NATURE 



241 



THURSDAY, JULY 14, 1904. 



/.S RADIL'M .l.V ELEMENT? 



Uadin-activity. By Prof. E. Rutherford, F.R.S. 



Pp. viii + 399. (Cambridge : L'niversity Press, 



1404.) Price loi'. 6d. net. 

 liadio-activity. By F. Soddy, M..A. (The Electrician 



Printing and Publishing Co., 1904.) 

 Radium. By L. A. Levy and H. G. Willis. 



(London: Percival Marshall and Co., 1904.) 



I\ February, 1896, M. Henri Becquerel found that 

 uranium salts emit rays capable of affecting a 

 photographic plate and of penetrating black paper and 

 other bodies opaque to ordinarj- light. In the eight 

 years which have elapsed since, a startling series of 

 di>coveries of extraordinary interest to the physicist 

 and chemist has rewarded those experimental in- 

 ve>tigators who followed up the clue given by 

 Becquerel's observation just mentioned. .'\s the result 

 of their labours, a new branch of physical chemistry 

 has been created which already possesses a bulky 

 literature, growing with ever-increasing velocity. The 

 following are approximately the number of papers on 

 radio-activity published in scientific journals for each 

 year since Becquerel's original discovery: — 1896, 7; 

 1S97, 6; i8qS, 7; 1899, 18; 1900, 39; 1901, 36; 1902, 

 41 ; 1903, 90. Thus at present the literature of the 

 subject comprises several hundred papers, and new 

 papers are appearing at the rate of several per week. 



-Among those who have contributed most to the 

 exact study of radio-activity. Prof. Rutherford occu- 

 pies a foremost place, so that a connected account of 

 the experimental results obtained and theories pro- 

 posed to explain them from his pen cannot but '.« 

 welcomed by all those interested in the subject. The 

 volume under consideration is the third of the " Cani- 

 bridge Physical Series," edited by Mr. F. H. Neville, 

 F.R.S., and Mr. \V. C. D. Whetham, F.R.S. The 

 first volume was " The Theory of Solutions," by Mr. 

 U'hetham, and the second " The Conduction of Elec- 

 tricity through Gases," by Prof. J. J. Thomson. The 

 remarkably high standard of scientific excellence set 

 by the first two volumes of the series is fully main- 

 tained by Prof. Rutherford in the third. 



The first chapter contains an historical account of 

 the discovery of the radio-active properties of uranium 

 .-end thorium, of Madame Curie's magnificent discovery 

 of radium, and of the discovery of the other less known 

 radio-active elements. The second chapter contains a 

 short account of the ionization theory of conduction 

 through gases, on which so much ot the work on 

 radio-activity depends, and the third a very useful 

 account of the experimental methods employed in in- 

 vestigating the properties of the radiations emitted by 

 the radio-active substances. The remaining chapters 

 contain a very complete and concise account of the 

 nature of the radiations, of the amount o.' energy 

 emitted, and of the remarkable atomic transforma- 

 tions of radio-active matter. The book is not of a 

 popular character; it is intended for those who wish 

 (ostudy the subject scientifically, possibly with ihe view 

 NO. 181 I, VOL. 70J 



of undertaking research work on it. For such students 

 it is admirably adapted, and possible openings for re- 

 search work are suggested implicity or explicitly on 

 almost every page. Such a work cannot fail to be of 

 great service to scientific students. 



The remarkable phenomena exhibited by the radio- 

 active elements have led to the adoption of theories 

 which a few years ago would have appeared almost 

 ridiculous. One gram of radium gives out more than 

 800,000 gram calories of heat per year. This heat is 

 apparently due to the spontaneous disintegration of 

 radium atoms into matter possessing less energy. 

 Radium is, in fact, an endothermic compound in pro- 

 cess of decomposition. .So far as we know the process 

 is not reversible, but it may be that at extremely high 

 temperatures radium atoms could be formed by the 

 combination of their products of disintegration with 

 absorption of heat. 



The radium atom first emits an a-particle which is 

 a positively charged body having a mass about twice 

 that of a hydrogen atom. The rest of the atom con- 

 stitutes radium-X. The radium-X then disintegrates 

 into an o-partic!e, and the gaseous radium emanation, 

 this in turn disintegrates, and the process goes on 

 through a whole series of transformations. The final 

 product is, it is suggested, perhaps polonium. A 

 radium atom, therefore, appears to consist of a 

 polonium atom, and about six a-particles. But there is 

 reason to believe that the a-particles, when their 

 charge is neutralised by a negative corpuscle, become 

 helium atoms. If this is so, then a radium atom is 

 really the compound radical PoHe,, and is not an 

 elementary atom at all. On the other hand, radium is 

 from the chemical standpoint closely analogous to cal- 

 cium, strontium, and barium, and it finds a place in 

 the periodic arrangement of the elements. If, then, 

 radium is really a compound radical, it is probable that 

 all the other elements, except, perhaps, helium, and a 

 few others of small atomic weight, are compound 

 radicals also. The chemist must, in fact, either adopt 

 a new definition of an element or else prepare for a 

 large reduction in the number of such bodies. 



The velocity of the radio-active processes is in- 

 dependent of the temperature. This remarkable fact 

 is said to indicate that the changes taking place are 

 of a purely atomic character. It must be admitted that 

 the meaning of this statement is not very clear. If 

 the radium atom consists of several parts which are 

 separated during the process of disintegration, then the 

 radium atom is really a molecule, and its disintegration 

 is, strictly speaking, a molecular process. Moreover, 

 molecular processes are known the velocity of which is 

 independent of the temperature within certain limits. 

 Fur e.xample, the rate of solidification of many super- 

 cooled liquids increases at first with the supercooling, 

 but then attains a constant value independent of the 

 supercooling over a considerable range of temperature. 

 The energy set free during radio-active processes is 

 enormous compared with the kinetic energy of the 

 molecules due to heat motions, and there is no known 

 reason why such irreversible decomipositions should 

 not proceed at a rate independent of the temperature, 

 even if they are not of a purely atomic character. 



