Effects of Heat modified ly Compression. 303 



geology. These four experiments differ from each other 

 only in the heat employed, and in the quantity of air intro- 

 duced. 



The first of these experiments was made on the 27th of 

 April 1S03, in one ofthe large barrels of old sable, with all 

 tUe above-mentioned arrangements. The heat had risen, 

 contrary to my intention, to 78° and 79°. The tubes came 

 out uncontaminated with fusible metal, and every thing l)ort; 

 the appearance of soundness. The contents of the little 

 tube, cmisisting of pounded chalk, and of a small piece of 

 lump chalk, came out clean, and quite loose, not having 

 adhered to the inside of the tube in the smallest degree. 

 There was a loss of 41 per cent., and the calcination seemed 

 to be complete ; the substance, when thrown into nitric acid, 

 turning red, without effervescence, at first, though, after 

 lying a few minutes, some bubbles appeared. According 

 to the method followed in all these experiments, and lately 

 described at length, (and shown in fig. 24. and £5.) the 

 large tube was filled over the small one, with various masses 

 of chalk, some in lump, and some rammed into it in pow- 

 der ; and in the cradle there lay some pieces of chalk, filling 

 up the space, so that in the cradle there was a continued 

 chain of carbonate of four or five inches in length. The 

 subslance v\as found to be less and less calcined, the more 

 it was removed from the breech of the barrel, where the 

 heat was greatetit. A small piece of chalk, placed at the di- 

 stance of half an inch from the small tube, had some saline 

 substance in the heart, surrounded and intermixed with 

 quicklime, distinguished by its dull white. In nitric acid 

 this substance became red, but effervesced pretty briskly ; 

 the effervescence continuing till the whole was dissolved. 

 The next portion of chalk was in a firm state of limestone; 

 and a lump of chalk in the cradle was equal in perfection to 

 any marble I have obtained by compression j the two last- 

 mentioned pieces of chalk effervescing with violence in the 

 acid, and showing no redness when thrown into it. These 

 facts clearly prove that the calcination of the contents of 

 the small tube had been internal, owing to the violent heat 



Vol. 21. No. 96. May 1806. U which 



