November 23, 1917] 



SCIENCE 



495 



atom at which attachment to correspond- 

 ing points on other atoms may occur. 

 Polar number is the number of negative 

 electrons which an atom has lost (in an 

 algebraic sense). 



The evidence of, perhaps, indeed, the cause of the 

 mobility of polar compounds is the freedom of one 

 especially important atom, the atom of electricity, 

 or the electron, to move from one position to 

 another. 



From a study of the reactions of chem- 

 ical compounds, and in particular of or- 

 ganic compounds, it seems doubtful whether 

 the classification into polar and non-polar 

 based upon phj^sical values, such as the 

 dielectric constants' of compounds in the 

 gaseous state, is of any more significance 

 than the terms electrolyte and nonelectro- 

 lyte were to the older supporters of the 

 theory of Arrhenius. In time, it came to 

 be known that it was no easy matter to 

 draw the dividing line between these two 

 classes, and that one class seemed to merge 

 imperceptibly into the other. So, with polar 

 and non-polar compounds, it seems theo- 

 retically probable that there is no per- 

 fectly non-polar compound, unless it be a 

 molecule composed of two like univalent 

 atoms, such as hydrogen;* and that other 



7 Stark (' ' Die Elektrizitiit im Chemischen Atom, ' ' 

 p. 29) says: "Between the properties 'dielectric' 

 and 'conducting' there is a connection. In a di- 

 electric medium, since there are positive and neg- 

 ative 'Quanten' bound to one another, it follows 

 that the medium may become conducting when, 

 through proper application of energy from without, 

 the 'Quanten' pairs become partially dissociated, 

 or ionized; that is, into freely moving positive and 

 negative 'Quanten.' Conversely, the ions of a 

 conducting medium by mutual union to form 

 ' Quanten ' pairs may make the medium dielectric ; 

 and in general a material medium is at the same 

 time dielectric and conducting, so that by as- 

 signing a dielectric constant and a specific con- 

 ductivity, the medium is characterized for a finite 

 electric field and a finite electrical current. ' ' 



8 Bohr concludes that the hydrogen molecule 

 consists of two hydrogen nuclei (at a distance 

 apart of 0.60 x lO-s cm.), and two electrons which 



compounds are polar in varying degrees, 

 depending upon the mutual attractions be- 

 tween valence electrons and the positive 

 surfaces or cores of the atoms combined, 

 and upon the distances to which these elec- 

 trons, in forming such compounds, are de- 

 flected from their normal positions rela- 

 tive to the positive areas of the uncombined 

 atoms themselves. 



Even before the electron theory had been 

 proposed, an application of the theory of 

 ion formation and charges upon ions led 

 to 1 he recognition of polar characteristics 

 in compounds not known to be ionogens. 



In a study of chloroamines, RNHCl and 

 RjNCl, Seliwanow'' observed that, during 

 hydrolyses, the chlorine in these compounds 

 was replaced by hydrogen ; and that they 

 interacted with hydrogen iodide with the 

 liberation of two equivalents of iodine for 

 each equivalent of combined chlorine, 



E,Na -f 2 HI = E,NH -f HCl -1- I,. 



Usually, during hydrolysis, combined 

 chlorine in organic compounds is exchanged 

 for hydroxyl and has no tendency to lib- 

 erate iodine from hydriodic acid. Seliwa- 

 now ascribed this peculiar behavior of the 

 chlorine atom in chloroamines to the fact 

 that, even in combination, it existed as 

 " hypochlorous chlorine." He pointed out 

 that the chlorine atoms in nitrogen tri- 

 chloride, NCI3, also showed the same pe- 

 culiar behavior. 



In 1901, Noyes and Lyon,^" in perform- 

 ing Hofmann's well-known lecture experi- 

 ment for demonstrating the composition of 

 ammonia, observed that, under certain 

 favorable conditions, the amount of ni- 

 trogen liberated as free nitrogen was about 

 one sixth, instead of one third, the volume 



revolve in an orbit in a plane perpendicular to the 

 line joining the nuclei. 



Seliwanow, Ber., 25, 3612 (1892). 



10 W. A. Noyes, A. C. Lyon, J. Am. Chem. Soc, 

 23, 460 (1901). 



