Soil on Local Atmospheric Radioactivity. 



181 



In all the foregoing experiments the relation between the 

 amount of thorium emanation per cubic centimeter and the 

 activity as measured in the electroscope was deduced from 

 equation II by substituting the proper values for the constants 

 \, Jc 3 , and P. 



The experiment designated " surface diffusion " was made 

 bj placing a rectangular metal plate of about 2400 square cen- 

 timeters, one centimeter above a leveled surface of cellar earth 

 and drawing air, into the electroscope, through a tube soldered 

 in the middle of the plate. In this way the air was made to 

 pass slowly over the surface of the soil, which was quite moist. 

 An experiment was also made with rather large fragments of 

 broken red sandstone. The fifteen-liter cylinder was filled with 

 this material and air drawn through it as before. It is obvious 

 that equation II does not apply in either of these cases. 



The third column gives the amounts of the thorium in one 

 cubic centimeter of sand, under the specified conditions, which 

 will liberate the same amount of emanation as one cubic centi- 

 meter of the material considered. The fourth column gives 

 the amount of thorium present in one cubic centimeter of the 

 material, in those cases where this was known. 





Activity in 



Thorium equiv- 



Am't of Thori- 



Material 



scale divisions 



alent in grams 



um actually 



tested 



per minute 



per e. c. 



present per c.c 



Cellar Earth 



2-06 



i-35 xitr 6 







Surface Soil 



... . 1-13 



1-08X10- 6 





Sandstone JI 



1-41 



1-35X10- 6 





Sea Sand . 



o-oo 



0-OOxiCr 6 





Surface Diffusion . 



0'20 







Broken Sandstone. 



0-55 







Thorianite Sand .. 



... 12-32 



i-5o xicr 4 . 



2-04X10- 4 



Monazite 



6-86 



2-04X10- 4 



1240X10- 4 



Thorianite 



. .. 95-2 



3-58 X10" 4 



30400 xicr 4 



8 Liters of treated earth 0*50 







8 Liters of cellar eai 



•th. 1-01 







Enriched earth 



6'48 



5-15X10- 6 



"/•OOXIO" 6 



It will be seen from the table that the thorium in the sand 

 treated with thorianite solution is about four hundred and 

 twenty times as emanating as the thorium in monazite, and 

 about six thousand, one hundred times as emanating as the 

 thorium in thorianite. 



The Radium Standard. 



The radium emanation obtained on dissolving - 0907 gram 

 of North Carolina uraninite (containing 76 per cent of uranium) 



After standing for about 



was introduced in the electroscope. 



