LIGHT. 125 



ing them in hot alcohol. The chlorophyl will thus be 

 extracted and the tincture is ready for examination. 



A few pieces of the hulls of horse-chestnuts, or of 

 the inner bark of the horse-chestnut tree digested half 

 an hour in cold water, will be sufficient for this. 



Alcoholic tinctures of madder, stramonium, night- 

 shade, and Brazil wood will be needed. 



A grain of sulphate of quinine may be put into 

 a pint of pure water and shaken up occasionally. 

 This substance is sparingly soluble in water. A 

 little tartaric acid may be added to the water with 

 advantage : the fluorescence will be more strongly 

 marked. 



A good method of exhibiting this is to have a rather 

 large glass vessel containing pure water set in the path 

 of the violet rays. Pour the quinine solution into it : 

 opalescent clouds at once appear to form, though noth- 

 ing is precipitated. 



Thallene and anthracine are obtained from some of 

 the products of the distillation of petroleum and coal 

 tar, and are not in the market. 



The Aurora tube and Geisler tubes when lighted by 

 the electric spark may be used to obtain fluorescent 

 effects. With the former, writing and drawings made 

 with proper solutions, may be seen when such markings 

 would be entirely invisible in common white light. 

 Geisler tubes are often made to contain some pretty 

 design in uranium glass, or there is some vessel con- 

 taining a fluorescent solution surrounded with a jacket 

 filled with some gas which gives a violet light like 

 nitrogen. 



A very beautiful effect is produced by exposing a 

 number of highly fluorescent media to the flame of 

 sulphur burning in oxygen in a dark room. 



