6o2 



NATURE 



[May 13, 1922 



colliding a-particles. This is explained by assuming 

 that the H-particle in the aluminium atom is describing 

 an orbit around the nucleus, when the direction of 

 escape would depend on the relative positions of the 

 a-particle and nucleus at the moment of collision with 

 the satellite. 



In the case of aluminium the maximum energy of 

 the H-particle is 1-4 times that of the incident a-particle, 

 and part of the energy must, therefore, have been 

 derived from the nucleus itself. The disintegration 

 is effected on an extremely minute scale ; only about 

 two a-particles in every million get near enough to the 

 inner nucleus to dislodge an H-particle. If all the 

 a-particles from i gram of radium were fired into 

 aluminium, only one-thousandth of a cubic millimetre 

 of hydrogen could be liberated in one year. 



It has been surmised that the a-particle, or helium 

 nucleus, of mass 4, is one of the units of which atoms 

 are built up. The experiments referred to show that 

 the hydrogen nucleus is also one of the units of structure, 

 at least of some of the lighter elements. H-particles 

 are only liberated from elements of atomic masses 

 4n + 2 or 4W + 3, where w is a whole number. Elements 

 like oxygen and carbon, the atomic masses of which 

 are 4«, give no H-particles. This result would follow 

 if the nuclei of the former elements are built up of 

 helium nuclei, of mass 4, and hydrogen nuclei as 

 sateUites. The mass of the latter should not differ 

 much from the free H-nucleus of mass 1-0077 ^^ terms 

 = 16, on account of the weaker biriding of the satellite 

 to the nucleus. If the nitrogen nucleus is made up 

 of three helium nuclei of mass 12 and two hydrogen 

 nuclei, the mass of the nitrogen atom should not be 

 14-00 but more nearly 14-01, as found by chemical 

 methods. In the case of light elements the effective 

 masses of the hydrogen nuclei should vary from 1-007 

 to i-ooo in different atoms, depending on the closeness 

 of combination. 



In earher experiments particles of mass 3 with two 

 positive charges appeared to have been liberated from 

 oxygen and nitrogen. These, however, are now known 

 to have their origin, at least in the case of oxygen, 

 in the radioactive source and not in the volume of the 

 gas. 



We think it no exaggeration to say that these 

 experiments are some of the most fundamental which 

 have ever been made. It is not often that a scientific 

 discovery excites interest outside the narrow circle of 

 the laboratory or the scientific lecture - room. The 

 discovery of radium by the Curies appealed to the 

 larger world with a force which was equalled only by 

 the profound interest aroused by the discovery of 

 phosphorus by Brand in 1669, and of potassium by 

 Davy in 1807, and so fundamental are the consequences 

 NO. 2741, VOL. 109] 



of this new discovery that the intellectual world at 

 large must follow with the keenest interest the progress 

 of the experiments associated with the name of 

 Rutherford. It was soon evident that increasing 

 knowledge of the properties of radioactive substances 

 was bound to alter fundamentally some of the cherished 

 conceptions of the ancient science of chemistry. Sir 

 William Ramsay held very tenaciously to the view that 

 the immensely concentrated energy of^ the a-particle 

 offered a means of testing that apparent simplicity of 

 the chemical elements which they had succeeded in 

 preserving, in trying circumstances, since the time of 

 the alchemists. His experiments, however, could not 

 at the time be convincing. 



When Sir Ernest Rutherford went to Cambridge 

 he had already made some progress in the most 

 difficult task he has yet attempted. The means 

 he used appear simple, as he describes them, but the 

 experimental skill which was required to achieve these 

 results is of a very high order. We feel sure that all 

 our readers will join us in congratulating him on the 

 work he is doing, and in expressing the hope that his 

 further researches will continue to add to the splendid 

 harvest of positive knowledge which is so rapidly 

 growing under his hand. 



It is obvious that the results so far achieved in this 

 region are but the beginnings. There are many things 

 we need to know, and some of the yet unsolved problems 

 which suggest themselves may soon be cleared up by 

 further researches. The chemist will be curious to 

 know what is left when hydrogen is expelled from 

 nitrogen, boron, aluminium, or other atoms. If 

 boron is a mixture of two isotopes, of masses 10 and 11, 

 these will be of the forms 4W + 2 and 4« + 3, both of 

 which should give H-particles, as is found to be the 

 case ; but if lithium is a mixture of isotopes of 6 and 7, 

 these ought also to give H-particles, although they 

 were not detected under the conditions of experiment. 

 If chlorine is a mixture of two isotopes, 35 and 37, the 

 first is of the form 4« -I- 3, which should give H-particles, 

 and the second of the form 4W+1, which is not re- 

 ferred to by Sir Ernest Rutherford. Apparently, no 

 H-particles were expelled from chlorine. This element, 

 however, has an atomic mass higher than the limiting 

 value 31, beyond which no H-particles were in any 

 case found. 



It may be that there is some change in the mode of 

 building up the nucleus at this point, or, what seems 

 more likely, that H-particles are, in fact, expelled, 

 but are of such a range and velocity that they could 

 not be detected in the present experiments. These 

 difficulties will no doubt soon be cleared up, and we 

 must await with such patience as we can the continua- 

 tion of Sir Ernest Rutherford's work. 



