SIR W. CROOKES ON ACQUIRED RADIO-ACTIVITY. 
44:i 
development the image showed action as before where the face touched the film, but 
the line of scratch where the surface of the glass had been abraded by the diamond 
was blank, showing no action whatever (fig. 13). 
39. A triangular plate, about 1 mm. thick, was polished on its three edges, and 
kept in a bottle of solid radium bromide for sixty-eight hours, then laid on a sensitive 
film for four hours. There was very little action to be seen on development on the 
part where the face touched the film, but there was strong action radiating from the 
edges, with a continuation of the line of edge from each point (fig. 14). The plate 
was now cut into two equal parts, and the two halves, separated about a centimetre, 
were laid on a sensitive film and there kept for forty-eight hours. On developing, it 
was seen that the action of the flat surface was the same as before, but while the 
overflow action from the original corners was also the same, there was no action at all 
along the cut surface (fig. 15). 
40. A glass tube that had contained 25 mgrm. of pure radium bromide was cut in 
half to remove the radium, and well washed and boiled in acids. It was of a dark 
blue colour. After being in a cabinet for many months the two halves were laid on 
a sensitive film in a line, the cut surfaces opposite each other and separated about 
2 mm. After four hours’ contact the film was developed when the appearance 
presented that of a streaming brush discharge from the two ends of each half—the 
part where the tubes themselves rested having made no impression (fig. 16). 
Superficial Action of Radium on Mica. 
41. Radium bromide has been imported from the Continent in small ebonite 
boxes covered with a disc of mica. One of these discs was first well washed to 
remove any adhering grains of radium salt—it was then split into four flakes. 
The upper flake, of a strong brown colour, discharged the electroscope in three 
seconds. The next film, also showing brown discolouration, required 3'5 seconds. 
The third film, not discoloured at all, required twelve seconds, while the last film, 
which had been furthest from the radium, required eighteen seconds for discharge, 
showing that the greater part of the activity was near the surface and corresponded 
with the coloration. 
Action of X-Rays on Diamond. 
42. Experiments were instituted to ascertain how X-rays affected the diamond. 
A tray full of crystals of diamond was exposed to X-rays from a hard tube, 
covered in card and velvet so as to prevent interference from the luminosity of 
the glass. Most of the stones became luminous—but in different degrees. Two 
stones specially were noticed. One large stone shone very brightly, with a blue 
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