154 Effects of Heat modified hy Compression. 



the barrel in succession. (This operation is shown in fig. 8.) 

 In some of the first of these experiments I loosened the 

 cradle by plunging the barrel into heated brine, or a strong 

 solution of muriate of lime, whicli last bears a tempe- 

 rature of 250° of Fahrenheit before it boils. For this pur- 

 pose I used a pan three inches in diameter, and three feet 

 deep, having a flat bason at top to receive the liquid when it 

 boiled over. The method answered, but was troublesome, 

 and I laid it aside. I have had occasion lately, however, to 

 resume it in some experiments in which it was of conse- 

 quence to open the barrel with the least possible heat*. 



By these methods I made a great number of experiments, 

 with results that were highly interesting in that stage of the 

 business, though their importance is so much diminished by 

 the subsequent progress of the investigation, that I think it 

 proper to mention but very few of thenj. 



On the 31st of March 1801 I rammed forty grains of 

 pounded chalk into a tube of green bottle-glass, and placed 

 tl in the cradle as above described. A pyrometer in the 

 muffle along with the barrel indicated 33''. The barrel was 

 exposed to heat during seventeen or eighteen minutes. On 

 withdrawing the cradle, the carbonate \i as found in one solid 

 mass, which had visibly shrunk in bulk, the space thus left 

 within the tube being accurately filled with metal, which 

 plated the carbonate all over without penetrating it in the 

 least, so that the metal was easily removed. The weight was 

 reduced from fortv to thirty-six grains. The substance was 

 very hard, and resisted the knife better than any result of the 

 kind previously obtained ; its fracture was crystalline, bear- 

 ing a resemblance to white saline marble ; and its thin edges 

 had a decided semitransparency, a circumstance first ob- 

 served in this result. 



On the 3d of March of the same year I made a similar 



• In many of the following experiments lead was used in place of the 

 fusible metaj, and often -with success; but I lost many good resulls in this 

 vray : for the htat required to liquefy the lead, approaches so near to red- 

 rew, that it is difficult to disengage the cradle without applying a tempe- 

 rature by which the carbonate is injured. I have found it answer well, to 

 surrcnnd the cradle and a few inches of the rod with fusible metal, and to 

 £11 the rest of the barrel with lead. 



4 experiment. 



