518 Transactions. — Miscellaneous. 



matter ; and, granted these, there is practically no limit to the 

 activity of their processes, nor to the amount of noxious 

 organic matter they can dispose of, converting it into harmless 

 innocuous compounds. These useful little organisms exert a 

 powerful influence in nature, the magnitude of which is seldom 

 realised. They have a wonderful power of adaptability, and 

 can modify their constitution to suit the circumstances, be- 

 coming, like most living things, educated to their environments. 

 This will be exemplified later. 



Sewage, the other factor in the chemico-biological process 

 I am about to describe, delivered at an outfall after flowing a 

 considerable distance in a closed channel, consists of nitro- 

 genous compounds, chiefly in solution, the solids, for the most 

 part, being suspended in finely-divided particles ; but sewage 

 contains also within itself, potentially, the power of its own 

 destruction. Countless myriads of the bacteria of decomposi- 

 tion carry on their disintegrating processes, and all that is 

 required to complete the chemico-biological change initiated 

 by the vital process is a plenteous supply of the ever-obliging 

 oxygen of the air, readily accessible. 



We have, then, on the one hand soil — a medium containing 

 in its interstices oxygen as air, and myriads of bacteria, whose 

 favourite diet is dead animal or nitrogenous matter ; and on 

 the other hand the water of an abundant water-carriage sys- 

 tem — a medium containing this very dead nitrogenous mate- 

 rial, with an equal number of greedy bacteria. The oxygen 

 and bacteria in the soil and the nitrogen and bacteria in the 

 sewage are the factors which, when brought together under 

 suitable circumstances, bring about a transformation of the 

 most impure liquids into a pure and sparkling water that the 

 most fastidious could drink of and commend, soluble mineral 

 constituents, known generally as nitrates and nitrites, only 

 being present — the chemical indication that the change known 

 as oxidation or nitrification has been complete. 



To illustrate, corroborate, and amplify this, let me de- 

 scribe an experiment conducted in the laboratory : A long 

 glass cylinder is filled with pure sand. There are few or no 

 bacteria and little or no organic matter, but because of the 

 looseness of the sand-particles there is abundance of oxygen 

 as air — about 50 per cent. A small pipe leads a supply of 

 very impure water on to the surface of the sand in this arti- 

 ficial filter, while a tap at the bottom of the cylinder allows 

 the filtrate to be caught and examined. 



The first of the fluid filtering through is found to be almost 

 entirely as impure as that distributed on the surface of the 

 sand, only some of the coarser particles being retained. The 

 bacteria are as numerous, the amount of putrescible nitro- 

 genous compounds and ammonia is the same, and there is an 



