400 Dr. G. von Hevesy on the 



(a) The diffusion constant of Radium. 



Radium chloride dissolved in 1/100 normal HC1 solution 

 diffused in a solution o£ 1/100 normal HC1. The concen- 

 tration of radium in the solution was in one experiment 

 4*51 . 10~ 7 , and in another 4*72 . 10~ 8 gram per c.c, so 

 that practically an infinite excess of chlorine ions was present 

 with the radium ions. The radium content of the different 

 layers was determined by the emanation method. The 

 emanation was completely removed from the solution by 

 boiling. It was allowed to accumulate for a definite time, 

 then completely removed by boiling, collected over a satu- 

 rated solntion of calcium chloride, and transferred to the 

 ionization-chamber of the electroscope. The reason for using 

 a saturated solution of calcium chloride is that in this liquid 

 the emanation is very insoluble. In this respect it is nearly 

 as good as mercury, and is besides much more easy to work 

 with. 



The following values of the diffusion constant were ob- 

 tained. The signs I. and II. indicate the layers which were 

 examined. 



W D ^ 8 = 2^53^318 =0 ' 632 • D "°=°- 669 



0-57 

 2-83x0-316 



Dg- 8 = a o, !„■ =0-639 • D 1S c=0-G75 



(2) DU= 3. 12 ° X 5 7 286 =0-634 . D ls ,=0-669 

 ^=3^285 =°- 635 " D -=°- 67 ° 



(3) D --F8-2 < S)W5= - 637 • D -=°- 672 



D -= lWSl92 =°- 640 • D - = °- 675 - 



Mean value D 1S ° = 0'667 sq. cm. per day. 



. 1*25 



Since the mean value of the diffusion coefficient is - - f 



it follows that the valency of radium is 2. 



(b) Diffusion constants of ThX and ActX. 



In these experiments also the radioactive substances were 

 dissolved in 1/100 normal HC1 and diffused in 1/100 normal 

 HC1. At this dilution the cation (?'. e. the ThX or the 



