SPECIMENS OF SIR J. HALL's EXPERlMENTg. 315 



arc still harder and more compact, approaching nearly in these Specimens of 

 qualities to common limestone. Numbers 2, 4, and 7, possess g^p^^jg^ ^o^ ^^* 

 a degree of semitransparency, most remarkable in Number 4. strong iieat 

 And all of these specimens exhibit an uneven fracture, ap- "j".^^ ^v^^r 

 proaching to that of beeswax and marble. Their colours are James HalL 

 variously, though slightly, tinged with yellow and blue. In 

 particular Number 3, which, though produced from common 

 white chalk, resembles a yellow marble. Numbers 3, 5, and 

 6, have taken a tolerable polish. Number/, contains a shell 

 introduced along with the pounded chalk, and now closely in- 

 corporated with it. Along with Number 3, is a specimen (A, 

 3.) of common yellow marble, bearing a strong resemblance to 

 the artificial stone. 



Numbers 8, 9> 10, and 11, all formed from pieces of chalk 

 exposed unbroken to heat and pressure. Number 8 is re- 

 markable for a shining grain and semitransparency. 



Numbers 9 and 10, shew parallel planes like internal strati- 

 fication, which has often appeared in calk in consequence of the 

 action of heat, though nothing of the kind could be seen in the 

 native mass. Number 11, very compact, and of a yellow- 

 colour. 



Numbci-s 12 and 13, examples of welding, in which the 

 pounded chalk has been incorporated with a lump of chalk 

 upon which it had been rammed, so that their joining ishardly 

 visible in the fracture. 



Numbers 14, 15, and l6, shewing the fusion of the carbonate 

 well advanced, with a considerable action on the porcelain tube. 

 In Number 15, the red of chalk is half melted, and a yellow 

 substance produced by a mixture of the carbonate with the 

 porcelain. Number 1 6, is a lump of chalk in a state indicating 

 softness, a piece of porcelain which lay in contact with it 

 having sunk a little into the substance of the carbonate. 



Numbers 17 and 18, and all the following numbers, being 

 delicate, are enclosed in tubes of glass, and fixed with seahng- 

 wax on little cups of wood. Number l7j formed from pounded 

 chalk, shows in one part the most complete formation of spar, 

 with its rhomboidal fracture, I have ever obtaiaed. The car- 

 bonate having lost some of its carbonic acid, had crumbled so 

 much in its essential parts by the action of the air, that the 

 crystallization was no longer visible, and 1 had given up the 

 S 5 2 specimen 



