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APPENDIX. 127
lapse of a few days an abundant deposit of carbonate and hvdrated
oxide of lead is found at the bottom of the vessel. If the
experiment be made with distilled water that has been previously
agitated with air, so as to completely aerate it, the lead is more
rapidly acted upon, even in a closed vessel, thus clearly showing
how much the action of the water upon the lead depends upon the
presence or absence of atmospheric air.
Now, in a minor degree, this is precisely what takes place in a
leaden pipe conveying water capable of eroding lead. While the
pipe is full, comparatively but little action occurs; but when the
pipe is filled alternately with air and with water, it is placed under
the most favourable circumstances to ensure a rapid erosion of its
substance, and consequent contamination of the water.
The rush of water necessarily produced by an intermittent flow
must also detach portions of carbonate of lead from the sides of
the pipe, even in those cases where the water has no very decided
action on lead, and it is therefore far from improbable that in this
manner the poison of lead is occasionally conveyed into our
kitchens, and becomes mixed with our food.
According to your desire, I have examined the action of the
waters from the above-mentioned sources on clean lead, and have
arrived at the following conclusions :—The water from Haslemere
has a slow though decided action upon the metal, no effect
taking place until the lead had been partially immersed for four
or five days. After that time, a small deposit of carbonate of
lead was perceptible at the bottom of the vessel, although none
could be detected in solution. The absence of carbonic acid in
the water from Haslemere, Boorley, and Barford, would in all
probability prevent their acting upon lead, were atmospheric air
at the same time excluded. A piece of lead that had been kept
for a week in a closed bottle filled with water from Haslemere did
not exhibit the least trace of carbonate of lead, nor could the presence
of lead be detected in the water.
It is scarcely necessary to add, that the water as drawn from
the pipes of the New River and East London companies does not
exhibit the least solvent action upon lead; when, however, purified
by boiling, and placed in contact with lead, crystals of carbonate
of lead were observable after the lapse of three days in the
water of the New River Company, while, owing to its greater
hardness, the water of the East London Company did not exhibit
any traces of carbonate of lead until the expiration of more than