350 Prof. McCoy and Dr. Viol : Chemical Properties and 



value for the period. Our preliminary results show that 

 Blanc's figure is of the right order. We have not observed 

 any facts that would seem to confirm Miss Leslie's supposi- 

 tion that the period of Rt is only a few months*. 



IV. Periods of Thorium Products. 



Since the trustworthiness of our results would depend in 

 so large a measure upon the accuracy of the decay constants 

 used in the calculations, we have made careful redetermina- 

 tions of these constants for ThX, B, and 0, and a less accurate 

 determination for Ms 2 . From experiments started several 

 months ago we expect to get accurate data for Rt, the 

 period of which is so long that an accurate determination 

 of its constant will require two or three years. The period 

 of ThX was found in connexion with the determination of 

 the ratio x ; the others were the results of special experi- 

 ments. Mesothorium-two was precipitated with aluminium 

 hydroxide by means of ammonia, in the Msj barium chloride 

 preparation. The Ms 2 was then freed from traces of Msi by 

 reprecipitation of the aluminium hydroxide. Radiothorium 

 was removed by precipitating a few milligrams of thorium 

 chloride in the faintly acid solution of aluminium chloride by 

 means of hydrogen peroxide. The thorium had just been 

 several times reprecipitated with ammonia to remove Ms x 

 and ThX, while B and C were removed from the aluminium 

 as has been described under the preparation of pure Rt. 

 Finally, a precipitation of barium sulphate was made in the 

 acid solution of aluminium chloride. This barium sul- 

 phate-Ms 3 was made into thin films on metal disks. The 

 beta-ray activity of Ms 2 was measured by placing the film in 

 a brass box with a tightly-fitting lid, the top of which was a 

 thin sheet of aluminium. Table III. gives the data obtained 



Table III.— Period of Ms.,. 



Interval, Hours. 



Activity. 



Period, Hours. 



00 



3-086 





3-783 



2012 



012 



14-75 



05842 



614 



2373 



02118 



614 



* Lc Radium, viii. p. 35(3 (1911). 



