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ACTION OF EADIUM SALTS ON GLASS. 
By W. A. Douglas Eudge, M.A., RE.S.S.Af. 
(Eead October 18, 1911.) 
In 1908 the author began some experiments on the action of radium 
salts on glass, by sealing up a small amount of the salt in thick-walled 
glass tubes. These have been recently opened and examined, and in 
view of the interest now being taken in the formation of pleochroic halos 
in rocks, the results observed may be of some value. 
The method employed was as follows : — 
Some pieces of barometer tubing were selected, and a number of 
pieces about 5 cm. in length cut off. In some cases the radium salt was 
hermetically sealed in by fusing the ends of the glass, and in others the 
ends of the tube were merely plugged by paraffined cork. 
The radium salt was one purchased from Messrs. Harrington in 1903, 
when it was stated to contain yoVo weight of radium bromide. On 
being tested against black oxide of uranium, it has at the present time an 
activity about 5,000 times as great as that substance. 
Two kinds of tubing were employed, one which showed a very faint 
pink tinge when looked at through the tube endwise, while the other had 
a pale greenish colour, but both colourations were very slight. After 
sealing the tubes were put away in a box, to which no light was admitted. 
Two control tubes of each sample were also used, one being kept in the 
dark and the other exposed to the brilliant sunlight of South Africa. This 
last was done because ordinary white glass exposed on the veldt acquires 
a dark amethyst tint in a few months. Unfortunately these samples were 
swept away in a storm. 
On examining the tubes containing the radium from time to time, a 
progressive colouration was seen to be developed, more particularly at the 
end of the tube where the radium was lying, but it spread for some dis- 
tance above. In one case, for example, the radium salt occupied a portion 
of tube to the extent of not more than 2 mm., while the colouration extended 
for 8 mm., diminishing gradually in intensity. On observing this the 
