"Here, for the first time, we find ourselves a little at issue with the accepted system of chemistry. Fluorine stands at the head of a group—called the inter-periodic—whereof the remaining members are (see Crookes' table, p. 28), manganese, iron, cobalt, nickel; ruthenium, rhodium, palladium; osmium, iridium, platinum. If we take all these as group V, we find that fluorine and manganese are violently forced into company with which they have hardly any points of relationship, and that they intrude into an otherwise very harmonious group of closely similar composition. (Chapter III. The Later Researches, Part V.—The Bars Groups)"