SOILS — FERTILIZERS. 7l9 



Investigations on the solution and precipitation of iron in the formation of 

 iron pan or ortsteiu are reported. The occurrence of iron pan is described and 

 several theories on the subject are briefly reviewed, the authors sigreeing with 

 the theory of INIiins « that the formation of iron pan is due to the formation of 

 colloidal humus compounds of iron and aluminum which are precipitated in the 

 soil depths by soluble salts, loss of water, or by change of bases. 



Experiments mainly concerned with investigations of the properties of vari- 

 ous so-called humates and with attempts to dissolve iron either as ferrous hu- 

 niate or as ferrous bicarbonate under approximately natural conditions led 

 to the following conclusions: (1) Peat is a strong reducing agent but is not 

 capable of reducing ferric oxid to ferrous oxid; (2) the solution obtained by the 

 action of peat on ferric oxid docs not contain ferrous humate, which appears 

 to be accompanied by the presence of ferrous ions; (3) peat in the presence 

 of water removes considerable quantities of minerals, especially ferric oxid, 

 aluminum, and calcium oxid, from the soil as colloidal suspensions, which do 

 not seem very sensitive to changes in concentration, although their capacity 

 for suspension is to a certain extent destroyed by evaporation to dryness; (4) 

 in the case of iron the compound formed is probably ferric humate, but possibly 

 an absorption complex of colloidal humus and colloidal ferric hydroxid. 



The authors suggest that " the most probable course of events" in the forma- 

 tion of the pan is as follows: Acid substances are produced as the first results 

 of the accumulation of the surface layers of peat, and they remove the more 

 readily attacked soil constituents probably in the state of true solution. At the 

 same time colloidal humates of iron, aluminum, and calcium are formed, prob- 

 ably as gels on account of the comparatively high concentration of the soil 

 solution. As the concentration diminishes during the winter seasons, the gels 

 pass into the sol form w^hich, as the soil dries, follow the receding water table 

 and the colloidal suspensions are deposited by rapid desiccation at a level just 

 above the permanent water table. 



A bibliography is appended. 



Ferrous iron in soils, C. G. T. Morison and H. C. Doyne {Jour. Agr. Set. 

 [EnvJancU, 6 {1914), No. 1, pp. 91-101; ahs. in Jour. Soc. Chem. Indus., 3S 

 {1914), No. 4, p. 210). — Experiments in which 10 gm. of each of four different 

 soils were digested in dilute sulphuric acid and titrated with potassium per- 

 manganate, apparently showed large amounts of ferrous iron, which the authors 

 believe are indicated '"not because of any large amount really present in the 

 soil, but because the ferric iron which is dissolved by the acid is partially 

 reduced by the organic matter present." 



Similar experiments, using clay to which varying quantities of acid peat 

 were added, showed like results. The use of acetic acid as a solvent was found 

 to be unsatisfactory, and it is concluded from these and other experiments that 

 no known method is satisfactory for the determination of ferrous iron in soils, 

 and that the existence of ferrous iron in normal soils to any extent, and of 

 ferric iron in normal soil solution, seems improbable. 



Mineral deposits, W. Lindgren {New York and London, 1913, pp. XV-^883, 

 Jigs. 257). — Keferring to the fact that "mineral deposits are usually classified 

 and described by the metals or the substances which they contain . . . with 

 little or no effort to separate them into genetic groups" the author states that 

 " this book is the outcome of a desire to place the knowledge of mineral de- 

 posits on the broader and more comprehensive basis of a consistent genetic 

 classification. . . . The general plan has been to select a few suitable ex- 

 amples to illustrate each genetic group of deposits." 



•Zentbl. Agr. Chem., 41 (1912), No. 1, pp. 3-10. 



