Action of Badium Salts on Glass. 
363 
4. This specimen was of the same kind of glass as that referred to in 
the first part of the paper. The tube was 2 cm. in length, and the free 
space when plugged about 1-5 cm. The radium salt got mixed up with the 
balsam used for sealing, and was rather irregularly spread over about 
0-3 cm. The action extended along the tube for a greater distance than 
that occupied by the radium, even penetrating to the portion covered by 
the cork. With this tube the progressive colouration could be followed and 
the time for each successive zone to be developed noted. 
In 20 days a decided colouration was visible, and this extended for 
a certain distance and then stopped abruptly at the end of the first layer 
of the glass. In 53 days the second zone could be traced and was quite 
distinct at the end of 120 days, when the third zone had begun to show 
itself. In 250 days the third zone was well marked, and at the present 
time, 337 days from the commencement, five zones can be seen. The 
colouration does not yet extend right through the wall of the tube. The 
width of the zones does not change with time, but the depth of coloura- 
tion does. 
The measurements made on the tube were as follows : — 
Internal diameter 3 mm. 
External ,, 8*5 ,, 
Thickness of wall 2-5 ,, 
1st and deepest coloured zone 0*05 
2nd zone 0*1 ,, 
3rd ,, 0-3 
4th „ 0-5 „ 
The width of a zone is not uniform, as it depends upon the original 
zonal structure present in the glass, and the values given are average 
ones, as a reference to Fig. 3 will show. The zonal structure is not 
developed by the radio-active action. 
5. This was a specimen of fairly homogeneous glass, without zonal 
structure, and it showed a progressive depth of colouration from the 
inner to the outer wall. The depth of colour developed in a given time 
was greater than that of any other glass examined. 
From the papers of Professors Joly and Eutherford it might be inferred 
that they consider the colouration as being due to the a particles alone. 
If this is so, then the range of the a particles must be much greater than 
that indicated, for there is no question as to the depth of penetration in 
the glass tubes. But why is the development of the colour to be limited 
to the a particles ? The /3 and y rays pass through the material and clearly 
must exert some influence ; in fact, the total change must be due to this 
combined effect. 
