i86 SEWAGE AND ITS PURIFICATION 



Raw sewages from this and other places, and effluents from 

 septic tanks, primary, secondary, and tertiary filters, were 

 treated with the solution under varying conditions to ascertain 

 its efficiency as regards (i) putrefactive organisms, and (2) 

 sewage organisms comparable in origin and vitality with those 

 which cause typhoid fever and cholera. The tests were also 

 directed to secure such freedom of the effluent from suspended 

 solid material as would prevent the formation of mud banks, 

 and from organic matter in solution, as to render it impossible 

 for it to become putrid when subsequently mixed with water. 



My experiments indicated that the germicidal value of the elec- 

 trolytic solution, containing chlorine oxides and other com- 

 pounds, was greater than that of the equivalent of free chlorine 

 liberated chemically. I have, however, always stated the strength 

 of the addition in parts of available chlorine {av. CI, as ordinarily 

 measured by arsenious acid), added to 100,000 parts of sewage 

 or effluent. The actual volume used would depend upon its 

 strength : at Guildford the machine gave a solution containing 

 0*2 to 0*5 per cent, of available chlorine. By daily bacterial 

 and chemical analyses I was enabled to establish at Guildford, 

 in reference to the amount of reagent required, an easy practical 

 guide that may be applied to other places. There was a very 

 nearly constant relation between the five minutes' oxygen- 

 consumed figure, representing the amount of the agent that 

 would be at once taken up by the organic matter, and the 

 quantity of the oxychloride that was needed, so that there 

 should be an excess capable of killing the bacteria. The five 

 minutes' oxygen multiplied by 1*7 gave the amount of available 

 chlorine required in parts per 100,000, and the strength of the 

 solution being determined, the proportion to be added is easily 

 calculated. 



Raw Sewages. — The following is a type of the results : 



The untreated sewage had a very foul odour : it gave, in parts 

 per 100,000, CI in chlorides i8'6, oxygen consumed in five 

 minutes 4'i4, in two and a half hours i8*8, free and saline 

 ammonia 7*2, albuminoid 2*4, B. coli 1,000,000 per c.c. The 

 addition of 3 parts of available chlorine per 100,000 reduced 

 the coli to less than i per c.c, and spores of B. enteritidis 

 sporogenes to less than 10 per c.c, after four and a quarter 

 hours' contact. With 5 to 7 parts of av. CI, negative results 

 were obtained for both these organisms with 5 c.c. after four 

 and a quarter hours' contact. The total number of organisms 



