582 



SCIENCE 



[N. S. Vol. L. No. 1304 



The atoms whose nuclei carry 28 or less 

 positive charges are much more sta)ble than 

 those of higher atomic number. This is illus- 

 trated by the relative abundance of such ele- 

 ments as represented by the following table: 



TABLE 11 



Proportion in Various Materials of the Elements 

 of Low Atomic Numbers 



Percentage of Ele- 

 ments with Atom- 

 ic Numbers 



Material 1-29 30-92 



Meteorites as a whole 99.99 0.01 



Stone meteorites 99.98 0.01 



Iron meteorites 100.00 0.0 



Igneous rocks 99.85 0.15 



Shale 99.95 0.05 



Sandstone 99.95 0.15 



Lithosphere 99.85 0.15 



When there are several varieties of atomic 

 nuclei all carrying the same positive charge, 

 as is the case with lead, with 82 positive 

 charges on the nucleus, the nuclei differ in sta- 

 bility, but the complete atoms do not differ in 

 their chemical properties nor in their spec- 

 |;rum. This has been shown very beautifully 

 by Soddy, by Merton, and by Eichards and 

 Baxter, but most accurately by Dr. Aronberg, 

 who worked at my suggestion. Two isotopes 

 may have practically the same atomic weights, 

 and differ only in the stability of their nuclei, 

 as I pointed out four years ago. 



THE BUILDING OF ATOM NUCLEI AGAIN 



Let us now pay attention to the building of 

 nuclei of even numbered charge, since the time 

 is not sufficient to consider those of odd num- 

 ber also. Three, four, five, six, seven, eight 

 or ten alpha particles may unite to form 

 the nucleus of a complex atom, but two alpha 

 particles alone, or more than ten alone, do not 

 make a stable system. 



I In all heavier atoms there are some alpha 

 particles which are bound on by two negative 

 electrons. Thus the sulphur nucleus is a com- 

 pound of 8 alpha particles alone, while the 

 argon nucleus contains 10 alpha particles and 

 two negative binding electrons. It is the pres- 

 ence of an extra alpha particle in the ai^on 



nucleus which makes its atomic weight higher 

 than that of potassium. 



The number of binding electrons does not 

 increase to 4 until element 32 (germanium) is 

 reached, but rises to 26 in the thorium atom. 

 It is these binding electrons which are given 

 off in the heta disintegrations of the radioac- 

 tive elements, and if time permitted it could 

 be shown that this disintegration is exactly in 

 accord with the system of structure proposed 

 for the nuclei of the lighter atoms. For ex- 

 ample a radioactive atom may lose five alpha 

 particles in direct succession, but never more 

 than two of the binding electrons. Further- 

 more, if it loses a single binding electron it 

 always loses a second one, but not more than 

 two, which indicates that, corresponding to our 

 theory, such binding electrons are associated 

 in pairs. 



The principal difficulty to be encountered in 

 the artificial disintegration of atoms, that is, 

 jn the disintegration of their nuclei, is that 

 of getting sufficient energy into such a small 

 volume as that of a nucleus. In the building 

 of atoms there is the additional difficulty of 

 securing the proper arrangement of the alpha 

 particles to give stability.^ 



WlLLLAM D. HaEKINS 



TJniveksitt of Chicago 



THE DISRUPTION OF ATOMS BY 

 ALPHA RAYS 



Eecently under the modest title " An 

 Anomalous Effect in Nitrogen,"^ Rutherford 

 reported the remarkable discovery that when 

 nitrogen molecules are bombarded by alpha 

 rays, penetrating rays with a range of 28 cm. 

 in air are produced which are certainly lighter 

 than nitrogen atoms and which are probably 



3 The details of the system of atom building pre- 

 sented here may be found in the following refer- 

 ences: Journal of the American Chemical Society, 

 37, 1367-1421, 1915, 38, 186-214, 1916, 39, 856-879, 

 1917; 41, 970-992, 1919. Phil. Mag., 30, 723-734, 

 1915. Science, N. S., 46, 419-427, 443-448, 1917. 

 Proc. NationaX Academy of Sciences, 1, 276, 1915; 

 2, 216-224, 1916. 



^Phil. Mag., 37, 581-87, June, 1919; cf. Sci- 

 ence, 50, 472, November 21, 1919. 



