r 



BACTERIAL PURIFICATION 255 



were kept in suspension by the gases and passed off in the 

 flow, so that the quantity did not sensibly increase. 



At the end of iSgS I found this peaty deposit to contain : — 



No. I. No. 2, No. 3. 



Distance from bottom, inches 

 Organic matter, per cent. 

 Ash, per cent. 

 Nitrogen, per cent. 

 Percentage of N in organic matter 



Microscopical Characters. — No. i. Black amorphous matter, 

 small sand particles, fragments of muscular fibre, dark coloured 

 and corroded, and of other animal tissue ; large amoebae, clado- 

 thrix, micrococci and bacilli, fragments of faecal matter, vege- 

 table tissue and hairs. 



No. 2. Spiral vessels of a plant, anguillulse, egg of an ento- 

 zoon, fewer amoebae, otherwise like the last. 



No. 3. Anguillulae, vegetable hairs and spiral vessels, faecal 

 fragments rather abundant, sponge spicules, animal hairs. No 

 amoebae and very few muscle fibres : otherwise similar to the 

 preceding. It will be seen that the older matter is mixed with 

 recent substances lately arrived in the tank. 



A sample from the top of the deposit contained 88*8 per cent, 

 of moisture, from mid-depth 83*9 per cent., from the bottom 

 80 per cent. Comparing the last with the 90 per cent, moisture 

 in ordinary sludge, it will be seen that the difference reduces 

 the bulk of the deposit by one-half, even if no liquefaction had 

 taken place. Clowes tabulates the moisture in septic tank 

 deposits in a number of towns (the average is 86 per cent.),^ 

 also the reductions effected by the tank in the sewage solids. 

 It is generally agreed that this should in good working be not 

 less than 50 per cent. 



The deposit from an open septic tank at Manchester in April, 

 1900, contained organic matter 5'24, inorganic matter 6-78, 

 water 87*98 per cent., or in the solids 57 per cent, inorganic 

 and 43 per cent, organic.^ 



In the sediment from a septic tank at Hanwell Sewage Works 

 in July, 1905, I found amorphous granular matter, numerous 

 fragments of disintegrating muscular fibre and particles of 

 faeces, cladothrix and gelatinous colonies of micrococci, numerous 

 ova of aquatic worms and large numbers of paramoecium and 



^ Fourth Report to London County Council. 



2 Royal Commission on Sewage, Second Report, 1902, No. 2, 



