Experiments en Iron at elevated Temperatures^ isfc. 107 



in an air furnace, and the heat was ralfed gradually for an hour. During a fecond hour it 

 was continued at its higheft pitch ; after which the apparatus was removed from the fire *. 

 The heat marked by the pyrometer was 152°. 



The iron had retained its (hape perfeflly, and its properties remained unchanged. The 

 felfpar was reduced to a glafs, perfeftly tranfparent and colourlcfs, except that it had re- 

 ceived a greeni(h tinge where it was in conta£l with the iron. This, I prefume, it derived 

 from a fmall portion of oxide formed on the furface of the iron, by the air unavoidably 

 included in the crucibles. 



Wifliing to exclude the felfpar from the iron, I varied the procefs by placing a piece of 

 iron alone in a coniifh clay crucible, luting on a lid, and imbedding this in another cru- 

 cible filled with felfpar. The heat was continued for an hour and a half. I found that 

 the melted felfpar had penetrated into the interior crucible, and that part of it had reached 

 the iron which fliU remained unaltered. 



In order efFe£lually to prevent the felfpar from coming into contaft with the metal, I 

 next put a piece of iron into one of the fmall cornifli clay crucibles, and inverted another 

 of a larger fize over it. The two crucibles were luted together with a mixture of Cornifh 

 clay baked in a heat of 160°, and a little of the fame clay in its raw ftate. I placed them 

 in a Heffian crucible, furrounded them with fragments of felfpar, and luted on a lid as 

 before. The heat was managed as in the former experiment, and continued in its greateft 

 intenfity for an hour and a half. I found the fmall crucibles intire, and imbedded in the 

 glafs of the felfpar. The oxide of the iron had a£led on the interior crucible, and formed 

 a fmall quantity of brownifli glafs. The iron retained its (hape and foftnefs, and pofTefled 

 none of the properties of fteel. 



Mr. Mufliet is of opinion, that carbon dlflblved in caloric, penetrates but flowly through 

 earthy bodies. It therefore occurred, that he might obje£l: to thefe refults as unfatisfaiSlory, 

 becaufe I had not allowed fufficient time for the carbon to find its way through the thick 

 mafs of crucibles and felfpar in which the iron was imbedded. This I hoped to obviate by 

 the following experiments. 



Having placed in a Heffian crucible a piece of foft iron, weighing about half a pound 

 troy, I furrounded it with fand. This crucible was included in two others of the fame 

 kind, and the fpace between each being filled with fand, lids were luted on, and the whole 

 was placed in the reverberatory at Mr. Barker's Iron Foundcry, and allowed to remain in 

 its utmoft heat for fix hours. When taken out, I found that the aflies carried up by the 

 flame had vitrified a great part of the crucibles, fo as to form two fmall apertures in the 

 interior crucible which contained the iron 5 but to my furprize I found the iron .unaltered, 

 except that it was flightly oxidated on the furface. The pyrometer was deftroyed. 



In a fecond experiment with another piece of iron, I filled the interftices between the 

 crucibles with lute made of fand and clay. The heat was continued for four hours only, 



• In all thefe experiments the fuel was coak. 



P2 at 



