420 



The Amethystine Colouration produced in Glass by 

 Ultra= violet and X=Ray Radiation. 



The amethystine colouration of bottles from the Far 

 North of South Australia, where they have been exposed to 

 sunlight, has upon several occasions been brought to the notice 

 of the Society. 



In these cases, the colouration was presumably caused by 

 solar ultra-violet radiation. The tabled exhibit showed a 

 similar colouration produced in glass owing to bombardment 

 by X-rays produced by the "Coolidge" Electron type of X-ray 

 tube. 



In the walls of the "Coolidge" tube itself, the colouration 

 is very beautifully shown, unless masked by a deposit of 

 tungsten, caused by volatilization at the focal spot, due to 

 excessive energy imputs. In the old gas tubes, it was similarly 

 masked, where present, owing to the deposit of tiny particles 

 of platinum torn from the target by the bombardment of 

 cathode rays. 



Reference was made to various work relative to the 

 subject, including that of Dr. M. Luckiesh, of the Nela 

 Research Laboratory, who possessed samples of glass showing 

 a bluish tinge in the case of potash and a yellowish-green tint 

 in the case of sodium glass, produced by exposure to solar 

 radiation. A sample of lead glass exhibited a muddy yellow 

 colour after exposure to X-rays. 



The purplish colour is assumed to be due to a change in 

 the chemical or physical state of the manganese contained in 

 the glass. The colouration is quite unstable, and disappears 

 upon the application of heat. There appears to be no agree- 

 ment as to whether the manganese is present as in solution, 

 or in the colloidal form. 



The effect when brought about by solar radiation is 

 supposedly due entirely to the ultra-violet rays. In manganese 

 glass used in connection with electric lighting, the colour has 

 only been observed where the electric source of light is very 

 rich in ultra-violet rays, such as in a powerful arc. 



The big variation in wave lengths of the ultra-violet and 

 the X-rays, which are roughly of the order of 10 5 cms, and 

 10 8 cms., respectively, is an interesting consideration, in view 

 of the similarity of effects on the manganese constituents of 

 the glass. 



Why the effect apparently ceases so abruptly when the 

 wave lengths pass from the ultra-violet to the visible radiation 

 is a point also worthy of investigation. 



A. R. Riddle. 



Evening Meeting, August 14, 1919. 



