LIGHT. 



123 



FLUORESCENCE. 



Only blue or violet or ultra-violet rays are capable of 

 producing this phenomenon, and these may be obtained 

 either by passing common white light from the sun, or 

 the electric light, or the lime light, through a piece of 

 blue or violet glass or through a solution of ammonia, 

 sulphate of copper; or, better still, by producing a pure 

 spectrum. The best effects are to be observed by using 

 a prism of great dispersive power, like quartz. 



Fig. 93. 



When colored glass is to be used to obtain the 

 violet light, it suffices to place a lens of a foot focus 

 near the orifice and the glass just in front of it. 

 Fluorescent solids and solutions may then be examined 

 at S. A piece of uranium glass or a solution of quin- 

 ine in a test tube or bottle will exhibit; this property 

 so that many can see it at the same time. It will be 

 well to use two bottles or beakers of clear glass, — one 

 to contain pure water and the other the solution of 

 quinine — and examine them side by side in this blue 

 light. The fluorescence will then be more noticeable. 



When artificial light is used in a lantern it will only 

 be necessary to place the colored glass in front of the 

 condenser, as if to project a picture upon it, and 

 otherwise use the light as with sunlight. 



Pictures are sometimes made of fluorescent material. 



