MODIFIED by COMPRESSION. 149 



capable of forming a limeftone in a proper heat : That under 

 S6 atmofpheres, anfwering nearly, to 3000 feet, or about half 

 a mile, a complete marble may be formed : and laftly, That 

 with a prefTure of 173 atmofpheres, or 5700 feet, that is, little 

 more than one mile of fea, the carbonate of lime is made 

 to undergo complete fufion, and to acT: powerfully on other 

 earths. 



VIII. 



Formation of Coal. — Accidental occurrence which led me to undertake thefe 

 Experiments. — Refults extracted from a former publication. — Explana- 

 tion offome difficulties that have been fuggejled. — The Fibres of Wood in. 

 fame cafes obliterated, and in fome preferved under comprefjion. — Re- 

 femblance which thefe Refults bear to aferies of Natural Subflances de- 

 fcribed by Mr Hatchett. — Thefe refults feem to throw light on the 

 hiflory of S urtur brand. 



As I intend, on fome future occafion, to refume my ex- 

 periments with inflammable fub fiances, which I look upon as 

 far from complete, I mall add but a few obfervations to what 

 I have already laid before this Society, in the fketch I had the 

 honour to read in this place on the 30th of Auguit laft. 



The following incidental occurrence led me to enter upon 

 this fubjec"l rather prematurely, fince I had determined firft to 

 fatisfy myfelf with regard to the carbonate of lime. 



Observing, in many of the laft-mentioned clafs of experi- 

 ments, that the elaftic matters made their efcape between the 

 muzzle of the barrel and the cylinder of lead, I was in the ha- 

 bit, as mentioned above, of placing a piece of leather between 

 the lead and the barrel j in which petition, the heat to which 

 the leather was expofed, was necefTarily below that of melting 



lead. 



