14 Prof. T. Carnelley on the Periodic Law. 



of the first and second groups. In some . cases, too, there 

 appear to exist relations between the melting-points of the 

 even members of these two groups different from those 

 which exist between the other groups. The compounds of the 

 elements usually placed in the odd division of the first and 

 second groups are generally altogether irregular. In the 

 case of the odd members of the first group this may be ex- 

 plained to some extent by the fact that it is very uncertain 

 whether Ag, Cu, and Au really belong to the same group as Na. 

 This was pointed out by Mendeljeff in his original memoir, 

 in which he places these metals provisionally in both the first 

 group along with Na, and in the eighth group along with 

 Fe, Pd, Pt, &c. 



II. Calculation of Melting- and Boiling-Points by 

 the Method of Limits. 



It will be readily seen that the relations referred to in the 

 foregoing pages may be made the basis of a method for cal- 

 culating (within certain limits) melting- and boiling-points 

 which have not been experimentally determined. Thus, take 

 the case of the boiling-point of AsBr 3 . Supposing we know 

 the boiling-points of As01 3 and Asl 3 , then, according to 

 Kelation 3, the boiling-point of AsBr 3 lies between those of 

 As01 3 and Asl 3 ; again, the boiling-point of AsBr 3 , according 

 to Relation 4, lies between those of PBr 3 and SbBr 3 . We 

 thus obtain a number of limits between which the boiling- 

 point of AsBr 3 must lie ; and by selecting from all of them 

 the lowest superior and the highest inferior limit, we obtain 

 two limits between which the boiling-point of AsBr 3 lies, and 

 these limits are generally very near together ; so that by pro- 

 ceeding in this way we may calculate the melting- or boiling- 

 point of a substance within a very few degrees. Thus, if 

 x — the boiling-point of AsBr 3 , then 



By 



Relation 1, 



x < 972, but > 331. 



?? 



?? 



3, 



x < 677, but > 405. 



?> 



V 



4, 



x < 549, but > 444. 



» 



V 



5, 



O-405) < 124, but > 51. 



!9 



» 



6, 



(677-*) > 59. 

 (#-405) > 45. 



» 



V 



7, 



(#-405) <(677-#). 

 (677-*) < 272. 



V 



-)•> 



8, 



(#-405) < 93, but > 53. 



>? 



V 



% 



(#-444) < 54. 



(549 -x) < 91, but > 49. 















(749 -x) < 298, but > 200. 



