The Curies 65 



A year later Becquerel, who was a colleague and friend of 

 the Curies, discovered other radiations (from compounds 

 of the very heavy metal uranium), and these, like X-rays, 

 could penetrate opaque substances. 



The Curies were intensely interested, and Mme Curie 

 began the work of testing all known elements to see 

 whether any others, apart from uranium, showed signs of 

 emitting these extraordinary rays. She used a little 

 instrument called the electroscope, which is fitted with 

 leaves of fine gold-foil. These are electrified, and any 

 radio-active substance causes these leaves to collapse. 

 But the leaves do not collapse at once, and the rate at 

 which they do so can be used to measure the radio- 

 activity of the substance being tested. In testing a 

 sample of pitchblende, which is the mineral from which 

 uranium is extracted, Mme Curie was astonished to notice 

 that the amount of radio-activity shown was four times 

 as much as could be expected. 



The Curies agreed that this indicated the presence of 

 some hitherto undiscovered element which was enor- 

 mously more powerful than uranium. They decided to 

 collaborate in trying to find this new element. 



The next question was how to get enough pitchblende 

 for their purpose. Certainly they had not money to buy 

 it. Then the Austrian Government kindly sent them a 

 whole ton of pitchblende from its own mines in Bohemia. 

 It was a handsome present, for this ore is worth more 

 than two thousand pounds a ton. Then began the 

 colossal task of trying to reduce this mass of intensely 

 hard rock and of searching through it for the unknown 

 element. 



The method employed was what is called fractional 

 crystallization, and the work had to be done over and 

 over again, first in a foundry, then in an old wooden 

 building used as a laboratory. Weeks passed, and still 

 the pair worked unceasingly, testing and testing as they 



