SIR W. CROOKES ON ACQUIRED RADIO-ACTIVITY. 
437 
After well washing and drying it was put on a sensitive film for five hours. On 
developing it was seen that the stone had made a good impression on the film. 
13. The stone was then sent to a diamond cutter to be cut into a brilliant. On 
receiving it back it was quite white and free from trace of colour. The stone was 
then placed on a sensitive film and kept in darkness for twenty-two hours. On 
developing no impression was apparent, although, before cutting, the active diamond 
had impressed a film in five hours (12, 16). 
Effect of Heat on Induced Radio-activity. 
14. A New South Wales diamond which had always been kept away from radium 
salts, was tested in the electroscope (2) and found to give a fall in two seconds, the 
natural leak being 180 seconds. The stone was then put in a silica crucible and 
heated in an electric tray furnace until visibly red. No change was observed. After 
five minutes — a,t, say, 700° C.— it was allowed to cool. The time of discharge in the 
electroscope was found to be six seconds. 
15. The diamond was then packed in a silica crucible with graphite and heated 
with a Meker burner to 700° C. several times, cooling and testing the diamond each 
time when cold. ] 
Heated to 700° C. for 10 mins, and cooled, time of fall = 6 secs. 
„ 15 „ ' „ =10 „ 
,, 20 ,, ,, = 10 ,, 
„ 20 „ „ = 30 „ 
It was now left for the night, and measurements resumed next day. 
Hea.ted to 700° C. for . . 60 mins., time of fall = 9 secs. 
,, in new graphite for 30 ,, „ = 7 ,, 
New graphite again used. 
Tested again after 48 hours, time of fall .,...= 4 secs. 
Heated to 700° C. for 30 mins., and allowed to cool 
for 2 hours, time of fall.= 2 ,, 
The diamond after the last measurement (2 .secs.) was laid on a sensitive film and 
kept in the dark for twenty-one days; on development it gave a good image. 
This experiment shows a temporary loss of activity by the heat treatment followed 
in a short time by complete recovery. 
16. A Kimberley diamond, rather flat, octahedral shaped, was kept in a bottle of dry 
radium bromide for some weeks until it was quite green. By means of a steel wheel 
fed with diamond dust part of one face was cut away, and the surface of an adjoining 
