36 THE NATURE OF ANIMAL LIGHT 



Wiedemann and Schmidt (1895) as a light accompanying 

 the solution of colored (from exposure to cathode rays) 

 cr^'stals of Li, Na, or K chlorides, is probably due to a 

 triboluminescence from stirring of the crj^stals dur- 

 ing solution. 



Chemiluminescence. — As the name implies, chemilu- 

 minescence is the production of light during a chemical 

 reaction at low temperatures. This does not mean that 

 the other types of luminescence are not connected with 

 chemical reactions — using the word reaction in a broad 

 sense — for we have reason to believe that in some cases 

 spectra are not characteristic of the element as such but 

 are rather characteristic of a particular reaction in which 

 the element takes part (dissociation into ions, changes 

 from monovalent to bivalent condition, etc.) and that this 

 is the reason one element may show various spectra under 

 different conditions (Bancroft, 1913). The chemilumines- 

 cences are rather oxidation reactions involving the ab- 

 sorption of gaseous or dissolved oxygen and may be very 

 easily distinguished from all the previously mentioned 

 luminescences by this criterion. They should, perhaps, 

 more properly be called oxyluminescences. 



The glow of phosphorus is the best known case, recog- 

 nized since phosphorus was first prepared by Brandt in 

 1669. It is interesting to note that when first prepared 

 phosphorus was regarded as a peculiarly persistent type 

 of phosphor, i.e., a material akin to the impure alkaline 

 earth sulphides. 



Fresh cut surfaces of Na and K metal will glow in the 

 dark for some time, especially if warmed to 60°-70° 

 (Linnemann, 1858). A film of oxide is formed over the 

 surface, showing definitely that oxidation has occurred. 



