CHAPTER II. 



WATER ANALYSIS. 



The examination of water samples is most commonly 

 made to determine the presence or absence of evidence of 

 sewage pollution. If the pollution is gross, the evidence 

 of the unaided senses will cause its rejection. Few people 

 would use for domestic purposes water which was turbid, 

 or contained suspended matter, or had a peculiar colour, 

 or smelt badly, or had a disagreeable taste. Yet a water 

 may have none of these characteristics, and still be 

 dangerous or unfit for domestic use. Chemical analysis 

 is then often of service in distinguishing good from bad 

 waters. Except in the case of a poisonous metal, the 

 analysis does not aim at finding things deleterious in them- 

 selves, but the search is made for constituents which 

 suggest- the presence of deleterious or dangerous substances. 

 In the case of sewage pollution, the latter are micro- 

 organisms, and the former are those constituents of sewage 

 which are readily detected, namely, chlorides from the 

 urine, ammonia from the urea, and so-called albuminoid 

 ammonia from any albuminous matter. As the average 

 adult excretes 6 to 9 grammes of chlorine daily as chlorides, 

 and 1 part of chlorine per 100,000 parts of water is easily 

 estimated, the pollution produced by one day's excretion 

 of urine into a water would thus be inferable from a rise 

 of the chlorine content 1 per 100,000 even where the dilu- 

 tion was into 600-900 litres or 120-180 gallons of water. 

 The ammonia estimation is much more sensitive, a rise of 

 1 part in 50,000,000 being detectable. The urea excretion 

 of an adult averages 33 grammes per day, and by the influ- 

 ence of the micrococcus ureae this is changed to ammonium 

 carbonate, thus : 



CO(NH 2 ) 2 + 2H 2 = CO 3 (NH 4 ) 2 



60 96 



Hence, if 60 grammes of urea give rise to 96 grammes of 



ammonium carbonate, containing 34 grammes of ammonia, 



33 grammes of urea will give rise to the formation of 187 



