XI] AND OF ORDINARY MATERIALS 363 
increased with the time, rising to three times the normal value 
after several days. Little difference was observed whether the 
earth was dry or moist. The activity of the soil seemed to be 
permanent, for no change in the activity was observed after the 
earth had been laid aside for eight months. 
Attempts were then made to separate the radio-active con- 
stituent from the soil by chemical treatment. For this purpose 
a sample of clay was tested. By extraction with hydrochloric 
acid all the calcium carbonate was removed. On drying the 
clay, the activity was found to be reduced, but it spontaneously 
regained its original activity in the course of a few days. It thus 
seems probable that an active product had been separated from 
the soil by the acid. Elster and Geitel consider that an active 
substance was present in the clay, which formed a product more 
readily soluble in hydrochloric acid than the active material itself. 
There seemed to be a process analogous to the separation of Th X 
from thorium by precipitation with ammonia. 
Experiments were also made to see if substances placed in the 
earth acquired any radio-activity. For this purpose samples of 
potter's clay, whitening, and heavy spar, wrapped in linen, were 
placed in the earth 50 cms. below the surface. After an interval 
of a month, these were dug up and their activity examined. The 
clay was the only substance which showed any activity. The 
activity of the clay diminished with the time, showing that activity 
had been excited in it by the emanations present in the soil. 
Elster and Geitelt have recently found that a large quantity of 
the radio-active emanation can be obtained by sucking air through 
clay. In some cases, the conductivity of the air in the testing 
vessel was increased over 100 times. They have also found that 
“fango”—a fine mud obtained from hot springs in Battaglia, 
Northern Italy—gives off three or four times as much emanation 
as clay. By treating the fango with acid, the active substance 
present was dissolved. On adding some barium chloride to the 
solution, and precipitating the barium as sulphate, the active 
substance was removed, and in this way a precipitate was obtained 
over 100 times as active, weight for weight, as the original fango. 
Comparisons were made of the rate of decay of the excited activity, 
1 Phys. Zeit. 5, No. 1, p. 11, 1903. 
