268 INORGANIC CHEMISTRY 



begins to appear, proving that a spontaneous change is in progress; 

 and last, as the emanation disappears its volume decreases to zero; 

 and on heating the capillary glass tube which contained it, helium is 

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

 imbedded in volume equal to three and a half times that of the eman- 

 ation. The a rays, as foreshadowed by Rutherford and Soddy, con- 

 sist of helium particles. 



All these facts substantiate the theory, devised by Rutherford and 

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

 products being a gas, which itself undergoes "further disintegration, 

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

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

 be complex, and to be capable of decomposition. It is true that only 

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

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

 the most rapid rate of disintegration, has a comparatively long life; 

 the period of half-change of any given mass of radium is approximately 

 1 100 years. The rate of change of the other elements is incomparably 

 slower. This change, too, at least in the case of radium and its eman- 

 ation, 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 have 

 been made) that one pound of emanation 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 place if an extremely compli- 

 cated hydrocarbon were to disintegrate; its disruption into simpler 

 paraffins and defines 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 one which will meet the case. 



If radium is continually disappearing, and would totally disappear 

 in a very few thousand years, it follows that it must be reproduced 

 from other substances, at an equal rate. The most evident conjecture, 

 that it is formed from uranium, has not been substantiated. 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 evident, therefore, that 

 radium must owe its existence to the presence of some other substances, 

 but what they are is still unascertained. 



During the investigation of Rutherford and Soddy of the thorium 

 emanation, a most interesting fact was observed, namely, that precipi- 

 tation of the thorium as hydroxide by ammonia left unprecipitated a 

 substance, which they termed thorium X, and which was itself highly 

 radioactive. Its radioactive life, however, was a short one; and as 



