THE ANOMALOUS DISPERSION, ABSORPTION, AND SUR- 

 FACE COLOR OF NITROSO-DIMETHYL-ANILINE. 



By R. W. Wood. 



Presented May 13, 1903. Received May 30, 1903. 



The very high dispersion of the aniline dyes and other absorbing 

 media is due, as is well known, to the fact that the absorption band 

 lies within the visible spectrum. The absorbing power of these sub- 

 stances for wave-lengths far removed from the centre of the absorp- 

 tion band is so great that only prisms of very small angle can be used, 

 which puts a limit on the length of the spectrum which can be obtained 

 with them. 



In the case of the so-called transparent substances, the absorption 

 band lies so far down in the ultra-violet, that the steepness of the 

 dispersion curve in the visible spectrum is not comparable with that 

 of the substances which are said to exhibit anomalous dispersion. If, 

 however, we push the curve down to the absorption band, employing 

 some photographic method, we find that it may be even steeper than the 

 curve for cyanine in the red and orange. 



I have found that uitroso-dimethyl-aniliue is of peculiar interest, in 

 that it fills in the gap existing between the aniline dyes and ordinary 

 transparent substances. It has a band of metallic absorption in the 

 violet, and is at the same time fairly transparent to the red, yellow, and 

 green. The substance melts at 85° C. and can be formed into prisms 

 between small strips of thin plate glass. The strips should be about 

 two centimeters long and are best fastened together with one of the 

 small clamps used with rubber tubing. It is best to melt the material 

 on the end of one of the strips, the other being warmed over the same 

 flame, and then clamp the two together with a piece of a match between 

 the ends, to give the required prismatic form. A candle flame viewed 

 through the prism is spread out into a most remarkable spectrum fifteen 

 or twenty times as long as one given by a glass prism of the same angle. 

 It is instructive to have a prism of the same angle made of Canada 

 balsam or some such substance pressed out between two similar glass 

 strips. 



