AE 
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226 RADIO-ACTIVE EMANATIONS [CH. 
It was soon observed that the thorium emanation passed 
unchanged through acid solutions, and later the same result was 
shown to hold true in the case of both emanations for every 
reagent that was tried. Preliminary observations! showed that the 
thorium emanation, obtained in the usual way by passing air over 
thoria, passed unchanged in amount through a platmum tube 
heated electrically to the highest temperature obtainable. The 
tube was then filled with platinum-black, and the emanation passed 
through it in the cold, and with gradually increasing temperatures, 
until the limit was reached. In another experiment, the emana- 
tion was passed through a layer of red-hot lead-chromate in a 
glass tube. The current of air was replaced by a current of 
hydrogen, and the emanation was sent through red-hot magnesium- 
powder and red-hot palladium-black, and, by using a current of 
carbon dioxide, through red-hot zinc-dust.. In every case the 
emanation passed through without sensible change in the amount. 
If anything, a slight increase occurred, owing to the time taken for 
the gas-current to pass through the tubes when hot being shghtly 
less than when cold, the decay en route beg consequently less. 
The only known gases capable of passing in unchanged amount 
through all the reagents employed are the recently discovered. 
members of the argon family. 
But another possible interpretation might be put upon the 
results. If the emanation were the manifestation of a type of 
excited radio-activity on the surrounding atmosphere, then, since 
from the nature of the experiments it was necessary to employ in ° 
each case as the atmosphere, a gas not acted on by the reagent 
employed, the result obtained might be expected. Red-hot mag- 
nesium would not retain an emanation consisting of radio-active 
hydrogen, or red-hot zinc-dust, an emanation consisting of radio- 
active carbon dioxide. The incorrectness of this explanation was 
shown in the following way. Carbon dioxide was passed over 
thoria, then through a T-tube, where a current of air met and 
mixed with it, both passing on to the testing-cylinder. But 
between this and the T-tube a large soda-lime tube was mtro- 
duced, and the current of gas was thus freed from its admixed 
carbon dioxide, before being tested in the cylinder for the emana- 
1 Rutherford and Soddy, Phil. Mag. Nov. 1902. 
