The Eighteenth Century 185 



Luft," and also contributing to knowledge of combustion. Scheele's 

 observations on luminescence come from another more general 

 chemical interest, the composition of fluorspar, whose thermolumi- 

 nescence he had observed. His experiments and views on the light 

 emitted by this compound are highly specific, and will be found in 

 the chapters devoted to thermoluminescence and phosphorescence. 



Antoine-Laurent Lavoisier also paid little attention to lumines- 

 cence of any kind, despite his recognition of the analogy between 

 animal respiration and combustion and despite the similarity of 

 luminescence to combustion processes. He did make a suggestion 

 regarding the luminescence of fish, which appealed to many later 

 writers, an idea expressed in his Traite Elementaire de Chimie 

 (1789) . In speaking of putrefaction, Lavoisier wrote: ^* 



In putrefaction of animal substances sometimes the ammoniac predomi- 

 nates, which is easily perceived by its sharpness upon the eyes; sometimes 

 as in feculent matters, the sulphurated gas is most prevalent, and some- 

 times as in putrid herrings, the phosphorated hydrogen gas is most 

 abundant. 



It was natural to suppose that phosphoretted hydrogen, often 

 called phosphine or hydrogen phosphide, a self-inflammable gas, 

 was the cause of the light of fish. Like all plant and animal material, 

 fish are especially rich in phosphorus but unfortunately for Lavoi- 

 sier's theory, later work has indicated that hydrogen phosphide, 

 unlike hydrogen sulphide, is not a naturally occurring decomposi- 

 tion product or organic material. Phosphoretted hydrogen is usually 

 prepared by boiling phosphorus in caustic alkali and is actually a 

 mixture of PH3 and (PHo) 2, the latter gas only being the self-inflam- 

 matory one. 



Lavoisier's idea that phosphine is responsible for the light of 

 shining fish, flesh, and wood has been espoused by many workers 

 and has been suggested in explanation of the light of the glowworm 

 and other luminous animals. Phosphine also is a ready explanation 

 of the ignes fatui or feux follets, alleged to appear over swamps and 

 damp boggy ground, where decomposition of vegetation might give 

 rise to this gas. However, no actual formation of self-inflammable 

 phosphine has ever been observed in decaying plant or animal tissue 

 and the ignis fatuus must have another explanation. Marsh gas 

 (CH4) and sulphuretted hydrogen (H2S) are the gases of anaerobic 



(Oxford, 1669) . Lavoisier's claim to discovery comes from demonstration of the 

 elemental nature of oxygen. 



^^ Elements of chemistry by Mr. Lavoisier, trans, by Robert Kerr, 201, Edinburgh, 

 1793. 



