” 
MODIFIED by COMPRESSION. 105 
nate, carefully weighed, in the fame barrel with a large quanti- 
ty of that fubftance ; and by arranging matters fo that the {mall 
fiducial part fhould undergo a moderate heat, while a ftronger 
heat, capable of producing internal calcination, fhould be ap- 
plied to the reft of the carbonate. In this manner, I made _ 
many experiments, and obtained refults which feemed to con- 
firm this reafoning, and which were often very fatisfactory, 
though the heat did not always exert its greateft force where I 
intended it to do fo. 
On the 28th of February, I introduced fome carbonate, ac- 
curately weighed, into a {mall porcelain tube, placed within a 
larger one, the reft of the large tube being filled with pounded 
chalk ; thefe carbonates, together with fome pieces of chalk, 
placed along with the large tube in the cradle, weighing in 
all 195.7 grains. On opening the barrel, air rufhed out with 
a long-continued hifling noife. The contents of the little tube 
were loft by the intrufion of fome borax which had been in- 
troduced over the filex, in order to exclude the fufible metal. 
But the reft of the carbonate, contained in the large tube, came 
out in a fine ftate, being porous and frothy throughout ; fpark- 
ling every where with facettes, the angular form of which 
was diftinguifhable in fome of the cavities by help of a 
lens: in fome parts the fubftance exhibited the rounding of 
fufion ; in many it was in a high degree tranfparent. It was 
yellow towards the lower end, and at the other almoft colour- 
lefs. At the upper end, the carbonate feemed to have united 
with the tube, and at the places of contact to have {pread up- 
on it; the union having the appearance of a mutual action. 
The general mafs of carbonate effervefced in acid violently, 
-but the thin ftratum immediately contiguous to the tube, fee- 
bly, if at all. 
On the 3d of March, | introduced into a very clean tube of 
porcelain 36.8 of chalk. The tube was placed in the upper 
VOL. VI.—P. I, O part 
