1905.] 



with reference to the Purification of Sewage. 



257 



the following further experiments were therefore made, and confirmed the 

 preceding ones. 



Experiment 8. — Exactly the same coke as had been used for the filters was taken and 

 thoroughly washed and dried. An amount occupying a volume of 30 c.c. was placed in a 

 flask with 50 c.c. NH 4 C1 solution of concentration equal to about 5 parts ammonia 

 per 100,000. In a control flask 50 c.c. of the liquid was placed alone. After 24 hours 

 and after 48 hours the liquids in the two cases were examined, a small quantity (0'5 c.c. 

 to 1 c.c.) being removed, diluted to 50 c.c. with NH 3 -free water and tested with Nessler's 

 reagent. In no case was the reaction fainter where the liquid had been in contact with 

 the coke. (It was shown that the coke did not of itself yield ammonia by a control 

 experiment in which NH 3 -free water replaced the NH 4 C1 solution.) 



Experiment 9. — Coke, which had been thoroughly washed, dried, and sterilised, was 

 placed in a cylinder to form a small filter, and a solution of NH 4 C1 (10 parts NH 3 

 per 100,000) allowed to drop slowly through.* The filter occupied a volume of about 

 1 litre and during the first hour 50 c.c. came through, while in 15 hours a total of 500 c.c. 

 was filtered. The first filtrate of 50 c.c. was tested for ammonia and compared with the 

 original liquid. The tint given by the filtrate (after suitable dilution and addition 

 of Nessler's reagent) was, if at all, only a shade paler, indicating only a negligible 

 difference. After a second hour the filtrate was again compared with the control, and a 

 similar result was obtained. The filtrate coming through in the next 13 hours was 

 similarly tested, but no absorption of ammonia was detected.t 



It may be objected that experiments with raw, cleansed, filtering material 

 are not applicable to the occurrences in the mature filter, where the surface 

 of the coke is probably coated, in some manner not yet investigated, and 

 might possess the faculty of absorbing ammonia in a manner similar to that 

 already demonstrated in the case of certain colloidal substances.}: Therefore 

 it is hoped, in the future, to make experiments with matured coke, elimi- 

 nating, if possible, the action of bacteria. The available evidence is, however, 

 opposed to such absorption, for it is in the uppermost layers of the filter 

 that such a coating would be greatest, and yet disappearance of ammonia, at 

 any rate during the maturing period, has been shown to take place lower 

 down, and in any case coinciding, both as regards time and place, with 

 nitrification. 



Upon consideration of the experimental data at present available, one is 

 therefore inclined to reject the current theory of nitrification and to consider 



* The concentration of ammonia was greater than in the preceding experiments, where 

 it approximated to that in ordinary sewage ; here a more concentrated liquid was 

 employed, in order to be comparable with the diluted urine which was then being treated 

 on the filters. 



t These last two experiments are in perfect accord with some of A. Mayer (' Lehrbuch 

 d. Agrikultuichem.,' 1871), who showed that pure carbon in a porous condition was 

 unable to effect any significant absorption with many salts long known to be absorbed by 

 the soil. 



\ Van Bemmeden, ' Landw. Versuchsst.,' vol. 35, 1888, ' Zeitschr. f . physikal. Chem., 

 vol. 18. 



