126 abstracts: chemistry 



reagent most successfully used in. the case of soil is aloin, a solution of 

 which in water is changed from yellow to claret red by the oxidation. 

 The depth of color can be measured and indicates the extent of the oxi- 

 dation . 



This oxidation appears to be mainly nonenzymotic, the result of inter- 

 action between inorganic constituents and certain types of organic 

 matter. It may also be brought about by organic matter in a state of 

 autoxidation and by inorganic oxygen carriers, such as manganese and 

 iron. Both processes activate oxygen. 



The oxidation in soils was increased by the addition of salts of mangan- 

 ese, iron, aluminum, calcium, and magnesium, especially in the presence 

 of simple hydroxyacids, such as citric, tartaric, malic, glycolic, and their 

 salts. The best oxidation was obtained by the addition of manganese, 

 and the stimulating action of manganese used as a fertilizer is attributed 

 to its oxidizing power; i.e., to its amelioration of soil conditions rather 

 than its function as a plant nutrient. Fertilizer salts augment the oxidiz - 

 ing power of roots, and the fertilized soil has an increased oxidizing power 

 after cropping. The fertilizer salts alone sometimes increase, sometimes 

 decrease, the oxidative functions of the soil, thus showing that the fer- 

 tilizer salts are effecting changes directly or indirectly in the soil con- 

 stituents more particularly in the organic matter. Some type ; s of organic 

 matter inhibit oxidation but in the main the oxidative power is augmented 

 by a plentiful supply of organic matter, the nature of which in the soil 

 is the limiting factor of oxidation. Excessive oxidation is harmful to 

 vegetation. 



Oxidation, in soil is parallel to oxidation in plants and animals. Soils 

 oxidize substances in a manner analogous to an oxidase, and the increase 

 noticed by the addition, of certain hydroxyacids is closely paralleled by 

 the recently discovered activating action of salts of tartaric and citric 

 acids on the oxidative action of manganese acetate. This analogy 

 between the oxidative power of a soil and the action of an oxidase is 

 especially significant in that an oxidizing enzyme, laccase, of alfalfa, 

 has been found to be more simple in composition than formerly supposed 

 and to consist of neutral salts, mainly calcium, of glycolic, mesoxalic, 

 malic, and citric, and probably glyoxylic acid. It is well known that 

 the oxidase whatever may be their nature, play an important part in 

 the proper functioning of plants, and that with changes in the oxidizing 

 ability are associated changes in plant condition. Similarly, oxidative 

 power of the soil is a symptom of soil condition. 



Whatever decreases the oxidation in soils tends also to bring about 



