February 21, 1919] 



SCIENCE 



179 



Werner in discussing this point, and also in 

 discussing the Walden inversion and other 

 topics, rejects the idea of localized attraction 

 and prefers the notion of a general attraction 

 of the atom as a whole. But a general at- 

 traction seems hard to reconcile with the fact 

 that it is never satisfied by more or less than 

 foiu: univalent atoms or groups. 



In 1887 Arrhenius proposed his theory of 

 electrolytic dissociation, or, as it is better 

 called, of ionization. The attention of chem- 

 ists was once more directed to the intimate 

 relation between electrical forces and chemical 

 affinity'. About ten years later J. J. Thom- 

 son demonstrated the existence of electrons as 

 definite units of n^ative electricity having a 

 mass eighteen hundred times smaller than 

 that of the hydrogen atom. Almost at the 

 same time the first discoveries of radioactive 

 elements were made and as these were devel- 

 oped Rutherford brought out his theory of the 

 disintegration of atoms. It soon became evi- 

 dent that atoms are not homogeneous, indi- 

 visible particles, as had been more or less 

 tacitly supposed but that they must be com- 

 plex aggregates of electrons and much more 

 dense material with a positive charge. J. J. 

 Thomson made an attempt to account for 

 the properties of atoms by supposing a uni- 

 form positive sphere into which electrons 

 found their way and distributed themselves 

 in accordance with their attraction for the 

 positive matter and their repulsion for each 

 other. In contrast with this Bohr, Ivuther- 

 ford and others have assumed a very dense 

 central nucleus, with a positive charge, about 

 which electrons are in very rapid rotation. 

 Experimental evidence based especially on the 

 scattering of helium atoms which are shot 

 through a thin film of gold or other metals 

 has given very positive evidence in favor of 

 atoms with a central nucleus. Some progress 

 has been made in the discussion of the rela- 

 tion between the spectra of some of the ele- 

 ments and the revolving electrons of their 

 atoms. 



While physicists have been busy with stud- 

 ies of radioactivity and have reached some 

 rather positive conclusions about atoms, which 



are certainly dynamic, rather than static, 

 chemists have been busy with the applications 

 of tlie new electro-chemistry in its relation to 

 the electron theory. It is evident that in 

 ionization a positive univalent ion has lost 

 an electron and a negative ion has gained one. 

 Chemists have usually been very reticent 

 about the fate of these electrons when ions 

 unite but it seems rather certain that some 

 atoms still retain their position or negative 

 character in their compounds. This was first 

 definitely pointed out for nitrogen trichloride, 

 in which the chlorine is positive, as contrasted 

 with nitrosyl chloride, NOCl, in which it is 

 clearly negative. 



The evidence for the existence of positive 

 chlorine in nitrogen trichloride and of nega- 

 tive chlorine in nitrosyl chloride is usually 

 stated to be that the trichloride hydrolyzes to 

 ammonia and hypochloroua acid while nitrosyl 

 chloride hydrolyzes to nitrous acid and hydro- 

 chloric acid. Recent experiments, not yet 

 published, have shown that dry ammonia and 

 chlorine react witli the formation of the 

 trichloride and also that a dry solution of the 

 trichloride reacts with dry hydrochloric acid 

 to form anunonium chloride and chlorine. 

 These facts seem to prove that the trichloride 

 is formed by the addition of chlorine to am- 

 monia, forming chloroammonium chloride, 

 NII3CI+CI-, followed by the splitting off of 

 hydrochloric acid, and a repetition of the 

 process till all of the hydrogen is gone. On 

 the other hand, the decomposition of the 

 trichloride by hydrochloric acid is caused by 

 the addition of the acid, giving trichloroam- 

 monium chloride, NCUH^Cl", followed by the 

 splitting off of a positive and a negative atom 

 of chlorine, as free chlorine. Under suitable 

 conditions the.se reactions may be practically 

 quantitative in either direction. 



The close analogy between these reactions 

 and those which take place in the substitution 

 of chlorine for hydrogen in methane or in 

 benzene is very striking and recalls ilichael's 

 theory that addition compounds are at first 

 formed in such cases. The idea which is 

 partly new is that such additions are always 

 of two atoms or groups, one of which is 



