EXPERIMENT STATION BULLETINS. 329 



are important soil processes and the carbonates of potassium and sodium 

 resulting from these processes being much more soluble than the carbonates 

 of calcium and magnesium similarly formed, may be leached from the sur- 

 face section of soils to a much greater extent; the general effect would then 

 be an indirect replacement of potassium and sodium in sihcate combination 

 with calcium and magnesium, and after sufficient time had elapsed only small 

 quantities of potassium or sodium could be expected to be present in hydro- 

 lyzing combinations, while calcium and magnesium would probably be 

 present for a considerable period of time in a hydrolyzable state after the 

 original potassium and sodium of similar combinations had practically 

 disappeared. Much evidence supporting this conclusion may be found 

 in the literature concerning researches on soils and minerals. Further elab- 

 oration of the subject is not desired in this paper. 



The elements potassium and sodium, then, must be in a much less soluble 

 state in many surface soils than calcium or magnesium; and if their com- 

 pounds do not hydrolyze, they undoubtedly occupy a different position in 

 the molecular structure of their compounds than do calcium or magnesium, 

 at least the portions of these elements that split off from their compounds 

 as hydroxides and may easily be carbonated. If potassium or sodium are 

 fixed in soils from chemical compounds, however, they probably occupy the 

 same position of molecular structure as the elements they release because 

 they may in turn be replaced in quantity by cations of other salts. These 

 relationships should be of great scientific and practical significance. 



The situation with respect to iron and aluminum of the soils was prob- 

 ably similar in some respects at least to that of potassium and sodium in that 

 the evidence at hand points to the conclusion that they were not exchanged 

 in quantity for the other elements fixed. The main points of evidence in 

 this connection were as follows: (1) Except in two cases the solutions were 

 alkaline to red litmus paper, hence acid salts of iron and aluminum com- 

 bined ^vith the anions of the neutral salts used in the treatments were probably 

 not present. (2) Fixation and exchange were closely equivalent without 

 considering the presence of iron or aluminum combined with anions of the 

 salts used. (3) Iron and aluminum are present in the soils used generally 

 in very much greater total quantities, and in the acid soils in much greater 

 quantities soluble in 0.2 N HCl than are calcium and magnesium, and pro- 

 viding exchange took place during the neutral salt treatments the accompany- 

 ing phenomena would probably have been recognized. The conclusion seems 

 justified that iron and aluminum were not present in the soils in exchangeable 

 states, at least in any considerable quantities, but that they exist in the 

 soils principally as hydroxides from the hydrolysis of soil minerals containing 

 them or on the acid side of soil components as ferro-alumino-silicates. The 

 soil component of non-carbonate soils reacting with neutral salts may then 

 be a calcium-magnesium-ferro-alumino-sihcate. These considerations refer 

 to the mineral portions of the soils studied. The author does not assume that 

 all soils contain no appreciable quantities of replacable potassium, sodium, 

 iron or aluminum, but is of the opinion that the relative quantities of replace- 

 able elements contained in soils is an individual characteristic. The possi- 

 bility of secondary reactions should also be considered in this connection. In 

 case of the KCl treatments iron or aluminum chlorides may have been 

 formed and neturalized again by the soils and the reaction not observed at 

 the low concentration of neutral salts used; however, this reaction would 

 not explain the iron and aluminum combinations in the soil solutions studied. 



