September 8, 1911] 



SCIENCE 



297 



one of the inactive series of gases, like 

 argon. Helium is an undoubted element, 

 with a well-defined spectrum; it belongs 

 to a well-defined series. And radium-ema- 

 nation, which was shown by Rutherford 

 and Soddy to be incapable of chemical 

 union, has been liquefied and solidified in 

 the laboratory of University College, Lon- 

 don, its spectrum has been measured and 

 its density determined. From the density 

 the atomic weight can be calculated, and 

 it corresponds with that of a congener of 

 argon, the whole series being: helium, 4; 

 neon, 20; argon, 40; krypton, 83; xenon, 

 130; unknown, about 178; and niton (the 

 name proposed for the emanation to recall 

 its connection with its congeners, and its 

 phosphorescent properties), about 222.4. 

 The formation of niton from radium would 

 therefore be represented by the equation: 

 radium (226.4) = helium (4) + niton 

 (222.4). 



Niton, in its turn, disintegrates, or de- 

 composes, and at a rate much more rapid 

 than the rate of radium; half of it has 

 changed in about four days. Its investiga- 

 tion, therefore, had to be carried out very 

 rapidly, in order that its decomposition 

 might not be appreciable while its proper- 

 ties were being determined. Its product 

 of change was named by Rutherford "ra- 

 dium A," and it is undoubtedly deposited 

 from niton as a metal, with simultaneous 

 evolution of helium; the equation would 

 therefore be: niton (222.4) = helium (4) 

 + radium A (218.4). But it is impos- 

 sible to investigate radium A chemically, 

 for in three minutes it has half changed 

 into another solid substance, radium B, 

 again giving off helium. This change would 

 be represented by the equation: radium A 

 (218.4) =lielium (4) + radium B (214.4). 

 Radium B, again, can hardly be examined 

 chemically, for in twenty-seven minutes it 

 has half changed into radium C^. In this 



case, however, no helium is evolved; only 

 atoms of negative electricity, to which the 

 name "electrons" has been given by Dr. 

 Stoney, and these have minute weight 

 which, although approximately ascertain- 

 able, at present has defied direct meas- 

 urement. Radium C^ has a half-life of 

 19.5 minutes; too short, again, for chemi- 

 cal investigation; but it changes into 

 radium C^, and in doing so, each atom parts 

 with a helium atom; hence the equation: 

 — radium C^ ( 214.4 )=helium (4)-|-radium 

 C= (210.4). In 2.5 minutes, radium C^ is 

 half gone, parting with electrons, forming 

 radium D. Radium D gives the chemist a 

 chance, for its half-life is no less than six- 

 teen and a half years. Without parting 

 with anything detectable, radium D passes 

 into radium B, of which the half -life 

 period is five days; and lastly radium E 

 changes spontaneously into radium F, the 

 substance to which Madame Curie gave the 

 name "polonium" in allusion to her native 

 country, Poland. Polonium, in its turn, is 

 half changed in 140 days with loss of an 

 atom of helium into an unknown metal, 

 supposed to be possibly lead. If that be 

 the case, the equation would run : polonium 

 (210.4) =lielium (4),+ lead (206.4). But 

 the atomic weight of lead is 207.1, and not 

 206.4 ; however, it is possible that the atomic 

 weight of radium is 227.1, and not 226.4. 



"We have another method of approaching 

 the same subject. It is practically certain 

 that the progenitor of radium is uranium; 

 and that the transformation of uranium 

 into radium involves the loss of three alpha 

 particles ; that is, of three atoms of helium. 

 The atomic weight of helium may be taken 

 as one of the most certain; it is 3.994, as 

 determined by Mr. Watson, in my labora- 

 tories. Three atoms would therefore weigh 

 11.98, practically 12. There is, however, 

 still some uncertainty in the atomic weight 

 of uranium; Richards and Merigold make 



