July 15, 1920] 



NATURE 



619 



yj, with possibly another at 39. The lines at 

 36, 38 are due to the corresponding^ HCl's. 



Particles with two, three, or more electronic 

 charges will appear as though having half, a 

 third, etc., their real mass. The corresponding 

 lines are called lines of the second, third, or 

 higher order. In spectrum ii. the lines of doubly 

 charged chlorine atoms appear at 17-5 and 185. 

 Analyses of argon indicate that this element con- 

 sists almost entirely of atoms of weight 40, but a 

 faint component 36 is also visible. Spectra v. and 

 vi. are taken with this gas present; the former 

 shows the interesting third order line at 13^. 

 Krypton and xenon give surprisingly complex 



method (see Phil. Mag., May, 1920, p. 621), some 

 results of which are given in spectrum vii., hydro- 

 gen is found to be 1008, which agrees with the 

 value accepted by chemists. This exception from 

 the whole number rule is not unexpected, as on 

 the Rutherford " nucleus " theory the hydrogen 

 atom is the only one not containing any negative 

 electricity in its nucleus. 



The results which have so far been obtained 

 with eighteen elements make it highly probable 

 that the higher the atomic weight of an element, 

 the more complex it is likely to be, and that there 

 are more complex elements than simple. It must 

 be noticed that, though the whole number rule 



-Typical 



results ; the former is found to consist of no fewer 

 than six isotopes, the latter of five (spectra viii. 

 and ix.). Mercury is certainly a complex element 

 probably composed of five or six isotopes, two of 

 which have weights 202 and 204; its multiply 

 charged atoms give the imperfectly resolved 

 groups, which are indicated in several of the 

 spectra reproduced in Fig. 2. 



By far the most important result obtained from 

 this work is the generalisation that, with the ex- 

 ception of hydrogen, all the atomic weights of all 

 elements so far measured are exactly whole 

 numbers on the scale 0=i6 to the accuracy of 

 experiment (i in 1000). By means of a special 

 NO. 2646. VOL. 105] 



asserts that a pure element must have a whole 

 number atomic weight, there is no reason to sup- 

 pose that all elements having atomic weights closely 

 approximating to integers are therefore pure. 



The very large number of different molecules 

 possible when mixed elements unite to form com- 

 pounds would appear to make their theoretical 

 chemistry almost hopelessly complicated, but if, 

 as seems likely, the separation of isotopes on any 

 reasonable scale is to all intents impossible, their 

 practical chemistry will not be affected, while 

 the whole number rule introduces a very desir- 

 able simplification into the theoretical aspects of 

 mass. 



