Radium Standard Solutions. 663 



Finally, the number of divisions per minute for 10~ 9 curie 

 of radium emanation could be calculated by using the value 

 of 1 — e~ xt directly from the tables given by Kutherford, 

 interpolating for a fraction of a day : this value we call a 

 "figure of merit." By comparing the "figures of merit," 

 and finally reducing to percentages, we can obtain the 

 relative values of the two standards. 



Section 3. Difficulties and their Solution. — Results. 

 A number of sets of results were obtained, and practically 

 all showed a very close agreement between the two solutions 

 compared. As the work proceeded, a deterioration in values 

 of the " figure of merit " occurred, as if boiling had a weak- 

 ening effect. Each value was less than the preceding one. 

 This suggested that some of the radium might have been 

 deposited with boiling, and so a qualitative experiment was 

 carried out with a solution which had been boiled a number 

 of times, by adding some HOI to see if it would dissolve the 

 supposed radium deposit, and hence cause a rise in the value 

 of the " figure of merit." This is precisely what occurred. 

 A higher value, however, was now obtained than any pre- 

 vious one. This suggested the probability of radioactive 

 matter in the HC1 which had been added. To test this, a 

 "blank" solution was prepared, consisting of 50 c.c. of 

 approximately 1 ( J per cent, strength HOI, obtained by dilu- 

 ting 38 per cent, commercial HOI to half strength. After 

 eight days it was tested, and on deducting the natural leak, 

 which was *083, it gave 2*71 divisions per minute. Two c.c. 

 of this same preparation had been added previously to the 

 Rutherford solution standard, which had been boiled fourteen 

 times. A reading was taken previous to adding the HC1, 

 and it showed the steady decline due to boiling. On next 

 boiling, however, a rise of 12"2 per cent, occurred in the 

 " figure of merit." By calculation, 2 per cent, of this was 

 due to the radioactive matter in the acid which was added : 

 the remainder must therefore be due to the re-dissolved 

 radium, which had been deposited by boiling or otherwise 

 rendered " de-emanating." This quantitative experiment 

 amplifies and confirms the behaviour of the solution in the 

 qualitative experiment mentioned in the first part of thi* 

 section. In the first trial when acid was added, the "figure 

 of merit" went above the normal, due obviously to an excess 

 of acid added, which had sufficient radioactive matter in it 

 to account for the abnormal rise. In the second case, it did 

 not reach the normal value when 2 per cent, was deducted 

 for the radioactive matter in the acid added. Apparently 

 all the radium had not been re-dissolved in the second case. 

 These sets of experiments also established the fact that a 



