122 
to the simple removal of carbon, nor, as Dr Ban- 
croft believes, to the simple iaddition of oxygen, but 
rather to the action of the acid compound, which 
these elementary bodies compose. 
368. M. Bergman is said to have proved that alco- 
hol attracts double its bulk of carbonic acid ; and, 
therefore, this acid will necessarily be attracted by 
these solutions, as fast as it may be formed. To 
prove that, like other acids, it is able to discharge 
their colour, we inverted a bottle, filled with green 
solution, in the pneumatic trough, and passed up in- 
to it a stream of carbonic acid, as it issued from the 
mouth of a retort, that contained carbonate of lime 
and diluted sulphuric acid. A considerable portion 
of the solution was allowed to escape, and the colour 
of the remainder was rapidly discharged, so that it 
was reduced nearly to a colourless state : and when 
suffered to remain at rest, a flocculent precipitate sub- 
sided, and left the liquor perfectly transparent. A 
similar effect was produced, but much more slowly, 
by breathing through a tube into a bottle which 
contained a quantity of green solution ; and as nitro- 
gen gas has been shewn (561.) to effect no change in 
the solution, the discharge of its colour must also, 
in this inslance, have been caused by the action of 
carbonic acid gas. Thus, then, we see, not only 
that carbonic acid is formed by the solution, when it 
is exposed to the light and air, but that it possesses, 
also, the power of discharging its colour, in circum- 
stances where it must be considered to act by the 
exertion of its acid properties alone. 
369. This conclusion is farther supported by the 
