40 Messrs. A. C. and A. E. Jessup on the 
elements set forth in our Table. A most interesting point 
arises in connexion with the potentials of those elements 
which arise from manganese. We have shown above that the 
element manganese first gives rise to iron, nickel, and cobalt, 
whose outer rings theoretically are octovalent. This is 
accompanied by a considerable fall in the value of the 
potentials. This is a perfectly natural sequence, because it is 
quite evident that elements possessing this type of octovalent 
ring should show considerably decreased affinity, or, in other 
words, that their electro-potentials should be small. 
Now we pointed out that tbis octovalent ring must not be 
looked upon as being completely established in the case of 
iron, nickel, and cobalt, and that it becomes more established 
as the normal evolution proceeds through ruthenium &c, to 
osmium &c. This establishment of the octovalent character 
is naturally accompanied by a still further fall in value of 
the potential. When the recovery occurs from iron, nickel, 
and cobalt, to copper, the value of the potential falls to a 
minimum and then rises again to copper, and a still further 
rise occurs when the evolution proceeds to zinc, and again to 
gallium. A similar rise in the potential takes place when 
the recovery passes from ruthenium, rhodium, and palladium 
through silver and cadmium to indium, and again from 
osmium, iridium and platinum, gold, and mercury, to 
thallium. 
It will be noticed that the recovery from ruthenium, 
rhodium, and palladium is steeper than the recovery from 
iron, nickel, and cobalt, and further, that the recovery from 
osmium, iridium, and platinum is even steeper still. The 
result is that the three recovery curves cross one another 
after passing through gallium, indium, and thallium before 
they arrive at lead, tin, and germanium. At first sight it 
might be expected that the three elements germanium, lead, 
and tin should have a higher value of potential than gallium, 
indium, and thallium respectively; but it must be remembered 
that the three former elements are tetravalent, that is to say, 
the tendency of the four electrons to enter into combination 
is distinctly less than in the case of the gallium, indium, and 
thallium triads. The values of the electric potentials there- 
fore of lead, tin, and germanium should be less than those of 
gallium, indium, and thallium. 
We may point out that this accounts for the fact that the 
electric potentials of the three groups, copper, silver and 
gold, zinc, cadmium and mercury, gallium, indium and 
thallium are inverted. It is for this very reason that we 
do not consider these three groups to consist of normally 
developed elements, that silver and gold, for example, are 
