d lime soaps, formed in hard
waters. Now in washing and scouring wool and other fibres, these sticky
lime soaps adhere so pertinaciously that the fibres, be they of wool,
silk, or any other article, remain in part untouched, impermeable to
mordant or colouring matter, and hence irregular development of colour
must be the consequence. Also an unnatural lustre or peculiar bloom may
in parts arise, ruining the appearance of the goods. In some cases the
lime soaps act like mordants, attracting colouring matter unequally, and
producing patchy effects. In the dye-baths in which catechu and tannin
are used, there is a waste of these matters, for insoluble compounds are
formed with the lime, and the catechu and tannin are, to a certain
extent, precipitated and lost. Some colours are best developed in an
acid bath, such as Cochineal Scarlet, but the presence of the
bicarbonate of lime tends to cause neutralisation of the acidity, and so
the dyeing is either retarded or prevented. Such mordants as "red
liquor" and "iron liquor," which are acetates of alumina and iron
respectively, are also wasted, a portion of them being precipitated by
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 "p