334 



NATURE 



[May 29, 19 1 3 



same path they branch off into different directions. 

 No two particles will travel along the same path unless 

 they have the same mass as well as the same velocity ; 

 so that if we know the path of the particle we can 

 determine both its mass and its velocity. In chemical 

 analyses we are concerned more with the mass than 

 with the velocity, and we naturally ask what is the 

 connection between the paths of particles which have 

 the same mass but move with different veloci- 

 ties. The anssver is that all such paths lie on the 

 surface of a cone, and that each kind of particle has 

 its own cone ; there is one cone for hydrogen, another 

 for oxygen, and so on. Thus one cone is sacred to 

 hydrogen, and if it exists there must be hydrogen 

 in the vessel ; so that if we can detect the different 

 cones produced from the original pencil, we know 

 at once the gases that are in the tube. Now, there 

 are several ways of identifying these cones, but I 

 shall only refer to the one I have used in the experi- 

 ments I wish to bring before you this evening. These 

 moving electrified particles, when they strike against 

 a photographic plate, make an impression on the 

 plate, and a record of the place where they struck 



the plate can be obtained. Thus, when a plate is 

 placed in the way of the particles streaming along 

 these cones, the sections of these cones by the plate 

 (parabolas) are recorded on the photograph, hence we 

 can identify these cones by the parabolic curves 

 recorded on the photograph, and these parabolas will 

 tell us what gases are in the vessel. 



The first application of the method which I shall 

 bring before you this evening is to detect the rare 

 gases in the atmosphere. Sir James Dewar 

 kindlv supplied me with two samples of gases obtained 

 from the residues of liquid air; the samples had been 

 treated so that one might be expected to contain the 

 heavier gases, the other the lighter ones. I will take 

 the heavier gases first. The photograph of these is 

 shown in Fig. 2. When the plate is measured up it 

 shows a faint line corresponding to the atomic weight 

 12S (xenon), a very strong line corresponding to the 

 atomic weight S2 (krypton), a strong argon line 40 

 (argon), and the ne"on line 20. There are ^ no lines 

 unaccounted for, and hence we may conclude that in 

 the atmosphere there are no unknown gases of large 



XO. 2274, VOL. 91] 



atomic weight occurring in quantities comparable with 

 those of xenon or krypton. This result gives an 

 example of the convenience of the method, for a 

 single photograph of the positive rays reveals at a 

 glance the gases in the tube. I now turn to the 

 photograph "of the lighter constituents shown in 

 Fig. 3 ; here we find the lines of helium, of neoft 

 (very strong), of argon, and, in addition, there is a 

 line corresponding to an atomic weight 22, which 

 cannot be identified with the line due to any known 

 gas. I thought at first that this line, since its atomic 

 weight is one-half that of CO,, must be due to a 

 carbonic acid molecule with a double charge of elec- 

 tricity, and on some of the plates a faint line .it 44 

 could be detected. On passing the gas slowly through 

 tubes immersed in liquid air the line at 44 completely 

 disanoeared, while the brightness of the one .it 22 

 was not affected. 



The origin of this line presents many points of 

 interest; there are no known gaseous compounds of 

 any of the recognised elements which have this mole- 

 cular weight. Again, if we accept Mendeleefs 

 periodic law, there is no room for a new element 



with this atomic weight. The fact that this line is 

 bright in the sample when the neon line is extra- 

 ordinarily bright, and invisible in the other when 

 the neon is comparatively feeble, suggests that it 

 may possibly be a compound of neon and hydrogen, 

 NeH,, though no direct evidence of the combination 

 of these inert gases has hitherto been found. I have 

 two photographs of the discharge through helium in 

 which there is a strong line, 6, which could be ex- 

 plained by the compound HeH,, but, as I have never 

 again been able to get these lines, I do not .wish to 

 lay much stress on this point. There is, however, the 

 possibility that we may be interpreting Mendeleefs 

 law too rigidly, and that in the neighbourhood of 

 the atomic weight of neon there may be a group of 

 two or more elements with similar properties, just 

 as in another part of the table we have the group 

 iron, nickel, and cobalt. From the relative intensities 

 of the 22 line and the neon line we may conclude 

 that the quantity of the gas giving the 22 line is only 

 a small fraction of the quantitv of neon. 



Let me direct your attention again to the photo- 



