The question of corrosion is one which is gradually being answered as
time goes on; and so far very satisfactorily for steel. Some steel
boilers were examined a few weeks ago which were among the first made;
and the superintending engineer reports: "There is no sign of pitting
or corrosion in any part of the boiler; the boilers are washed out very
carefully every voyage, and very carefully examined, and I cannot trace
anything either leaking or eating away. No zinc is used, only care in
washing out, drying out, and managing the water." This is the evidence
of an engineer with a large number of vessels in his charge. On the
other hand, some of the most prominent Liverpool engineers always use
zinc, and take care to apply it most strictly. The evidence of one
of them is as follows: "We always fix slabs of zinc to most boilers,
exposing not less than a surface of one square foot for every twenty
indicated horse-power, and distributed throughout the boiler. This zinc
we find to be in a state of oxide and crumbling away in about three
months. We then renew the whole, and find this will last twelve months
or more, when it is renewed again. Meanwhile we have no pitting and no
corrosion; but on the contrary, the interior surfaces appear to have
taken a coating of oxide of zinc all over, and we have no trouble with
them."