LIGHT DISCHARGES OXYGEN. 83 



a golden color and a blue ; by addition of vinegar the blue 

 vanished; oil of tartar asdeliquium restored the blue. Boyle's 

 Works, by Shaw, page 60. 



Glass is affected by time :permanent prismatic colors are 

 exhibited on its surface. This may be observed by examining 

 the windows of old buildings, where it frequently appears that 

 scales or lamina have been actually removed from some parts, 

 rendering the surface uneven. 



It has also been remarked that nitric acid which is colorless, 

 when exposed for some time to light becomes yellow, and a 

 quantity of oxygen gas is found floating on its top. If it be 

 then carried to a dark place, the oxygen is gradually absorbed, 

 and the acid becomes again colorless. The color of nitrous 

 acid is yellow, derived from the predominancy of proportion 

 which the azote bears to the oxygen and hydrogen in the first 

 combination ; however, on excess of oxygen in the second combi- 

 nation as nitric acid, the preponderating influence as to color is 

 lost to the nitrogen, which is then no longer in maximum, 

 but, on the application of light, the first combination is ( 

 priori) induced by absorption of the azotic ray, the oxygen in 

 excess is separated, and appears in the state of gas ; but on 

 removal to the dark it is again absorbed, and the second combi- 

 nation is induced, and when completed the colorless appearance 

 is restored. 



There is a proof also of the yellow color afforded to flame by 

 the presence of azote in a proportion beyond what is requisite 

 to constitute white light. When a burning taper is let down 

 into ammoniacal gas it goes out three or four times succes- 

 sively, but at each time the flame is considerably enlarged by 

 the addition of another flame of & pale yellow color, and at last 

 this flame descends from the top of the vessel to the bottom. 

 Priestley, ii., 381. 



The composition of ammonia is well known to be hydrogen 

 and azote, the oxides of manganese, gold, or mercury, when 

 treated with it are reduced, the ammonia disappears, and azotic 



