RADIUM 91 



radioactive new elements in almost infinitesimal 

 quantity, the best known of which is radium. The 

 radium is present in pitchblende in very minute 

 quantity, not more than one part in five or ten 

 millions of the mineral at most. Small as the 

 quantity was, they succeeded in isolating the com- 

 pounds of radium in the pure state, and ultimately 

 accumulated enough, not only for a detailed investi- 

 gation of its extraordinary radioactivity, but also of 

 its chemical character, spectrum, and atomic weight. 

 They found its atomic weight to be 226, which is 

 next to that of uranium, 238, and thorium, 232. This 

 and its chemical character put it into a position in 

 the periodic table in the family of the alkaline-earth 

 elements, comprising calcium, 40, strontium, 85, and 

 barium, 137. In its whole character it has the 

 closest resemblance to the latter element, and can 

 only be separated from it by prolonged and tedious 

 fractionation processes. Chemically it was normal in 

 every respect, and its chemical character could have 

 been predicted from the Periodic Law before its 

 discovery. But in addition to its chemical character 

 it had a whole new set of surprising radioactive 

 properties in a very intense degree. 



These discoveries naturally aroused the very 

 greatest scientific interest. The very existence of 

 radium, a substance capable of giving off spontane- 

 ously powerful new radiations which can be trans- 

 formed into light and heat, and, indeed, not only 

 capable of doing this, but, so far as we know, 

 incapable of not doing it, ran counter to every 

 principle of physical science. For whence comes 

 the energy that is being given out in the process? 

 So soon as pure radium compounds became available, 

 the amount of this energy was measured and it was 

 found to be sufficient to heat a quantity of water 

 equal to the weight of the radium from the freezing- 



