Effects of Heat modified by Compression . 151 



experiments of this kind, in a barrel with the large bore of 

 0*75 of an inch. 



No. 10. was made with a- compressing force of only 

 3 cwt. A small eruption at the muzzle being observed, 

 water was thrown on the barrel : the pyrometer gave 2 1°: 

 the chalk was in a firm state of limestone. 



No. 1 1 . with 4 cwt. The barrel stood, without any erup- 

 tion or exudation, till the heat ro?,e to £5°. There was a 

 loss of 3-6 per cent. : the result was superior, in hardness 

 and transparency, to the last, having somewhat of a saline 

 fracture. 



No. 12. with 5 cwt. The result, with a loss of 2-4 per 

 cent., was of a quality superior to any of those lately ob- 

 tained. 



These experiments appear to answer the end proposed, of 

 ascertaining the least pressure, and lowest heat, in which 

 limestone can be formed. The results, with, various barrels 

 of different sizes, agree tolerably, and tend to confirm each 

 other. The table shows, when we compare Nos. 1, 2, 8, 

 JO, 1 1, 12, that a pressure of 3S atmospheres, or 1700 feet 

 of sea, is capable of forming a .limestone in a proper heat : 

 that under SO atmospheres, answering nearly to 300.) feet, 

 or about half a mile, a complete marble mav be formed : 

 and lastly, that with a pressure of 173 atmospheres, or 5700 

 feet, that is, little more than one mile of sea, the carbonate 

 of lime is made to undergo complete fusion, and to act pow- 

 erfully on other earths. 



§ vnr. 



Formation of Coal. — Accidental Occurrence which led me to 

 undertake these Experiments. — Results extracted from a 

 former Publication. — Explanation of some Difficulties that 

 have been suggested. — The Fibres of Wood in some Cases 

 obliterated, and in some preserved, under Compression, — 

 Resemblance which these Results tear tod Series if \.:- 

 tural Substances described by Mr. Hatchet t. — These Re- 

 sults seem to throw Eight on the History of Sitrturbrand. 



As I intend, on some future occasion, to resume my c\'- 



•ethnjentfl with inflammable substances, which I lock upon 



K 4 as 



