512 



Prof. T. Carnelley on the Periodic Law. 



Relation 9. (a) The differences referred to in Relation 8 

 increase algebraically as the algebraic difference between the 

 atomic weights of the hydrocarbon radicals increases. (See 

 Table VII.) 



(b) In the case where several pairs of hydrocarbon radicals 

 have a common difference in atomic weights, then the differences 

 between the boiling-points of their halogen compounds increase as 

 the sum of the atomic weights of the several pairs of hydrocarbon 

 radicals increases. This rule also holds for the alkyl compounds 

 so long as the difference between the boiling-points is a minus 

 quantity (i. e. so long as the boiling-point of the alkyl com- 

 pound of the polyvalent hydrocarbon radical is lower than 

 that of the corresponding alkyl compound of the monovalent 

 hydrocarbon radical), but when this difference becomes a plus 

 quantity the rule is reversed. (See Table VII.) 



For the purpose of illustrating the above relationships we 

 have chiefly made use of the compounds of the sixth and 

 seventh groups of hydrocarbon radicals, because the sets of 

 compounds belonging to these groups are much more complete 

 than in the case of the other groups ; the rules, however, hold 

 equally with the latter as with the former. 



The above nine rules have been applied in 1997 cases, of 

 which 71 (or 3*6 per cent.) are exceptions. The exceptions 

 are distributed as follows : — 





Halogen Compounds. 



Alkyl Compounds. 





Melting- 

 points. 



Boiling- 

 points. 



Melting- 

 points. 



Boiling- 

 points. 



No. of 

 cases. 



No. of 

 excep- 

 tions. 



No. of 



•cases. 



No. of 

 excep- 

 tions. 



No. of 

 cases. 



No. of 

 excep- 

 tions. 



No. of 

 cases. 



No. of 

 excep- 

 tions. 





20 

 20 



*8 

 1 



2 







2 

 



68 



60 



104 



35 



66 



78 



100 



103 



108 



106 



1 

 1 

 1 

 1 

 

 1 

 

 

 

 2 



5 



8 

 6 



2 









 



"6 



48 



49 



73 



26 



30 



42 



73 



102 



285 



361 



















1 



6 



7 

 14 





 32 



60 



=5-5% 



„ II 



Ill 



IV 



>> -*• T 



v 



J> T 



VI 



„ VII. a. ... 

 VII. b. ... 



VIII 



IX. a & b. 



Total 



49 



4 



=8% 



828 



7 

 =0-8% 



21 







1089 





