and Surface- Colour of NitrosO'dimetliyl-aniline. 99 



measured between the extreme red and wave-length '00050, 

 below which point the prims refused to transmit sufficient 

 lioht to make readings possible. The values obtained in this 

 wav are oiven in the followino- table. 



Prism-augle 8° 7'. 



Prism -angle 53'. 



X. 



n. 



\. 



n. 



508 

 516 

 525 

 536 

 546 

 557 

 569 

 584 

 602 

 6]1 

 620 

 626 

 636 

 647 

 659 

 669 



2025 



1-985 



1-945 



1-909 



1-879 



1-857 



1-834 



1-815 



1-796 



1-783 



1-778 



1-769 



1-764 



1-758 , 



1-750 



1-743 



497 

 500 

 506 

 513 

 577 

 647 

 669 

 696 

 713 

 730 

 749 

 763 



2-140 

 2-114 

 2074 

 2020 

 1-826 

 1-754 

 1-743 

 1-723 

 1-718 

 1-713 

 1-709 

 1-697 



The results are shown graphically in Plate VI., together 

 with the dispersion-curve for bisulphide of carbon for the 

 same region of the spectrum. The remarkable dispersive 

 power of the nitroso is at once apparent when we compare 

 the two curves, and contrast it with that of the bisulphide, 

 which has the highest dispersive power of any substance in 

 common use. 



Over the region of the spectrum given above, the nitroso 

 can be considered as a transparent substance, and the dis- 

 persion formula for transparent substances can be applied to 

 it. From three values of n and the corresponding values of 

 X, the value of V the centre of the absorption-band can be 

 calculated. 



In the case of selenium, which has a dispersion-curve 

 resembling that of the nitroso, the absorption appears to 

 increase steadily from the yellow down to the extreme ultra- 

 violet, making it impossible to determine experimentally the 

 centre of the absorption-band which is chiefly responsible for 

 the dispersion. Applying the formula for transparent sub- 

 stances to the values found for selenium, I found that if we 

 assume a single absorption-band, its centre must be at wave- 

 To account for the continued absorption as. 



length -00056. 



H2 



