490 History of Luminescence 



lar, both using up oxygen and producing acid, but Tychsen was 

 surprised that wood should luminesce under water while phosphorus 

 did not, and that phosphorus would light *^ in Ho, Ng and nitric 

 oxide, while wood did not. Neither wood nor phosphorus would 

 light in pure oxygen. This result is correct for phosphorus but 

 suggests that the pure oxygen Tychsen used must have contained 

 some harmful ingredient, for the light of fungi continues in oxygen 

 as well as in air. 



VON HUMBOLDT, GAERTNER, AND BOECKMANN 



The chief interest of these three Germans was to determine 

 whether the light of rotten wood resulted from a slow burning, as 

 Spallanzani and others believed. Von Humboldt (1799) did find 

 that the light would disappear in COo and in azotic gas (Na) and 

 other non-respirable gases, but that it reappeared in oxygen or air, 

 leading to the conclusion that the luminescence was dependent on 

 oxygen, which was apparently absorbed by the wood. He also 

 stressed the fact that the luminescent process could be affected in 

 many other ways, by high temperature, or acids, alcohol, etc.— even 

 though oxygen was present. 



Von Humboldt concluded that luminescence must depend on a 

 certain equilibrium between the organic constituents in the wood, 

 an equilibrium which was changed by temperature or by substances 

 in the surrounding medium. For example, at low temperatures, 

 oxygen would combine with hydrogen, forming water, a process 

 accompanied by luminescence, but at a high temperature with 

 carbon to form CO2, and the light would disappear, as it did in 

 absence of oxygen. The cause of the light was sought in a delicate 

 balance between such reactions at the time putrefaction begins. 



Gaertner (1799) , an apothecary at Hanau, believed that the light 

 of rotten wood was different from that of light resulting from com- 

 bustion, since oxygen appeared to be less essential for wood, and 

 he asked, " whether the luminous appearance of wood be not pro- 

 duced by the union of phosphorus and carbon in a certain propor- 

 tion still unknown to us? " Gaertner concluded that it was not yet 

 possible to give a satisfactory explanation of the phenomenon. 



Boeckman, a professor of physics at the Gymnasium at Carlsruhe, 

 published two papers in 1800, one on phosphorus (see Chapter 

 Xni) and one on luminous wood. The two luminescences were 

 compared as regards the effect of gases, with the following conclu- 

 sions: ** (1) Wood is luminous in oxygen gas at low temperatures 



*^ Owing to impure gases containing very small amounts of oxygen. 

 ** From the translation in Phil. Mas:, for 1803. 



