IX, A, 1 Wright and Smith: Radium Emanation 53 



past year a liquid-air plant has been received, and we expect in 

 the near future to be able to check our results obtained with the 

 charcoal method by observations with the liquid-air condenser. 

 Since the general method of procedure which we finally adopted 

 is not radically different from that of Eve and Satterly, our 

 results ought to be directly comparable. A portion of a standard 

 solution of radium bromide prepared by Rutherford, Boltwood, 

 and Eve was kindly furnished us by Professor Eve. This 

 solution contains 6.28x10"^ gram of radium per cubic centi- 

 meter, being of the same strength as that used by both Eve 

 and Satterly. At first we used 0.5 cubic centimeter of the 

 standard, diluting it with distilled water to 50 cubic centi- 

 meters, but we found that the emanation given off from the 

 solution in the time of a test was considerably greater than that 

 collected from the volume of air with which we were dealing. 

 For a comparative method it is desirable to deal with approxi- 

 mately equal amounts of emanation in the two branches of the 

 experiment. Consequently, in our later tests we used 0.1 cubic 



<zx 



<D=<: 



Fig. 1. Collecting apparatus, a. Inlet ; b, cotton-wool tube ; c, distributing bottle ; d, standard 

 solution ; e, condensers ; /, sulphuric acid bottles ; g, calcium chloride tubes ; h, charcoal 

 tubes ; i, manometers. 



centimeter of the standard solution, diluting it as before to 50 

 cubic centimeters. This gave us for our standard a solution 

 containing 6.28 X 10~^^ gram of radium. 



The arrangement of apparatus for the determination of the 

 amount of radium emanation in the atmosphere is shown in fig. 

 1. The air to be tested was drawn through a tube projecting 

 from a second-story window of the Bureau of Science at an 

 elevation of about 10 meters. In order to extract all the dust 

 from the air, a tube containing cotton wool was placed between 

 the intake and the distributing bottle. From the distributing 

 bottle the current of air was divided into two exactly equal parts, 

 one-half passing through the branch containing the radium- 

 bromide solution, the other half passing along what we have 

 been pleased to call the "air-emanation" branch. 



The bottle containing the radium-bromide solution was so 

 arranged that it could be heated by immersing in a solution of 

 sodium chloride. Both a spherical and a cylindrical condenser 

 were attached in series to the bottle to prevent loss of the 

 solution during the process of heating. 



