Faraday to Robert Dundas¹ and John Deas Thomson²   10 February 1832

Royal Institution | Feby 10th. 1832.

Gentlemen

Since I received the sheet of bronze I have been engaged in experiments on it, with the endeavour if possible to find some test of its comparative durability, relative to copper, when on ships bottoms³.

The bronze is an alloy of copper and tin; and yields me nearly 6.2 per cent of the latter metal. I can discover only very minute traces of other metals, not more than occur in ordinary copper, and I believe they are accidental[.]

But I have been more anxious to find, if possible, indications of the properties of the bronze as a whole, than to search after its minute composition; inasmuch as the former could by no means be deduced from the latter. - On comparing the bronze voltaically with copper, I do not find that its energies are less; they appear to be as nearly as possible the same; from which I should be led to expect, that their chemical action, relative to sea water, (upon which the cor‑rosion depends) would also prove nearly the same.

Then again, I have compared the action of an artificial sea water upon similar pieces of this bronze and of sheet copper. I find them both corroded; and the action is so nearly equal that I cannot say whether it is greatest upon the copper or the bronze. Out of many specimens, some of bronze may be selected surpassing others of copper; but it is just as easy to select some of copper surpassing others of bronze[.]

I am of opinion, therefore, that it is only by actual trial and comparison with copper of equal weight, upon ships bottoms, that a true and useful result can be obtained; and though from the facts I have stated, I should not expect any superiority in the bronze; yet it is possible that when tried under the circumstances of time, motion, &c. &c. attending upon the sheathing of a ship, it may, from corroding more equally, (for corrode it certainly will) or in some other way not to be anticipated, exhibit some point of superiority.

Its broken and cavernous surface might be expected rather to assist chemical action. The coat of oxide upon it may perhaps be favourable as an envellope, or it may be voltaically injurious; But I think it useless to speculate in this report upon points which can only be correctly and usefully ascertained by a practical experiment.

I am | Gentlemen | Your Very Obedient Humble | Servant | M. Faraday

Honble Robert Dundas &c &c &c

John Deas Thomson Esq &c &c &c

Endorsed: Read[.] Thank Mr Faraday for his obliging communication - then put these with the other Papers[.]