Makch 7, 1913] 



SCIENCE 



363 



washed out of the tube, and the foil bom- 

 barded for a second day. The gases formed 

 proved to be much the same as on the first 

 day; there was no appreciable diminution. 

 The examination of the result of the third 

 day 's bombardment showed that the X, line 

 had diminished considerably, the lines due 

 to helium and neon perceptibly. Wlien the 

 gases produced on the fourth day's bom- 

 bardment were examined it was found that 

 the X3 and helium had diminished to such 

 an extent that the lines were barely visible. 

 I could not see the neon line at all. In this 

 case the helium was not eliminated until 

 the fourth day. In general I have found 

 that the helium disappeared long before 

 the X3 gas. Thus a piece of old lead I bom- 

 barded gave off appreciable quantities of 

 helium from the first day's bombardment, 

 very little on the second day, and none that 

 I could detect on the third or subsequent 

 days. The Xg, on the other hand, came off 

 in considerable quantities up to the end of 

 the experiment, which lasted for six days. 

 I attribute the superior elimination of X3 

 in the case of the platinum foil to the fact 

 that during the whole time the bombard- 

 ment was concentrated on a patch only 

 about 2 mm. in diameter, while the lead 

 melted under the bombardment, so that 

 fresh portions were continually being ex- 

 posed to the rays. A piece of Kahlbaum's 

 chemically pure lead gave appreciable 

 amounts of Xg and helium, though not 

 nearly so much as the old lead. I tried 

 some lead which had just been precipitated, 

 but could not detect either X3 or helium. 



In the course of the experiments with 

 old lead I let hydrogen into the experi- 

 menting chamber to see if it would increase 

 the amount of X3, but could not detect any 

 effect. On one occasion I let in oxygen 

 when nickel was bombarded, also without 

 any appreciable effect. I think these ex- 

 periments are in favor of the view that 



these gases are present in the metal inde- 

 pendently of the bombardment, and are 

 liberated by the action of the kathode rays. 

 They are surprisingly firmly held by the 

 metal, and can not, so far as my experience 

 goes, be got rid of by heating. I kept a 

 piece of lead in a quartz tube boiling in a 

 vacuum for three or fotir hours, until all 

 but a quarter of the lead had boiled away, 

 and examined the gases given off during 

 this process ; neither X3 nor helium could 

 be detected. I then took the quarter that 

 remained and bombarded it, and got appre- 

 ciable amounts of Xg and helium. On a 

 second bombardment the Xg was visible but 

 the helium had disappeared. As an in- 

 stance of the way these gases can stick to 

 metals even when in solution or chemical 

 combination, I may mention that though, 

 as I have said, platinum foil after long 

 exposure to kathode rays is freed from 

 these gases, yet I got appreciable quanti- 

 ties of Xg and helium, though no neon from 

 platinum sponge freshly prepared from 

 platinic chloride. 



The reason helium is obtained by heat- 

 ing the glass of old Rontgen-ray bulbs is, 

 I think, that after liberation by the kathode 

 rays, the helium either adheres to the sur- 

 face or is absorbed in a much looser way 

 than before it was liberated. The ques- 

 tion as to how these gases get into the 

 metals is a most interesting one; are they 

 absorbed in the process of manufacture? 

 In this connection it is interesting to note 

 that Xg does not appear to occur to any 

 appreciable extent in the atmosphere. 

 Sometimes when suffering from the diffi- 

 culty of clearing out these gases I have 

 been goaded into speculating whether they 

 do not represent the partially abortive at- 

 tempts of ordinary metals to imitate the 

 behavior of radio-active substance; but 

 whereas in these substances the a particles 

 and the like are emitted with such velocity 



