xii. a, 3 Wright and Heise: Philippine Waters 149 



glass tube entering the flask was broken off at L and the flask 

 was washed out with a current of air, regulated by means of a 

 screw-stopcock J, until the pressure in the system had been 

 equalized. The cock / was then closed, and after fifteen minutes, 

 readings of the leak were taken as described above. 



The standardization was checked with a known quantity of 

 standard radium-bromide solution put directly into the shaking 

 vessel used in field determinations. After the closed vessel had 

 been allowed to stand one month to ensure radioactive equili- 

 brium, a determination was made by the usual field method. 

 Two different determinations showed satisfactory agreement 

 with each other and with the results previously obtained. This 

 procedure is much simpler than the usual method of standardiza- 

 tion, and since determinations both with the standard solution 

 and with water samples of unknown activity are thus performed 

 under identical conditions, the chance for error is minimized. 

 Our data indicate that this method can be relied upon for ac- 

 curate results. 



■The field determination of radium-emanation content. — The 

 manner of taking water samples was, of course, dependent on 

 the exigencies of travel and on the location and type of the 

 source of the water to be examined. All reasonable precautions 7 

 necessary to secure representative samples without loss of ema- 

 nation were observed. Whenever possible, the collecting can 

 (shaking vessel) was dipped directly into the water to be exam- 

 ined; otherwise the water was allowed to flow directly into the 

 can from the source (for example, a flowing well) , or was trans- 

 ferred from the source in a second vessel and poured into the 

 can. In all cases care was taken to prevent loss of emanation 

 through shaking or aeration. 



The method of taking samples was not free from objection in 

 every instance, and sometimes, for example, when a spring 

 emerged from the bed of a river or in the bottom of a large 

 pool, it was found impossible to obtain a representative sample. 

 However, we believe that with the exception of these cases the 

 error due to the method of taking the sample did not affect ap- 

 preciably the accuracy of the results. 



The shaking method of Schmidt 8 was employed in field work. 

 Determinations were made as soon as practicable after a sam- 



' Engler, C, Sieveking, H., and Koenig, A., Neue Beitrage zur Messung 

 der Radioaktivitat von Quellen, Chem. Zeitg. (1914), 38, 425-427. 



s Schmidt, H. W., Tiber eine einfache Methode zur Messung des Emana- 

 tionsgehaltes von Fliissigkeiten, Pliysik. Zeitschr. (1905), 6, 561-566. 



