196 Prof. T. Carnelley on the Periodic Law, 



now so well known that any further remarks as to its arrange- 

 ment are not required in the present place, except to say that 

 in what follows it will be necessary to bear in mind three facts 

 in connexion with the table, and which were noticed by Men- 

 deljeff in his original paper on the Periodic Law : — 



§ 4. (a) That though all the elements in each group are 

 nearly related to one another, yet those elements belonging to 

 even series are much more nearly related to one another than 

 to those of odd series, whilst those belonging to odd series are 

 much more nearly related to one another than to those of even 

 series. 



This fact is proved by many chemical relationships which 

 will at once suggest themselves ; for instance, elements be- 

 longing to even series never, or only rarely, unite with organic 

 radicals to form methides, ethides, &c, whereas elements of 

 odd series do so readily. Whilst as regards physical proper- 

 ties I have shown (Deut. chem. Ges. Ber. xii. p. 1958) that, as 

 a rule, elements belonging to even series are paramagnetic, 

 whereas those belonging to odd series are diamagnetic. 



In the table, elements of even series are printed in ordinary 

 type and those of odd series in thick type. 



§ 5. (b) In the case of elements of the second series from 

 carbon to fluorine, and of the third series from sodium to 

 silicon inclusive, the rule stated under (a) is frequently re- 

 versed. This fact is rendered evident by an inspection of 

 Lothar Meyer's curve of the elements {Mod. Theor. Chem.), 

 in which it is seen that when the curve reaches carbon it rises 

 until it comes to sodium, instead of continuing to fall, and 

 thence from sodium to silicon it falls instead of rises. Hence 

 the curve is exceptional at this part of its course. The ex- 

 ceptional or reversed character of the curve at this point 

 represents exactly what occurs with many of the other pro- 

 perties of the elements lying within the boundaries indicated 

 above. 



§ 6. (c) Elements belonging to Group VIII. are in many 

 respects peculiar, due no doubt to their forming the connecting- 

 link between even series on the one hand and odd series on 

 the other ; so that in some cases (as in ' their magnetic pro- 

 perties) they resemble the even series, whilst in others (as in 

 the ease with which they are reduced to the metallic state) 

 they resemble the odd series. 



It is therefore somewhat uncertain whether the elements of 

 this group should be placed at the end of the even series or at 

 the beginning of the odd series. This uncertainty, however, 

 does not arise in the case of Meyer's curve ; for the position 

 of these elements on the curve makes it quite evident that they 



