THE PRESIDENTIAL ADDRESS.
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tion, viz., the Water Supply of the Lea Valley. Half a century ago
the question would have seemed below the notice of a society like
ours. Any fairly palatable water from a stream, whatever happened
to it above the intake of the water, or from a well, about which no
questions were asked as to the neighbourhood of cesspools and
drains, was considered fit for domestic use. Some of the pumps,
the water of which was specially sought after, owed their pleasant
flavour to an abnormal amount of carbonic acid and nitrates, which
were easily accounted for by the close proximity of churchyards.
Twenty-five years ago the subject would have been considered
unfit for us, as being merely chemical, and only suited for Burlington
House. We now find that the question of water supply involves the
study of biology and physiology not less than that of geology and
chemistry.
It is an interesting lesson on the interdependence of different
sciences when they are to be brought into practical use.
The first advance towards purity in water supply was made by
the help of chemistry. Even the very crude methods of analysis of
my student days (taking the dry residue of the evaporation of the
water and reckoning as organic matter the loss sustained on heating
to redness, and treating with solution of carbonate of ammonia and
again drying) was sufficient to condemn a large proportion of the
water supply. Residues of over 100 grains to the gallon, which
when heated lost 20 to 30 grains, giving off a strong smell of burnt
horn, were not uncommon. It is not to be wondered at that
outbreaks of cholera and fever were plainly traceable to the
accidental supply of such organic matter a little fresher than usual.
When more reliable methods of analysis were brought to bear,
and methods were introduced for the estimation of the oxygen con-
sumed in oxidizing organic matter by permanganate solution ; of
ammonia and albuminoid nitrogen by the various applications of the
Nessler test ; and for the accurate determination of carbon and
nitrogen in the dry residue by combustion with copper oxide ; the
difficulty arose how to interpret the results.
Albuminoid ammonia certainly seemed a danger signal, but how
could we condemn a water supply on evidence of its presence, when
Loch Katrine, and most other peat waters, gave higher results than
some wells and streams undoubtedly polluted by sewage. It was
easy also to regard any nitrogen as the result of previous sewage
contamination, but it would seem in view of the presence of soluble