178 



SCIENCE 



[N. S. Vol. XLIX. No. 1260 



but the tension which, results renders the com- 

 pound less stable. 



He explained in this manner the extreme 

 instability of acetylene compounds and the 

 ease with which additions are made to double 

 unions; also, the instability of rings of three 

 carbon atoms in comparison with those of 

 four or five atoms. This so-called "tension 

 theory" has been very suggestive and useful. 

 An interesting confirmation of the ease with 

 which rings containing six atoms are formed 

 and evidence that rings containing seven 

 atoms are not so natural was discovered, al- 

 most by accident, by Mr. Potter and myself 

 a few years ago. Aminocamphonanic acid, 

 usually written, 



/CO2H 



C8Hu< 



is a compound in which the carboxyl and 

 amino groups are separated by three carbon 

 atoms. It is derived from c^-camphoric acid, 

 /COiH 



CsHh/ 



\CO2H 



and we should expect it to have a right handed 

 rotation for polarized light. Both the free 

 acid and its anhydride. 



<l 



are, however, left-handed in rotation. The 



anhydride of its homologue, a-aminocampholic 



acid, 



/CO. 

 CsHuC >NH, 



is also a Isevo compound. 



The hydrochloride of aminocamphonanic 

 acid, 



/CO2H 



C8Hh< 



^NHaCl 



has the right-handed rotation which would 

 be expected of the free acid. If we add to 

 a solution of the hydrochloride one mol of 

 sodium hydroxide, liberating the free acid, the 

 rotation of the solution changes, from right- 

 handed to left-handed. The addition of a 



second mol of sodium hydroxide, forming the 

 sodium salt, 



/COzNa 

 aHn< 



again causes a right-handed rotation in the 

 solution. Similar relations were found for a 

 number of allied compounds. The only sim- 

 ple ex-planation which is apparent is that the 

 free acid has the cyclic structure. 



The homologue, 



/CO. 



C8Hl4< >0. 



^nh/ 



CsHi.,: 



/' 



^CH2NH2 



on the other hand, is a dextro compound and 

 both its hydrochloride and its sodium salt are 

 right-handed, indicating that the free acid, 

 which would require the formation of a ring 

 of seven atoms to form a cyclic salt, does not 

 form such a salt. 



These relations seem to establish, also, the 

 quadrivalenee of nitrogen in ammonium salts. 

 It seems impossible to reconcile this with 

 Werner's idea that the fourth hydrogen of the 

 ammonium group remains combined with the 

 acid radical in such salts. 



In 1899 Thiele proposed his theory of par- 

 tial valences to account for the addition of 

 bromine, hydrogen, or two other atoms or 

 groups to the end carbon atoms in conju- 

 gated double unions, which have the structure 

 >C=CH— CH=C<. The compound formed 

 has the structure >CX — CH= CH — CX<. 

 This relation always reminds me of two bar 

 magnets in which the north pole of one is in 

 contact with the south pole of the other 

 I JV S\ N S\ . At the center of such a system 

 no attraction will be exerted but the free ends 

 will exert their usual attraction. While this 

 is an analogy rather than an explanation, and 

 is also rather closely related to Thiele's idea, 

 it seems to me better than that which he has 

 expressed. If we attach any definite meaning 

 of localized attraction to the term valence it 

 is difficult to conceive of the valence as being 

 divided, as seems to be implied in the term, 

 " partial valence." 



