are very distinctly shown by plate 27 (a). 

 The negative for this spectrum was taken with a Cramer trichromatic plate. 

 The solutions were the same as for plate 27 (6), and their spectra were photo- 

 graphed in the same order. The strip corresponding to the aqueous solu- 

 tion is adjacent to the scales. The depth of the cell was 2 cm. and the 

 length of exposure for the glower was two minutes. The extreme limits of 

 transmission for the solution of acetone were 0.370/e and 0.562/<. The corre- 

 sponding limits for the solutions in methyl alcohol were about 0.385/ and 

 0.497,".. The strips pertaining to the last two solutions showed no return 

 to transparency in the yellow and orange. The solution in methyl alcohol 

 transmitted light from about 0.390, to 0.500,. This was followed by an 

 absorption band from 0.500/( to 0.547/<. The aqueous solution had a band 

 of complete absorption from about 0.462/< to0.543,. The region of trans- 

 mission in the yellow and yellow-orange was much more intense for the aque- 

 ous solution than for the one in methyl alcohol. The shifts experienced 

 by the centers of the regions of absorption and transmission, when the sol- 

 vents were changed (due allowance being made for the several concentrations), 

 were large, and are rather strikingly shown by plate 27 (a). The results of 

 eye observations on the spectra of the four solutions in question have already 

 been given, so that nothing more than a brief resume of the facts is necessary. 

 The solution in acetone transmitted a faint band of red, the middle of which 

 was near 0.761,. The solution in methyl alcohol transmitted more strongly 

 a region of red from about 0.775/< to 0.735/-.. The spectrogram of plate 27 

 (a) gives the photographic positions of the less refrangible limit of the absorp- 

 tion band in the green. The solution in methyl alcohol showed a weak 

 absorption band near 0.704/<, while the aqueous solution was too dilute to 

 give the bands in the red. Therefore, that region of absorption, which for 

 brevit} 7 may be called the band in the green, moved its center to shorter and 

 shorter wave-lengths as the solvents successively used were acetone, ethyl 

 alcohol, methyl alcohol, and water. 



Plate 25 (6) gives the ultra-violet absorption of the four solvents used. 

 The strip adjacent to the numbered scale corresponds to distilled water, 

 and the next strip belongs to methyl alcohol. The strip nearest to the 



