MODIFIED by COMPRESSION. 8$ 



being filled with pounded filex, or with whatever occurred 

 as moll likely to prevent the intrufion of the fufible metal 

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

 placed in a frame or cradle of iron [d f k b, fig&. 3, 4, 5, and 

 6,) fixed to the end (m) of a ram-rod {jn n). 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 eompofed 

 of two circular plates of iron, (d efg and h i k I, feen edge- 

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

 of thefe plates (d e f h) being fixed to it by the centre (m), 

 Thefe plates were connected together by four ribs or flattened 

 wires of iron {d h> e i,fk, and g /,) which formed the cradle 

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

 duced by thrufting the adjacent ribs afunder. Along with the 

 tube juft mentioned, was introduced another tube (B), of iron 

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

 pyrometer * piece (C) was placed in contact with (A) the tube 

 containing the carbonate. Thefe articles generally occupied. 



the 



* The pyrometer-pieces ufed in thefe experiments were made under my own - 

 eye- Neceffity compelled me to undertake this laborious and difficult work, in., 

 which I have already fo far fucceeded as to obtain a fet of pieces, which, though 

 far from complete, anfwer my purpofe tolerably well. I had lately an oppor- 

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

 tures, in furnaces of great fize and fteadinefs. The refult has proved, that my 

 pieces agree as well with. each other as his, though with my fet each tempera- 

 ture is indicated by a different degree of the fcale. I have thus been enabled to 

 conftruct a table, by which my obfervations have been corrected, fo that the 

 temperatures mentioned in this paper are fuch as would have been 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 % 2d degree. I am well aware, that the late Mr 

 Wedgwood, in his Table of Fufibilities, has ftated that fufion as taking place at 

 the 28th degree ; but I am convinced that his obfervations muft have been msde. 

 with fome fet different from that which was afterwards fold, 



