ISO J. C. Sanderson — Probable Influence of the 



A sample, culled " surface soil," was of the same general 

 nature as the earth under the laboratory floor, bnt contained a 

 considerable proportion of loam. It was a specimen of the soil 

 in the rear of the Laboratory, and was removed from just be- 

 neath the surface. 



The results of the measurements of the different specimens 

 were of the same general character, although, as might be 

 expected, the earth taken from near the surface was less active 

 than the material lying deeper. This is probably due to the 

 leaching action of the surface water. 



A test on white beach-sand showed no activity. This was 

 significant and made it seem probable that the activity of soil 

 is due for the most part to the material covering the separate 

 grains and not to mineral constituents of the grains themselves. 

 To test this point some cellar earth was heated with fairly 

 strong hydrochloric acid, filtered and washed. The sand thus 

 obtained was thoroughly dried and placed in the larger cylin- 

 der, which it half filled. As will be seen from the table, fully 

 half of the activity was removed by this process. This speci- 

 men is called " treated earth" in the table. 



A solution was prepared by dissolving 08135 gram of thori- 

 anite, containing 78 per cent Th0 2 , in a little concentrated 

 nitric acid with gentle heating, evaporating to dryness, dissolv- 

 ing and diluting to 50 cubic centimeters with distilled water. 

 10 cubic centimeters of this solution was diluted still further 

 and mixed with 884 grams of neutral beach sand in the same 

 manner as has been described in the case of thorite. As is 

 shown by the results given in the table, the emanating power 

 of the thorium nitrate thus prepared is noticeably less than that 

 of the thorium chloride contained in a gelatinous film of silicic 

 acid. 



Another experiment was made in which a volume of 10 cubic 

 centimeters of the thorianite solution w y as freely diluted and 

 thoroughly mixed with 15 liters of the cellar earth. The nor- 

 mal activity of the earth was subtracted from the reading 

 obtained, and this gave the activity due to the thorianite alone. 

 The table shows that in this condition the thorium is slightly 

 more emanating than when mixed with sand, but the difference 

 is not so striking as in the case of thorite. In the table this 

 specimen is designated " enriched earth." 



Measurements were also made of the amount of thorium 

 emanation escaping from the thorium minerals monazite (5 per 

 cent Th0 2 ) and thorianite (78 per cent Th0 2 ). The monazite 

 was in the form of fine sand, and the thorianite in the form of 

 cubical crystals about 3 millimeters on a side. About 500 

 grams of each were placed in a glass cylinder and held in place 

 by glass wool. Air was drawn through and readings taken as 

 before. 



