624 Lester — Radioactive Properties of the 



P, threaded at e for the attachment of the electrode and 

 carrying on its upper end the leaf support A, which is 

 firmly attached to the rod by means of a four-jawed 

 friction clamp. The heavy front and back plates of the 

 head, which carry small windows, are not shown in the 

 figure. They are easily removed by taking out a few 

 screws when it is necessary to get at the leaf system. 

 A Pye telemicroscope serves to read the deflections of 

 the leaf. The microscope is rigidly attached to the head 

 in such a way that it can not change its focusing position 

 on the leaf. C is a charging device and DB is merely 

 an arrangement for protecting the leaf when traveling. 



The electroscope head inclosing the insulated leaf sys- 

 tem was so carefully made that it formed an almost air- 

 tight chamber. This enabled the instrument to be used 

 in the open with little or no disturbance to the leaf even 

 when a considerable breeze was blowing. To cut down 

 the natural leak due to ionization produced by sunlight 

 a strong corrugated pasteboard box with suitable open- 

 ings was fitted over and around the electroscope when in 

 use in the open. This box also served as a protection in 

 bad weather. In the field the leaf system was charged 

 negatively by means of a metal tipped celluloid " charg- 

 ing rod. ' ' 



The behavior of the electroscope, often under very 

 trying field conditions, was practically perfect. Even in 

 rainy weather the only trouble experienced was in keep- 

 ing the charging rod dry. After standing charged for 

 about half an hour the natural leak was usually between 

 0-05 and 0-15 division per minute although there were a 

 few occasions when it amounted to nearly 04 division 

 per minute. 



The boiling-out apparatus for the field tests of water 

 samples is shown in -^g. 2. The water to be tested was 

 carefully introduced into a vessel I containing caustic 

 soda when necessary. This vessel has a stop cock and 

 communicates through the cock H and a three-eighths 

 inch brass tube with the collecting chamber BB made of 

 brass tubing two inches in diameter and ten inches long. 

 The neck J is made air-tight by the rubber gasket B. 

 G is a glass tube serving as a water gauge. The vessel I 

 was made in three sizes with capacities of 0-5 liter, 1 liter, 

 and 2 liters respectively. The two-liter vessel was used 

 in most cases although there were some springs for which 



