Page:Proceedings of the Royal Society of London Vol 1.djvu/204

Rh ticularly described, from which Mr. Mushet deduces the following general remarks.

The formation of wootz, he says, appears to him to be in conse- quence of the fusion of a particular ore, which he supposes to be cal- careous, or to be rendered so by a mixture of calcareous earth, along with a portion of carbonaceous matter. The fusion, he thinks, is performed in a clay vessel or crucible, in which vessel the separated metal is allowed to cool. Hence, in his opinion, arises the crystalli- zation that occupies the pits and cells observed in and upon the under or round surface of the cakes.

The want of homogeneity and solidity in these cakes, appears to Mr. Mushet to be owing to the want of a sufficient degree of heat to effect aperfect reduction ; and this opinion, he thinks, is strength- ened by observing, that those cakes which are the hardest, or which contain the largest portion of carbonaceous matter, and, of course, form the most fusible steel, are always the most solid and homoge- neous; while, on the contrary, those cakes which are the most easily cut by the chisel, are in general cellular, and abound with veins of malleable iron. If the natives of the country which produces the wootz were capable of rendering it perfectly ﬂuid, Mr. Mushet thinks they would certainly have run it into moulds, by which, he says, they would have acquired a kind of steel more uniform in its qua- lity, and more ﬁt for the purpose of being worked and applied to the arts.

Some of the cakes here described had, around the feeder, and upon the upper surface in general, evident marks of the hammer. This appearance Mr. Mushet accounts for by supposing, that when the cake was taken from the pot or crucible, the feeder was most probably slightly elevated, and the top of the cake covered in part with small masses of ore, which, from want of a sufﬁcient degree of heat, had not been perfectly fused. These, he thinks, are cut off at a second heating, and the surface then hammered smooth, to make the cakes more fit for sale. Mr. Mushet says he has observed similar appearances in operations of a like nature, where the heat has been insufﬁcient; and that such phenomena sometimes take place in se- parating crude iron from its ores, when, from its containing an excess of carbon, it is difﬁcult to be fused.

The division of the cakes, by the native manufacturer, he thinks, is done merely to facilitate its subsequent application to the purposes of the artist, and to serve as a test of the quality of the steel.

In order to determine by direct experiment whether wootz owes its hardness to an excess of carbon, Mr. Mushet made some comparative experiments upon the cakes, and upon common cast steel and white cast iron. In operations of this kind, he says, he has always found the proportion of carbon best ascertained by the quantity of lead reduced from ﬂint glass. He therefore mixed a certain quantity of wootz, or of steel, or iron, with three times the weight of pounded ﬂint glass, and exposed the mixture to a heat of 160° of Wedgwood's pyrometer.