Faraday to John Henry Vivian   2 December 1823

Royal Institution | Dec. 2, 1823.

Dear Sir

I have been trying some experiments on the two sheets of copper I have received from Messrs Terrill & Nell¹ with the object of getting a rapid test of their application as sheathing². Inasmuch as vessels at sea are exposed to a strong solution of Muriate of soda I put these coppers into such a solution but added a little sulphuric acid to hasten action. The results were not good from the formation of a quantity of proto muriate of copper which being insoluble coated the plate in all places and defended it from the constant and undiminished action of the solution but the copper which I has marked I was more irregularly acted on than the one marked II[.] In both pieces one side had been acted on more than the other and striae appeared on them in the direction of the length of the plates[.]

I then tried the effect of diluted sulphuric acid alone and after 8 or 10 days have obtained an effect very similar to that on the bad sheathing from a ship sent me by your agents. No. I is very considerably honey-comb’d the edges of the holes being sharp and this occurred on both sides of the plate[.] No. II is affected in a similar way but comparatively to a very slight extent. It is certainly by this trial far superior.

I have just now prepared pieces of No. I & II and a piece of Mushets copper³. They were cleaned by first oil of turpentine then alkali & water so as to have uniform surfaces as they are left by the mills. They were put into dilute sulphuric acid (1 vol acid + 5 vols water) and immediately took the following appearances. I was speckled all over on both sides. II Not speckled but striped on one side & perfectly uniform on the other. Mushett [sic] Black patches appeared on it but no tendency to speckle on either side. Here No. II is again superior -but these shall be watched from day to day & the appearances noticed[.] I am in hopes you will by a dilute sulphuric acid be enabled to test your copper as to its tendency to eat into holes in the course of a few days or even in one day[.]

Whilst making the experiments I did not look to see what the coppers were that no bias should be on the mind but I find that I is what is called best Regular copper and II Common sheathing. The effects are the reverse of what I expected but are far too decided to be a mistake[.]

I have not yet analysed your coppers for the same reason that I had not looked to the kinds[.] I want to see how they behave before I know what is in them. I thought you would like to hear of these results and have therefore not waited for any others.

Perhaps you will let me know what you think of this and if you have copper any otherways prepared will either try them or send them to me. I cannot help thinking that some harm happens to the copper at the rolling mills[.]

I am dear Sir | Your Obedient Servant | M. Faraday

J.H. Vivian, Esq.