80 ABSORPTION" SPECTRA OF SOLUTIONS. 



of the corresponding band is A 4290. It has a width of from 12 to 13 Ang- 

 strom units, and is not nearly as intense as in the aqueous solution. 



Throughout the first six strips the A 4275 band maintains its position 

 and intensity almost unchanged. Its position does not change in the 

 least, but its intensity in the sixth strip is a trifle less than in the others. 

 In the seventh strip there is not the faintest trace of it left. In the third 

 strip, corresponding to the solution whose alcohol content was 33.3 per 

 cent, there appears at A 4285 an extremely faint and narrow line. In the 

 fourth strip it is somewhat wider and more intense, but its center is still 

 at A 4285. In the fifth strip it is beginning to be fairly conspicuous, and 

 in the sixth it is a band of moderate intensity, having its center at about 

 A 4287. This band is undoubtedly the same one which in the pure alcoholic 

 solution has its center at A 4290 or very near there, the exact wave-length 

 being perhaps nearer to A 4292. We see, then, that even when the mixed 

 solvent contains only about one-half alcohol, this band exists independent 

 of and distinct from the band characteristic of the aqueous solution; that 

 it is at first only a very narrow and faint line, which widens towards the 

 red as the percentage of alcohol is increased. 



The band whose center is at A 4760 has the following appearance in the 

 aqueous solution: Faint absorption begins at A 4748 and rises rapidly to 

 a maximum between A 4755 and A 4760, then decreases slowly to nothing 

 at A 4775. The band is accordingly a trifle asymmetrical, the slope towards 

 the violet being considerably steeper than that towards the red. The 

 corresponding band in the alcoholic solution is double and answers the 

 following description: Very faint absorption begins at A 4753, and rises to a 

 faint maximum at about A 4757, becoming again zero at A 4760. It begins 

 again at A 4772, rises rapidly to a strong maximum at A 4780, and falls 

 to zero at A 4790. The component whose center is at A 4757 is very faint 

 compared with the main band. 



In the first and second strips we have nothing but the band correspond- 

 ing to the aqueous solution. In the third strip the red side of the band has 

 increased slightly in intensity, making it appear much more nearly sym- 

 metrical. This change increases in the fourth and fifth strips, the band at 

 the same time widening considerably. In the sixth strip its appearance is 

 as follows : Absorption begins at A 4748 and rises to a maximum just to 

 the violet side of A 4760, then decreases slightly towards A 4770, after which 

 it increases somewhat to A 4778, then falls off to zero at A 4787. It is very 

 evident from a study of the change in this band that the two bands char- 

 acteristic of the aqueous and alcoholic solutions coexist, and that the 

 band appearing in our photographic strip is the sum of the two taken in 

 different proportions, the proportion of the alcohol band being, however, 

 very much smaller than the proportion of alcohol in the corresponding 

 solution. A similar description might be given for any one of the other 

 bands, but this is not necessary, as the changes are of exactly the same 

 nature as those we have already indicated. In every case where the alco- 

 holic solution has a strong band which differs somewhat in position from any 

 band in the aqueous solution, we begin to see traces of this band when the pro- 

 portion of alcohol in the mixture reaches 50 per cent; but the band remains 

 comparatively faint even when the proportion is as high as 83.3 per cent. 



