44 Messrs. A. C. and A. E. Jessup on the 
involves the least interchange o£ electrons. An excellent 
example of this is afforded by the halogens. These elements 
form the following compounds among themselves : — IF 5 , 
IC1 3 , and IBr ; BrF 3 and Br CI. Fluorine is electronegative 
enough to make iodine give up five electrons, chlorine will 
only make it give three, and bromine can extract one only. So, 
bromine will give three to fluorine, but only one to chlorine. 
Now it has been already pointed out that if the atom is 
built up of rings of different valency, or, in other words, is 
deranged, the properties will be affected, and consequently 
the above statements as to valency will not rigidly hold in 
such cases. A typical example of this is afforded by nitrogen, 
where there is a pentad ring on a triad. Here the principal 
valency is unaltered, being five, and five only, as nitrogen 
will take up only three electrons from hydrogen to form 
NH 3 . NH and NH 2 are not known. The secondary 
valencies are, however, affected, with the result that nitrogen 
can lose either two or four electrons in NO and N0 2 . A 
similar state of affairs exists with vanadium, chromium, and 
manganese, where both even and odd valencies are. found. 
The next thing is to consider the valency of the elements 
normally derived from the above. It would naturally be 
supposed that, as these elements add on rings of the same 
valency as the outer one of the elements from which they are 
derived, their structure would tend to become more regular, 
and this is found to be so with nitrogen, oxygen, and fluorine 
derivatives. We should expect this influence to be best 
evidenced in the cases of antimony, tellurium, and iodine; 
and it is undoubtedly shown by the compounds of these three 
elements, Sb 2 3 , Sb 2 5 ; TeO, Te0 2 , TeO s ; IBr, IC1 3 , I 2 5 , and 
I 2 7 (in compounds). Here, antimony exerts the secondary 
valencies of 3 and 5, tellurium of 2, 4, and 6, and iodine of 1, 
3, 5, and 7, so that they have become perfectly normal. The 
intermediate elements are in a state of transition so to speak, 
and therefore nothing can be definitely argued from them. 
In vanadium and chromium derivatives, however, there is 
practically a double derangement, since in the first place 
carbon is deranged (tetrad on triad), and then either a penta- 
or hexavalent ring is added to the tetravalent ring of silicon. 
The result is that these elements do possess even and odd 
valencies ; for example, molybdenum forms MoCl 2 , MoCl 3 , 
MoCl 4 , M0CI5, and probably MoCl 6 . 
In the series carbon, silicon, titanium, zirconium, there is 
only one derangement, and consequently, only even valencies 
are found. 
Before concluding this section of our paper, it might be as 
well to make a few remarks on the rare earth elements. It 
