636 i 



acid and a yellow substance. The action was slower than in the former 

 case, owin*;- probably to the commencement of the oxidation while the 

 material was being- prepared under the iutiuence of the air and the 

 potash. 



These observations indieat<^ that the brown substances of humus and 

 their analogues undergo direct oxidation under the influeiue of the air 

 and sunliglit. forming carbonic acid and (-hanging their color. These 

 reactions are purely chemical, taking place without the influence of 

 microbes. This oxidation of humus is rendered more active by the 

 division and mellowing of the humus materials as the result of the 

 cidtivation of the soil. While in this way the humus appears to be 

 made more assimilable by i)lants the same processes ha.sten the destruc- 

 tion of the organic substances in arable soil, either under the influence 

 of vegetation, (»r by the hel]) of microbes, or by purely «heniical nn-ans 

 when the soil is exposed to the light. The bare surfaces of the soil gi\ ( 

 oft carbonic aci<l and form s(»lnb|e <-ompounds, which are carried away 

 by the meteoric waters, fhns the humus mateiials (»f the soil need 

 constant renewal as well liy the decomposition of dead j.lants as by the 

 addition of fertilizers. 



Effects of different proportions of clay and of organic nitrogen 

 on the fixation of atmospheric nitrogen, the conservation of 

 nitrogen, and nitrification, P. Pichard {('ompt. mid., ill (i.s!):j), pp. 

 >/-s/j. — -Mixtuics ot pure >iiiciuns .^and and clay which showed no 

 traces of nitrogen at the beginning of the experiment contained notice 

 able quantities after 7 months— (M)7 pr. in a kg. of soil containing 10 

 per cent of clay, 0.12 gv. in soil with LM» per cent of clay, O.L'O gr. in soil 

 Mith 30 i»er cent of clay. The amounts of nitrogen fixed were nearly 

 l)roi>ortional to the amounts of clay. Small quantities of nitric and 

 annnonia<al nitrorren were also found in these soils. These observa 

 tions agree with i>revious ones by Berthelot and others, including the 

 author. 



The addition of plaster sligditly increased the proportion of nitrogen 

 lixed, as well as of nitric acid and ammoiiiacal nitrogen. The favor 

 able inlluence <»f clay ami of i(last<'r was also seen in mixtures of clay, 

 sand, and cotton oil cake. The inflnenee ol chiyon the conservation of 

 the nitrogen and the fixation of atmosi>heiic nitr(»gen was clearly seen 

 in '•(•omitlete" soils, containing sand, clay, oilcake, plaster. an(i lime. 

 In soils containing ai»i)roxiniately 2 and 3 gr. of organic nitrogen i»er 

 kg. the eftiect of the clay on the conservation of the nitrogen was still 

 seen but did not directly nmnifest itself in the fixation of atmosplu-ric 

 nitrogen. In these soils there was no gain of nitrogen. 



The proi)ortion of clay within the limits of from 10 to 40 per cent did 

 not clearly affect the nitrification. Increasing the quantity of organic 

 nitrogen from 1 to 3 gr. per kg. of soil was «learly unfavorable to nitri- 

 fication. Not only the relative proportions, but also the absolute (pmu- 

 tities of nitric nitrogen decreased as the amount of organic nitrogen 



