897 



partial equilibrium is established when the annual destrnction of organic matter 

 amounts to little more than the annual residue of crop and weeds, but an absolute 

 equilibrium is reached only when the annual loss of nitrogen is equaled by the atmos- 

 phere supply. In every case nature seeks to establish an equilibrium. 



The method of soil sampling practiced at Eothamsted is described and 

 discussed. 



Lecture III. — Mtrification (pp. 42-59). — The natural sources and the 

 artificial production of niter are described. The conditions favorable 

 to nitrification have been understood for many years and applied in the 

 manufacture of niter. The theories formerly held regarding nitrifica- 

 tion were that it is due to oxidation of na.scent lutrogen or of ammonia 

 by the oxygen of the air, ozone, or peroxide of hydrogen. Pasteur first 

 advanced the idea that this process is due to a living organism, and in 

 1873Miiller suggested that the rapid change of ammonia into nitric acid 

 ill sewage is due to the action of a ferment, but " to the French chemists 

 Schlosing and Miintz beJong.s the credit of establishing by experiment 

 the true nature of nitrification." At the time that their results were 

 announced experiments in the same line were in progress in the Eoth- 

 iimsted laboratory. These were continued with the result of confirming 

 the previous conclusions of Schlosing and Miintz. 



It was shown that (1) the power of nitrification could be communicated to medi- 

 ums which did not nitrify by simply seeding them with a nitrified substance; (2) 

 tlie process of nilrification in garden soil was entirely suspended by the presence of 

 the vapor of chloroform or carbon disulphide. These two facts taken together 

 clearly jjointed to a living agent as the cause of nitrification. It was also shown 

 that light is unfavorable to its action. 



The conditions necessary to nitrification are discussed at some length. 

 These have been found to be the presence of phosphates, a liberal sup- 

 ply of oxygen, a salifiable base, a suitable temperature (about 37<^C.), 

 and the absence of strong light. 



For the nitrification of ammonium salts, urea, or other nitrogenous matter to be 

 complete, some salifiable base must be present. The substance which usually plays 

 this part iu soil is calcium carbouate. A soil which contains little or no available 

 base is sure to be very deficient in fertility. Such soils are greatly benefited by 

 dressings of chalk or lime. 



Although an alkaline coudition of the medium is essential for nitrification, the 

 ])resence of anything beyond a small proportion of soluble alliali is a hindrance to 

 fhe process, and a Large amount will prevent the action altogether. ^ * ^ 



A heavy dose of lime applied to land may thus suspend for a time the process of 

 nitrification in the surface soil, but this action will soon cease as the lime unites 

 Avith carbonic acid, and the final result will be favorable to nitrification if the land 

 was originally deficient in lime. 



By a simple chemical expedient it is possible to diminish the alkalinity of liquid 

 manure or other liquids containing alkali carbonates, and thus render them suit- 

 able for nitrification; this maybe done by the addition of gypsum {Ti-ans. Chem. 

 Soc, 188.5, 758). 



Experiments by Dr. J. M. ]S'. Munro and also by the author suggested 

 that the nitrifying organisms could subsist on purely organic food, but 

 to Winogradsky is due the credit of supi)lying actual proof of the fact 

 26624— Ko. 12—5 



