386 History of Luminescence 



might be called a tribophosphorescence. No temperature rise accom- 

 panies triboluminescence, but the light emission is favored if the 

 material is warmed and the harder the substance the more likely it 

 is to luminesce. 



Grotthus (1815) had also observed light from percussion but 

 made no extensive study, merely attributed it to light " which the 

 body had absorbed and preserved between its elementary parts." 



Heinrich's treatment of triboluminescence in the fourth section 

 (1820) of his book is quite thorough. He included the light phe- 

 nomena accompanying the compression of gases and the rapid rush 

 of gas into a vacuum (see Chapter VII) , as well as luminescence on 

 compression of solids. He held that all substances which emit under 

 compression were also thermoluminescent. His list of tribolumi- 

 nescent materials is large. In general silicious substances are best, 

 followed by clayey (Thon) , calcareous and talc-like material. Hein- 

 rich did not endeavor to connect triboluminescence with acid but 

 held that it was due either to: (1) separation of parts {Abspringen 

 der Unehenheiten) through friction, or to (2) electricity generated 

 by friction, or to (3) the chemical decomposition of the material. 



In 1855 J. Schneider took the position that triboluminescence 

 had nothing to do with rise of temperature or electrification, as he 

 was able to select diamonds easily electrified but not tribolumi- 

 nescent and minerals triboluminescent on such slight rubbing that 

 no rise in temperature was possible. 



During the rest of the century the subject of triboluminescence 

 was somewhat neglected. It was hardly considered by E. Becquerel. 

 The communications merely recorded new triboluminescent ma- 

 terial, but with the important discovery that many organic com- 

 pounds are triboluminescent. E. Becquerel (1859) and T. L. Phip- 

 son (1860) described the scintillations of milk sugar and uranyl 

 nitrate ^^ when crushed, while J. Noggerath (1823) and H. C. Lewis 

 (1884) discovered new triboluminescent minerals among organic 

 compounds. F. Krafft (1888) added high molecular weight benzol 

 derivitives like pentadecylparatolylketone; ^* J. Reuland (1889), 

 tetramethyldiphenylin; P. Gucci and G. Grassi-Cristaldi (1892) and 

 others, santonin compounds; Arnold (1897) , hippuric acid; W. J. 



^^ E. Becquerel {Ann. Chim. et Phys. (3rd ser.) 55: 86, 1859) first described the short 

 (3-4 milliseconds) phosphorescence of uranyl nitrate. J. Dewar (1901) and H. 

 Becquerel (1901) reported that light appeared when the crystals were placed in 

 liquid air during cooling and then during rewarming. Presumably the effect is a 

 triboluminescence connected with cracking or breaking of crystals from contraction 

 and expansion. Ice shows the same phenomenon. 



^* E. Wiedemann (Ann. d. Physik 37: 229, 1889) demonstrated a short phosphores- 

 cence of this compound after exposure to light in his new phosphoroscope. 



