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128 APPENDIX.
a week, and even then only in a slight degree. The same waters
purified by the patented process of Clark did not exhibit so decided
an action upon lead as when purified by boiling; but after
evaporating to dryness the water in which lead had been immersed
for three weeks, and dissolving the residue in dilute nitric
acid, the presence of a minute quantity of lead was rendered
evident.
It therefore appears that if leaden pipes, and especially if leaden
cisterns, are to be employed in the distribution and storage of
water, on the system of interrupted supply, it will be a necessary
safeguard, that the water thus conveyed and stored should not be
of less hardness than from six to seven degrees, compared with
distilled water as unity ; and conversely, it also follows, that if
the inhabitants of the metropolis are to gain the advantage of
using a still purer and softer water, it will be requisite to do away
with the existing leaden pipes and cisterns, and to substitute for
them some material which shall not communicate any poisonous
or noxious ingredient to the water. As matters now stand, we
escape daily poisoning by the use of water loaded with earthy
salts, and are thus compelled to drink an impure water on account
of the impurity of our vessels. Would it not be better, and is it
impossible, to drink the pure element from a pure cup ?
I remain, dear sir, with much respect,
Yours obediently,
Thomas Taylor.
To John Simon, Esq., F.R.S.,
Officer of Health to the City of London.
Taylor, Printer, 39, Coleman street.