152 Effects of Heat modified by Compression. 



]onger than the barrel, by which it could be introduced or 

 withdrawn at pleasure. 



A small tube of glass*, or of Reaumur's porcelain, about 

 a 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 possible ; the other half of the 

 tube being filled with pounded silex, or with whatever oc- 

 curred as most likely to prevent the intrusion of the fusible 

 metal in its liquid and penetrating state. This tube so filled 

 was placed in a frame or cradle of iron [dfk h, figs. 3, 4, 5, 

 qnd 6,) fixed to the end {m) of a ramrod {mn). The cradle 

 was from six to three inches in length, and as much in dia- 

 meter as a gun-barrel would admit with ease. It was com- 

 posed of two circular plates bf iroq {defg and hikl, seen 

 edgewise in the figures), placed at right angles to the ram- 

 rod, one of these plates (defh) being fixed to it by the 

 centre (7»), These plates were connected together by four 

 ribs or flattened wires of iron [dh, ei,fk, and gl), which 

 formed the cradle into which the tube (A), containing the 

 carbonate, was introduced by thrusting the adjacent ribs 

 asunder. Along with the tube just mentioned, was intro- 

 duced another tube (B) of iron or porcelam, filled only with 

 jiir. Likewise, in the cradle, a pyrometer t piece (C) was 



* I have since constantly used tube* of comrjion pprcdain, finding glass 

 much too fusible for this purposp, 



I The pyrnmcter-pieces used in these experiments were made under my own 

 eye. Necessity compelled me to undertake this laborious and difficult work, 

 in which I have already so far succeeded as to obtain a set of pieces which, 

 though far from complete, aijswer my purpose tolerably well. 1 had lately 

 an opportunity of comparing my set wllh that of Mr. Wedgwood, at various 

 temperatures, in furnaces of great size and steadiness. The result has proved 

 that my pieces agree as well with each other as his, though with my set each 

 temperature is indicated by a different degree of the scale, I have thus been 

 enabled to construct a table, by which my observations have been corrected, 

 so that the temperatures mentioned in this papor are such ao would hav^ 

 been indicated by Mr. Wedgwood's pieces. By Mr. Wedg^vood's pieces, I 

 mean those of the only set which has been sold t-;) the public, and by which 

 the melting heat of pure silver is indicated at the 2~A degree. I am well aware 

 that the late Mr. Wedg\vood, in his Table of Fusibilities, has stated th.nt 

 fusion as taking place at the TSth degree ; but I am convinced that his ob- 

 servations must have been made with some set different from that which was 

 after'.vards sold. 



placed 



