2 Prof. T. Carnelley on the Periodic Law. 



has now, however, been in great part removed ; for in several 

 previous papers (Journ. Chem. Soc. xxix. p. 493, xxxiii. 

 pp. 273 and 283*, xxxv. p. 564*, xxxvii. p. 125*) methods 

 have been proposed for determining both high melting- and 

 high boiling-points. 



I. Illustkation of the Pekiodic Law. 



The Periodic Law states : — (1) That the properties of the 

 elements are a periodic function of their atomic weights; 

 (2) that the properties of the compounds of the elements are 

 a periodic function of the atomic weights of their constituent 

 elements. 



It is this second part of the law which we shall endeavour 

 to illustrate. For this purpose we shall make use of the 

 melting- and boiling-points and heats of formation of the 

 chlorides, bromides, and iodides of the elements. The term 

 normal chloride, bromide, or iodide will be used to indicate 

 halogen compounds of the form, represented thus: — LiCl, 

 BeCl 2 , B01 3 , OOI4, NCI3, 001s, FC1, for members of Men- 

 deljeff's second series. In all the tables the symbols given to 

 still undiscovered elements are those proposed by MendeljefFin 

 his memoir on the Periodic Law {Ann. Chem. Pharm. Suppl. 

 1870-72, p. 151). In addition to the experimental values 

 given in Table I. A, melting- and boiling-points (see Table IX.), 

 calculated by a method to be presently explained, are also 

 inserted in the tables, in order that the latter may be as com- 

 plete as possible. In all cases the heat of formation given is 

 the heat evolved by the combination of one atom of 01 or its 

 equivalent. 



Now, however we may arrange the melting-points, boiling- 

 points, or heats of formation of the normal halogen compounds 

 of the elements, provided only that we arrange them systema- 

 tically, we always find that certain definite and regular relations 

 may be traced between them. Some of the more important 

 of these relations are as follows t : — 



Relation 1. If the elements be arranged in the order of 

 their atomic weights, then the melting-points, boiling-points, and 

 heats of formation of their halogen compounds rise andf all perio- 

 dically. These periods correspond exactly with the series of 

 elements in Table 1.%, the maxima occurring at the positive and 

 the minima at the negative end of each series. The exceptions 



* In conjunction with Prof. Carleton- Williams. 



t Throughout this paper all temperatures are reckoned from the absolute 

 zero (-273° C). 



X Table I. represents the natural classification of the elements according 

 to Mendeljeff's arrangement, and is g\\en here for reference. 



