ritESIDEiNT's ADDKESS. 9 



cxamiuoil the uic called pitch- bleude which is Avorkud iu miuea in 

 Bohemia and is found also in Cornwall. It is the ore from which all 

 commercial urciniuni is extracted. The Curies found that pitch-blende 

 has a radio-activity four times more powerful than that of metallic 

 uranium itself. They at once conceived the idea that the radio-activity 

 of the uranium salts examined by Becquerel is due not to the uranium 

 itself, but to another element present with it in variable quantities. This 

 proved to be in part true. The refuse of the first processes by which in the 

 manufacturer's works the uranium is extracted from its ore, pitch-blende, 

 was found to contain four times more of the radio-active matter than 

 does the p\n-e uranium. By a long series of fusions, solutions, and 

 crystallisations the Curies succeeded in ' hunting down,' as it were, the 

 radio-active element. The first step gave them a powder mixed with 

 barium chloride, and having 2,000 times the activity of the uranium in 

 which Becquerel first proved the existence of the iiew property — radio 

 activity. Then step by step theypurified it to a condition 10,000 times, then 

 to 100,000 times, and finally to the condition of a crystalline salt having 

 1,800,000 times the activity of Becquerel's sample of uranium. The 

 purification could go no further, but the extraordinary minuteness of the 

 quantity of the pure x'adio-active substance obtained and the amount of 

 labour and time expended in preparing it may be judged of from the 

 fact that of one ton of the pitch-blende ore submitted to the process of 

 purification only the hundredth of a gram — the one-seventh of a grain— 

 lemained. 



The amount of radium in pitch-blende is one ten-millionth per cent. ; 

 rarer than gold in sea-water. The marvel of this story and of all that 

 follows consists largely in the skill and accuracy with which our chemists 

 and physicists have learnt to deal with such nfinitesimal quantities, and 

 the gigantic theoretical results which are securely posed on this pin-point 

 of substantial matter. 



The Curies at once determined that the minute quantity of colourless 

 crystals they had obtained was the chloride of a new metallic element 

 with the atomic weight 225, to wliich they gave the name radium. Tiio 

 proof that radium is an element is given by its ' sign-manual '■ — the spectrum 

 which it show-s to the okserver when in ihe incandescent state. It con- 

 sists of six bright lines and three fainter lines in the visible part of the 

 spectrum, and of three very intense lines in the ultraviolet (invisible) part. 

 A very minute quantity is enough for this observation ; the lines given 

 by radium are caused by no other known element in heaven or earth. 

 They prove its title to be entered on the roll-call of elements. 



The atomic weight was determined in the usual way by precipitating 

 the chlorine in a solution of radium chloride by means of silver. None 

 of the precious element was lost in the process, but the Curies never had 

 enough of it to venture on any attempt to prepare pure metallic radium. 

 This is a piece of extravagance no one has yet dared to undertake. 

 Altogether the Curies did not have more than some four or five grains of 



