Triboluminescence and Piezoluminescence 389 



necessary for light production, namely, solution of the AS2O3 in 

 HCl, and slow cooling so that the AS2O3 would crystallize in the 

 vitreous modification. 



In 1841 Rose was unable to observe crystalloluminescence from 

 pure K0SO4 but found that light accompanied the crystallization of 

 the double salt NaKS04 or double NaK chromates and selenates. 

 They were also triboluminescent. He held that the light emission 

 was connected with formation of an isomeric modification. Von 

 Reichenbach described crystalloluminescence of Na^SOi in 1861. 



No further important studies of crystalloluminescence were made 

 until E. Bandrowski reinvestigated the above cases in 1894 and 

 1895. In the meantime the Arrhenius theory of ionic dissociation 

 had been formulated and was in the height of popularity, leading 

 Bandrowski to the conclusion that light emission is connected with 

 the formation of molecules from charged dissociated ions, whose 

 union before crystallization produces sparks on discharge. In favor 

 of this view he found that addition of concentrated hydrochloric 

 acid or alcohol to saturated NaCl or KCl solutions, would result in 

 luminescence, although the light was sometimes homogeneous rather 

 than in spark-like flashes. Both these procedures were supposed to 

 result in recombination of ions in solution preceding crystal forma- 

 tion. Thus the subject was left at the end of the century, to be 

 continued by M. Trautz (1904) , M. Trautz and P. Schorigin (1905) , 

 J. Guinchant (1905) , and D. Gernetz (1905) . Despite the research 

 of these men and others who followed them, the understanding of 

 crystalloluminescence is not too satisfactory at the present time. 



Lyoluminescence 



This term was applied by E. Wiedemann and G. C. Schmidt ^^ 

 (1895) to light which appeared when chlorides of lithium, sodium, 

 and potassium which had become colored from exposure to cathode 

 rays, dissolved in water. " One can observe the phenomenon when 

 the strongly colored substances are thrown into a small amount of 

 Avater or when water is slowly poured over them in a mortar, or 

 finally if the powder is poured in a test-tube, covered with water 

 and shaken." Later, G. Schwarz " (1903) observed light from sugar 

 on solution, brighter the higher the temperature. Kayser (1908: 

 683) was inclined to believe the phenomenon a triboluminescence 

 from contact of crystals, but reinvestigation of all aspects of lyolumi- 

 nescence is much to be desired. 



^^Ann. der Physik 56: 210-254, 1895. 



" Oesterr. Chem. Ztg., 1903. Abstract in Fortsch. d. Phys. 59 (2) : 452, 1903. 



