30 SEWAGE AND ITS PURIFICATION 



that they include each hour of the twenty-four, taken twice, 

 extending over seven days. The periodic fluctuations that I 

 have mentioned are also shown. 



In 1898, a British Association Committee, after having had 

 the advantage of considering the earlier reports of the Royal 

 Commission on Sewage Disposal, recommended as follows :^ 



** That it is desirable that results of analysis should be ex- 

 pressed in parts per 100,000, except in the case of dissolved 

 gases, when these should be stated as cubic centimetres of gas 

 at 0° C. and 760 millimetres in i litre of water. This method 

 of recording results is in accordance with that suggested by the 

 Committee appointed in 1887 to confer with the Committee of 

 the American Association for the Advancement of Science, with 

 a view to forming a uniform system of recording the results of 

 water analysis.^ 



" 2. The Committee suggest that in the case of all nitrogen 

 compounds the results be expressed as parts of nitrogen per 

 100,000, including the ammonia expelled on boiling with 

 alkaline permanganate, which should be termed albuminoid 

 nitrogen. The nitrogen will therefore be returned as — 



(i) Ammoniacal nitrogen from free and saline ammonia. 



(2) Nitrous nitrogen from nitrites. 



(3) Nitric nitrogen from nitrates. 



(4) Organic nitrogen (either by Kjeldahl or by combus- 



tion, but the process used should be stated). 



(5) Albuminoid nitrogen. 



*' The total nitrogen of all kinds will be the sum of the first 

 four determinations. 



" The Committee are of opinion that the percentage of nitrogen 

 oxidized — that is, the ratio of (2) and (3) to (i) and (4) — gives 

 sometimes a useful measure of the stage of purification of a 

 particular sample. The purification effected by a process will 

 be measured by the amount of oxidized nitrogen as compared 

 with the total amount of nitrogen existing in the crude 

 sewage. 



" In raw sewage and in effluents containing suspended matter 



1 British Associaiion Report, 1899. Parts per 100,000 can be converted into 

 grains per imperial gallon (277^ cubic inches) by multiplying by 07, and into 

 grains per United States gallon (231 cubic inches), by dividing by "171. 



2 " It would be a great convenience if this mode of expressing results were 

 generally agreed to and adopted by chemists throughout the country, and by 

 managers of sewage farms or works.''— Reports to the Roval Commission on 

 Seivagc^ vol. iv., part v., 1904, p. 9. 



