352 Prof. McCoy and Dr. Viol : CJtemical Properties and 



period of the B obtained on the plate was found to be 10*65 

 hours, for measurements extending over an interval of forty- 

 three hours. The first measurements were made on this 

 film two days after it had been activated, so that only a thir- 

 teenth of the original activity was left. Had the film 

 contained any ThX, this would have still been present to the 

 extent of about 70 per cent, of its original amount. The 

 period obtained shows that practically no ThX can penetrate 

 the tissue paper. We have used as the period 10" 6 hours in 

 our calculations of the ratios x and y. The period of C has 

 been variously given between 55 minutes * and about an 

 hour f . Lerch % has given a value GO'l minutes, in which 

 he corrected his observed period owing to the supposed pre- 

 sence of a little B. Following the directions given by Schlundt 

 and Moore § for the separation of B and C by the use of 

 fumaric acid, we found it possible to obtain C entirely free 

 from B, as was shown by the activity measurements. 

 Twenty c.c. of a very active solution of B and in dilute 

 nitric acid was made just neutral with dilute ammonia, using 

 methyl orange as an indicator. The solution was then made 

 faintly acid with dilute nitric acid ; three drops of 10 per 

 cent, ferric chloride solution was added, and the solution 

 boiled. Then 10 c.c. of a hot 1 per cent, fumaric acid 

 solution was added, and the iron fumarate which precipitated 

 was filtered out. This contained the C with a little B. The 

 precipitate and paper were boiled with 1 c.c. of six times 

 normal hydrochloric acid to dissolve the iron fumarate, and 

 then after diluting to 20 c.c. with water the solution was 

 filtered. The filtrate was treated with an excess of ammonia 

 to precipitate ferric hydroxide, which is readily soluble in 

 dilute acid while the fumarate is not. The ferric hydroxide 

 precipitate, which contained the 0, was then dissolved in 

 1 c.c. of: normal nitric acid, and to this was added enough 

 ammonia solution to neutralize the acid. This solution was 

 boiled and the iron precipitated as before by the addition of 

 10 c.c. of hot fumaric acid solution. This treatment was 

 carried out four or five times, and then the iron fumarate 

 precipitate containing the purified C was dried on the paper 

 and its activity measured at frequent intervals during a 

 period of about seven hours. It may be added that the 

 measurements were not begun until sufficient time had 



* Rutherford, Phil. Trans. Roy. Soc, London, A. cciv. p. 169 (1904). 

 t Pegran, Phys. Rev. xvii. p. 424 (1903). Lerch, Ann. de Phys. xii. 

 p. 745(1903). 



X Wien. Sitz.-Ber. cxvi. (II a), p. 1443 (1907). 



§ Trans. Am. Electrochem. Soc. viii. p. 269 (190-j). 



