before and after receiving the Cambridge sewage effluent. 355 
Sewage Farm on Milton Road, and also the Cam itself above 
and below the effluent outfall, to see how far the conditions of the 
river and the effluent are comparable with the standards suggested 
by the Commissioners. 
A very extensive research would be necessary for a complete 
survey. It would mean a daily examination of the river and the 
effluent, and perhaps twice a day. But a fairly comprehensive 
view may be obtained by obtaining an analysis once a week, 
during the summer and winter months. The condition of the 
river can be investigated in the dry and wet seasons; and the 
dilution, as well as the varying pollution, should give a fair 
indication of the general conditions of the river and the 
effluent. 
In connection with the condition of the Cam above and 
below the sewage effluent outfall, reference may be made to a 
paper by Purvis and Rayner*. In the investigation it was 
shown that the chemical purification, as distinct from the bacterial 
purification, was moderately good, as determined by the estima- 
tion of the two ammonias and the amount of oxygen absorbed 
from potassium permanganate in four hours. At two miles below 
the outfall, the river showed a definite amount of purification 
notwithstanding the fact that at ? of a mile below there was some 
contamination from another source. They also proved that above 
this contaminating influence, at half a mile below the outfall, 
the chemical purification was fairly good. 
The method of analysis of the present investigation was that 
used by Letts and Blake+. The process is simple, and the details 
can be obtained in these publications. ‘The results of the various 
determinations are given in the tables (pp. 8363—368). 
The more important facts which arise from a comparison of 
these analyses are the following: (a) The solids in suspension in 
the effluent were, on several occasions in the summer months, 
above the standard of 3 grams per 100,000; and on these occasions 
an offensive smell was noticed after five days’ incubation. On four 
occasions during the winter months the suspended solids were 
also above the standard; but, on the other hand, there was no 
smell after five days’ incubation. On examining these solids 
microscopicaily it was found that they chiefly consisted of zooglcea 
masses of a filamentous bacillus which had developed and had 
grown on the inside of the drain pipes and inspection chambers. 
They were not fxcal substances which produced an unpleasant 
smell like those noticed in the summer. The appearance of the 
* Journ. Roy. Sanitary Inst., 1913, vol. xxxtv. p. 479. 
+ Proc. Roy. Dub. Soc., vol. 1x. (N.S.) pt. iv. No. 33. Also the 5th Report, 
Royal Commission on Sewage Disposal, Appendix 6, p. 221, and the 8th Report, 
vol. 11. Appendix. 
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