Boltwood — Radio-active Waters, Hot Springs, Ark. 131 



troscope. No indication of any activity in the solid substance 

 could be obtained. The mineral salts in the residue were con- 

 verted into chlorides, dissolved in water, and the resulting 

 solution was sealed up for thirty days. The accumulated gases 

 were boiled off and tested. The observed radio-activity was 

 too slight to measure with any accuracy, and corresponded at 

 most to the smallest detectable trace of radium salts in the 

 waters. 



Tufa from Springs. 



On issuing from the ground a number of the springs form a 

 deposit of " tufa," consisting chiefly of carbonate of calcium. 

 A sample of this material weighing 100 grams was dissolved 

 in dilute hydrochloric acid and the gas evolved was conducted 

 into a strong solution of sodium hydroxide. A small residue 

 of gases not absorbed by the sodium hydroxide solution was 

 examined in the electroscope. The radio-activity of these gases 

 indicated that the quantity of radium present in the tufa was 

 less than one-millionth of the quantity of radium associated 

 with an equal weight (100 grams) of uranium in pitchblende. 



Gas from Springs. 



Samples of the gases which rise with two of the springs 

 were tested under conditions identical with those under which 

 the gas obtained on boiling the water was tested. The measure- 

 ments were carried out eight days after the gases had been col- 

 lected at the springs, and the activity of the gases was found 

 to be less than that of equal volumes of gases obtained by boil- 

 ing the waters from the same springs. 



Water from Cold Sjyrings. 



In addition to the hot springs, there are on the grounds of 

 the Reservation two cold springs, situated on the northern slope 

 of Hot Springs Mountain, and issuing from the earth about 

 800 feet from the nearest hot spring. An examination of the 

 waters of these springs gave the following results : 



Laboratory 

 number. 



Observed activity 



per liter water 

 g x 10" 4 uranium. 



Days from 



time of 

 collection. 



Calculated 



initial 



activity. 



73D 



6-0 



6 



17 4 



HD 



18*1 



10 



106-8 



Discussion of Results. 



One of the most interesting results of the present investiga- 

 tion is the demonstration of such marked variations in the 

 activity of the water from such a closely related series of 

 springs. The temperature of the different springs varies from 



