Radio-activity of Uranium. 



•417 



The filtrate was evaporated to dryness, and heated with nitric acid. 

 The yellow precipitate and the residue of the filtrate were put into 

 cells, and laid on a sensitive plate. After twenty-four hours' action 

 the plate was developed, when it was seen that the whole of the 

 radio-activity resided in the ammonium uranate, the other substance 

 showing nothing. This experiment proves that the active body is 

 precipitated by ammonia, and is insoluble in excess. 



23. Another portion of active uraniiun nitrate was dissolved in 

 water, with an excess of ammonium carbonate. The first formed 

 precipitate almost entirely re-dissolved, lea-vdng a small quantity of 

 insoluble light brown flocculent precipitate. This collected on warming, 

 like alumina. It was filtered off, well washed and dried, and put in a 

 glass cell. 



The filtrate from the above precipitate was evaporated to drive 

 the ammoniimi carbonate, when a yellow precipitate came down 

 This was filtered, washed, dried, and put into a cell. 



These precipitates were exposed for twenty-four hours in a lead 

 screen apparatus. On developing, it was seen that the residue insoluble 

 in ammonium carbonate instantly flashed out black and dense, while 

 the salt precipitated from the ammonium carbonate solution gave a 

 scarcely discernible image. 



24. The action of the precipitate insoluble in ammonium carbonate 

 was so strong that another experiment was tried, exposing the sensitive 

 plate to its action for one hour. On development, the disc of action 

 came out strong and black, although not so black as in the twenty- 

 four hours' experiment. It was now laid for five minutes on a sensitive 

 plate. Here the action was distinct — about as strong as that given 

 by ordinary uranium nitrate in twenty-four hours. These experiments 

 prove that the active body can exist apart from uranium. 



If a sheet of thin glass or celluloid is laid on a sensitive plate, and 

 the dried filter-paper with its contents laid on that, and kept down by 

 a weight, an impression is given in as short a space of time as if a glass 

 cell had been used. 



25. The radio-active body is not entirely insoluble in ammonium 

 carbonate. A portion of the very active precipitate left after separa- 

 tion from the uranium was dissolved in dilute hydrochloric acid, and 

 an excess of ammonium carbonate added. The precipitate was very 

 brown due to the presence of iron ; it was dried and tested. The 

 filtrate was well boiled, and as the ammonium carbonate evaporated 

 a sHght precipitate came down. This was collected on a filter and 

 tested by the side of the first precipitate. On developing the plate- 

 the images produced by each precipitate were of about equal intensity. 

 The brown precipitate was digested in very dilute hydrochloric acid 

 in the cold. The iron partially dissolved before the rest of the sub- 

 stance, lea™g the residue decidedly paler in colour. This pale body 



