Transformations in the Active Deposit of Actinium. 697 



was adjusted in each case so that the range of the u particles 

 was practically the same, viz. 9 cm. Thus tor the expe- 

 riment with polonium, the range of whose a particles is known 

 to be 3*77 cm. at 15° C. and 76 cm. Hg : — The temperature 

 in a particular experiment was 17° C, and thus the pressure 



• j. ' m + i * na- 3-77 273 + 17 _, 



required inside the apparatus was 7b X ~^r X 97 q , -i r = ^ U- 



Subtracting this from the barometric height 75*3 cm. gives 

 43*3 cm. as the required difference of level of the two limbs 

 of the manometer. 



In this way curves were obtained under exactly similar 

 circumstances as regards configurations of the apparatus. To 

 compare the shapes of the curves they were reduced to the 

 same scale of pressure, viz. 76 cm. and 15° C. Thus in the case 

 of actinium the curve marked (a) in fig. 5 was calculated as 



l 3 4- 



Rance- Centimetres. 



the mean of several curves, and similarly for the other 

 substances. For a strict comparison of the curves another 

 correction is necessary, namely, that for the finite depth of 

 the ionization chamber. This depth was 0*3 cm., and thus 



