CHAPTEE XVI 



PHOSPHORESCENCE AND MOLECULAR AGGREGATION 



Phosphorescence and catalytic action — Effect of molecular 

 concentrations on freedom of corpuscles — Dependence of 

 phosphorescence upon free-paths and velocity of cor- 

 puscles — Existence of separate phosphorescent molecules 

 in liquids, and of separate active molecules in luminous gases 

 — That separate large molecules exist in flames — The 

 process of catalysis and metabolism once more. 



A CONNECTION between phosphorescence and 

 radio-activity undoubtedly exists. Many phosphor- 

 escent substances are radio-active, and all radio- 

 active substances produce phosphorescence. Al- 

 though radio-activity, so far as our knowledge goes, 

 is not dependent upon combustion, nor accompanied 

 by any permanent chemical or molecular change in 

 the structure of the body, it may yet be associated 

 with some temporary molecular or pseudo-chemical 

 interactions ; whilst the study of phosphorescence 

 indicates that molecular interactions appear to 

 underlie the most simple, as well as the most com- 

 plicated, facts of observation. There is, however, 

 no permanent change in the chemical composition 

 of the body, even when the luminosity which results 



