SiO ACTION OF HEAT UODIVIEO 



Dcfcrlption of A fmall tube of glafs, • or of Reaumur's porcelain, about 

 liappara as. ^ quarter of an inch in diameter, and one or two inches in 

 length, (fig. 2, A) was half filled with pounded carbonate of 

 lime, rammed as hard as poilible ; the other half of the tube 

 being filled with pounded filex, or with whatever occurred 

 as moft likely to prevent the inlrufion of the fufible metal 

 in its liquid and penetrating ftate. This tube fo filled, was 

 placed in a frame or cradle of iron {dfk It, figs. 3, 4-, 5, and 

 6), fixed to the end (ni) of a ram-rod {m «). The cradle 

 was from fix to three inches in length, and as much in diame- 

 ter as a gun-barrel would admit with eafe. It was compofed 

 Of two circular plates of iron, [defg and h i k I, feen edge- 

 wife in the figures), placed at right-angles fo the ram-rod, one 

 of thefe plates {d e f ^) being fixed to it by the centre (to). 

 Thefe plates were connected together by four ribs or flattened 

 wires of iron {dk, ei,fk, and g Z,) which formed the cradle 

 into whicii the tube (A), containing the carbonate, was intro- 

 duced by thrufting the adiactnt ribs afunder. Along with the 

 lube jutl mentioned, was introduced another tube (B), of iron 

 or porcelain, filled only with air. Likewife, in the cradle, a 

 pyronieter •{• piece (C) was placed in contaft with (A) the tube 



con- 



* I have fmce conftanlly ufed tubes of common porcelain, find- 

 ing glais much too fufible for this purpofe. 

 \ T The pyrometei'-pieces ufed in thefe experiments were made 



/ under my own eye. Necellity compelled me to undertake this 

 laborious and difficult work, in which I have already fo far fuc- 

 ceeded as to obtain a fet of pieces, which, though far from com- 

 plete, anfwer my purpofe tolerably well. I had lately an oppoi'- 

 tunity of comparing my fet with that of Mr. Wedgwood, at various 

 temperatures, in furnaces of great fize and (teadinefs. The refult 

 has proved, that my pieces agree as well with each other as his, 

 though with my fet each temperature is indicated by a different 

 degree of the fcale. I have thus been enabled to conftruft a 

 table, by which my obfervations have been correfted, fo that the 

 temperatures mentioned in this paper are fuch as would have beew 

 indicated by Mr. Wedgwood's pieces. By Mr. Wedgwood's 

 pieces, I mean thofe of the only fet which has been fold to the 

 public, and by which the melting heat of pure filver is indicated 

 at the 22d degree. I am well aware, that the late Mr. Wedg- 

 wood, in his Table of Fufibditics, has ftated that fufion as taking 



place 



