Boltwood — Ratio of Radium to Uranium. 101 



broken off and the external air was allowed to sweep through 

 the system of tubes until the pressure within and without the 

 electroscope was the same. The stopcock of the electroscope 

 was then closed and the other apparatus disconnected. 



For determining the rate of leak or discharge of the gold- 

 leaf, measurements were made of the time required for the 

 gold-leaf to fall through a distance equal to eight divisions of 

 the scale in the eye-piece in the microscope. The time required 

 was recorded by means of a stop-watch divided to fifths of a 

 second. Because of the initial rise in the activity, due to the 

 formation of induced activity within the electroscope, the rate 

 of leak at the end of three hours was chosen in comparing the 

 results obtained with different minerals. 



In order to determine the quantity of uranium present in 

 the mineral under examination, the solution in the bulb B was 

 washed out into a beaker and the quantity of uranium deter- 

 mined by one of the ordinary methods of analysis. 



The capacities of the two final sections of the apparatus 

 were determined by tilling them with water and weighing 

 them, and then weighing them when empty. The average 

 capacity of A in the different experiments was about 48 cc and 

 the average capacity of the rest of the apparatus was about 

 9 CC . In comparing the results obtained with different minerals 

 it was in general assumed that the distribution of the emana- 

 tion throughout the different parts of the apparatus was uni- 

 form and the volume occupied by the solution was neglected. 

 Since the capacities of the different pieces of apparatus used 

 were in all cases approximately the same and the volumes of 

 the different solutions were all approximately equal, this pos- 

 sibly doubtful assumption would cause no serious error in the 

 results when used for purposes of comparison. 



The results obtained with eight different samples of uranium 

 minerals are given in a 'table below. For decomposing the 

 uraninites strong hydrochloric acid containing a little nitric acid 

 was used, the gummite and uranophane were treated with 

 strong hydrochloric acid and the carnotite was dissolved in 

 dilute (1 : 1) nitric acid. The sample of samarskite used was 

 obtained in a very finely divided condition by suspension in 

 water and decantation from the coarser material. In this form 

 it could be readily decomposed with concentrated sulphuric 

 acid. 



The samples No. 1, .2, 3 and 4 were from North Carolina, 

 No. 5 from Branch ville, Conn., Nos. 6 and 7 from Colorado 

 and No. 8 from Saxony. 



Between experiments 5 and 6 the adjustment of the electro- 

 scope became slightly altered from an accidental movement of 

 the microscope support. A re-determination of the constant 



