30 THE SHALLOW AND DEEP WELL WATERS OF ESSEX.
or less seriously affected by the filthy deposits of the centuries
during which Writtle village has existed. In all the gravel waters I
have examined I have found that when the chlorine exceeds about
two grains per gallon (corresponding to 3-3 grains of chloride of
sodium, common salt), there are other signs of pollution and of
change in character due to such pollution. For instance, you will
find that whenever the chlorine is high the nitric nitrogen (which
is a measure of the amount of nitrates present derived from the
oxidation of organic filth) is also high ; whereas generally, but not
invariably, when the chlorine is low the nitrogen is low also.
On Table I. some analyses are given of waters from the Bagshot
sands and pebble beds. One peculiarity of such waters is the low
temporary hardness (due to carbonate of lime) and the comparatively
low total hardness (due to carbonate and sulphate of lime). My
attention has been particularly drawn to these waters, because I find
they have a powerful action upon lead pipe, and upon iron pipes,
whether galvanised or not. I found, however, that I was not the
first person to note this peculiarity, since, upon communicating the
fact to Dr. Barry, one of the inspectors of the Local Government
Board, who is at the present time engaged upon an exhaustive
examination as to the cause of the lead-dissolving power of certain
waters, he informed me that Dr. Harcourt had already sent him a
series of analyses of waters from the Bagshot beds, all of which
waters acted powerfully on lead. Dr. Barry, at the time, appeared
to think that this was a property possessed only by waters from this
particular source. Analyses showed that such waters contained little
or no carbonate of lime (temporary hardness) and therefore had no
alkaline reaction ; and in the north of England, where moorland sur-
face waters often act strongly on lead, the reaction of the water is either
neutral or faintly acid, and the addition of a little chalk (carbonate
of lime) effectually destroys this solvent power. Such waters, how-
ever, are yielded by gravels which, on the Drift maps, are referred to
as "Glacial Drift," especially if such gravels occur on the tops of
hills, or far removed from any Boulder clay. Table II. contains
analyses of many waters containing little or no carbonate of lime,
and most of them can dissolve lead freely. Such waters occur at
Asheldham (an isolated gravel patch), Great Baddow, Little Baddow,
Danbury, Woodham Mortimer, and Woodham Walter, the gravel
upon which these parishes lie being far from any Boulder clay. At
Galleywood, Writtle, Fryerning, Ingatestone, and Stock, the Bagshot