I 



CHEMICAL ANALYSIS 



27 



cone, with a recording apparatus placed on the pipe leading to 

 the smaller Venturi, but measuring the total flow through both 

 tubes, which is equivalent to that of the main. The accuracy 

 of the register can be tested at any time by opening a connec- 

 tion on the outlet side, so that the flow can be diverted through 

 a hose into a measuring tank. 



Samples of effluents should be taken corresponding to the raw 

 sewage. This is sometimes rendered difficult by the time of 

 passage through the tanks or filters not being accurately known. 

 The capacities of the beds and tanks and the flow at the time of 

 sampling will, in most cases, give the necessary data, but even 

 then allowance must be made for streaming. I have found the 

 only accurate method is to spread the sampling over successive 

 days, choosing different times each day until the cycle of twenty- 

 four hours is complete ; in this way, even on small systems, 

 irregular discharges do not cause error. 



Collection of Samples 



in a representative manner requires considerable labour and 



attention. Many published analyses are based on specimens 



taken casually, and the opinions formed are of little or no value. 



The sewage is continually flowing, but varies both in volume and 



quality from hour to hour. I found, for instance, in a town 



sewage — 



Parts per 100,000. 



Time and Circumstances. 



Dry weather, no rain 

 10 a.m to 5 p.m. 

 6 p.m. to I a.m. 

 2 a. m to 9 a.m. 



n : 



Heavy storm : 

 10 a.m. to 5 p.m. 

 6 p.m. to I a.m. 

 2 a.m. to 9 a.m. 



:::| 



None. 



Total chlorine, 41 pounds per day 



79,000 



Total chlorine. 



None. 

 Trace. 



[Very 

 heavy 



44 pounds per day. 



Physical Characters. — Dry weather : Thick and foetid ; fragments of paper 



and lumps of faecal matter abundant. 

 Heavy storm : Turbid, yellow-brown ; earthy odour. 



In the morning urine is prominent, as shown by the chloride 

 and by other signs ; later on, soapy water makes its appearance. 



