st, sometimes several pails full,
and will then run clear for weeks or months, perhaps. In the tub which
receives the water, there is always a large deposit of this same colored
substance; and along the street near by, where the water oozes out of
the bank, there is this same appearance of iron. This deposit is, in
common language, called per-oxide of iron, though this term is not, by
chemists of the present day, deemed sufficiently accurate, and the word
sesqui-oxide is preferred in scientific works.

Iron exists in all animal and vegetable matter, and in all soils, to
some extent. It exists as protoxide of iron, in which one atom of iron
always combines with one atom of oxygen, and it exists as sesqui-oxide
of iron, from the Latin _sesqui_, which means one and a half, in which
one and a half atoms of oxygen combine with one atom of iron. The less
accurate term, per-oxide, has been adopted here, because it is found in
general use by writers on drainage.

The theory is that the iron exists in the soil, and is held in solution
in water as a protoxide, and is converted into per-oxide by contact with
the air, either in the drains or at their outlets, and is then deposited
at the bottom of the water.

In a pipe running full there would be, upon this theory, no exposure to
the air, which should form the per-oxide. In the case stated, it is
probable that the per-oxide is formed at the exposed surface of a large
cask, at the spring, and is carried into the pipe, as it is
precipitated. Common drain pipes would be full of air, which might,
perhaps, in a feeble current, be sufficient to cause this deposit.

Occasionally, cases have occurred of obstruction from this cause, and
whenever the signs of this deposit are visible about the field to be
drained, care must be used to guard against it in draining.

To guard against obstruction from per-oxide of iron, tiles should be
laid deep, closely jointed or collared, with great care that the fall be
continuous, and especially that there be a quick fall at the junctions
of minor drains with mains, and a clear outlet.

Mr. Beattie, of Aberdeen, says: Before adopting 4 feet drains, I had
much difficulty in dealing with the iron ore which generally appeared at
two to three feet from the surface, but by the extra depth the water
filters off to the pipes free of ore. Occasionally, iron ore is found at
a greater depth, but the floating substance is then in most cases
lighter, and does no