832 THE POPULAR SCIENCE MONTHLY. 



in it, and rapidly increased in amount until all the nitrogen of the 

 filtrate was in this combination. If nitrification is due to simple oxida- 

 tion, it is difficult to see why it was so slow in commencing ; but, if it 

 is due to an organism which required time to develop in the artificial 

 soil, the delay is at once explained. 



Sewage was passed through the soil in this way for four months, 

 with complete oxidation of its nitrogen. As soon, however, as vapor 

 of chloroform, which is known to be inimical to the action of organized 

 ferments, was caused to penetrate the soil, nitrification ceased, and did 

 not recommence after the chloroform was withdrawn. After the sew- 

 age had passed unchanged for seven weeks, a small amount of turbid 

 washings of a soil known to nitrify with ease was poured upon the top 

 of the soil. After eight days (i. e., exactly the time required for the 

 liquid to traverse the column of soil), nitrates reappeared in the strata, 

 and continued to be formed as long as the experiment was continued. 

 All these facts point plainly to an organism as the cause of nitrifica- 

 tion. It developed in the soil during the first twenty days of the ex- 

 periment from germs introduced by air or sewage ; it was killed by 

 the chloroform-vapor, and reintroduced in the soil-washing. 



In 1878 appeared the results of experiments made by Warrington * 

 in the Rothamsted Laboratory, which fully confirmed those of Schloe- 

 sing and Miintz. He first showed that a very considerable nitrification 

 took place in a good garden-soil when a current of air was aspirated 

 through the moist soil, but that hardly any formation of nitrates took 

 place when this air contained vapors of chloroform or carbon disul- 

 phide, while vapor of carbolic acid seemed to produce the same effect 

 so far as it was brought in contact with the soil. Thus far the results 

 were simply confirmatory of those of Schloesing and Miintz. Further 

 experiments, however, developed the important fact that nitrification 

 could be brought about in dilute solutions of ammonium salts, by seed- 

 ing them with a small amount either of a nitrifying soil or of a similar 

 solution which had undergone nitrification. The first experiments 

 were made with the dilute solutions employed in the determination of 

 ammonia by Messler's method, with the addition of small quantities of 

 tartrate and phosphate of potassium, and precipitated carbonate of 

 calcium. The solutions used in later experiments had the following 

 composition per litre : 



Ammonium chloride 80 milligrammes. 



Sodium potassium tartrate 80 " 



Potassium phosphate 40 " 



Magnesium sulphate 20 " 



Precipitated calcium carbonate was added to supply the necessary 

 base. By this discovery the way was opened for the easy and fruitful 

 study of the process and of the conditions affecting it. 



Since the publication of Warrington's paper, a large amount of 



* " Transactions of the Chemical Society," 1878, p. 44. 



