ea 
120 EFFECTS of HEAT 
periment proved, that quicklime by itfelf, could neither be 
melted, nor,act upon porcelain, even in the violent heat of 79° ; 
whereas, in the laft experiment where the carbonic acid was 
retained, both of thefe effects took place in a very low tempe- 
rature. : 
V. 
Experiments in which Water was employed to increafe the Elafticity of 
the included Air.—Cafes of complete Compreffion.—General Obferva- 
tions. —Some Experiments affording interefting refults ; in particular, 
Joewing a mutual action between Silex and the Carbonate of Lime. 
FinpineG that fuch benefit arofe from the increafe of elafti- 
city given to the included air in the laft-mentioned experi- 
ments, by the diminution of its quantity ; it now occurred to 
me, that a fuggeftion formerly made by Dr Kennepy, of ufing 
water to aflift the comprefling force, might be followed with 
advantage: That while fufficient room was allowed for the 
expanfion of the liquid metal, a reacting force of any requi- 
red amount, might thus be applied to the carbonate. In this 
view, I adopted the following mode, which, though attended 
with confiderable difficulty in execution, I have often practi- 
fed with fuccefs. The weight of water required to be intro- 
duced into the barrel was added to a {mall piece of chalk or 
baked clay, previoufly weighed. The piece was then dropped in- 
to atube of porcelain of about an inch in depth, and covered with 
pounded chalk, which was firmly rammed upon it. The tube 
was then placed in the cradle along with the fubject of expe- 
riment, and the whole was plunged imto the fufible metal, 
previoufly poured into the barrel, and heated fo as merely 
to render it liquid. The metal being thus fuddenly cooled, 
the 
