200 THE RADIO-ACTIVITY OF MATTER. 



After this precipitation the uranium salt brought back to the solid 

 state is less radio-active than before; this loss of radio-activit}- can 

 even be accentuated by successive operations, but the products gradu- 

 all}" and spontaneously regain their original activit•\^ The temporary 

 dimiiuition' of activity after solution is a general fact for salts of 

 uranium and radium. With salts of actinium M. Debierne has com- 

 numicated a very great activity to barium. The barium thus excited 

 can be separated from inactive barium; it can be fractioned like radif- 

 erous chloride of barium, the most active portions l^eing the least 

 soluble in water and h3^drochloric acid. M. Debierne in this manner 

 obtained a product a thousand times more active than uranium. 

 Barium thus excited behaves as a false radium, but it differs from the 

 true radium in the aV)sence of the spectrum and in gradually losing its 

 power with time. 



Among the radio-active preparations a large number may be tem- 

 porarily excited bodies. Such is the case with "polonium," which is 

 apparently only excited bismuth. 



Uranium and radium are characterized by their emission spectra 

 and by the stability of their radio-activity. The spontaneous growth 

 that is observed in the salts deposited by the solutions " might tind an 

 explanation in a phenomenon of auto-induction of the active molecules 

 on the inactive one they are associated with. 



The oi'igin of the radiant energy of these radio-active bodies is still 

 an enigma. By the material hypothesis it does not appear imreason- 

 able, by applying the phenomenon of the evaporation of an odorifer- 

 ous body to compare the emanation to a sort of gas of which the 

 molecules would have masses of the same order of size as electroh'tic 

 ions, and to identify the radiations with the cathodic rays resulting 

 from the dislocation of these ions and causing at the same time the 

 emission of X-rays. We might thus ascribe the expenditure of energy 

 to the dissipation of active matter. Although this hypothesis will 

 account for most of the known facts, still there does not exist any 

 precise experiment which sanctions it. 



I must not, however, dwell longer on this subject, of which 1 have 

 incompletely summarized the present position, by emphasizing the 

 physical part, which comes more especially within my province, 

 although the chemical side has given rise to work of the greatest 

 interest. 



These (luestiouH have raised new h<)})es on the transformation of 

 matter, B(\sides the exceptional conditions under which they enable 

 us to examine the cathodic rays, they have raised, and continue to 

 raise, fresh ])ro])leins every day of which the Hi'st and most mysteri- 

 ous is the spontaneity of the radiations. 



L'accroissement spontane que I'on observe sur les sels deposes des dissolutions." 



