IK) 



A STUDY OF THE ABSORPTION SPECTRA. 



Uranyl Acetate in Water, Conductivity and Temperature Coefficients. 

 It will be seen that the temperature coefficients expressed in per cent 

 decrease with increase in the dilution. This is rather unusual; these coeffi- 

 cients, as a rule, increasing with the dilution. 



The Phosphorescent and Fluorescent Spectra of Uranyl Salts. 



Many bodies on being exposed to light, X-rays, a, /?, y, or cathode rays, 

 on being heated or rubbed, emit light. This is generally called phospho- 

 rescence when the light is emitted after the stimulating agent ceases to act, 

 and fluorescence when the excited light ceases to be emitted as soon as the 

 exciting cause ceases. In general, liquids and gases fluoresce while solids 

 phosphoresce. Some of the strongest phosphorescent compounds are the 

 uranyl salts. These salts emit bands of phosphorescent light in the green 

 region of the spectrum. 



The researches of Lecocq de Boisbaudran, Lenard and Klatt, Urbain, 

 and others, upon the rare earths, the sulphur compounds of the alkaline 

 earths, and the oxides of the earth metals, have shown that these substances 

 do not phosphoresce when in the pure state, and that the presence of an 

 impurity seems to be essential to the formation in those substances of the 

 complex molecules or " centra" that emit the phosphorescent light. On the 

 other hand, the uranyl salts always phosphoresce. 



Lenard and Klatt 1 have investigated very thoroughly various cal- 

 cium phosphates of bismuth, manganese, and nickel. At ordinary tem- 

 peratures the bands are very broad, ill-defined, and are unaffected by a 

 magnetic field. Lenard and Klatt believe that there are certain places 

 in atoms that can store electrons. These dynamids are only supposed to 

 hold the electrons at low temperatures. At high temperatures the electrons 

 possess a much greater freedom of motion. The different states of motion 

 are visualized as three kinds: the "gaseous," "liquid," and "solid" states. 

 In the "gaseous " state the electrons can occasion the conduction of elec- 

 tricity between the atoms if the latter exist in the same way as they do in 

 metals. In the "liquid" state the electrons are in a state of motion sensi- 

 tive to light vibrations and, hence, they take part in light absorption. In 

 the "solid" state the electrons take part neither in conduction nor in 



1 Ann. Phys., 15, 225, 451, 633 (1904). 



