CHANGES IN INORGANIC CONSTITUENTS 425 



in the transformation of inert potash compounds may be illustrated by 

 the following reaction: 



A1 2 O 3 K 2 O 6SiO 2 + CO 2 + 2H 2 O = A1 2 O 3 2SiO 2 2H 2 O + K 2 CO 3 + 4SiO 2 



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

 bacteria] 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 believed 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. 



Compounds of iron are of considerable significance in the life 

 processes of many bacterial species. For instance, it was shown by 

 Lipman and after him by Koch, that Azotobacterwil]. not develop in cul- 

 ture media devoid of iron compounds. In field practice small applica- 

 tions of ferrous sulphate often seem to exert a favorable effect on crop 

 growth, and there is reason to suspect that soil-microbial activities are 

 of some moment in bringing about the results noted. 



ALUMINUM, MANGANESE, COPPER. Weathering processes and the 

 relation of carbon dioxide to these processes have already been dis- 

 cussed in connection with calcium and potassium compounds. To a 



