[376] See the equations for KBase and KAcid, on p. [184], and their premises.

[377] See p. [172]. The concentration of water may be considered a constant and is included in KAcid (and KBase, below).

[378] Only the primary ionization (of aluminium hydroxide) is considered in the text, because only that is involved, as a rule, in the neutralization of very weak bases by very weak acids (see footnote 2, p. [194]). The relations are also simpler and clearer, if we limit the discussion to the formation of a salt AlO(AlO2).

[379] See the similar equation, p. [185].

[380] Amphoteric substances of a different class are also known, which have, at the same time, moderately strong acid and moderately strong basic functions. Glycocoll, H2N.CH2COOH, a derivative of acetic acid and ammonia, contains an acid group, the —COOH group, the hydrogen of which is approximately as ionizable as the hydrogen in the corresponding group in acetic acid, CH3COOH. The ammonia residue, H2N—, in glycocoll, forms with water a hydroxide, corresponding to ammonium hydroxide, which likewise is approximately as ionizable as is ammonium hydroxide. In the hydroxide of glycocoll we have, consequently, both a moderately strong acid, and a moderately strong basic, group. In this, and in similar cases, salt formation between the acid and the basic groups of the amphoters takes place to as great an extent as if the functions were attributes of distinct compounds. Glycocoll in aqueous solution is present, then, chiefly in the form of a salt, for instance,

H3N.CH2.COO
└───────┘

[381] The carbonates are occasionally partially hydrolyzed to basic carbonates.

[382] Stokes, J. Am. Chem. Soc., 29, 304 (1907).

[383] A complication, which leads to the precipitation of alkaline earths, along with these groups, as phosphates and similar insoluble salts (not as hydroxides or sulphides), when phosphate or certain other acid ions are present, is treated in Part IV (q.v.) under the systematic analysis of the groups.

[384] Cf. Fresenius, Quantitative Analysis.