BULLETIN INTERNATIONAL 
DE L’ACADEMIE DES SCIENCES DE CRACOVIE. 
CLASSE DES SCIENCES MATHEMATIQUES ET NATURELLES. 
N° 4. Ba 1905. 
Sommaire: 16. M. T. GODLEWSKI. L'’actinium et ses produits. 
Séance du lundi 3 Avril 1905. 
Pk&£sıpence DE M. N. CYBULSKI. 
16. M. T. GODLEWSKI. Aktyn i jego produkty. (Actinium and its suc- 
cessive products). \L’actinium et ses produits). Mémoire présenté par 
M. A. Witkowski m. t. 
Rutherford and Soddy !) in their well known investigations on 
the activity of thorium have shown that it is possible to separate 
from it a very active constituent which they call ThX. The acti- 
vity of this product decays with the time according to an expo- 
nential law i. e. the equation of monomolecular chemical reactions, 
falling to half value in about four days. At the same time, the 
thorium, which by the removal of thorium X, had been deprived 
of about 75°/, of its activity, recovered its activity, the recovery 
eurve being complimentary to the eurve of decay of ThX. The 
substance UrX, discovered earlier by Crookes, acts in a manner 
analogous to ThX. The activity of this substance decayed accor- 
ding to an exponential law, with the time falling to half value 
in 22 days. 
Rutherford and Soddy have explained these phenomena on the 
supposition that the radioactive bodies are produeing fresh radio- 
active matter at a constant rate and that the activity of the mat- 
ter so formed decreases according to an exponential law with the 
time. The discovery of these phenomena supplied the basis for 
the disintegration theory which supposes that the atom of a radio- 
active body breaks up through a series of well marked stages. The 
1) Rutherford and Soddy: Phil. Mag. Sep. and Nov. 1902. Trans. Chem. Soc. 
81 321. and 807, (1902). 
