Extract

Amongst the various clay deposits in the kingdom, there are none of equally deserving importance to this town as those which occur in the coal formation, and are known as fire-clays. Of these there are fortunately several very considerable ones in the neighbourhood of Sheffield, skirting the border of the coal formation and the millstone grit of the high moors. To these my attention has been more particularly directed than to those obtained from other deposits in the same formation. As all seem to possess one property in common, that of making fire-bricks, yet, as is well known to the manufacturers who require fire-bricks in the construction of their furnaces and fire-clays for crucibles, a very considerable difference exists amongst them as regards their qualification to resist heat and withstand any sudden change of temperature when intensely heated, as in the case of the withdrawal of crucibles, containing metal in a high state of fusion, and in the cooling of furnaces. With the object in view of accounting for this difference of quality, I commenced some time ago a course of experiments on several of them, intending as any opportunity might occur to continue them until I had completed my researches, so far as to comprise all the various deposits of the neighbourhood. So far I have examined rather more than a dozen, and from these I shall select a few for reference to on this occasion, premising that I must nevertheless request your indulgence for any incompleteness in the ...