1 6 Lapworth, Latent Polarities of Atoms 



by sulphuric acid is shown in (i), Fig. 3 ; any process of 



+ + 



normal substitution of H in this phase by SO a H must give 

 rise to the rae£a-sulphonic acid. Formula (ii), Fig. 3, repre- 

 sents a hypothetical stage in the intermediate compound 

 which, by breaking down in the manner indicated, gives 

 nitrobenzenera<?£asulphonic acid and water. Attention may 

 be drawn to a figure which was developed by the writer in 

 1898 (Trans. Chem. Soc, 1898, 73, 456) in order to account 

 for meta-substitution in nitrobenzene ; the older figure is in all 

 essentials wholly consistent with the one given above. In (ii), 

 Fig. 3, the identity of the intermediate stages involved in 

 direct sulphonation in the nucleus and in migration of the 

 SO3H from a hypothetical position on the O atom of the 

 nitro-group to the m<?ta-position, is most clearlv suggested ,* 

 with the introduction of the conception of partial valencies, 

 however, the need of representing the msta-carbon atom as 

 strictly doubly bound at any stage to each of two others as in the 

 earlier explanation no longer exists. 



In the preceding pages the writer has endeavoured to 

 demonstrate the generality of the principle of alternate 

 latent polarities as set by a " key atom." He has made no 

 attempt to account for the principle, which at least is certainly 

 not a consequence of Thomson's theory of the bond, but is 

 possibly a mathematically necessary corollary of the mechan- 

 ism of chemical change as regulated by the requirements of 

 constant valency. For the present he is content (1) to have 

 demonstrated that the generality of the principle is indepen- 

 dent of hypothetical considerations, and (2) to have indicated 

 a number of applications of the principle which may prove 

 fruitful in suggesting new lines of investigation. 



In taking the present opportunity of outlining his views 

 on the questions of latent polarities and mechanism of reaction, 

 the writer is conscious that these views have to a large extent 

 been built up by the selection from many sources of ideas 

 which appeared to be helpful in developing the generalisations 

 to which he drew attention in 1898 (loc. cit.) and 1901 (Trans. 

 Chem. Soc, 1901, 79, 1265 et seq.). Thiele's views have since 

 virtually determined the lines of development of the valency 

 aspects of organic chemical theorv, but the writer has also 

 been greatly influenced from time to time bv the work of 

 Hantzsch and Flurscheim, and of late bv those especially of 

 Briggs and of Robinson, to each of whom acknowledgments 

 are due. 



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