of Copper and its Salts. 



223 



daylight from a window was reflected from its surface verti- 

 cally upwards through the tube. The length of the column 

 of solution of cupric sulphate was then varied by letting out 

 small portions at a time through the side tube. It was found 

 that the plate of copper, viewed through a certain thickness 

 of the blue solution, appeared like a plate of polished silver. 

 This certainly tends to show that the colour transmitted by 

 solutions of copper is complementary to that reflected by the 

 metal. 



I now placed a hollow glass prism before the slit of a spec- 

 troscope, in such a manner that the light passed through a 

 strong solution of cupric sulphate contained in it before reach- 

 ing the prism of the spectroscope. The accompanying sketch 

 (fig. 1) shows the effect of this upon the spectrum. 



Eed. 



Yellow. 



Green. 



Fig. 1. 



Blue. 



Violet. 



Solar spectrum. 



Solar spectrum 

 after passing 

 through copper 

 solution. 



Absorbed 

 portion. 



All light less refrangible than the sodium-line is very much 

 diminished by passing through the copper solution, while the 

 rest seems un affected. 



I next endeavoured to determine in wbat particulars the 

 light reflected from copper differs frcm ordinary light; and for 

 this purpose I compared the reflection frcm a polished sbeet 

 of copper with that from a piece of white note-paper. The 

 result appears in fig. 2. 



FiV. 2. 



Spectrum of 



rt flection 

 from copper. 



Spectrum of 

 reflection 

 from paper. 



Eed. 



Yellow. Green. Blue. Violet. 



Interne 

 JRed, 









Limit o fsolar 

 spectrum. 



The part of the spectrum to the red side of the D line is more 



