CHAPTER VIL. 
CONTINUOUS PRODUCTION OF RADIO-ACTIVE MATTER. 
118. Uranium X. The experiments of Mme Curie show 
that the radio-activity of uranium and radium is an atomic pheno- 
menon. The activity of any uranium compound depends only on 
the amount of that element present, and is unaffected by its 
chemical combination with other substances, and is not appreciably 
affected by wide variations of temperature. It would thus seem 
probable, since the activity of uranium is a specific property of 
the element, that the activity could not be separated from it by 
chemical agencies, 
In 1900, however, Sir William Crookes! showed that, by a single 
chemical operation, uranium could be obtained photographically 
inactive while the whole of the activity could be concentrated 
in a small residue free from uranium. This residue, to which 
he gave the name Ur X, was many hundred times more active 
photographically, weight for weight, than the uranium from which 
it had been separated. The method employed for this separation 
was to precipitate a solution of the uranium with ammonium car- 
bonate. On dissolving the precipitate in an excess of the reagent, a 
hight precipitate remained behind. This was filtered, and constituted 
the Ur X. The active substance Ur X was probably present in 
very small quantity, mixed with impurities derived from the 
uranium. No new lines were observed in its spectrum. A par- 
tial separation of the activity of uranium was also effected by 
another method. Crystallized uranium nitrate was dissolved in 
ether, when it was found that the uranium divided itself between 
the ether and water present in two unequal fractions. The small 
part dissolved in the water layer was found to contain practically 
1 Proc. Roy. Soc. 66, p. 409, 1900. 

