36 Messrs. A. 0. and A. E. Jessup on the 
respectively, yet these valencies are not usually exerted, the 
salts o£ these metals being due to the existence of secondary 
valencies of some form or other ; in fact, the principal 
valencies are hardly exerted at all, consequently the direct 
derivatives in the process of evolution from these elements 
should be produced in much smaller quantities than in the 
case of the typically pentavalent, hexavalent, and heptavalent 
elements, nitrogen, oxygen, and fluorine. If we take the 
case of the elements vanadium and chromium, it will be seen 
that their direct derivatives which are placed under them in 
our Periodic Table occur much less frequently upon the earth 
than the two elements themselves. 
In the case of manganese, we have a heptavalent element, 
which is the last possible indirect derivative of silicon, and 
we might point out that the heptavalency of this element is 
only exerted in the case of the heptoxide, which itself is only 
known in combination. Conversely we can argue that the 
tendency of the seven electrons of manganese to complete 
their system of eight is extraordinarily small. So small is 
this tendency that manganese is incapable of giving rise to 
any direct derivatives, that is to say, it has not the capability 
of adding on a complete ring and producing a heptavalent 
element more electro-positive than itself. Now the evolution 
process when it has arrived as far as the element manganese 
cannot stop, for manganese is a perfectly stable element, 
showing no sign of radio-activity, and consequently we must 
assume that the evolution process can and does proceed 
further. On the other hand, manganese cannot give rise to 
any indirect products of evolution such as we have described 
above, for when an indirect process of evolution takes place,, 
an outer ring is produced with the transference of electrons 
numbering one less than those transferred in the direct process 
of evolution; inasmuch as the direct process of evolution from 
manganese would require the transference of one electron only, 
it is clearly impossible for a truly indirect evolution to take 
place, because this would mean the transference of no electron. 
The oxides and halogen derivatives of manganese show, as 
before stated, that this element nearly always acts by secondary 
valencies and very rarely by its principal valency. We 
should therefore expect that any evolution derivatives of 
manganese should be peculiar and quite different from any 
which have previously occurred. The only thing that man- 
ganese can do is to add on very small quantities of matter, 
and give rise to substances with quite abnormal rings. 
Theoretically these rings should have a maximum valency of 
eight, that is to say, rings which could give rise to tetroxides 
