PRKflKNT PROBLKMS OF INORGANIC CHEMISTRY. 217 



iiizcd by iiicans of its s})(H'tniin: I'lii'ther, the fivsli oinaiKition shows 

 i\o helium spcctnim, but after a few days the spectnini of heiiuin 

 begins to appear. i)r()viim- that a spontaneous change is in j)rogress; 

 and List, as the emanation (bsappears its vohune deci'eases to zero: 

 and on heating tlie capilhiry ghiss tube which contained it, helium 

 is driven out from the glass walls, into which its molecules had been 

 embedd(>d in Nolume eipuil to tlu-ee and a half times that of the emana- 

 iion. The /<'-i-ays, as foreshadowed by Rutherford and Soddy, con- 

 sist of helimn particles. 



All these facts substantiate the theory, devised by Rutherfoi-d and 

 Soddy, that the radiinn atom is capable of disintegration, one of the 

 products being a gas, which itself undergoes further disintegi'ation, 

 forming helium as one of its products. Up till now the sheet anchor 

 of the chemists has been the ;dom. But the atom itself appears to 

 be complex, and to be capal)le of decomposition. It is true that only 

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

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

 fai- the most i-ai)id rate of disintegration, has a comjiaratively long 

 life: the ])eri()d of half-change of any given mass of radium is ap- 

 pi'oximately eleven hundred years. The rate of change of the other 

 elements is incomparably slower. This change, too, at least in the 

 case of radium, and its emaiuition, and presnnnibly 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 have been nnide) that 1 pound of emana- 

 tion is capable of parting with as much energy as several hundred 

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

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

 of the change. But the nature of the change is parallel to what 

 would take i)lace if an exti-emely complicated 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 tlie disintegration hypothesis of Rutherford and Soddy 

 is the oidy one which will meet the case. 



If radium is continually disappearing, and would totally disap- 

 pear in a very few thousand years, it follows that it nuist be repro- 

 duced fi-(mi other substances, at an equal rate. The 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 contain one ten-thousandth part of the 

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

 dent, therefore, that radium must owe its existence to the presence of 

 some other sulistances. but what they are is still unascertained. 

 ■ Dm-ino- the investigation of Rutherford and Soddy of the thorium 



