93^J '^^"^IL PHYSICS, CHEMISTRY AND MICROBIOLOGY 



mind, they determined the nitrogen in alkali extracts of soil with or without 

 the addition of proteins and other organic nitrogenous compounds. The 

 proteins were precipitated by trichloracetic acid. 



The principal conseqence of the results obtained appears to be that 

 the alkali extract docs not contain a definite group of nitrogenous com- 

 pounds. In an}^ case, however, the non-protein fraction remaining in 

 solution after precipitation by trichloracetic acid ma}' contain most of 

 the simpler nitrogenous compounds, and therefore its determination would 

 give an index of the degree of decomposition of organic matter in the soil. 



A bibliography of 8 works completes the article. 



725 - Influence of Resin and Tannin on the Balance of Nitrogen in the Soil.— koch 



Alfred ami Oelsner Alice, in Ccn'rulblutt fiir B(iktcnoJos,ic, Parasitcnkundc iind In- 

 'ck'ionskrankhcilcn, Vol. 45, No. 1-5, pp. 107-11S. Jena, February 26, iyi6. 



In previous experimentation with forest soils (deciduous and coniferous 

 respectively) one of the writers found that in soils containing nitric nitro- 

 gen the proportion of the latter was reduced after adding tannin or resin. 

 These two substances greatly reduced nitrification, but without stopping 

 it completely. 



Tannin and resin being important products of vegetable metabolism, 

 it was proposed to study their influence on the soil on the basis of previous 

 experiments. The fact that a soil fertilised with siUphate of ammonia contains 

 only a small amount of nitric nitrogen when the above two substances are 

 present ma 3' be explained in two ways : a) the two substances may unfavour- 

 ably affect the nitrifying power of the bacteria ; h) nitrification is not 

 impeded, but the nitrates formed are afterwards decomposed. The former 

 hypothesis seemed the more probable, tannin and resin being used as 

 antiseptics in leather tanning. 



Influence of Resin. In Giltay's solution citric acid was replaced 

 b}" resin, after which bacteria obtained either from horse dung or from the 

 soil were put in. A few days later a reduction of nitrates by the bacteria 

 was found to have taken place. In the same solution without bacteria 

 no reduction of the nitrates was observed, from which it is concluded that 

 resin exerts no chemical action en the nitrates. 



In further experiments 5 gr. of resin and 0.025 &^- o^ sodium nitrate 

 were added to 100 gr. of dry earth. After 4 weeks there was no further 

 trace of nitrate in the soil. The total nitrogen content being unaltered, it is 

 concluded that the bacteria had not decomposed the nitrate into free nitro- 

 gen, but had used it to build up their cells. This very interesting fact 

 proves that resin, which is so difficult of solution in water, supplies energy to 

 the denitrif^dng bacteria enabling them to reduce the nitrates in the soil. 



The experiments were repeated both with Giltay and Raulin solu- 

 tions, and it was found that the latter, owing to the potassium carbonate it 

 contained, promoted the conversion of nitrates a little more than the former. 

 The behaviour of resin in the presence of alkalies also showed that when al- 

 kalies or salts are present in the soil, the resin is decomposed into substances 

 which can be utilised by the bacteria. Resin is therefore clearl}" a source 



