Faraday to William Tierney Clark   3 August 1831¹

Royal Institution | August 3d 1831

Dear Sir,

In answer to your last enquiries² I have only to state that I know of no method under the circumstances of diminishing the action on the Boiler except by diminishing the proportion of sulphurous acid or of the sulphur in the Coal.

I am not prepared to state that all small coal is greatly more sulphurated than larger Coal, nor can I give an opinion on the best kind of Coal to be used for Engine purpose. It must depend entirely upon the price and practical result, and I profess to have no knowledge of either.

With regard to the application of Gas tar to Iron: that must also be decided by experiment. The tar itself would I have no doubt be a very useful substance, but as it is accompanied by an acid, it may happen that a commencement of corrosion of the iron may occur, and the oxide so produced may be useful by forming with the tar a more permanent and adhering coating, or it may, if it break up and admit the weather prove injurious. I cannot tell experience must decide but I should expect the tar would be useful.

I am Dear Sir | Very faithfully Yours | (signed) W Farraday

W. Tierney Clark Esq &c