XIII, A, 2 Wright and Heise: The Radium Content of Water 53 



Since we were dealing with several times the quantity of sea 

 water used in similar tests by previous investigators, we decided 

 to try the charcoal absorption method. This method is fully 

 described in an article by Wright and Smith ^- on the emanation 

 content of atmospheric air. After the water had remained 

 sealed in the flask for a period of thirty days or longer, the 

 flask was placed in a water bath and heated to about 80 "" C, 

 when the tips of the tubes leading into the bottle were broken, 

 and emanation-free air was pulled through at the rate of 1 

 liter per minute. The air was then passed through a bottle con- 

 taining sulphuric acid and a tube containing calcium chloride 

 and finally through two tubes in series, each of which contained 

 70 grams of finely granulated coconut charcoal. At the same 

 time air was bubbled through an identical system, except that 

 in place of the bottle containing the sea water there was sub- 

 stituted a small bottle containing 615 ^; 10-'^ grams radium 

 from a standard solution furnished by the Bureau of Standards 

 at Washington, D. C. The portion of solution used had been 

 sealed up, after having been freed from all emanation, for a 

 period of exactly twenty-six and one-half hours, so that the 

 emanation obtained from our standard was equivalent to that 

 in equilibrium with 110.7 X 10"^^ grams of radium. Air was 

 bubbled through the boiling solutions until we were certain that 

 all the contained emanation had been transferred to our charcoal 

 tubes. Since in a previous work by Wright and Smith '' on 

 the quantitative determination of the emanation content of at- 

 mospheric air it had been shown that these same charcoal tubes 

 absorb approximately 99 per cent of the emanation passing 

 through them even for much larger quantities of emana- 

 tion, it was assumed that by this method we would obtain at 

 least as great accuracy as by the more direct method. More- 

 over this method has the advantage of being a comparative one, 

 so that any errors that are due to inaccuracy of observation 

 will cancel in the final calculations. The arrangement of the 

 apparatus in the collecting system is shown in fig. 1. 



After the emanation had been collected in the charcoal tubes, 

 they were heated in an electric furnace, and the gas was driven 



" The variation with meteorological conditions of the amount of radium 

 emanation in the atmosphere, in the soil gas, and in the air exhaled from 

 the surfaca of the ground, at Manila, Phys. Rev. (1915), n. s. 6, 459-482. 



" A quantitative determination of the radium emanation in the atmos- 

 phere and its variation with altitude and meteorological conditions, Phil. 

 Journ. Sci., Sec. A (1914), 9, 51-76. 



