" Miracula sine doctrina nihil valent " is the principle now generally recognized.
Group III.: B, trivalent; Al, trivalent, but possibly also tetra-or penta-valent; Ga, divalent and trivalent; In, mono-, diand tri-valent; Tl, monovalent and trivalent..
Group VI.: 0, usually divalent, but tetravalent and possibly hexavalent in oxonium and other salts; S, Se, Te, di-, tetraand hexa-valent; Cr, di-, triand hexa-valent; Mo, W, di-, tri-, tetra-, pentaand hexa-valent.
The mean values of the relative coagulative powers of sulphates of mono-, di-, and tri-valent metals have been shown experimentally to be approximately in the ratios 1 :35:1023.
It gives origin to three classes of salts: M'H 2 PO 4 or M"H 4 P 2 0 8; M' 2 HPO 4 or M"HP04, M'3P04, M" 3 P 2 0 8 or M"'PO 4, wherein ll',M",M"' denote a mono-, di-, and tri-valent metal.