276 MR. J. GIBBONS ON THE ACTION OF LIGHT 



XXXVI. Action of Light on certain Vanadium. Compounds. 

 By Mr. James Gibbons. Communicated by Professor 

 H. E. Roscoe, F.R.S. 



Read November 17th, 1874. 



Potassium divanadate in combination with organic matter 

 is at first rendered green, and ultimately blue, by exposure 

 to light, being reduced probably to the state of vanadium 

 trioxide. 



The salt is not sensitive to light in the absence of organic 

 matter. 



Gelatine mixed with potassium divanadate becomes 

 slightly less soluble in warm water after being exposed to 

 light. This is apparent by the unexposed portions of the 

 film swelling and dissolving more quickly when treated 

 with water than the exposed part. 



If a colourless film of dry sodium orthovanadate (Na ? 

 V0 4 ) , free from organic matter, be exposed on glass to the 

 sun for several hours, it only acquires a faint brown tint. 

 The film kept in the dark for some hours, regains its 

 normal colourless condition. 



The salt does not undergo any change when exposed to 

 diffused daylight. 



Paper which does not contain any size of an animal origin, 

 when coated with a solution of sodium orthovanadate, is 

 darkened on exposure to light, the depth of tint depend- 

 ing on the length of exposure and on the strength of the 

 solution used. The tint, however, never becomes darker 

 than a slate-colour. 



If the paper thus prepared be immersed, after exposure 

 to light, in a solution of silver nitrate, the colour in the 

 exposed parts instantly changes to a deep brown or to a 



