226 



NATURE 



[August 31, 19 11 



in properties), about 2224. The formation of 

 niton from radium would therefore be repr — nted by the 

 equation: radium (226-4) = helium U)+niton (222-4). 



Niton, in its turn, disintegrates, or decomposes, and at 

 a rate much more rapid than the rate of radium ; half of 

 it has changed in about four days. Its investigation, there- 

 fore, had to be carried out very rapidly, in order that its 

 decomposition might not be appreciable while its properties 

 were being determined. Its product of change was named 

 by Rutherford " radium A," and it is undoubtedly de- 

 posited 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 impossible to investigate radium A chemically, 

 for in three minutes it has half changed into anothei "lid 

 substance, radium" B, again giving off helium. This change 

 would be represented by the equation : 



radium A (2 184) = helium (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 1 . In this case, however, no helium is evolved ; onlv 

 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 measurement. Radium C 1 

 has a half-life of 19-5 minutes, too short, again, for 

 chemical investigation ; but it changes into radium C = , 

 and in doing so each atom parts with a helium atom, 

 hence the equation : 



radium C 1 (2i4-4) = helium (4)-r-radium C 2 (210-4). 

 In 2-5 minutes radium C : is half gone, parting with elec- 

 trons, forming radium D. Radium D gives the chemist 

 a chance, for its half-life is no less than sixteen and a 

 half years. Without parting with anything detectable, 

 radium D passes into radium E, of which the half-life 

 period is five days ; and, lastly, radium E changes spon- 

 taneously 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 (2 104) = helium (4) + lead (206-4). 

 But the atomic weight ol lead is 207-1, and not 206-4; 

 however, it is possible that the atomic weight of radium 

 is 227-1, and not 2264. 



We have another method of approaching the same sub- 

 ject. It is practically certain that the progenitor of 

 radium is uranium, and that the transformation of uranium 

 into radium involves the loss of three a 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 laboratories. 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 it 239-4, " 3ut 

 the general mean, calculated by Clarke, is 2390. Subtract- 

 ing 12 from these numbers, we have the values 2270, and 

 227-4 f° r 'he atomic weight of radium. It is as yet 

 impossible to draw any certain conclusion. 



The importance of the work, which will enable a definite 

 and sure conclusion to be drawn, is this : For the first 

 time, we have accurate knowledge as to the descent of 

 some of the elements. Supposing the atomic weight of 

 uranium to be certainly 239, it may be taken as proved 

 that, in losing three atoms of helium, radium is produced, 

 and, if the change consists solely in the loss of the three 

 atoms of helium, the atomic weight of radium must ni 1 es 

 sarilv be 227. But it is known that £ rays, or electrons, 

 are also parted with during this change ; and electrons have 

 weight. How many electrons are lost is unknown; there- 

 fore, although Hi- weight of an electron is approximately 

 known, it is impossible in saj how much to allow for in 

 estimating thi .lit of radium'. But it is possible 



to solve this question indirect!) by determining exactly the 

 atomic weight- ol radium and of uranium; the difT' 

 between the atomic weight of radium plus 12, i.e. plus 

 the weight of three atoms of helium, and that of uranium. 



will give the weight of the number of electrons which 

 escape. Taking the most probable numbers available, viz. 

 239-4 f° r uranium and 220 8 for radium, and adding 12 to 

 ih. latter, the weight ol the escaping electrons would 

 be 00. 

 The correct solution of this problem would in 



ne clear up the mystery of the irregularities in the 

 periodic table, and would account for the deviations from 

 Trout 's Law, that the atomic weights are multiples of 

 some common factor or factors. 1 also venture to suggest 

 that it would throw light on allotropy, which in some 

 1 at least, may very well be due to the loss or gain 



"I electrons, accompanied by a ;i" ith tegative heat- 



change. Incidentally, this suggestion would afford places 

 in the periodic table for the somewhat overwhelming 

 number of pseudo-elements the existence of which is made 

 practically certain by the disintegration hypothesis. Of 

 ■ In twenty-six elements derived from uranium, thorium. 

 and actinium, ten, which are formed b) the emission of 

 electrons alone, may be regarded as allotropes or pseudo- 

 elements; this leaves sixteen, for which sixteen or 31 

 teen gaps would appear to be available in the periodic 

 table, provided the reasonable supposition be made that a 

 second change in the length of the periods has taken 

 place. It is. above all things, certain that it would be a 

 fatal mistake to regard the existence of such elements as 

 irreconcilable with the periodic arrangement, which has 

 rendered to systematic chemistry such signal service in the 

 past. 



Attention has repeatedly been drawn to the enormous 

 quantity of energy stored up in radium and its descendants. 

 That, in its emanation, niton is such that if what it parts 

 with as heat during its disintegration were available, it 

 would he equal to three and a half million times the 

 • available by the explosion of an equal volume of 

 detonating gas — a mixture of one volume of oxygen with 

 two volumes of hydrogen. The major part ol I 

 ..nil'-, apparently, from the expulsion of particles (th 

 of atoms ol helium) with enormous velocity. It is easy 

 to convey an idea of this magnitude in a form more 

 realisable by giving it a somewhat mechanical turn. Sup- 

 pose that the energy in a ton of radium could be utilised 

 in thirty years, instead of being evolved at its invariabli 

 slow rate of 1700 years for half-disintegration, it would 

 to propel a ship of 15,000 tons, with engines of 



[5, horse-power, at the rate of 15 knots an hour for 



thirty years — practically the lifetime of the ship. To do 

 this actually requires a million and a half tons of coal. 



It is easily seen that the virtue of the energy of the 

 radium consists in the small weight in which it is con- 

 tained ; in other words, the radium-energy is in an 

 enormously concentrated form. I have attempted to apply 

 the energy contained in niton to various purposes ; it de- 

 composes water, ammonia, hydrogen chloride, and carbon 

 dioxide each into its constituents ; further experiments on 

 its action on salts of copper appeared to show that the 

 metal copper was converted partially into lithium, a metal 

 of the sodium column ; and similar experiments, of which 

 there is not time to speak, indicate that thorium, zirconium, 

 titanium, and silicon are degraded into carbon ; for solu- 

 tions of compounds of these, mixed with niton, invariably 

 generated carbon dioxide, while cerium, silver, mercury, 

 and some other metals gave none. One can imagine the 

 very atoms themselves, exposed to bombardment by 

 enormously quickly moving helium atoms, failing to with- 

 stand the impacts. Indeed, the argument a priori is a 

 strong one; il we know for certain that radium and its 

 descendants decompose spontaneously, evolving energy, why 

 should not other more stable elements decompose when 

 subjected to enormous strains? 



This I.ads to the speculation whether, if elements are 

 capable of disintegration, the world may not have at its 

 disposal a hitherto unsuspected source of energy. If 

 radium were to evolve its stored-up energy at the same 

 rate that gun-cotton does, we should have an undreamt-of 

 explosive; could we control the rate we should have a 

 useful and potent source of energy, provided always that 

 .1 sufficient supply of radium were forthcoming. But the 

 supply is certainly a very limited one; and it can be safely 

 affirmed that the production will never surpass half an 



NO. 2 1 S3, VOL. 87] 



