O. Kröhnke ("Wochensch. Brauerei," XVII. 233) gives the following equations:
Fe + 2CO_{ 2} + H_{ 2}O = Fe(HCO_{ 3})_{ 2} + H_{ 2}. 2Fe(HCO_{ 3})_{ 2} + O + H_{ 2}O = 2Fe(OH)_{ 2} + 4CO_{ 2}.
Comp. also Dammer, "Handbuch der anorg. Chem.," Vols. III. and IV. (supplement).
Considerable attention has also been directed to the influence of bacteria upon iron. Thus the growth of Crenothrix may cause much trouble in waterworks, vide "Centralblatt für Bakterien und Parasitenkunde," II. 12, 681. A variety, Chlamydothrix (Gallionella) ferruginea (Mig.) appears to play an important part in the formation of rust (comp. Zopf, "Crenothrix polyspora die Ursache der Berliner Wasser-Calamität," Berlin, 1879. De Vries, "Unter. der Crenothrix Commission," Rotterdam, 1887 and 1890).
Neufeld ("Chem. Centralblatt," 1904, I. 1621--abstracted from "Zeitschrift für Untersuchung der Nährungs- und Genussmittel," VII. 478) gives particulars of three varieties: Crenothrix polyspora, which separates iron; Cr. ochracea, which separates aluminium and some iron; and Cr. manganifera, which separates manganese.
Jackson ("Journal of Society of Chemical Industry," 1902, p. 681) gives micro-photographs of these varieties. Microscopically the masses of Crenothrix are seen enclosed in a gelatinous sheath, in which is imbedded the precipitated metallic hydrate. It is anaërobic and its action is favoured by absence of light. In the absence of dissolved oxygen, the bacillus appears to take its iron from the pipes. Cr. polyspora is found however ("Zeitschrift für analytische Chemie," XLII. 590) to separate the iron not from the ferrous carbonate (FeCO_{ 3}) but from iron organically combined. See also Winogradsky, Ueber Eisenbakterien, "Bot. Zeit.," 1888, and "Chem. Centralbl." 1904, II. 1332. Transl.]
[17] Wagner in Dingler's "Polyt. Journal," CCXVIII. p. 70. Axel Krefting in the above-quoted "Forhandlinger," p. 4.
[18] Olshausen often noticed on freshly excavated antiquities of various kinds a peculiar smell of resin or gum, especially after treatment with hydrochloric acid ("Verhandl. d. Berl. anthropol. Ges.," 1884, p. 520). It may be supposed that this odour is due to the traces of hydrocarbons present.
[19] Termed by E. Friedel "Dunstperlen." "Eintheilungsplan d. Märk. Prov.-Museums," p. 9.