NATURE 



[May 29, 19 1 3 



rjave got all the gas you can out of the solid by heat- 

 ing it, you have only to expose it to kathode rays to 

 get a fresh outburst. This effect of increased tem- 

 perature in renewing the stream of gas from the solid 

 seems to me to be too large to be accounted for merely 

 by an increase in the rate of diffusion of the absorbed 

 gas from the interior to the surface ; it seems to be 

 more analogous to the case of the emission of the 

 water of crystallisation from some salts. There are 

 some salts, for example, copper sulphate, which when 

 heated lose their water of crystallisation in stages ; 

 thus, if the temperature is raised to a certain value, 

 some of the water of crystallisation comes off, but 

 the rest remains fixed, and you may keep the salt at 

 this temperature for ever without getting rid of all 

 the water of crystallisation ; on raising the tempera- 

 ture, however, fresh water of crystallisation is given 

 off. Something of this kind seems to take place in 

 the case of gases absorbed in metals, and there seem 

 to be indications that there is some kind of chemical 

 combination between the gas and the metal. This 

 absorbed ^as mav influence the behaviour of the sub- 

 stance. For example, an ordinary carbon filament 

 skives off, when raised to a white heat, large quantities 



of negatively electrified corpuscles ; but Pring and 

 Parker 3 have shown that when great precautions are 

 taken to get rid of the absorbed gas, the emission 

 of these corpuscles falls to less than one-millionth of 

 their previous value. It is in the gases given off by 

 certain metals when they are bombarded by kathode 

 rays that I have found an unfailing source of the 

 substance, which I shall denote by X,, giying the line 

 corresponding to the atomic weight 3. The arrange- 

 ment I have used for investigating the presence of 

 this gas is shown in Fig. 4. A is a vessel communi- 

 cating with the bulb B in which the positive rays are 

 produced by two tubes, one of which is a very fine 

 capillary tube, while the other one is five or six milli- 

 metres in diameter ; taps are inserted so that one or 

 both of thes£ vessels can be closed, and the vessels 

 A and B isolated from each other. A is provided with 

 :i curved kathode such as are used for Rontgen ray 

 focus tubes, and the kathode rays focus on the plat- 

 form on which the substance to be bombarded is 

 placed. (It is not absolutely necessary to focus the 

 kathode rays in this way, but it makes the supply of 

 the gas X, more copious.) After the metal or other 

 <olid to be examined has been placed on the platform, 



3 Phil. Mag., xxiii.. p. 192. 



NO. 2274, VOL. 91] 



the taps betwun A and B being turned so as to cut 

 off the connection between them, A is exhausted until 

 the vacuum is low enough to give the kathode rays ; 

 the discharge is then sent through A, and the kathode 

 rays bombard the solid. The result of this is that in 

 a few seconds so much gas, mainly CO, and hydrogen, 

 is driven out of it that the pressure gets too high 

 for the kathode rays to' be formed, and unless some 

 precautions to lower the pressure were taken the bom- 

 bardment would stop. To avoid this, a tube contain- 

 ing charcoal cooled by liquid air is connected with A, 

 and this absorbs the CO, and enough of the hydrogen 

 to keep the vacuum in the kathode ray state. To see 

 what new gases are given off in consequence of the 

 bombardment, a photograph is taken while the con- 

 nection between A and B is cut off. After this is 

 finished, and when the bombardment has gone on for 

 about four hours, the tap is turned and a little of 

 the gas from A is allowed to go into B ; another 

 photograph is taken, and those lines in the second 

 photograph which are not in the first represent those 

 gases which are liberated by the bombardment, and 

 have escaped being absorbed by the charcoal. 

 I have here a slide (Fig. 5) representing the result of 

 bombarding nickel. There are two photographs, one 



Fir.. 5. 



(a) before turning the tap, and the other {&) after ; 

 in the second you see the 3 line very distinctly, 

 while it is absent from the first, showing that the gas 

 giving the 3 line has been liberated by the bom- 

 bardment. I have got similar results to these when, 

 instead of nickel, iron, copper, lead, and zinc have been 

 bombarded. I have tried two specimens of meteorites 

 kindly lent to me from the Mineralogical Museum, 

 Cambridge, and found there the 3 line. Nearly 

 every substance I have tried gives, the first time it is 

 bombarded, the helium line as well as this line due to 

 X, ; if, however, the same substance is bombarded a 

 second time, the helium line is in general absent (occa- 

 sionally it is still to be detected, though exceedingly 

 faint) ; and on the third bombardment is invisible in 

 all the substances I have tried except monazit sand, 

 where it is eiven off in exceedingly Ia~ge quantities 

 so lone as the bombardment continues. It is remark- 

 able that monazite sand, which contains so many 

 elements, gives no trace of the 3 line when bom- 

 barded. 



I have also obtained the X, line and also the helium 

 line when the tube A was replaced by one containing 

 a Wehnelt kathode; with this the current of kathode 

 rays through the tube was much larger than with the 

 other kathode, though the velocity of the ravs was 



