Polytechnic Association. 657 



168 hours 43.3 per cent had undergone oxydation ; and they 

 estimate that sewage flowing in a river, where it would be 

 deluged with twenty times its volume of water, would, by 

 flowing at the rate of one mile per hour, be conveyed at 

 least 168 miles before two-thirds of the organic matter in it 

 would be reduced by oxydation. Another very conclusive proof 

 that this oxydation goes on exceedingly slow, particularly in the 

 nitrogeneous portions of the sewage, is that almost the entire nitrogen 

 that is found in the sewage is in combination with organic matter, 

 scarcely a trace of nitrates or nitrites being discernable, and it is only 

 where the sewage undergoes a proper filtration that oxydation takes 

 place energetically. The examination of the effluent water of the 

 sewage of a large number of cities in England, where irrigation or 

 filtration was in use, shows this to be the case. I think we may, 

 therefore, safely conclude that the theory of oxydation of the 

 sewage, in its flow through the sewers, has very little to rest 

 upon. It is possible, however, that a part of the nitrogen may 

 unite with some of the material of the walls of the sewers, and 

 with the earth surrounding them, and that insoluble compounds 

 may be formed in this way ; but as this process would have its 

 limit we need hardly consider it. It is evident, then, that neither 

 of the theories put forward are correct, and we must, therefore, con- 

 clude that a physical change takes place, to a great extent, in the 

 organic matter that enters the sewers before it is again discharged 

 from them. The precise nature of this change has not yet been suffi- 

 ciently investigated to enable us to determine its character with any 

 absolute certainty; but observations lead us to conclude that it is 

 more of a physiological than of a chemical nature ; although we find 

 the workings of both principles involved in it. For instance, the 

 rapid development of carbonate of ammonia that takes place, may be 

 partly the result of the chemical affinity of the nitrogen of the urea 

 and the carbonic acid of the sewage ; but this transformation is 

 attended with the development of myriads of living organisms, chiefly 

 vibria and bacteria, which rapidly set up putrefaction, attended with 

 an escape of vile and putrescent gases. In the report to the magistracy 

 of Berlin, upon the subject of purifying and draining that city, Pro- 

 fessor Virchow and Dr. Hausmann have given a most interesting state- 

 ment of their miscroscopical observations upon not only the 

 sewage itself, but also the air of the sewers ; the results of which I 

 will convey to you in as few words as possible. The sewage was 

 taken from the sewer in Koniggratzer street, and was found to be of 

 [Inst.] 42 



