120 BACTERIA AND SOIL FERTILITY 



It is interesting, however, to note the careful work of Boussin- 

 gault in the years between i860 and 1878 on the natural -occur- 

 ring saltpeter beds, especially those of Peru and Ecuador. He 

 raised the question "have not the nitrates in the natural deposits 

 resulted from the breaking down of organic substances rich in 

 nitrogen," for it had long been the practice to use blood, urine, 

 and other animal refuse for the production of nitrates. For 

 this reason Boussingault did not think it likely that the gaseous 

 nitrogen of the air played a very great part in the process of 

 nitrification. In order to test this he placed soil with known 

 nitrogen content in 100-liter jars and allowed them to rerpain 

 for eleven years. At the end of this time they were analyzed, 

 and, in spite of the fact that a very active nitrification had taken 

 place, there was no increase in the total nitrogen of the soil. 

 From this he concluded that free nitrogen takes no part in the 

 formation of nitrates, but that they result from the organic matter 

 of the soil. In another set of experiments he added organic 

 manure to soil, sand, and chalk, and left them to nitrify. He 

 obtained an active nitrification in the soil, but none in the sand or 

 chalk. This fact had a great influence on the old theories of 

 nitrification. Why this difference if the soil acts merely as a 

 catalyzer ? 



The True Cause of Nitrification.— The brilliant investiga- 

 tions of Pasteur during the second half of the nineteenth century 

 on fermentation prepared the way for the true understanding of 

 the process of nitrification. In reality he actually expressed the 

 belief that nitrification was due to a ferment. The proof of 

 this was furnished in 1877 by two French chemists, Schlosing and 

 Miintz. They were trying to ascertain if the presence of humus 

 is essential in the purification of sewage by soil. They filled 

 glass tubes one meter long with ignited sand and powdered lime- 

 stone. Sewage passed through this filter at first unchanged, but 

 later nitrates began to appear, and soon the filtrate contained no 

 ammonium salts but an equivalent quantity of nitrate. They 

 suspected microorganisms as being the active agents, and hence 

 treated the contents with chloroform vapor. Nitrification entirely 



