Carbonic 
acid. 
Test for its 
presence. 
14 ON THE PLACE OF FISH IN 
be obtained, however, by interfering with the flame, for 
in a flame properly burning it will all be oxidized and 
pass away as carbonic acid. Indeed, if the Carbon 
collected on the plate be scraped off and put on to 
a shovel over the fire, the oxidation will be resumed, 
and it will all pass away as carbonic acid. 
Carbonic acid is an invisible gas, but there is a very 
simple way by which its presence can be detected. 
It readily unites with lime to form the compound 
carbonate of lime, and is therefore frequently used as 
a test for the presence of lime in water. The carbonate 
of lime forms as a fine white powder which gives at 
first a milky appearance t the water, clearing as 
the powder settles to the boitom. As the result of 
the combination of the two is always the same, lime 
water is a ready test for the presence of carbonic acid. 
It can be obtained cheaply at a druggist’s. The carbonic 
acid given off by a flame can easily be collected in any 
jar, which will not crack with heat, by holding it so 
that the flame is well within its mouth. It will be 
known when no more will be formed, as the light will 
then “go out,” that is oxidation will cease, because 
there is no more free Oxygen within the jar. If the 
jar is then turned over, and a little clear lime water is 
poured in and well shaken about, so as to absorb the 
carbonic acid, the milkiness, due to the white powder 
being formed, will be seen. 
It will probably help to bring home more forcibly 
some facts that will presently be referred to, if the 
experiment be repeated with some fat such as would 
be used for food. It is not much trouble to make 
a sort of candle of it with some darning worsted as 
a wick, so that the fat can be oxidized (i.e. burnt, 
