174 ESSAYS BIOGRAPHICAL AND CHEMICAL 



the amount of heat being enormous when their extremely 

 small quantity is considered. Thus the radium emana- 

 tion (the name applied to the gas which is continuously 

 evolved from salts of radium), during its decomposition 

 gives off no less than three million times the heat which 

 would be evolved during the explosion of an equal volume 

 of a mixture of oxygen and hydrogen in the proportion 

 requisite to form water. Now if radium is disappearing, 

 it must be continually in process of formation, else there 

 would be none on the surface of the earth ; it would all 

 have disappeared and have been changed into other 

 bodies during the lapse of time since the minerals con- 

 taining it were formed. As radium is always associated 

 with uranium, it appears not unreasonable to suppose that 

 uranium, too, which is a radio-active element, is slowly 

 changing into radium ; and there appears to be definite 

 ground for the surmise that polonium, the first of the 

 radio-active elements, also discovered by Madame Curie, 

 which has a half-life period of about one year, is a product 

 of the decomposition of radium, with which it is always 

 associated. It may be mentioned, too, that all minerals 

 containing uranium contain more or less helium. 



It will be noticed, on referring to the periodic table, 

 that all the radio-active elements, that is, all those which 

 are undergoing change of the nature described, have very 

 high atomic weights. That of uranium is 240; that of 

 thorium, 232 ; and that of radium, 226. Now it is a com- 

 monplace of the organic chemist that it is not possible to 

 build up compounds of carbon and hydrogen of unlimited 

 complexity; indeed, it is doubtful if any compound has 

 been prepared containing more than 100 atoms of carbon. 

 Attempts to prepare them lead to failure, owing to their 

 decomposing at the ordinary temperature into compounds 

 containing a smaller number of atoms. And it is pro- 

 bable that more complex hydrocarbons, as such com- 



