Thus potash, which has the largest value among the alkalies, is the strongest, while lithia, which has the smallest value, is the weakest, and soda, which holds the middle value between potash and lithia, is weaker than potash and stronger than lithia. Baryta, lime, and strontia behave in the same way. However, chlorine, which has the smallest value, is the most powerful, and iodine, which possesses the greatest value, is the weakest in salt formation, and bromine lies between both. Hydrogen, oxygen, nitrogen, and carbon appear to stand isolated from the substances which form bases, acids, and salts. The earth metals and the earths themselves belong together, according to their similarities, but I have not yet placed them successfully.
Magnesium stands entirely alone, and zirconium belongs with titanium and tin.
The group of heavy metal alum-forming substances is fully filled. According to Mitscherlich, Fe . , Mn . , Ni . , Co . , Zn . , and Cu . are isomorphic with magnesia. This is a highly interesting series of substances, since, first, they all belong to the magnetic metals, and second, they are the best conductors of electricity. In nature, Fe, Mn, and Co occur as oxides which are frequently found together, and the oxides of Ni, Zn, and Cu, as an Englishman says, occur together in an ore from which the Chinese prepare their white copper, which the Germans call Argentan . However, the atomic weight of Cu . is 495.695, and the specific gravity of copper is not the arithmetical mean of the specific gravities of nickle and zinc, and I therefore believe that these six oxides must be grouped in another way.