230 



NATURE 



[April 22, 1920 



Letters to the Editor. 



\The Editor does not hold himself responsible for 

 opinions expressed by his correspondents. Neither 

 can he undertake to return, or to correspond with 

 the writers of, rejected manuscripts intended for 

 this or any other part of Nature. No notice is 

 taken of anonymous communications.] 



The Separation of the Element Chlorine into Normal 



Chlorine and M eta-Chlorine, and the Positive 



Electron. 



The very important letter of Dr. Aston in Nature 

 of December i8, 19 19, gives much evidence in 

 favour of a theory of the structure and composition 

 of the nuclei of complex atoms as published by me five 

 years ago and in a number of more recent papers. 

 This theory led me to the idea, as published at that 

 time (Journal of the American Chemical Society, 

 xxxvii., pp. 1367-96, especially pp. 1390, 1391, and 1387), 

 that among the light elements magnesium, silicon, 

 and chlorine, in addition to neon (as found by Thorn- 

 son), are mixtures of isotopes. The atomic weights of 

 the normal isotopes were given as 24 for magnesium, 

 28 for silicon, and 35 for chlorine. It was also stated 

 that nickel, copper, zinc, and practically all the other 

 elements between atomic numbers 28 and 80, the 

 latter being mercury, are mixtures of isotopes ; while 

 radio-active evidence shows that elements 81 (thallium) 

 to 92 (uranium) exist in isotopic forms. This theory 

 was recently summarised in a paper sent to the 

 Physical Review in May and November, 1919. This 

 paper, as well as the others, should be consulted for 

 the details of the theory. 



In February, 19 16, I announced that we were work- 

 ing in this laboratory upon the separation of chlorine 

 into isotopes by diffusion {ibid., xxxviii., p. 221, 

 1916). Early in 1917 Mr. W. D. Turner, my research 

 assistant, found slight differences in density between 

 the heavy and light fractions obtained by difTusing 

 chlorine, but, since small amounts of impurities were 

 very difficult to exclude, this did not seem at all con- 

 clusive. Since if there are two isotopes of chlorine 

 there are three molecular forms of the substance, a 

 separation may be made more easily by the use of 

 hydrogen chloride gas, and this has been used in 

 nearly all our work for the last three years, though 

 practically nothing was done during the period of the 

 war. 



The diffusion of this gas, as carried out on a 

 moderately large scale by Mr. C. E. Broeker and 

 myself, seems now, judging by our preliminarv 

 analyses, to be resulting in a definite separation of 

 the gas into a heavier and a lighter fraction. The 

 separation, while extremely slow, seems from^ our 

 preliminary results on the heavy fraction to be of about 

 the order to be expected by the Rayleigh diffusion 

 theory, provided the atomic' weights "of the isotopes 

 are 35 and 37; so the work is in good agreement 

 with that of Dr. Aston. These results may be 

 modified somewhat when our precise atomic weight 

 determinations are made, since at the present time 

 all our determinations are made bv rapid methods. 

 Our results suggest, but are not of a sufficient pre- 

 cision really to indicate, the possibility that a third 

 isotope of higher atomic weight may exist, but since 

 the separation is extremely slow, and the positive 

 ray method as worked out by Dr. Aston gives results 

 very quickly, he should be able to test this sug-gestion 

 much more rapidly than ourselves. 



Since 1916 we have diffused about 19,000 litres of 

 hydrogen chloride gas as measured under standard 

 conditions. The apparatus now in use will diffuse 

 NO. 2634, VOL. 105] 



about 400 litres per day, and we hope soon to raise 

 the capacity to 1000 litres. These numbers refer to 

 the fresh or ordinary gas introduced into the apparatus, 

 and not to that which is rediffused in smaller units. 

 The total number of units now in operation is five, 

 and the method may be described as a fractional 

 diffusion. 



While the idea that the hydrogen nucleus may be 

 the positive electron is a very general one, the only 

 evidence I have found in print which gives real 

 support to this idea, and explains the facts which 

 seem opposed to the idea, is to be found in papers 

 by my associates and myself as cited above, and 

 in my other papers listed at the end of this letter. 

 The hydrogen nucleus or the positive electron has, 

 according to these papers, a weight, and presumably 

 a mass, of i-ooo, on the basis of oxygen as i6-ooo, 

 whenever the positive electron is combined in a com- 

 plex atom. The atomic weight of ordinary hydrogen 

 is 10077. The difference between 10077 ^nd 1000 

 is due either to the existence of meta-hydrogen of 

 atomic weight 3-00 and composition (?j3^2)+c- in 

 ordinary hydrogen, or else to an electromagnetic 

 packing (possibly to both), the latter as assumed by 

 Sir Ernest Rutherford and by myself, but the details 

 of which are to be found in my papers. In these 

 formulae f/+ is the positive electron, $- the negative 

 electron when it is contained in the nucleus, and e- 

 when it is a non-nuclear or planetary electron. 



The nuclei of atoms are built almost entirely from 

 the following particles ' : — 



Weight 



(oxygen 



basis) 



Alpha particle or helium nucleus ia'^'^)={vt^l)'^'*' 4'°^ 



Nu particle or meta-hydrogen nucleus (»'+) ={n+$-)+ yoo 



Mu particle (n) =(77+3^) 2-oo 



Of these the a particle forms the greater part of all 

 complex atoms ; one v particle is found in most 

 atoms of odd atomic number, at least among the 

 light atoms ; and the fx particle, which has no net 

 charge, is responsible for the existence of one of the 

 two known classes of isotopes. The other class of 

 isotopes is due to the presence of the group j/t/^i^ 

 which consists of an a particle, together with two 

 cementing- electrons. It is these cementing electrons 

 which are shot off in f3 disintegrations of radio- 

 atoms, and they always escape in pairs — that is, one 

 directly after the other, or one just before and one 

 just after the escape of an a particle. The number 

 of negative electrons in the nucleus of an atom is 

 almost always even, whether the nuclear charge is 

 odd or even, but the number of positive electrons is 

 nearly always odd in a nucleus of odd charge. How- 

 ever,^ the nuclei which contain an even number of 

 positive electrons, and are therefore built up either 

 of a particles alone or of a particles and negative 

 electrons, are, on the whole, much more stable than 

 those with an odd number; so the even-numbered 

 elements are much the more abundant, and make up 

 987 per cent, of the meteorites and the greater part 

 of the material of the earth. Furthermore, all 

 the seven most abundant elements in the meteorites 

 have an even atomic number, as is indicated in Fig. i. 

 In the exceptional case of nitrogen the group T]n/3 is 

 present, and in beryllium the group »/^. A suggested 

 structure for the a particle is given in Fig. 2, where 

 the large circles represent negative, and the small 

 ones positive, electrons. The v group probably has 

 a similar structure, but with three positive electrons 

 at the corners of a triangle; while the lithium nucleus 



1 The negative el-ctron-! in these particles maybe called *»«rf/>^e'ectrons, 

 while t' ose which afach extra a particles ate called cementing electrons. 



