July 1, 1921] 



SCIENCE 



is charged and collapses when it is discharged. 

 The electroscope then became the chief agent 

 by which radio-activity cotild be tested, and 

 Madame Curie with her husband — for she had 

 been married the year before to Pierre Curie, 

 professor of chemistry in the University of 

 Paris — ^began- the study of other substances 

 than uranium to see how general this new 

 property was, and they found that the two 

 heaviest elements in nature, uranium and 

 thorium alone of the then known elements, 

 possessed it, but they also found that the 

 natviral ore of uranium, which we commonly 

 call pitchblende, and which is more than fifty 

 per cent, uranium oxide, although it contains 

 many other minerals like barium and lead 

 and bismuth — that this pitchblende discharged 

 the electroscope approximately four times as 

 fast as did pure uranium oxide. This meant, 

 as the Curies at once interpreted it, that there 

 must be some hidden elements in the pitch- 

 blende which had the same radio-active prop- 

 erty as uranium but in larger degree. And so 

 they began the search to see if they could not 

 separate the element which was res]3onsible 

 for that activity, and after two or three years 

 of arduous work Madame and Monsieur Curie 

 were able to announce that, by using the or- 

 dinary methods of chemical analysis, by mak- 

 ing precipitates and testing the activity both 

 of the precipitate and filtrate to see with 

 which the activity went and therefore what 

 were the chemical properties of the substances 

 that had it, they had been able definitely to 

 discover the existence of these two new radio- 

 active elements of which Dr. Walcott spoke. 

 The first of these did not exist in sufiicient 

 amount so that it could be detected by any 

 other properties than its activity. This was 

 named polonium, in honor of the land in 

 which Madame Curie was born, for her father 

 was a professor in the Technische Hochschule 

 at Warsaw. This polonium, by the way, has 

 been one of our most useful agents in getting 

 at the inner properties of the atom, because 

 is has the power of emitting one type of ray 

 alone and not a mixture of rays as does the 

 other and more famous radio-active element 

 which the Curies discovered. This other new 



element they named, appropriately, radium 

 because it had a radio-activity a million times, 

 weight for weight, that of the pitchblende, 

 and three or four million times that of pure 

 uranium. 



This is the simple, unadorned tale of the 

 discovery of radium, but I am sure you do 

 not appreciate the kind of painstaking re- 

 search and labor which that simple tale re- 

 presents. Tou may perhaps get a little glimpse 

 of what it means — of what a search for a 

 needle in a haystack it was — when I say that 

 the amount of radium in uranium is one 

 part in 3,200,000; or that, in order to get the 

 little gram of radium which is being presented 

 to Madame Curie to-day it was necessary to 

 take 500 tons of Colorado carnotite ore, which 

 iwssesses two per cent, of uranium and to 

 treat it with 600 tons of chemicals, apart from 

 water and coal. So that, you see, the problem 

 of bringing to a successful issue that search 

 was one that places Madame Curie and her 

 husband in the front rank of the world's 

 scientific men and women. 



The Nobel prize for 1903 was awarded 

 jointly to Henri Becquerel and Monsieur and 

 Madame Curie for their studies in radio- 

 activity, and in 1911 the Nobel Prize was 

 awarded to Madame Curie alone for isolating 

 radium — getting it as a pure metal (in the 

 early experiments it was a bromide or chlo- 

 ride), and for determining its atomic weight, 

 which comes at 226.0. The heaviest element, 

 uranium, has an atomic weight of 238, so that 

 this is only twelve units lower than that. 



So much for the way in which the discovery 

 came about. But what is radio-activity? 

 Perhaps I can tell you in as few words as pos- 

 sible by this simple statement. This gram 

 of radium which you are giving to Madame 

 Curie to-day, the volume of which is just that 

 which I hold in my hand, and which you can 

 see when the room is darkened — that gram of 

 radium is continuously shooting off per sec- 

 ond 145,000 billion particles which we call 

 alpha particles, and with speeds which reach 

 the stupendous value of twelve thousand miles 

 per second. Now, when you recall that the 

 super-guns which bombarded Paris could not 



