94 THE NEW KNOWLEDGE. 



But if radium is an element, it should find a place in the 

 family grouping of the periodic law. And so it does. An 

 examination of the chemical behaviour of radium shows that 

 it is allied in all its properties to barium. It is, in fact, so 

 like barium that it is almost impossible to separate one from 

 the other. The family resemblance is unmistakable. Ba- 

 rium is a sister to radium. Now, if you will examine the 

 table of the periodic law, page 28, Part II, you will notice 

 that Barium (Ba=137) occurs in Group II and that there are 

 several vacant spaces in the groups marked with black lines 

 for elements hitherto undiscovered. Into one of these blank 

 Group II spaces radium ought to fit if the periodic law is 

 ~ the expression of a fact. The determining factor 

 Mo. is, of course, the weight of the atom. That set- 



B e 9 ties its place in the table. Now, the atomic 



weight of radium has been determined with ex- 

 jVlfr 24 



treme accuracy by Madame Curie, and her re- 



Ca 40 suits lead to the value 225. This is the atomic 

 Zn 65 weight of an element which should fill the blank 

 Td 112 s P ace below mercury (Hg 200) in Group II; and 

 Ba 137 so ^ i s no won der that, chemically, radium should 



resemble barium for they belong to the same family. 



The amount of radium in pitchblende is less 



& than one ten-millionth per cent., rarer than gold 



in sea water; and the quantities of the much rarer polonium 

 and actinium are literally infinitesimal. The difficulties of ex- 

 traction are immense. The residue of the mineral pitch- 

 blende, out of which the radium has been extracted Jat 

 Jochimsthal, Bohemia, is sent to Professor Curie's works at 

 Ivry, France, where it is precipitated and reprecipitated 

 and crystallized and recrystallized an amazing number 

 of times in order to separate it from the multitude of other 

 things contained in the pitchblende. Finally, a few grains 



