Production and Origin of Radium. 739 



found to be constant over the whole time of observation. 

 The value q — the initial amount of radium present — is best 

 determined from the first observation assuming that the rate 

 of growth of radium during the first few days is the same as 

 that found later. As an example of the method of calcula- 

 tion, let us consider the solution labelled actinium II. (see 

 § 7). The average rate of growth of radium per week cor- 

 responded to '2Q> divisions per minute of the electroscope; 

 i. <?., the equilibrium quantity of the emanation from the 

 amount of radium produced per week would give that rate 

 of movement of the electroscope. 



The first measurement was made after an interval of four 

 days, and the emanation from the solution gave "050 division 

 per minute of the electroscope. Since t 1 = 0, the equation 

 given above reduces to 



(?6-f)(l-*- W2 ) + <&=-050. 



For convenience we shall take a week as the unit of time. 

 Since the emanation is half transformed in 3*8 days, 

 X=l*28 (week)- 1 ; q = "26 and t 2 =$ week. 



Substituting these values, q ='02; i.e., the emanation from 

 the amount of radium initially present in the solution would 

 give a rate of movement of the electroscope of only *02 

 division per minute — a just detectable quantity. 



§ 4. New Experiments. 

 A part of the contaminated actinium solution, previously 

 mentioned, was chemically treated to free it from radium. 

 For this purpose, ammonium sulphide was added ; this pre- 

 cipitated the actinium and left the radium in solution. Bv 

 two successive precipitations the greater part of the radium 

 was removed. The precipitate was dissolved in hydrochloric 

 acid, and the radium content of the solution tested at in- 

 tervals. The quantity of radium initially present in the solution 

 (called actinium I.) was found from the first observation by 

 the method already described. The results are given in 

 the following table. Column I. gives the interval since the 

 preparation of the solution; column II. the time of collection 

 of the emanation ; column III. the observed movement of 

 the gold-leaf in scale-divisions per minute due to the emana- 

 tion in the solution. In column IV. is given the value of q. 

 the average quantity of radium produced per week, calculated 

 from equation (1) and expressed in terms of divisions per 

 minute of the electroscope. The value of q is calculated 

 from each observation on the assumption that the rate of 

 growth has been constant since the preparation of the solution. 



