Faraday to Charles Manby   9 February 1842

In reply to the inquiry why does the ore require or why does the iron take any of the carbon of the fuel [blank in MS] stated that the ore being essentially a carbonate of iron the first action of heat either in the ore kilns or in the furnace is to drive off the carbonic acid & leave oxide of iron and then the further action of the carbon of the fuel (besides sustaining a high temperature) is to abstract the oxygen of the oxide and so to reduce the iron to the metallic state after which a still further portion of the carbon of the fuel combines with the iron bringing it into the state of easily fusible or pig metal[.]

As carbon may be communicated to the ore or iron in two ways distinct in their nature i.e either by contact with solid carbon as in the process of cementation (that by which steel is commonly formed) or from the carbonated gasses either carburetted hydrogens or carbonic acid which occupy nearly every part of the air way of the furnace it would be desirable to distinguish as far as may be in any furnace having a particular form or action what proportion of the whole effect is due to the one mode of carbonization or the other¹[.]

My dear Sir

Above you have a rush note[.]

Ever Truly Yours | M. Faraday

9 Feby 1842