52 The Philippine Journal of Science 1914 



direct determinations of the radium-emanation content. In order 

 to attain this end, air was passed at a known rate for a given 

 time through tubes containing the coconut charcoal, which ab- 

 sorbed the emanation from the air. At the same time air was 

 bubbled through a solution of radium bromide containing a 

 known amount of radium, and the emanation from the solution 

 and the air was collected in another charcoal tube. The emana- 

 tion absorbed in the charcoal was then driven off by heating 

 to a dull red heat, collected over water in aspirators, and 

 finally measured by passing into an ionization chamber connected 

 either with an electroscope or an electrometer. The emanation 

 in a given volume of air can then be calculated from the ratio 



emanation generated in the standard solution in a known time 



emanation in a known volume of air 



provided the charcoal tubes absorb the same fraction of the total 

 amount of emanation passing through them. Since the method is 

 a comparative one, the determination should be independent of 

 variation of meteorological conditions. Ashman ^ and Satterly ^^ 

 determined the amount of emanation in the atmosphere by 

 another method. Air was passed through coils immersed in liquid 

 air, and the amount of emanation condensed in the tube then 

 rtieasured. Rutherford and Soddy had previously shown that 

 radium emanation is condensed at a temperature of about — 150°. 



It is hard to decide from the data at our command which is 

 the better method. Satterly, in his paper published in 1908, 

 makes the statement that "both methods gave about the same 

 results for the emanation in the air, but the method of the con- 

 denser is quicker and more accurate than the charcoal method," 

 but in a later article on the subject makes a diametrically oppo- 

 site statement without giving any reason for his change of 

 opinion. 



The following average results have been obtained for the 

 radium-emanation content of the atmosphere by Eve in Mon- 

 treal, Satterly in Cambridge, and Ashman in Chicago : 



Eve, 60x10-12 gram Ra per cubic meter. 

 Satterly, lOOxlO-12 gram Ra per cubic meter. 

 Ashman, 96x10-12 gram Ra per cubic meter. 



When the present series of observations was started, liquid 

 air was unobtainable in Manila. Consequently, we were limited 

 in our choice to the charcoal-absorption method. During the 



'Am. Journ. Sci. (1908), 119. 

 " Loc. cit. 



