﻿1 24 BACON. 



by Elster and Geitel 10 and by Mache 17 and other European workers in 

 their investigations on the radio-activity of ordinary materials. The 

 normal rate of movement (air leak) of the gold leaf of the electroscope 

 was forty divisions per hour and it was fairty constant over the period of 

 the investigation. The waters were examined according to the methods 

 of Mache, 18 air being sucked through the water, the emanation being 

 drawn with it into the jar containing the electroscope. Waters Nos. 1 

 and 2 showed no trace of activity. Water No. 3 was slightly active, the 

 gold leaf movement being increased by it to sixty divisions per hour. 

 Barium sulphate precipitates, formed in these waters, were all inactive. 

 In examining solids, 100 grams were generally placed in the jar contain- 

 ing the electroscope, according to the method used by Elster and Geitel 10 

 in testing clays and other materials. The sediments of waters Nos. 1 and 

 2 were inactive, that of No. 3 was active, the rate of movement of the 

 gold leaf being increased to two hundred divisions per hour; it was five 

 times the normal. The emanation obtained by decomposing the sediment 

 with hydrofluoric and nitric acids, and then blowing air through this 

 active specimen, fell to half the original value in about four days; this 

 phenomenon corresponds to that exhibited by radium ; the excited activity 

 also fell to half value in about thirty minutes, which likewise points to 

 radium as its source. For comparison one gram of uranium oxide 

 (black, Ivahlbaum) was placed in the apparatus, the rate of fall of the 

 gold leaf was then one hundred per minute, or six thounsand per hour. 

 One gram of pitchblende from Joachimthal, containing 26.1 per cent 

 of uranium, gave a rate of twelve thousand five hundred per hour, a 

 magnitude which is about six times the rate per unit for uranium from 

 the natural mineral, as compared with that from the chemical oxide. 

 This rate agrees very well with that found by McCoy 20 as the ratio 

 between a natural (uranium containing mineral) and a pure uranium 

 salt. 



Boltwood's determination of the amount of radium per gram of uranium in 

 any natural mineral is 8X10 -7 grams. The sediment which I found to be active 

 could then contain only 4.3X10" 11 gram of radium, a quantity which corresponds 

 to 4.3X10" 13 gram of radium per gram of sediment. 



Strutt 21 made tests on various igneous rocks from different parts of the world 

 and found them all to show radio-activity, the most active being the more acid 

 granites'and syenites, the least active, basalts and various ultra basic rocks. The 

 range in content is calculated at from 1.84X10" 12 to 25.5X10 -12 gram of radium per 

 cubic centimeter of rock, or 0.613X10~ 12 to 9.5X10" 12 gram of radium per gram of 

 rock. Rutherford calculated that samples of soil examined by Elster and Geitel 

 in Berlin contained 10 -13 gram of radium per gram of soil. 



10 Physikal, Zt. schr. (1904) 5, 321. 



17 Monatsh. f. ohem. (1905) 26, 595. 



18 loc. cit. 



19 Loc. cit. 



^Ber. d. chem. Ges. (1904) 37, 2641. 



^Proc. Roy. Soc. Lond. Sec. A. (1906) 77, 472. 



