CHANGES IN INORGANIC CONSTITUENTS 36 1 



Smaller amounts occur as nitrate, carbonate and in organic compounds. 

 The portion present as silicates is often very large in clay-loam Soils, 

 amounting not infrequently to 22,679 ^S- to 34,019 kg. (50,000 to 

 75,000 pounds) per acre-foot. Unfortunately for the farmer, the grow- 

 ing crops fail, in many cases, to secure suflScient quantities of available 

 potash for their rapid development, notwithstanding these enormous 

 stores of potassium compounds. However, when sufficient quantities 

 , of readily fermentable organic matter are present and the generation of 

 carbon dioxide is rapid the silicates weather sufficiently fast to meet 

 the demands of maximum harvests. The part played by carbon dioxide 

 in the transformation of inert potash compounds may be illustrated by 

 the following reaction: 



AI2O3K2O eSiOa + CO2 + 2H2O = AUO3 zSiOa 2H2O + K2CO3 -f 4Si02 



Under actual conditions it is the aim of the farmer to stimulate 

 bacterial activities (and, therefore, the production of carbon dioxide) in 

 his land by the use of animal manures or green manures and of com- 

 mercial fertilizers. Apart from the influence of carbon dioxide avail- 

 able potash compounds may likewise be formed on account of nitric, 

 sulphuric, acetic, lactic, butyric and other acids produced by different 

 soil bacteria. 



Other Mineral Constituents 



Iron. — The investigations of Ehrenberg, Winogradski, Molisch, 

 Adler, Ellis and others have accumulated a mass of data relating to the 

 so-called iron bacteria. These organisms belong to the class of higher 

 bacteria and recently forms, such as rod-shaped bacteria, have been 

 isolated which have a marked ability to precipitate iron oxide out of 

 solutions of iron salts. Winogradski beUeved that the reaction is a 

 physiological one in that the microorganisms oxidize ferrous to ferric 

 compounds, and utilize for their growth the energy thus made available. 

 The investigations of Molisch, Adler and Ellis show, however, that the 

 iron bacteria can exist very well without iron compounds; and that the 

 precipitation of iron oxide is due to mechanical rather than chemical 

 influences. But whether physiological or mechanical the influence of 

 these microorganisms is felt in the formation of bog iron, and in the 

 filling up of iron pipes; in the latter instance much annoyance is occa- 

 sionally experienced by those in charge of municipal water supplies. 



