3S2 Boltwood — Radio-activity of Natural Waters. 



Curie and Laborde the standard adopted is the quantity of 

 emanation produced by one milligram of pure radium bromide 

 in one second. Such a standard would suffice for all immediate 

 needs if it were not for the fact that it is impossible for others 

 to obtain at present even small quantities of radium bromide 

 of known and established purity. Other investigators have 

 adopted the plan of expressing the activity in terms of the 

 number of ions produced per second in a volume of one cubic 

 centimeter. This is difficult to determine with accuracy and 

 its indirect calculation is uncertain. 



The standard here suggested and employed is the quantity 

 of radium emanation set free when a known weight of uranium 

 in the form of a natural mineral is dissolved in a suitable 

 reagent.* The mineral which has been used is a pure urani- 

 nite from North Carolina. It was dissolved in aqua-regia, the 

 solution diluted with water and the gas removed by boiling. 

 The details of the operation follow : 



The sample of uraninite was finely pulverized in an agate 

 mortar. A portion on analysis was found to contain 82*46 per 

 cent of uranium. A quantity of the pulverized mineral equal 

 to 0*0121 was weighed out into a small tube made by cutting 

 off about 4 cm of the bottom of an ordinary glass test-tube. The 

 tube was lowered by means of a short piece of common thread 

 into a flask of about 100 cc capacity, which had been previously 

 filled about one-half full of distilled water. A rubber stopper 

 with which the flask could be closed carried a glass tube, which 

 could be pushed through the stopper until the lower end was 

 just above the surface of the water in the flask. Beyond the 

 stopper the tube was bent at a right angle. The stopper was 

 placed very loosely in the neck of the flask, the tube which it 

 carried being at the same time inserted in the top of the tube 

 containing the mineral. On releasing the end of the thread at 

 the right moment this dropped into the flask, leaving the tube 

 floating on the water and supported in an upright position by 

 the fixed tube within it. The rubber stopper was then tightly 

 inserted in the neck of the flask and about one cubic centi- 

 meter of aqua-regia was introduced into the tube containing 

 the mineral, a small pipette with a long, thin, capillary tube 

 being used for this purpose. 



The open end of the tube was then connected with the rub- 

 ber tube D (fig. 1), the vessel A having been removed. The 

 pinchcock I) was opened, the flask and contents were warmed 

 gently and the uraninite was dissolved. When the solution of 

 the mineral was complete the tube extending into the flask was 

 drawn out through the rubber stopper until the opening was 

 just below the stopper. This permitted the tube containing 

 * This Journal, xviii, 97 (1904). 





