Faraday to John Henry Vivian   7 February 1824

Royal Institution 7th Febry 1824.

My Dear Sir,

I have seen so few of the newspapers as scarcely to know what they say, though I know they have had various statements respecting Mushett’s [sic] plan, and the experiments of Sir H. Davy1. Sir Humphrey’s [sic] experiments are of the most simple & beautiful kind, & apparently perfect as to the results2: They must of course be subject to trial in the large way and such trials are now in progress3. The simple experiment may be thus described: take a slip of copper about 2 inches broad & 12 inches long, solder a piece of zinc or tin of about the size of a sixpence on to it at one end, clean the whole of the copper & the other metal with sandpaper, then cut the slip into two portions of 6 inches each, and entirely immerse into two distinct portions of the same sea water; leave them in for 2 or 3 days or a week, and you will find that the unprotected copper will be considerably acted on by the sea water, will have its surface tarnished, & will deposit a green powder; whilst the protected copper will remain bright & clean, will indeed not be at all acted on, and that a white powder only will (in some cases) deposit in the water, but containing no copper. Such is the experiment, but Sir H. Davy has varied it in many ways. Tin Zinc & Iron & also other metals will act as protectors but Zinc & Iron promise best. In still water tin becomes coated with an insoluble substance, which at last interferes with its action: this would probably not take place in the open sea, but zinc & iron seem to be free from objection even in glasses of sea water. The defending metal need not be applied at any particular part of the plate, but has the same effect, so that it be in contact with it, wherever it be placed. Copper has been completely protected by a piece of tin connected with it only by a long copper wire, but in all cases it is requisite that both the copper and the defending metal should be in contact with the sea water. Several plates of copper have been riveted together, and one of them connected with a piece of tin the other plates have been protected as much as the one directly in contact with the tin. All these effects are the same in acids of considerable strength as well as in sea water. At present Sir Humphrey [sic] is engaged in ascertaining the best means of applying this principle. One plan would be to rivet all the plates of copper on a ship’s bottom together, and connect a horizontal band of tin or zinc with the mass at about the water line. Another plan is to stud each plate of copper with discs of zinc, so that each one may be protected independently of its neighbour. A third plan which is to apply to ships already coppered, is to form a sort of zinc nail &c &c. Of these you shall hear more when they are perfected. For your private information I may say that a piece of Mushet’s copper put into sea water throws down a blue or green sediment just as soon as your copper (not the regular but the other) does, and seems just as much acted on. This certainly appears to me not to go into pits or cavities as your regular copper does, but these little differences will all merge into Sir H’s plan & the one be just as good as the other. There is I think good reason to suppose that the consumption of copper will be considerably diminished by this plan, and as Sir H. Davy has remarked a manufacture of zinc will probably now become a good affair inasmuch as the consumption of the metal will be increased i.e. supposing it be found in practice to be the best that can be used. The Admiralty are highly interested in the experiments and give every facility to experiments on a large scale. You see I have almost filled my paper. If any questions arise in your mind on reading this pray let me have them and I will answer them as I can. Sir H. Davy thinks it will not be worth while your making any preparation of copper till he has by experiment decided which arrangement will be best. In your next to me I wish you would do me the favour to tell me if you are acquainted with a Society at Swansea called the Cambrian Society, for the Promotion of Geology, Mineralogy & Natural History. The Society has done me the favour of making me an honorary member4 & I should be glad to know whether it be an active


See for example Times, 3 February 1824, p.3, col. c.
Davy (1824).
They were not yet commenced. See Times, 16 February 1824, p.2, col. c for details of the proposed trials about to be carried out.
See letter 217.

Bibliography

DAVY, Humphry (1824): “On the corrosion of copper sheeting by sea water, and on methods of preventing this effect; and on their application to ships of war and other ships”, Phil. Trans., 114: 151-8.

Please cite as “Faraday0220,” in Ɛpsilon: The Michael Faraday Collection accessed on 29 March 2024, https://epsilon.ac.uk/view/faraday/letters/Faraday0220