662 Mr. J. Moran on a Comparison of 



solution with the Washington, and thus also indirectly with 

 the International. In addition they served to show if the 

 strong and the weak solutions had remained unchanged 

 throughout the eleven years which have elapsed since their 

 preparation. These solutions having been prepared in the 

 ratio of 100 : 1, if any deposits of radium had occurred during 

 this interval the amounts deposited would probably be in a 

 different ratio, and there would then be a discrepancy in the 

 results. 



Section 2. Method. 



The emanation method was employed in making the above 

 comparisons. The required volumes of radium solution were 

 drawn off with a clean pipette, and accurately weighed. 

 Distilled water and a little HC1 were then added, and the 

 solution was sealed up air-tight in a 500 c.c. flask, the 

 solution occupying about half the volume of the flask. The 

 flask was then put aside for the emanation to collect, and 

 boiled off at intervals of about a week. 



The apparatus consisted of a sensitive, air-tight, gold-leaf 

 electroscope, carefully silvered on the inside, and well 

 earthed. It was exhausted by a water-pump, a sufficient 

 exhaust usually being obtained in a couple of minntes. The 

 air was deprived of moisture by phosphorus pentoxide con- 

 tained in a U-tube. The gold-leaves were protected from 

 a sudden inrush of air by using a capillary tube. The 

 emanation was admitted by means of a three-way tap, and 

 air allowed to enter afterwards until the pressure inside the 

 electroscope was atmospheric. 



The solutions were well boiled in order to drive off all 

 the emanation, which was collected with the air over water 

 in a bell-jar at room-temperature. Care was taken through- 

 out to minimise possible errors, by having the solutions 

 of nearly equal strength, by boiling each the same length of 

 time, and by observing the maximum value of the ionization 

 current the same interval of time after passing in the 

 emanation. In the earlier part of the work, readings were 

 taken every few minutes, and the growth of ihe ionization 

 current traced. The practical maximum wns reached in 

 about five hours. Here the ionization current appeared to 

 be constant, as the time-measurement of the movement of 

 the gold-leaf showed a slightly oscillating value of less than 

 one per cent., which was thus the probable error in taking 

 the time of a single reading. 



The theory of the work is well known. The natural leak 

 was taken before introducing the emanation, and deducted 

 from the value obtained when the ionization current had 

 reached a maximum. This value was corrected for atmo- 

 spheric pressure, reducing all results to standard pressure. 



