Prof. T. Carnelley on the Periodic Laic. 513 



Of the above 71 exceptions no less than 



45 are due to the b.p. of propane, C 3 H 8 , being too high. 



5 „ „ isobutane, CHMe 3 , being too low. 



2 „ m.p. of carbon tetrabromide, CBr 4 , being 



— too high. 



52 



So that 52 of the 71 exceptions would be accounted for by- 

 errors in the boiling-points of two of the above compounds, 

 and in the melting-point of the last one. As regards propane 

 there is certainly a considerable error in its boiling-point, or 

 rather in the number which has been assumed as the boiling- 

 point in our investigations ; for its actual boiling-point has 

 not been determined, the value used being in fact the mean 

 temperature of condensation, viz. —25° to —30° (cf. footnote 

 to Table V.). With respect to isobutane, the boiling-point em- 

 ployed was that ( — 17°) given by Butlerow( Annalen, cxliv. 10). 

 Konovaloff states that it boils below —10° (Bull. Soc. Chim. 

 (2) xxxiv. 333). Finally, carbon tetrabromide is not only an 

 exception to some of the relations noted above, but it was also 

 shown, in my paper on the Halogen Compounds of the Ele- 

 ments, that, owing to its abnormally high melting-point, it was 

 the most marked exception to some of the rules there stated. 



In conclusion it will be seen, by a comparison of this and 

 my previous papers, that the above nine relationships, together 

 with others of less importance, hold good for the following 

 four classes of compounds : — 



(1) The Halogen compounds of the Elements (i. e. of ele- 

 ments with elements). 



(2) The Alkyl compounds of the Elements (i. e. of elements 

 with hydrocarbon radicals). 



(3) The Halogen compounds of the Hydrocarbon Radicals 

 (u e. of elements with hydrocarbon radicals). 



(4) The Alkyl compounds of the Hydrocarbon Radicals (?'. e. 

 of hydrocarbon radicals with hydrocarbon radicals). 



Though the periodicity of Relation 1 holds for all the four 

 classes of compounds, yet the nature of the periodicity is not 

 exactly the same throughout for the compounds of the hydro- 

 carbon radicals as for those of the elements. 



We are therefore justified in concluding that, with the ex- 

 ception just stated, the physical properties of the compounds 

 of the hydrocarbon radicals (so far as investigated) follow the 

 same rules and exhibit exactly the same relationships as the 

 Corresponding compounds of the elements. 



In my next paper I hope to indicate the theoretical signi- 

 ficance of this general fact. 



