273 
Quantity of Carbon in carbonic Acid. 
the mercury bath, the whole of the vessels being also filled 
with mercury in order to exclude common air. Heat applied 
by an Argand's lamp produced gas equal to about half the bulk 
of the charcoal; but as soon as the temperature of the mercury 
rose to 21 4, 0 Fahrenheit, elastic fluid streamed from every 
piece of charcoal, which quickly condensed, and i~ inch of the tube 
was occupied with water. This proved that our suspicion of 
the increase of weight being principally attributable to water, 
was well founded. 
The result of these, and other experiments, plainly pointed 
out the precautions which were necessary in order to obtain an 
accurate result with charcoal ; for if we had weighed 4 grains 
of the charcoal a few hours after it was made, we should only 
in fact have had 3,5 grains of real charcoal, and our calculations 
would have been erroneous. To avoid this source of error, 
we subjected our charcoal to a red heat immediately before 
using it, and also weighed it as speedily as possible ; in fact, 
while it was still warm. It may be proper to state, that our 
weights were such as we could thoroughly depend upon. 
The volume of gas being so much influenced by temperature 
and pressure, these were noted during every experiment ; and 
thermometer 6o° Fahrenheit, barmometer 30°, were assumed 
as the standard. Gay Lussac remarks, that from 32°to 212® 
Fahrenheit, dry air expands 0,00208, or part of its bulk 
for every degree of the thermometer. Dalton makes it 
0,000207, or part ; we therefore divided the whole quan- 
tity of gas by 480, and multiplied the quotient by the degrees 
of difference under 6o°. 
It being of great consequence in these experiments to know 
