496 



SCIENCE 



[N. S. Vol. XLVI. No. 1195 



of the chlorine used. They explained this 

 reaction by the following equation: 



12 NH3 + 6 CI, = Nj + NCI3 + 9 NHiCl. 

 This observation led them to study the 

 chemical properties of nitrogen trichloride. 

 They found that each chlorine atom pres- 

 ent in nitrogen trichloride was equivalent 

 to two atoms of "available chlorine," or, 

 as Seliwanow had put it, the chlorine is 

 hypochlorous in character. Noyes and 

 X/yon represented nitrogen trichloride as 

 follows : 



— -1-a 



N — +C1 

 — +C1 



and, to account for the reaction between 

 ammonia and chlorine, assumed that am- 

 monia may ionize in two ways, 



N-|-\-|-3H- 



:NH3 



: N = + 3H* 



and, furthermore, that the chlorine mole- 

 cule may ionize to give both positive and 

 negative chlorine ions. 



In the same number of the Journal of the 

 American Chemical Society, Stieglitz^^ com- 

 mented upon the work of Noyes and Lyon, 

 and put forth arguments to show that this 

 reaction, 



H,o -f a, ?:± HCi + Hoa, 



a reversible reaction, was, at the same time, 

 an ionic reaction. In other words, hjT)o- 

 chlorous acid may ionize in two ways, 

 amphoterically. 



HOCl: 

 HOCl: 



: H+ + OCl- 

 : HO- + CI+ 



The chlorine molecule, therefore, must 

 yield negative chlorine ions, CI", and, also, 

 positive chlorine ions, Cl"^. 



These deductions, expressed originally 

 by Noyes and Lyon, as well as by Stieglitz, 

 in terms of ion formation, have since been 

 translated into the language of the electron 

 theory of valence. Thus, the chlorine mole- 



11 Stieglitz, J. Am. Chem. Soo., 23, 797 (1901). 



cule may be represented electronically by 

 the symbol, CI h CI- 



The striking difference in behavior of de- 

 rivatives of positive chlorine and of nega- 

 tive chlorine may be illustrated by compar- 

 ing the two compounds, nitrogen trichlo- 

 ride and phosphorus trichloride, which, by 

 virtue of the family relationship of nitro- 

 gen and phosphorus in the periodic system, 

 and the similarity in the formulas of the 

 two chlorides, would be expected to re- 

 semble one another in chemical behavior 

 ■about as closely as any two compounds 

 could. At the same time, the illustration 

 will serve to explain the significance of the 

 Statement made in an earlier part of this 

 paper, viz., that the polar characteristics of 

 compounds may be revealed by a study of 

 their chemical interactions. 



If the electronic formulas. 



are assigned to these two substances, we ob- 

 tain formulas which, iinlike those in general 

 use, show why it is that the two compounds 

 are most dissimilar in chemical deportment ; 

 why nitrogen trichloride, when hydrolyzed, 

 gives ammonia and hypochlorous acid, 

 while phosphorus trichloride yields phos- 

 phorus acid and hydrogen chloride; why 

 the chlorine atom in nitrogen trichloride 

 possesses oxidizing properties, while the 

 chlorine in phosphorus trichloride does 

 not. The oxidizing value of a positive 

 chlorine atom corresponds to a gain of two 

 negative electrons, if a negative chlorine 

 ion is the final stage in the change. 



Cl+-» Cl- 



C1-, 



Certain other halogen compounds have 

 been found to show similar polar diifer- 

 ences. Thus, Nef^^ observed that chloro- 

 cyanogen, upon hydrolysis, gave hydrogen 

 chloride and cyanic acid, while iodocyano- 

 geu gave hypoiodous acid and prussic acid, 



i2Nef, A)m., 308, 320 (1899); iUd., 329 (1899). 



