[389] The comparative stability of this basic salt represents an instance of the different ionizing power, or basic strength, of the three hydroxide groups of a trivalent base (see p. 106). The hydrolysis of ferric chloride seems to involve, primarily, only the third or least ionizable of the hydroxide groups of ferric hydroxide, and the hydrolysis, except in extreme dilution, proceeds chiefly according to Fe^{3+} + 3 Cl^{−} + HOH ⇄ Fe(OH)^{2+} + 3 Cl^{−} + H^{+}. ‹Vide› Goodwin, ‹Z. phys. Chem.›, «21», 1 (1896). In the case of the salt of the much weaker acid, carbonic acid, the hydrolysis goes further, involving two hydroxide groups of ferric hydroxide and, to some extent, all three. [390] The extreme insolubility of Al(OH)_{3}, Fe(OH)_{3} and Cr(OH)_{3}, together with their weakness as bases, facilitates their precipitation (see pp. 185–6). [391] There is a ‹small degree of hydrolysis› (see footnote, p. 189), but the hydroxides of the zinc group are not sufficiently insoluble to be precipitated under these conditions. [392] ‹Cf.› A. A. Noyes, Bray and Spear, ‹J. Am. Chem. Soc.›, «30», 496 (1908). [393] ‹Cf. The Elements of the Differential and Integral Calculus›, based on Nernst and Schönflies's ‹Lehrbuch, etc.›, by Young and Linebarger, pp. 363 and 364 (1900). [394] Losses due to the tendency of aluminium hydroxide to assume the colloidal condition (p. 136) must be guarded against by other precautions (‹loc. cit.›). [p199] CHAPTER XI «THE COPPER AND SILVER GROUPS. PRECIPITATION WITH HYDROGEN SULPHIDE»