354 Messrs Purvis and Gourtauld, Decomposition and nitrification 
The decomposition and nitrification of sewage (1) in alkaline 
solutions, (2) in distilled water. By J. E. Purvis, M.A., St John’s 
College, and R. M. Courtauld, M.A., M.B., Pembroke College. 
\_Read 25 November 1907.] 
In a paper by Purvis and Coleman on “The influence of the 
saline constituents of sea-water on the decomposition of sewage*,” 
the authors described a series of experiments to ascertain the 
influence of the chief salts found in sea- water, and also of sterilised 
and unsterilised sea-water, on the decomposition of sewage, and 
particularly with regard to the production of nitrates. 
With regard to the principal salts, solutions of NaCl, MgS0 4 , 
and MgCl. 2 were made of such strengths as to be equivalent to the 
corresponding salts found in the water of the British Channel. 
Samples of Cambridge sewage were analysed for the amounts 
of free and albuminoid ammonias and of nitrates and nitrites 
already present ; and they were then mixed with separate solu- 
tions of the salts so that each solution contained 1 per cent, of 
sewage. Similar quantities of sewage were added to a mixture of 
these three salts, and also to a normal sea-water obtained from 
Lowestoft and Stalham, off the Norfolk coast. The solutions were 
then allowed to incubate with free access of air and at a constant 
temperature, and they were analysed from time to time. 
In order to compare our own tabulated results with theirs, we 
are enabled to give a table showing the results of an incubation of 
1 per cent, sewage with a mixture of NaCl, MgS0 4 and MgCl 2 , 
when analyses were made after 1 day, 2 days, 3 days, 5 days, and 
8 weeks. The numbers represent parts per 100,000. 
Time 
Free NH„ 
Albuminoid 
nh 3 
Total NH 3 
Nitrates and 
Nitrites 
Commencement. . . 
0-346 
0-078 
0-424 
absent 
1 clay 
0-980 
0-550 
1-530 
2 days 
1-100 
0-650 
1-750 
3 clays 
1-130 
0-650 
1-780 
5 days 
0-960 
0-630 
1-590 
8 weeks 
0-950 
0-360 
1-310 
5 J 
The results showed (1) that at first and until about the third 
day there was a rise in the total ammonia and then a gradual fall, 
and (2) that there was no appearance of nitrates and nitrites. 
* Journal Roy. San. Inst. Vol. xxvii. No. 8 (1906), pp. 433 — 441. 
