440 History of Luminescence 



practically all workers since then. If the oxygen pressure is lowered, 

 luminescence reappears, and at a higher pressure, the higher the 

 temperature. C. F. Schonbein (1853) and also W. Muller (1870) 

 reported that phosphorus can be kept in pure oxygen for 2^ months 

 at room temperature with no luminescence and no oxidation or 

 ozone formation. This unusual relation of one of the most inflam- 

 mable substances led, during the second half of the nineteenth and 

 the first part of the twentieth century to a concerted effort to obtain 

 quantitative values for the luminescence intensity of phosphorus at 

 different oxygen pressures. 



One of the best general contributions was by J. Joubert in 1874, 

 a thesis on phosphorus luminescence in general. Joubert found that 

 the maximum luminescence pressure in oxygen is a linear function 

 of the temperature and a linear function of the volume per cent of 

 foreign gas added to the oxygen. He gave equations to express the 

 relationship and also held there is no doubt of the absence of lumi- 

 nescence in complete absence of oxygen, but found the pressure was 

 too low to measure accurately. Joubert also noted the effect of 

 inhibitors and the periodic flashes of light so characteristic of phos- 

 phorus luminescence. Since then additional studies have been made 

 by T. Ewan (1894, 1895) , with comment by J. H. van't Hoff (1895) , 

 by M. Centnerszwer (1898) . In fact the amount of research " which 

 was carried out during the nineteenth and early twentieth centuries 

 on the conditions for luminescence of phosphorus is truly over- 

 whelming, and no history could do justice to it without becoming 

 a monograph on the subject. Only two of several factors which 

 influence the luminescence can be considered, water vapor and 

 volatile inhibitors or quenchers. 



RELATION TO WATER VAPOR 



It has been observed for a long time that many reactions will not 

 proceed in absence of traces of water, which appears to act as a 

 catalyst. In the Dissertation on Elective Attractions (1785: 213) 

 translated from the Latin (1775), T. O. Bergman (1735-1784), 

 noted that water is necessary for the spontaneous combustion of 

 phosphorus, and K. W. Scheele ^^ reported that a pyrophore would 

 not ignite in air which had been dried over quicklime. In 1795 

 Wilhelm August Lampadius (1772-1842) demonstrated that phos- 

 phorus does not luminesce in dry air. 



Others who have studied the relation of phosphorus luminescence 



^* See the account in J. W. Mellor's Comprehensive treatise on inorganic and theo- 

 retical chemistry 8: 771-782, 1928. 



"^ Experiments on air and fire (1786: 112, 130). 



