436 History of Luminescence 



i. e., oxygen. He later established its simple character and included 

 it in his list of elements, together with light and caloric. 



RELATION TO OXYGEN 



One of the characteristics of phosphorus luminescence is its de- 

 pendence on the presence of oxygen. The history of this discovery 

 is long, involving many workers and contradictory results, and was 

 not finally settled until the nineteenth century, but is introduced 

 here, because some of the earliest experiments were designed to 

 answer the questions. It will be recalled that Boyle's experiment 

 with phosphorus smeared on paper and placed under his air pump, 

 gave inconclusive results, and his spectators agreed that the trials 

 should be repeated. No more complicated test could have been 

 undertaken, as the relation between phosphorus luminescence and 

 oxygen pressure depends on temperature and water vapor, as well as 

 oxygen. Moreover, the presence of small amounts of inhibitors 

 greatly affect the results. 



Nevertheless, a number of early workers repeated Boyle's experi- 

 ment with phosphorus in absence of air. Dr. Slare was one of 

 these and another was William Homberg, whose experiments were 

 carried out in the house of M. d'Alence, and are described by 

 Lemery. A small piece of solid phosphorus was placed in a little 

 glass bottle containing a brass cock which was connected with a 

 large evacuated jar. When the cock was opened a great flash of light 

 occurred as the air from the phosphorus bottle rushed into the jar, 

 the phosphorus became heated but the light practically disappeared. 

 On admitting air the light returned. The experiment would seem 

 to indicate the necessity of air for luminescence. However, a second 

 trial gave the opposite result: ^^ 



When the air was drawn out of the bottle the Phosphorus did shine 

 brighter; on the contrary when we let the air again into it, the Phos- 

 phorus went out: which is quite different from what hapned whilst 

 the bottle that held the Phosphorus was hot in the former Experiment. 

 We repeated the Experiments divers times, and saw the same thing 

 continually happen: that is to say, that Phosphorus being heated lost 

 much of its light, when the air was pumped out of the bottle wherein 

 it was contained, and it recovered light again when new air was let 

 into it: on the contrary, the Phosphorus being cold did shine when the 

 air was pumped out of the bottle, and the light disappeared when the 

 air was let into it. 



Lemery was puzzled by the fact that " the air does sometimes make 



^^ Quotations from W. Harris translation, A course of chymistry, 529-530, London, 

 1686, from fifth French edition. 



