EXPERIMENT STATION BULLETINS. 391 



He 'was soon followed by Proust, Braconnot, Sprengel, and Mulder. 

 Mulder was the most prominent. The work of all of them was, however, 

 characterized by the same empirical methods which were in vogue at 

 the time and which, as might be expected at this period of the develop- 

 ment of organic chemistry, gave no insight into the nature of the nitro- 

 genous substances present. In fact it was an open question at this time 

 whether or not humus compounds really contained nitrogen except as 

 an impurity. Mulder, while he seemed to hold plant protein as re- 

 sponsible for the presence of nitrogen, argued that it was present in the 

 form of ammonia or ammonium salts. Detmer.^ however, decided differ- 

 ently, finding the nitrogenous compounds of the soil to be very stable. 

 He obtained his humus as usual by digesting with alkali. After pre- 

 cipitating with acid, he redissolved it in ammonia and precipitated the 

 mineral constituents with phosphoric and oxalic acids and ammonium 

 sulfide. When he had washed out the silica with hydrochloric acid 

 he obtained an ash-free substance containing one and five-tenths per 

 cent, of nitrogen. No ammonia was evolved upon making alkaline, 

 but about twenty-one per cent, of the total nitrogen was removed by 

 treatment with nitrous acid. This seems to be the first tangible evi- 

 dence of the presence of any particular nitrogen group in humus. But 

 although in the light of modem work this point assumes great import- 

 ance, it seems to have attracted but slight attention then. Two years 

 afterwards he also decided that humic acid could be prepared free 

 from nitrogen. Simon- claimed that peat absorbed nitrogen from the 

 air with the formation of ammonium compounds, a fact which was 

 later disproved. Ritthausen^ attributed the high nitrogen content to the 

 formation of complex, difficulty decomposable materials by the absorp- 

 tion of ammon^'n and pointed to the low ammonia content as an indica- 

 tion of it, claiming that after absorption it was not present as such. 

 V. Sivers,* in attempting to disprove Ritthausen's theory, found that he 

 could drive otf only small amounts of ammonia by heating with potas- 

 sium hydroxide. He decided that all ammonia taken in remained there 

 as such. i. e. did not go to form complex compounds. He held that 

 most of the nitrogen was in the protein form but offered no conclusive 

 evidence. Grouven,^ in trying to show that the nitrogen of humus was 

 due to the absorption of ammonia by humic acids, found that in various 

 samples only one-fiftieth of the total nitrogen was given up when heated 

 several hours -with milk of lime and only one-twentieth when heated two 

 hours with potassium hydroxide. 



Such was the state of affairs up to the year 1887. Not only had no 

 individual organic nitrogenous compound been isolated but, with the 

 exception of Detmer's experiment with nitrous acid, neither was any- 

 thing of a definite nature known regarding the general form of the 

 nitrogen radicle. Even this experiment seems to have passed unnoticed 

 and to have had no influence upon subsequent work. The treatment of 

 humus compounds with alkali had been with the view of determining 

 the presence or absence of ammonia alone. During the year 1887, how- 



iVers. Stat. 14. 24S (1S71). 



2Bied. Cent. Bd. 8, (1875). Jahresber. Fort. Ag. Chem. 18, 6. 



sFuhlings Landw. Zeitung 1877, 161; see Vers. Stat. 25, 169, (1881). 



n'ers. Stat. 24, 183, (1880). 



«FQhlings Landw. Zeitung 188.3, p. 391. Abs. in Jahresber. Fort. Ag. Chem. 1883, 19. 



