■348 Prof. McCoy and Dr. Viol : Chemical Properties and 

 For the values taken,- — — =1-005. 



A.J — A, 

 If the interval is forty Jays, 



e~ Xi =0'96Z2 and £~V = o-00057. 



We may therefore neglect the term <?-'V for intervals greater 

 than forty days ; so that 



f 2 = 1-005 «-*'=l-005/i. . ...... (11) 



Equations (8) and (11) give 



Jin-'IM^J 



1-005 



1-005 



. . . . (12) 



The significance of the last equation is interesting ; it shows 

 that at any moment after about forty days, the amount of 

 ThX present in the Hfc originally free from the former 

 product is 0'5 percent, greater than the equilibrium quantity 

 corresponding to the amount of Rt present at that moment. 



Throughout the above argument there exists the tacit 

 assumption that the products of ThX will all be present in 

 equilibrium amounts, the amount of ThX present being the 

 basis of reference. This will be so nearly true after forty 

 •days that the error introduced by this assumption is entirely 

 .negligible. In Table II. are given the data obtained from a 



Table II. 



Interval, 

 Days. 



Observed 



Activity. 



Calculated 

 Activity 

 y 5-23. 



Calculated values 



of y, from the 

 observed Activity. 



000 



42-68 



45-73 



54-99 



104-86 



(1-000) 

 6-012 

 5-971 

 5-939 

 5-700 



1-000 

 6-010 

 5-993 

 5-940 

 5-669 





5-229 

 5-209 

 5-229 

 5-264 



foai'ium sulphate film of Rt. Column one gives the intervals 

 in days, column two the corresponding activities, and column 

 three the activities calculated by using the mean value of y 

 as determined from five such films, viz. 5'23. The last 

 «column gives the values for y calculated from the observed 



