EXP. Dry, pulverized potassium ferrocyanide is intimately mixed with dry potassium carbonate and the mixture heated in a hard glass test tube. When the whole mass has become red-hot, insuring complete decomposition, the hot (not red-hot) tube is plunged into water; the salts are extracted and particles of metallic iron are left undissolved. The action is K_{4}Fe(CN)_{6} + K_{2}CO_{3} → 6 KCN + FeCO_{3} FeCO_{3} → FeO + CO_{2} and FeO + KCN → KCNO + Fe. If the iron is dissolved in a little dilute hydrochloric acid and oxidized to the ferric condition, by the addition of a few drops of bromine water, the intensely red solution characteristic of ferric salts may be readily obtained, when a thiocyanate is added to the solution. FOOTNOTES: [114] Loomis. (‹Cf.› Whetham, ‹Theory of Solution›, p. 320 (1902).) [115] Loomis; and E. H. Griffith. (‹Cf.› Whetham, ‹loc. cit.›) [116] Expressed in moles per liter. [117] Δ_{1} : Δ_{2}... = ‹C›_{1} : ‹C›_{2}... or Δ_{1} / ‹C›_{1} = Δ_{2} / ‹C›_{2} = a constant. [118] ‹Cf.› Whetham, ‹loc. cit.›, pp. 147, 158. [119] ‹Ibid.›, p. 320. [120] In regard to the degrees of ionization, as shown by freezing-point depressions and conductivities of salts, see also A. A. Noyes, ‹Report of the Congress of Arts and Sciences›, St. Louis, 1904, Vol. «IV», p. 313. [121] See Chapter XII, in regard to so-called "complex ions" and their salts. [122] The term "acid ion" is used to designate the "acid radical," when it exists, in solution, as an independent charged particle or ion. "Acid ion" is thus a convenient synonym for anion, just as "metal ion," designating the metal or metal-like radical of a salt, is used as a synonym for cation. The term, acid ion, has been found to convey more quickly and definitely to the student's mind, than does the term anion, which component of an acid or salt is referred to. While it is not, in some respects, an ideal term, yet its use seems justified by its very close relation to the term "acid radical" and by its practical advantages. [123] The principle was first applied by Hittorf. [124] This does not preclude the possibility that the ion is combined with more or less water and is Na(H_{2}O)_{‹x›}^{+}; see pp. 42, 65. [125] Baker, ‹J. Chem. Soc.› (London), «65», 611 (1894), «73», 422 (1898). On page 623 of the first article is given a list of chemical actions for which the effect of the presence of moisture has been investigated (‹Stud.›). [126] Hughes, ‹Phil. Mag.›, «34», 117 (1892) (‹Stud.›).