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126
126 APPENDIX.
The following Table indicates the relative hardness of the different
waters as determined by the Soap test; distilled water being
taken as unity, as proposed by Professor Brande. It also shows
the effect of boiling in reducing the hardness of the water. The
numbers express the direct quantity of an alcoholic solution of
soap which an equal bulk of each water requires in order to form
a lather remaining permanent for from five to ten minutes.
Distilled water 1-0
Water from Haslemere 2.4
Boorley 1.5
Barford 2.4
Water of the New-River Company 13.3
Ditto after being boiled 4.7
Water of East-London Company 19.0
Ditto after being boiled 5.6
Water from the Well in Bishopsgate st. 47.4
Ditto after being boiled 26.6
The experiments which I have recently made on the action of
pure water upon lead, clearly point out the necessity of keeping
the pipes always full, especially in those instances in which the
water has a tendency, however slight, to erode the lead. As
the importance of this part of the question does not appear to
have been sufficiently appreciated by the advocates of a constant
instead of an intermittent supply, I will briefly recount the facts
of the case, although I do not offer them as presenting anything
particularly novel. If a piece of bright lead be placed in a stoppered
bottle, completely filled with recently distilled water, so that
the access of air be wholly excluded, the lead is but very slightly
acted upon, and it is only after the lapse of three or four days
that its surface becomes spangled with a few minute crystals of
carbonate of lead.
If the stopper of the bottle be now removed, the lead still remaining
beneath the surface of the water, the erosive action of
the water on the lead proceeds more rapidly, but still slowly.
But if now a portion of the water be poured off, so as to leave the
lead only partially immersed, rapid action on the lead immediately
commences. In the course of thirty-six or forty-eight hours, its
surface becomes coated with crystalline scales of carbonate of
lead, which, falling off, are succeeded by others, so that after the