164 



STUDIES IN LUMINESCENCE. 



cence of solid anthracene. 1 After investigating a number of substances, 

 they say: "It is highly probable that for organic substances, at least, the 

 photo-electric effect and fluorescence are intimately connected with each 

 other." Hence it would seem that the vapor of anthracene would be as 

 likely as any vapor to possess photo-electric properties. 



APPARATUS. 



The glass tube used to contain the anthracene is shown in Fig. 161. The 

 larger part of the tube was 15 cm. long and 2.5 cm. in diameter. The elec- 

 trodes between which the current passes consisted of an outer aluminum 



Fig. 161. 



cylinder, to which connection was made by sealing a platinum wire through 

 the glass at M , and an inner brass wire supported by a quartz tube Q and 

 visible through the slit in the outer electrode. 



The quartz tube served as insulation for the brass wire electrode. Further 

 protection was afforded by a deposit of silver on the inside of the glass tube 

 around the quartz, this silver layer extending around to the outside of the 

 open end, where it was wrapped with tinfoil and grounded to form a guard- 



Fig. 162. 



ring. Thus no charge could leak over the glass surface from the outer 

 electrode. 



The openings at the outer end of the quartz tube were sealed with de 

 Khotinsky cement. This would not stand heating, and the furnace was 

 arranged to inclose only the large part of the tube (see dotted outline in 

 Fig. 162). It was necessary to have the quartz tube fit snugly in place and 

 to provide a tight- fitting cap C (Fig. 161) at the inner end in order to pre- 

 vent the sublimation of the anthracene to the colder parts of the tube. 



'Stark and Rteubing, Phys. Zeit., 9, p. 481, 1908. Also, Pochettino, Nuovo Cim., 15, p. 171, 1906. 



