CHEMICAL ANALYSIS 31 



it is also desirable to determine how much of the organic 

 nitrogen is present in the suspended matter. 



" In sampling, the Committee suggest that the bottles should 

 be filled nearly completely with the liquid, only a small air- 

 bubble being allowed to remain in the neck of the bottle. The 

 time at which a sample is drawn, as well as the time at which 

 its analysis is begun, should be noted. An effluent should be 

 drawn to correspond as nearly as possible with the original 

 sewage, and both it and the sewage should be taken in 

 quantities proportional to the rate of flow when that varies 

 {e.g., in the emptying of a filter-bed). 



" In order to avoid the multiplication of analyses, the atten- 

 dant at the sewage works (or any other person who draws the 

 samples) might be provided with sets of twelve or twenty-four 

 stoppered I Winchester bottles, one of which should be filled 

 every hour or every two hours, and on the label of each bottle 

 the rate of flow at the time should be written. When the 

 bottles reach the laboratory, quantities would be taken from 

 each, proportional to these rates of flow, and mixed together, 

 by which means a fair average sample for the twenty-four hours 

 would be obtained. 



" The Committee at present are unable to suggest a method of 

 reporting bacterial results, including incubator tests, which is 

 likely to be acceptable to all workers." 



Processes of Analysis. 



Since samples of sewages and of effluents are usually in a 

 condition of rapid change, the chemical examination must be 

 carried out as quickly as possible after collection ; therefore such 

 processes as admit of rapid working must be chosen in pre- 

 ference to those which are longer, even if the latter be slightly 

 more accurate, more especially as a large number of specimens 

 have often to be examined at once. 



Physical character, as smell, colour, and turbidity,^ must first 

 be noticed, then the reaction to test-paper. Ordinarily this is 

 more or less alkaline, the alkalinity being of two kinds — volatile, 

 owing mainly to free ammonia ; fixed, due to washing soda and 

 soap and, more rarely, lime. These can be determined, if 

 necessary, by taking two measured quantities, say 10 to 50 c.c, 



^ Clark uses as a standard lor turbidity a suspension containing a known 

 amount of sewage deposit of average character [Journ, Amer. Assoc. Eng. Soc, 

 1904, xxxiii., p. 356). 



