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but unless it lias been immediately produced at the 
surface of the earth in some chemical process, this 
does not seem to be the case : elastic fluids of dif- 
ferent specific gravities have a tendency to equable 
mixture by a species of attraction, and the different 
parts of the atmosphere are constantly agitated and 
blended together by winds or other causes. De 
Saussure found lime-water precipitated on Mount 
Blanc, the highest point of land in Europe ; and 
carbonic acid gas has been always found, apparently 
in due proportion, in the air brought down from 
great heights in the atmosphere by aerostatic ad- 
venturers. 
The experimental proofs of the composition of 
carbonic acid gas are very simple. If 13 grains 
of well burnt charcoal be inflamed by a burning- 
glass in 100 cubical inches of oxygene gas, the 
charcoal will entirely disappear ; and, provided the 
experiment be correctly made, all the oxygene ex- 
cept a few cubical inches, will be found converted 
into carbonic acid ; and, what is very remarkable, 
the volume of the gas is not changed. On this 
last circumstance it is easy to found a correct esti- 
mation of the quantity of pure charcoal and oxy- 
gene in carbonic acid gas: the weight of 100 
cubical inches of carbonic gas is to that of 100 
cubical inches of oxygene gas, as 47 to 34 : so that 
47 parts in weight of carbonic acid gas, must be 
composed of 34 parts of oxygene and 13 of char- 
coal, which correspond with the numbers given in 
the second Lecture. 
Carbonic acid is easily decomposed by heating 
potassium in it ; the metal combines with the oxy- 
o 
