116 EFFECTS of HEAT 
On the 2rft of April 1805, a fimilar experiment was made with | 
a new barrel, bored in a fquare bar of old fable, of about two 
and a half inch in diameter, having its angles merely rounded ; 
the inner tube being filled with chalk. The heat was main- 
tained during feveral hours, and the furnace allowed to burn 
- out during the night. The barrel had the appearance of found- 
nefs, but the metals came off quietly, and the carbonate ‘was 
entirely calcined, the pyrometer indicating 63°. On examina- 
tion, and after beating off the fmooth and even fcale. of oxide 
peculiar to the old fable, the barrel was found to have yielded 
in its peculiar manner ; that is, by the opening of the longi- 
tudinal fibres. This experiment, notwithftanding the failure of 
the barrel, was one of the moft interefting I had made, fince 
it afforded proof of complete fufion. The carbonate had boil- 
ed over the lips of the little tube, ftanding, as juft defcribed, 
with its mouth upwards, and had run down to within half an 
inch of its lower end: moft of the fubftance was in a frothy 
ftate, with large round cavities, and a fhining furface; in 
other parts, it was interfperfed with angular mafles, which 
have evidently been furrounded by a liquid in which they 
floated. It was harder, I thought, than marble; giving no 
effervefcence, and not turning red like quicklime in nitric 
acid, which feemed to have no effec upon it in the lump. It 
was probably a compound of quicklime with the fubftance of 
the tube. 
Wiru the fame barrel repaired, and with others like it, 
many fimilar experiments were made at this time with great 
fuccefs ; but to mention them in detail, would amount near- 
ly to a repetition of what has been faid. I fhall take notice 
of only four of them, which, when compared together, throw 
much light on the theory of thefe operations, and likewife 
feem to eftablifh a very important principle in geology. Thefe 
four 
