( JO OXYGEN DERIVED FROM 



immersed in hot water continued for a shorter duration in a 

 luminous state, the quantum absorbed being equal in both. 



Now, if the pyrophorus had not possessed all the elements 

 of light, and nearly in appropriate quantities, the light would 

 not have appeared perfect. Mr. Wilson has proved that the 

 blue rays act with greater effect than the others, on many 

 pyrophori, and that they cause an extrication of red light. 

 M. De Grosser has shown, that the same occurs with the 

 diamond, which is a natural pyrophorus. Journal de Phys. 

 XX., 170. 



With respect to the chemical combination between light and 

 other bodies, as in the phenomena of the phosphori, it has been 

 attributed to light that it enters into the composition of oxygen 

 gas ; in proof of which, it has been advanced by Priestley and 

 Ingenhouse, " That when vegetables grow in the light they give 

 out oxygen gas ; but no oxygen is extricated in the dark> even 

 though heat be applied." 



It is evident, hence, that it is not from the atmospheric air, or 

 water, that the oxygen is discharged, as both were present in the 

 dark, as well as when the plant was exposed to light, but that 

 the color of the plant, which depends also on the presence of 

 light, is green, and that the nitrogen and the hydrogen of light, 

 or the greater part of them, are absorbed, and chemically com- 

 bined with the plant, and the excess of oxygen extricated and 

 discharged. 



It has been remarked by Scheele, that when the oxides of gold, 

 or silver, are exposed to light, they are reduced to their metallic 

 state, and oxygen gas evolved, as mentioned by Bertholet. 

 This may be accounted for by admitting it possible that the 

 other rays of light are absorbed by the metal, all but the oxy- 

 genating (red) ray, the excess of oxygen is discharged, the 

 metal is reduced, acquiring hydrogen in predominancy, as an 

 essential to such a slate. 



It can be shown, that substances termed inflammable do not 



