PRESENT PROBLEMS OF TNORGANIC CHP:MISTRY. 217 



nizcd by means of its s])(»etriiin ; further, the fresh eniuiiati(»ii shows 

 no heliuni sjx'rtnini. hii-t after a few (hiys the s])ertriini of heliiini 

 he<j,ins to aj^pear, proN'inii' that a spontaneous chan<j:e is in j)roi>ress; 

 and hist, as the emanation (lisa})})ears its vohnne decreases to zero: 

 and on heating the ea})iUarv ghiss tube which contained it, helium 

 is (h-iven out from the ghiss walls, into which its molecules liad been 

 embedded in volnme e(iual to three and a half times that of the emana- 

 tion. The «'-rays, as foreshadowed by Ruthei'ford and Soddy, con- 

 sist of helium particles. 



All these facts substantiate tlie theory, devised by IvutlKM'ford and 

 Soddy, that the radium atom is ca|)abl(' of disintcgTation, one of the 

 ])roducts l)eini>; a gas, which itself undergoes further disintegration, 

 forming helium as one of its ])i'oducts. Up till now the sheet anchor 

 of the chemists has l)een the atom. Bnt the atom itself appears to 

 be complex, and to l)e capable of decomjjosition. It is true that only 

 in the case of a very few elements, and these of high atomic weight, 

 has this been proved. Bnt even radium, the element which lias by 

 far the most ra])id rate of disintegration, has a com])ai"atively long 

 life: the period of half-change of any given mass of i-adium is ap- 

 ])roximattdy eleven hundred years. The rate of change of tlie o(he]' 

 elements is inc()mi:»ai'al)ly slower. This change, too, at least in the 

 case of radinm, and its emanation, and presumably also in the case 

 of other elements, is attended with an enormous loss of energy. It 

 is easy to calculate from heat measurements (and independent and 

 concordant measurements IniA'e been made) that 1 pound of emana- 

 tion is capable of parting with as mnch energy as several liundred 

 tons of nitroglycerine. The order of the quantity of energy evolved 

 during the disintegration of tlie atom is as astonishing as the nature 

 of the change. r)ut the nature of the change is parallel to what 

 would take jjlace if an extremely comj^licated hydrocarbon were to 

 disintegrate; its disruption into simpler paraffins and olefines would 

 also be attended with loss of energy. We may therefore take it, I 

 think, that the disintegration hypothesis of Rutherford and Soddy 

 is the only on(> which will meet the case. 



If i-adium is continually disaj^pearing, and would totally disap- 

 pear in a very few thousand years, it follows that it must be re])ro- 

 duced from other substances, at an ecpial rate. Th(^ most evident 

 conjecture, that it is formed from uranium, has not been substan- 

 tiated. Soddy has shown that salts of uranium, freed from radium, 

 and left for a year, do not contsiin one ten-thousandth part of the 

 radium that one would expect to be formed in the time*. It is evi- 

 dent, therefore, that radiinn must owe its existence to tlie presence of 

 some other substances, but what they are is still unascertained. 



Diirina' the investigation of Rutherford and Soddy of the thorium 



