﻿CLAYS FROM LUZON. 433 



conductivity observed in the gas was due to a radioactive emanation 

 which diffused from the clay into the air in the vessel. They 30 say : 



It did not matter in this experiment whether the earth was in the moist 

 condition in which it was removed, or whether it was introduced underneath 

 the hell-glass after protracted drying; after the lapse of eight months no decrease 

 of activity was apparent in the material. 



In another experiment several substances were placed one-half meter 

 in the earth, after four weeks they were dug up and the potter's clay, 

 which in the beginning was inactive, was unmistakably active. The 

 other substances used were still inactive. This shows that clays also 

 have induced activity. Elster and Geitel found at different places con- 

 siderable difference in the radioactivity of clays, it being invariably less 

 near the sea. 



The conductivity in the gas above the clay in the case already cited 

 has been calculated 31 to be the same as that produced by the emanation 

 from 7. 10" 10 grams of radium. Taking the density of clay as 2, this cor- 

 responds to about 10~ 13 grams radium per gram of cla\. This has been 

 calculated to be not greatly different from the amount of radium neces- 

 sary in the earth to emit sufficient heat to compensate for the loss by 

 conduction and radiation. On the basis of this Eutherford 32 expresses 

 it as his opinion that the present rate of loss of heat of the earth might 

 have continued unchanged for long periods of time. 



I have examined several different specimens of the clays of Luzon, 

 namely, numbers 8, 12, 32 and 33, by means of the leakage apparatus 

 and all efforts failed to discover a trace of primary radioactivity in the 

 material. The apparatus was of the general type of instrument used 

 by Elster and Geitel, 33 Mache and Meyer, 3 * Bacon 35 and other workers 

 in their investigations of the radioactivity of ordinary materials. (See 

 PL I.) 



Three methods of determination were used in each case. One por- 

 tion of the clay amounting to 10 grams was put immediately in the 

 measuring chamber and the fall of the charged gold leaf observed for a 

 period of hours; another was digested with acid in an Ehrlenmeyer 

 flask, for some time tightly stoppered and allowed to stand. A third 

 portion was fused with sodium carbonate, slaked in water, neutralized 

 with hydrochloric acid and tightly stoppered in an Ehrlenmeyer flask. 

 After one month these Ehrlenmeyer flasks in turn were connected in 

 circuit with the apparatus and air was sucked through the solution so 



w Chem. News (1903), 88, 30. 



31 Rutherford, E.: Radioactivity, Cambridge, Eng. (.1905), 507. 



32 Ibid., 496. . 



™Phijs. Ztschr. (1904), 5, 321. 

 "Monalsh. f. Chem. (1905), 26, 590. 

 36 This Journal (1900), 1, 435. 



