1246 Wisconsin Academy of Sciences, Arts, and Letters. 
of well water tested were taken directly from the discharge pip© 
of the pump after about two minutes of flow. 
The water samples were then taken to the laboratory where 
the dissolved gases were separated by boiling. This operation 
was carried out in a special form of apparatus described else¬ 
where. 1 The boiling was continued for at least 15 minutes. 
A few cubic centimeters of caustic soda were generally added 
just before boiling to fix the carbon dioxide. The separated 
gas was then transferred to an air tight electroscope which had 
previously been partially exhausted. The electroscope was sup¬ 
plied with a reading microscope for noting the rate of fall of the 
charged leaf. This apparatus had been carefully standardized 
beforehand by means of a known quantity of, emanation ob¬ 
tained from a small weight of pitchblende (uraninite) : 
Ey the foregoing operations the radium emanation present in 
the water was separated and stored in the electroscope for quan¬ 
titative measurement. Headings were then, taken on the rate of 
fall of the charged leaf. Owing to the induced activity that re¬ 
sults from the decay of the emanation the rate of fall of the leaf 
increases for fully three hours after the introduction of the gas, 
attaining a maximum value about 35 to 40 per cent greater than 
the initial value. This maximum value was made the basis for 
determining the quantity of emanation present. 
In this country the activity of waters (and gases) is generally 
expressed in terms of the standard first proposed by BoltWood. 2 
The standard is based upon the existence of a constant ratio be¬ 
tween the quantity of radium associated with uranium in 
natural minerals. 3 The unit of activity represents the quantity 
of emanation associated with unit weight of uranium in a 
natural mineral. The activity is thus expressed in terms of 
uranium, and as the ratio between uranium and radium i& 
known the activity may be expressed directly in terms of radium. 
When referred to waters the values of the activities represent 
the quantity of uranium (or radium) required to maintain in 
1 Schlundt and Moore, Jour. Phys. Chem. 9, 320 (1905). 
2 Am. Jour. Sci. (4) 18, 381 (1904). 
3 Boltwood, Am. Jour. Sci. (4) 18, 97 (1904), Phil. Mag. (6) 9, 599 
(1905), McCoy, Ber. d. Deutsch. Chem. Gesell. 37, 2641 (1904). 
