148 The Philippine Journal of Science ion 



used. With the precautions noted, the natural leak of the in- 

 strument was usually lower in laboratory work, and frequently 

 lower in field work, than the figures for the natural leak fur- 

 nished by the instrument makers. The electroscope was charged 

 by means of a bank of storage cells in the laboratory; in the 

 field, by means of an ebonite rod. 



Standardization of instrument. — The electroscope was stand- 

 ardized by means of a radium bromide solution of known strength 

 furnished for this purpose by the Bureau of Standards, Wash- 

 ington, D. C. A definite portion of this solution was kept sealed 

 in a proper vessel (essentially a "Curie tube" 6 ) for over one 

 month. The emanation was then removed from the solution by 

 boiling and by circulation of air and was drawn into the eva- 

 cuated ionization chamber. The arrangement of the apparatus 

 is shown graphically in Plate .1, fig. 2. 



A determination was conducted as follows: After the instru- 

 ment had been charged, it was allowed to stand until the leak 

 had become small and nearly constant. Readings both of the 

 natural leak and of the leak due to emanation content were 

 taken at intervals of five minutes, as measured by a stop watch, 

 and were estimated to tenths of a division on the telescope scale. 



The sealed vessel B, containing the acidulated sample to be 

 tested, was heated in a water bath F to about 90° C." Little 

 danger of breakage was incurred by this procedure, because the 

 vessels had been heated to about the same temperature before 

 being sealed. The ionization chamber A was evacuated by 

 means of an electrically driven Geryk oil pump D. A mano- 

 meter E was attached, in order to measure the pressure in the 

 chamber and to detect leaks in the joints of the tubing or in the 

 ionization chamber. When a vacuum had been secured, the stop- 

 cock H leading to the pump was closed. As the ends of the 

 glass aspirator tubes had been drawn to a point and notched 

 with a file, slight pressure with the fingers at M was sufficient 

 to break off the point of the delivery tube inside the rubber 

 tubing, thus allowing the vapors and gases from the vessel 

 B to pass slowly through the (calcium chloride) drying tube C 

 and into the evacuated ionization chamber. Under the decreased 

 pressure, the liquid in the flask B boiled readily, and all of the 

 emanation was rapidly drawn into the ionization chamber. In 

 order to remove the last traces of emanation, the point of the 



9 Curie, P., Dosage du radium par la mesure de l'emanation degagee, he 

 Radium (1910), 7, 65-70. 



