Serious
damage may be done to the dyer by either of these classes of impurities,
and I may tell you that the dissolved calcareous and magnesian
impurities are the most frequent in occurrence and the most injurious. I
told you that on boiling, the excess of carbonic acid holding chalk or
carbonate of lime in solution as bicarbonate, is decomposed and
carbonate of lime precipitated. You can at once imagine, then, what
takes place in your steam boilers when such water is used, and how
incrustations are formed. Let us now inquire as to the precise nature of
the waste and injury caused by hard and impure waters. Let us also take,
as an example, those most commonly occurring injurious constituents, the
magnesian and calcareous impurities. Hard water only produces a lather
with soap when that soap has effected the softening of the water, and
not till then. In that process the soap is entirely wasted, and the
fatty acids in it form, with the lime and magnesia, insoluble compounds
called lime and magnesia soaps, which are sticky, greasy, adhesive
bodies, that precipitate and fix some colouring matters like a mordant.
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