346 



SCIENCE. 



[N. S. Vol. XX. No. 506. 



which he suggests the name exradio. Ob- 

 taining this radiation ftom a specimen of 

 radium bromid, he finds that it possesses the 

 properties of a gas, obeying Boyle's law, being 

 condensed at a low temperature and having 

 a vapor pressure still appreciable even at the 

 temperature of liquid air. The gas, which is 

 at first strongly luminous but only temporarily 

 so, seems to be a member of the argon group, 

 having a density of about 80. If monatomic 

 this would give an atomic weight of about 

 160. This is but little less than would be 

 expected for the next eighth group element 

 above xenon, and it may turn out that the 

 inert elements of this group present the best 

 development found in the periodic table. 

 From the fact of its large atomic weight it 

 is clear that in the break up, if such there be, 

 of each radium atom, but a single atom of 

 the emanation is formed. The quantity of 

 the gas available was but 0.0254 cubic milli- 

 meter, but this proved suificient to obtain the 

 volume-pressure relations. 



In another paper in the Proceedings of the 

 Royal Society, Ramsay and Soddy describe 

 more fully these and other experiments. In 

 numerous instances the helium spectrum ap- 

 peared at once in the radium bromid emana- 

 tion; in other cases the line D^ appeared after 

 one to three days, and later the complete 

 helium spectrum. Fifty milligrams of radium 

 bromid produced 0.5 cubic centimeter gas per 

 day, chieily hydrogen and oxygen in the pro- 

 portion to form water, the remainder being 

 almost entirely air. The amount of helium 

 given off in sixty days was 0.1 cubic millimeter. 

 From this it was calculated that a gram of 

 radium would give oif in a year 0.0022 milli- 

 gram of helium. Since argon lines were 

 noticed in the spectrum, the possibility is not 

 absolutely excluded that both argon and 

 helium could have conie from an external 

 source. The change in volume of the emana- 

 tion was twice measured in minute capillary 

 tubes. In one ease it increased, in the other 

 decreased. The tubes showed a brilliant 

 helium spectrum. The amount of gas formed 

 from the emanation was about 3 X 10 — ® cubic 

 millimeters per second per gram radium; the 

 rate of decomposition of the emanation 



3 X 10 — ^^ cubic millimeters per second. The 

 mean life of a radium atom is calculated as 

 a little more than a thousand years. A cubic 

 centimeter of the emanation would evolve 

 eventually in complete decomposition 7.4 X 10® 

 kal. and one gram of radium 10^ kal., while 

 one cubic centimeter of an oxygen-hydrogen 

 mixture develops only 2.04 kal. 



In a paper in the Berichte, Herbert N. Mc- 

 Coy discusses the decomposition of radium 

 from the standpoint of the law of mass action. 

 He considers the order of decomposition to be 



Ur=^" UrXs-^ Ra=-^ RaEms-^ Em X5S^ He. 

 Since radium loses one thousandth of its mass 

 per year, it must itself be the product of 

 some mother substance which is itself de- 

 composing at a much slower rate. This sub- 

 stance is uranium, which is always associated 

 with radium. The content in radium must 

 have reached a maximum in all ores which 

 are more than 5,000 years old, and from this 

 time on there must be a constant ratio be- 

 tween the uranium and radium. The radio- 

 activity of all uranium ores should then be 

 proportional to their content of uranium, and 

 this McCoy finds to be the case. This has 

 also been found to hold in a large number of 

 minerals by B. B. Boltwood, an abstract of 

 whose recent paper on the subject has lately 

 appeared in Science. The activity of pure 

 uranium salts is relatively only one fifth of 

 that of uranium ores, owing to the fact that 

 the latter contain also the intermediate and the 

 decomposition products. The relative quantity 

 of uranium X, radium emanation and emana- 

 tion X to the amount of radium in any case 

 is exceedingly small, owing to the rapidity 

 with which they decompose. The ultimate' 

 decomposition product, helium, is a constituent 

 of all uranium ores, but owing to diffusion its 

 quantity bears no direct relation to the quan- 

 tity of uranium in the ores. The absolute 

 proportion of radium to uranium in ores is 

 about one part radium to 300,000 parts ura- 

 nium. The decomposition of thorium is 

 analogous to that of uranium, but about one 

 millionth part as rapid. 



Curie and Labord have examined a large 

 number of mineral springs from the stand- 

 point of radioactivity and find great varia- 



