444 History of Luminescence 



find no ozone or H2O2 in moist trioxide oxidation " despite the 

 luminescence. Therefore, it would appear that ozone is a by-product 

 of oxidation rather than an essential factor in luminescence. Thorpe 

 and Tutton held that the second step in oxidation resulted in light 

 emission. The result suggests that P2O5 molecules are the emittors 

 but the spectrum of phosphorescence was not studied until 1912.-* 



One early discovery that has had a lasting influence on later work 

 was the observation that the air which has passed over luminescent 

 phosphorus can discharge negative or positively charged bodies (C. 

 Matteucci, 1850) . This is a sign that the air has become a con- 

 ductor of electricity such as was generally observed for gases in 

 flames by W. Giese in 1882. In discussing the nature of ozone, R. 

 Clausius (1858) was led to assume that oxygen was split by phos- 

 phorus into atoms with positive and negative charges. These charged 

 atoms or ions would conduct the current. 



The electrical conductivity of phosphorus vapor was investigated 

 by Elster and Geitel (1890) and attributed to the changes resulting 

 in ozone formation, but they found ozone itself was not responsible. 

 That ions are formed is indicated by the fact that phosphorus vapors 

 will condense a steam jet (Helmholtz and Richarz, 1890) , which 

 led J. H. van't Hoff (1895) to postulate the formation of oxygen 

 atoms, one oxidizing the phosphorus and the other forming ozone 

 with oxygen. The possibility gave rise to much discussion by many 

 workers during the first decade of the twentieth century. 



The striking discoveries connected with radioactivity of uranium 

 and radium stimulated the claim that phosphorus produced pene- 

 trating rays -^ which would affect a photographic plate and an 

 emanation -*' of phosphorus was described like that of uranium. 

 These conclusions were later disproved, after a considerable amount 

 of research in the twentieth century but there is no doubt of the 

 formation of something w^hich increases the electrical conductivity. 

 Much of the twentieth-century discussion has dealt with the ques- 

 tion whether this material consists of charged particles or true 

 gaseous ions. 



^^ E. Scharff (1907) also claimed that no ozone is formed during oxidation of P4O8 

 although luminescence appears, but W. E. Downey (1924) has detected ozone. 



=* By M. Centnerszwer and A. Petrikaln. Ztschr. filr physik. Chemie 80: 235-240, 1912. 



"^ A similar penetrating radiation was supposed to be emitted from fireflies by H. 

 Muraoka (1896) . See Chap. XVI. L. Kann (1899) published preliminary experiments, 

 claiming penetrating radiation from Balmain's paint. 



^''R. Schenck and E. Breuning, Ber. d. d. cheni. Gesell. 47:2601-2611, 1914; see also 

 39: 1506-1521. 1906. 



