31ti 



DISCOVERY 



ton, and xenon — were isolated from the atmosphere by 

 Ramsay and his co-workers in the 'nineties, and the 

 fourth, radium emanation (or niton), was discovered 

 emanatinf,' from preparations of radium. 



Ill 



An element isolated for the first time on the earth 

 in 1894, and which had led directly to the discovery of 

 four more elements in the years immediately' following, 

 had certainly made its debut, as they say, with a 

 certain degree of eclat. But even Ramsay, who was 

 surprised at his own discovery in 1894, was still more 

 surprised in 1903 when Soddy, in conjunction with 

 him, proved definitely what Rutherford had suspected, 

 that helium was produced continually by the element 

 radium. The work of Ramsay and Soddy proved that 

 the radio-active element radium on disintegration 

 broke up cleanly into two elements, the emanation and 

 helium. 



Radium -» Emanation + Helium 

 solid gas gas 



Atomic weight 226 At. wt. 222 At. wt. 4 



This was shown by freeing a preparation of radium 

 completely, both from the emanation and from helium, 

 and proving by the spectroscope that the latter accu- 

 mulated in the preparation with time. This work 

 caused a mild sensation among scientific workers of the 

 period, because it proved definitely, what workers in 

 radio-activity had tentatively begun to assert, that 

 one element may decompose into two elements. The 

 suggested explanation of these facts is as follows : 



The atom of helium must be originally inside the 

 atom of radium, and for some reason it is shot out with 

 great velocit}'. All the expelled atoms of helium form 

 helium gas ; all the shattered atoms from which the 

 helium atoms have been shot out form radium emana- 

 tion gas. The atomic weights of radium, of the 

 emanation, and of helium are known by independent 

 experiments to be 226, 222 and 4 respectively, so that 

 the breaking-up of radium is numerically right, since 

 226 = 222 -f 4. 



Further study of radio-activity showed that the 

 expulsion of helium by radium was not an isolated 

 phenomenon. Several other elements expelled the 

 atoms of this gas. We now know that the clement 

 uranium (which is used commercially for making 

 pigments) has at least eight of these helium atoms in 

 the inside of its own atom, while the element thorium 

 (compounds of which are used for making incandescent 

 gas mantles) has at least six, and the element radium 

 five. These are experimental facts about which 

 physicists have no doubt. Helium, then, appears to be 

 a constituent of the very heaviest elements. It is not 

 joined to them in the loose way that atoms forming 



chemical compounds are, but in a more fundamental 

 way that is quite unlike any combination in chemistry. 

 If helium can be proved in the laboratory to be 

 produced by the breaking up of heavy atoms, then 

 clearly there should be relatively large quantities of the 

 gas in rocks containing these heavy bodies — untouched 

 for thousands and thousands of years. Experiments 

 have proved this to be true, and indeed one method 

 (though not a good one) of estimating the age of these 

 rocks is to measure accurate!}' the quantity of helium 

 which a known mass of these heavy elements has 

 produced. It is believed that the quantities of hehum 

 found in the atmosphere, in mineral springs, etc., have 

 come from the decomposition of rocks containing the 

 heaviest elements. These indeed, like the helium they 

 produce, are very sparsely distributed on the surface of 

 the earth, as the unfamiliarity of their names, uranium, 

 protactinium, thorium, ionium, etc., to all but special- 

 ists bears witness. 



IV 



Two important speculative ideas have been suggested 

 by the experimental fact that helium is a constituent of 

 the heaviest elements, namely : 



(i) That heUum is a constituent of all elements, or 

 at least of many elements besides the heaviest. 



(2) That hydrogen, which is the only known element 

 lighter than helium, may also be a constituent of 

 many elements. 



The first of these alone is germane to my subject, and 

 will be considered now. Helium is inside some heavy 

 elements ; it is natural to infer the possibility that 

 hehum is a constituent of most elements. This specu- 

 lation appears to work excellently on a sheet of paper. 

 A number of elements have atomic weights which 

 are nearly exactly whole numbers that are divisible 

 by 4, the atomic weight of hehum. For example, 

 carbon (12), oxygen (16), neon (20), sulphur (32), 

 titanium (48), chromium (52), iron (56), tungsten (184), 

 thallium (204), thorium (232). What is easier, when 

 one is speculating, than to assume that these 

 elements are built up exclusively of hehum, i.e. 

 that carbon is three helium atoms bound in a very 

 fundamental way, oxygen four, iron fourteen, and 

 thorium fifty-eight ? 



A simple speculation of this kind includes only those 

 elements which have whole numbers divisible by four 

 for their atomic weights, but if we consider a few proven 

 experimental facts we can extend it to a great many 

 more elements. These facts are : 



(i) That all atomic weights are probably whole 

 numbers. 



(2) That an atom of hydrogen, weighing i, exists in 

 certain atoms (boron, nitrogen, fluorine, sodium, phos- 

 phorus, etc.). 



