the lime, thus weakening the mordant baths.

_Ferruginous Impurities in Water._--Iron in solution in water is very
objectionable in dyeing operations. When the iron is present as
bicarbonate, it acts on soap solutions like the analogous lime and
magnesia compounds, producing even worse results. In wool scouring,
cotton bleaching, and other processes requiring the use of alkaline
carbonates, ferric oxide is precipitated on the fibre. A yellowish tinge
is communicated to bleached fabrics, and to dye bright and light colours
is rendered almost out of the question. You may always suspect iron to
be present in water flowing from or obtained directly out of old coal
pits, iron mines, or from places abounding in iron and aluminous shales.
Moreover, you sometimes, or rather generally, find that surface water
draining off moorland districts, and passing over ochre beds, contains
iron, and on its way deposits on the beds of the streamlets conveying
it, and on the stones, red or brown oxide of iron. All water of this
kind ought to be avoided in dyeing and similar operations. The iron in
water from old coal pits and shale deposits is usually present as
sulphate due to the oxidation of pyrites, a sulphuret or sulphide of
iron. Water from heaths and moorlands is often acid from certain
vegetable acids termed "peaty acids." This acidity places the water in
the condition of a direct solvent for iron, and that dissolved iron may
cause great injury. If such water cannot be dispensed with, the best way
is to carefully neutralise it with carbonate of soda; the iron is then
precipitated as carbonate of iron, and can be removed.

_Contamination of Water by Factories._--You may have neighbours higher
up the stream than yourselves, and these firms may cast forth as waste
products substances which will cause immense waste and loss. Amongst
these waste products the worst are those coming from chemical works,