MODIFIED by COMPRESSION. 131 
VI. 
Experiments made in Platina,—with Spar,—with Shells, —and with 
- Carbonate of Lime of undoubted purity. 
Stnce I had the honour of laying before this Society a 
fhort fketch of the foregoing experiments, on the 30th of Auguft 
laft (1804), many chemifts and mineralogifts of eminence have 
favoured me with fome obfervations on the fubject, and have 
fuggefted doubts which I am anxious to remove. It has been 
fuggefted, that the fufibility of the carbonates may have been 
the confequence of a mixture of other fubftances, either ori- 
ginally exifting in the natural carbonate, or added to it by 
the contaét of the porcelain tube. 
~Wiru regard to the firft of thefe furmifes, I beg leave ta 
obferve, that, granting this caufe of fufion to have been the 
real one, a material point, perhaps all that is ftriétly necefla- 
ry in order to maintain this part of the Huttonian Theory, was 
neverthelefS gained. For, granting that our carbonates were 
_ impure, and that their impurity rendered them fufible, {till 
the fame is true of almoft every natural carbonate ; fo that 
our experimenats were, in that refpeét, conformable to nature. 
And as to the other furmife, it has been fhewn, by com- 
paring together a varied feries of experiments, that the mu- 
tual ation between the lime and the porcelain was oc- 
cafioned entirely by the prefence of the carbonic acid, fince, 
when it was abfent, no aétion of this kind took place. The 
fufion of our carbonates cannot, therefore, be afcribed to the 
porcelain, 
Beinc convinced, however, by many obfervations, that the 
fufibility of the carbonate did not id upon impurity, 
R2 I 
