656 TRANSACTIONS OF THE AMERICAN INSTITUTE. 



a medium estimate, compared with other authors, I think we may 

 accept it as a basis. 



"We have, then, in this 100,000 pounds of sewage 10.95 pounds of 

 organic nitrogen contained in the human excrements. Allowing this 

 10.95 pounds to represent four-fifths of the organic nitrogen con- 

 tained in the sewage, the whole amount would be 13.14 pounds to 

 every 100,000 pounds of sewage. If no change should take place 

 in this sewage, it would be found to contain the above amount of 

 organic nitrogen, when examined at the place where it is discharged 

 from the sewer. This is found not to be the case, since the result of 

 lifty-two analyses of the sewage of the principal cities of England, 

 which are called " water-closet towns," shows an average of 22.05 

 pounds of organic nitrogen in the 100,000 pounds of sewage. The 

 same analysis shows also the presence of 6.703 pounds of ammonia, 

 making a total of 77.25 pounds combined nitrogen in the 100,000 

 pounds of sewage, a fraction over one-half of what it should con- 

 tain, nearly 6.5 pounds having escaped in some way during its course 

 through the sewers. It is important that we should know what form 

 these organic elements have taken, and fortunately we have already 

 sufficient reliable evidence to enable us to arrive at a tolerably 

 rational conclusion. In order to show that very little of these ele- 

 ments undergo oxydation from their combination with the oxygen of 

 the water of the sewage, I will refer again to the tabular statements 

 of the commissioners referred to. In their examinations of the waters 

 of the Irwell, the Mersey and the Darwin, into each of which an 

 immense amount of sewage was discharged, they found that in a flow 

 of eleven miles the average reduction of the organic nitrogen of their 

 contents was 8.5 per cent, and the reduction of organic carbon 10.5 

 per cent. They do not, however, take into consideration that during 

 that flow of eleven miles a large amount of these organic elements 

 were undergoing other combinations, in which they were, to a mate- 

 rial extent, disengaged and allowed to mingle with the atmosphere. 

 In order to test the subject fairly, they mixed five per cent of London 

 sewage with ninety-five per cent of water, and after determining the 

 amount of organic carbon, organic nitrogen and dissolved oxygen 

 contained in the fluid, it was placed in a series of well-stopped bottles. 

 These bottles were opened in succession, one every twenty-four hours, 

 and by determining the amount of dissolved oxygen still remaining 

 in the fluid, it was possible to estimate the amount of oxydation that 

 had taken place. The result of this experiment shows that in twenty- 

 four hours 6.5 per cent of the organic matter was oxydized, and in 



