CORROSION IN APPARATUS.--All natural water is a solution of oxygen and
may be regarded also as a weak solution of the hypothetical carbonic
acid. It therefore causes iron to rust more or less quickly; and since no
paint is absolutely waterproof, especially if it has been applied to a
surface already coated locally with spots of rust, iron and steel cannot
be perfectly protected by its aid. More particularly at a few inches
above and below the normal level of the water in a holder, therefore, the
metal soon begins to exhibit symptoms of corrosion which may eventually
proceed until the iron is eaten away or becomes porous. One method of
prolonging the life of such apparatus is to give it fresh coats of paint
periodically; but unless the old layers are removed where they have
cracked or blistered, and the rust underneath is entirely scraped off
(which is practically impossible), the new paint films will not last very
long. Another more elegant process for preserving any metal like iron
which is constantly exposed to the attack of a corrosive liquid, and
which is readily applicable to acetylene holders and their tanks, depends
on the principle of galvanic action.
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