Bolhvood — Radio-active Waters ', Hot Springs, Ark. 129 



radium associated with a definite weight of uranium in a radio- 

 active mineral has been shown* to be a perfectly definite and 

 unvarying quantity, this method of expressing the activity of a 

 given quantity of emanation affords a convenient and accurate 

 standard for the comparison of samples of water from different 

 sources. 



Samples of water from forty -four of the different hot springs 

 were examined. The properties of the gaseous, radio-active 

 constituent were found to be identical with those of the radium 

 emanation. The activity of the gas fell to one-half value in 

 about 3*9 days and the active deposit, after two hours from the 

 start, had a half-value period of twenty-eight minutes. 



In the following table are given 1 the quantitative results of 

 the examination of the waters. The first column gives the 

 laboratory number of the sample, the second column contains 

 the number representing the activity of the gas actually 

 obtained from one liter of water expressed in terms of the 

 uranium standard,f the third column gives the number of days 

 which transpired from the time of collecting the sample to 

 the time of testing the water, and the fourth column gives the 

 initial activity of the water (per liter) as calculated from the 

 equation : I = le 



■At 





Observed activity 



Days from 



Calculated 



ab oratory 



per 



liter water 



time of 



initial 



number. 



gxlO 



-4= uranium. 



collection. 



activity. 



22A 





0*9 



8 



3-7 



23A 





3*8 



7 



14-4 



24A 





1-8 



7 



6'8 



25A 





3-9 



7 



15'L 



26A 





8-4 



7 



31-9 



27A 





0-4 



8 



1-6 



29A 





6-3 



7 



23-9 



30A 





12-5 



7 



49-0 



32A 





7'6 



7 



28-9 



33 A 





3-1 



7 



11-8 



34A 





7-7 



7 



29-3 



35A 





17*2 



7 



65-4 



36A 





14-4 



7 



54-7 



37A 





2-1 



9 



10'3 



38A 





0-9 



7 



3-4 



39A 





8-5 



9 



41-6 



40A 





2-6 



10 



15-3 



41A 





1-3 



10 



7-7 



43A 





13 



7 



4-9 



*Boltwoocl, this Journal, xviii, 97 ; Phil. Mag. (6), ix, 599. 



f The number denotes the weight in grams of the quantity of uranium in 

 a radio-active mineral which is associated with a quantity of radium, the 

 total emanation from which would be equivalent to the emanation obtained 

 from one liter of the water. 



Am. Jour. Sci. — Fourth Series, Yol. XX, No. 116. 

 9 



-August, 1905. 



