434 
SIR W. CROOKES ON ACQUIRED RADIO-ACTIVITY. 
the diamond to 60° G. in an oxidising mixture of potassium chlorate and fuming nitric 
acid, prepared from monohydrated sulphuric acid and potassium chlorate fused and 
free from moisture (9, 12, 32). The action on the dark layer is very slow, requiring 
at least eight or ten days for its complete removal. There is at first produced 
graphitic oxide which at an increased temperature yields pyrographitic acid easily 
destroyed by nitric acid. Hence the variety of carbon which coated the diamond 
is graphite The transformation of diamond into graphite requires the temperature 
of the electric arc, and the higher the temperature at which it is formed the greater 
is its resistance to oxidation. M. Moissan came to the conclusion that the tempe¬ 
rature reached by the surface of the diamond blackened in my radiant matter 
tube was probably about 3600° C. 
4. Six diamonds—having different degrees of phosphorescence under cathode 
rays—were tested in a Becquerel phosphoroscope to see if the order of intensity 
of the residual phosphorescence due to illumination with an arc light was the same 
as the order under cathode rays. All had a slight residual phosphorescence, but 
the order of intensity differed in the two cases. 
Action of Cathode Rays on various Mineral Substances. 
5. For many years I have experimented on the changes produced in ordinary 
and quartz glass and various crystals by exposure to radium emanations and rays. 
Considering the identity of the cathode discharge in a high vacuum tube with 
the /3-rays from radium, experiments were started to ascertain if the cathode 
rays would confer radio-activity in various solid bodies submitted to its influence. 
A vacuum tube was prepared with a removable window at one end to allow the 
contents to be exchanged for other bodies. In the tube were placed pieces of 
uranium glass, a crystal of ruby, a crystal of garnet, a piece of quartz, a plate of 
platinum and one of gold. The tube was exhausted to a high vacuum just short 
of the non-conducting point. On excitation the whole tube was filled with the 
green glow of phosphorescent glass, the ruby and uranium glass became very 
phosphorescent, the other bodies remained .quite dark. After an hour’s exposure 
to the cathode discharge the tube was opened, the objects quickly removed in the 
dark and placed on a sensitive film ; the upper sides that had received most 
bombardment being placed downwards on the film. They were kept thus for 
eighteen hours and the film then developed. There was absolutely no impression 
of any of the bodies on the film. Thus it appears that the cathode stream will 
not confer radio-activity on the above-named bodies. 
* 
Action of Cathode Rays on Phosphorescent BodAes. 
6. Experiments were next tried to see if earths and compounds which became 
strongly phosphorescent under the influence of the cathode discharge would thereby 
