218 Specimens of Sir James Hall's Experiment*. 



No. 25. shows the substance produced by the combina- 

 tion of carbonate of lime with pure silex. Part of the porce- 

 lain tube in this specimen is filled with pounded silex, which, 

 having a very feeble agglutination, is supported by some 

 sealing-wax. Upon the silex during the experiment had 

 lain some carbonate of lime, the lower part of which had 

 united with the silex, producing a semi-transparent sub- 

 stance with a delicate tinge of blue. The termination of this 

 compound, as it had advanced downwards into the silex, 

 shows the round and mammillated form of chalcedony. 



No. 2S, result of an experiment with heat and compres- 



madc July '22, 180.5, with some pure carbonate of lime 



prepared bv Mr. Hatehett. The carbonate was^ inclosed in 



a small tube of platina, and was thus secured against all 



contamination. 



No. 27, result of an experiment made likewise in platina 

 With a fragment of a periwinkle shell : the form of the shell 

 is still visible, though the substance is glazed by semi- 

 t'usion. Along with, on the same stand, is a small drop 

 like a pearl, formed by the entire fusion of one of the frag- 

 ments; and a portion of shell of the same kind, in its na- 

 tural state, is introduced, in order to show what change had 

 taken place djring the experiment. 



No. 28. is a specimen of coal produced from horn; it is 

 a shining black substance, exactly resembling pitch, or black 

 sealing-wax : it was formed in a low red heat, and in cir- 

 cumstances of compression ; by which, while some of' the 

 volatile parts of the original were allowed to separate, others 

 were retained. It lias thus acquired a jet black colour, 

 while it retains its inflammability, and burns with bright 

 flame. 



No. 29. likewise produced from an animal substance, flan- 

 nel. In this case, none of the component parts of the ori- 

 ginal substance seem to have separated from it, owing either 

 to less heat or greater closeness than in the last case. The 

 consequence has been, that the original colour has under- 

 gone much less change, being of a yellow red, at the same 

 time the substance has been in a state, of fusion, and has 



assumed 





