Having had some inquiries made of us respecting the amount of corrosion which iron undergoes in water, we present the following remarks of Mr, Adie, of Liverpool, Eng,, which were read sometime ^go before the Institute of Civil Engineers. The object of his experiment was to testthe rate of corrosion of metals in fresh water, brine, and sea water, * These experiments were made with weigh-edpiecesof metal immersed in the three solutions under examination. Those which are compared together were tried in every respect under similar circumstances, as to weightand surface of metal; size and form of vessel; quantity of water employed ; light and temperature. The experiments on zinc were made with that metal in connection with a piece of copper, so as to form a galvanic couple ; for zinc, when unconnected with a less oxidizable metalj is soon covered with a crust of oxide, so that pieces, after a month's im- rersion in water, are found to be slightly heavier than at the beginning of the experiment, fhis is not the case when a piece of silver or :opper is in metallic connection with zinc; or then the white oxide of the metal is gra-lually precipitated to the bottom of the containing vessel, A plate of zinc, 1 superficial inch in area: mmersed for 60 days in sea waters lost 16 grains, A similar experiment in fresh water lost, .*I5 grains. A plate of zinc, 7 superficial inches in area, mmersed for 96 days in fresh waters lost 4'9 grains, A similar experiment in brine, or the sa-urated solution of common salt tested as ibove for dissolved air, lost 1"4 grains. Wrought iron wire :— Twenty pieces of iron, weighing 374 grains, mmersed for SO days in fresh waters lost 1"9 grains, A similar experiment in sea water, lost 2'6 grains, A similar experiment in brine, lost O'l grains. Cast iron:— Three rods ofcastirons weighing 787 grains, mmersed for 62 days in fresh waters lostl'6 j^ains, A similar experiment in sea water lost 2*0 grains, A similar experiment in brine lost G'4 grains. On comparing together the loss of weight f metal in the fresh water, sea water, and jrinej it will be observed, that in sea water jhe corrosion is about one-third more than in fresh water? while in brine, the loss of weigh s about one tourth part of the loss in fresh rvater, and one-fifth part of that experienced n sea watery showing that brine possesses :onsiderable power for preserving metals rom corrosion. The carbonates of potash and soda are still more effectual in arresting oxi-lation; for in saturated solutions of these ;altSj iron wire remained immersed for sixty lays without any amount of corrosion being ietected. The surface of the plate of zinc, tfhen taken from the brine, was the same as iB the commencement of the experiment, excepting in three spots, where there was deep tirrositfn. The principal of these Mftg irourul the jioint, where the copper wire connected the plate with the negative element, Che difference between fresh water and sea rvater, in their power of oxidizing metalsj is n the reverse order oi the quantities of oxygen dissolved by them, as given in the preceding experiments; where the sea water ft ?o the iresh ss IS to 85, The principle on ivhich the preserving power of alcohol is attempted to be explained may, in like manner, ae here applied to pure water. Although the experiments on the corrosion of iron were continued for eighty days, the difference be-;ween the action of common water and brine nay be made apparent in one day. In the resh water, the hydrated peroxide of iron is *een forming; while in the brine, only a dight tinge of a greenish infusion can be de--ectedj a sure indication of the scarcity of oxygen. The experiments given to determine the respective rates of corrosion in fresh and sea ivaterj are only correct for pieces of metal wholly immersed in them. Where the sur-aces are subject to be wet and drys the corrosive effect of sea water will greatly increase; on the same principle that iron once coated with rust decays much fester after the rust has provided a lodgement for moisture. Take for example a bar of iron in a field, and a similar piece on the deck of a ship. On bhe firstj the dew of night deposits waters which corrodes until the returiwrf the sun iries it off. On the seconds -oW the deck, it deposits sprays which acts like the dew, intil the sun dries it off^ but when dried, there is left a thin deposit of salts with a powerful affinity for moisture, which on the return oi evening will attrect moisture from the atmosphere, long before the dew wets the metal in the field. Thus it is that a coating )f salt or rust keeps metals much longer in a wet state than if their surfaces were clean. The steam propeller yacht, CoL John Stevens, has been sold to the Newfoundland Te-[egrah Co,, to overhaul the steamships from Liverpool for New York, and obtain news to be sent over the telegraph wires.
This article was originally published with the title "Corrosion of Metals in Water"