290 



ELEMENTARY GENERAL SCIENCE 



CHAP. 



B 



Fie. 137. To illustrate the High 

 Density of Carbon Dioxide. 



Shake up with water, and pour the water into some blue 

 litmus solution. 



Pour the gas from one jar into another, as shown in the 



diagram (Fig. 137), and test 

 both jars by a lighted taper. 

 It will be seen that the lower 

 jar contains the gas. 



AlR; 



Properties of Carbon Dioxide. 



It is thus seen that carbon 

 dioxide is a heavy gas which does 

 not burn nor support combus- 

 tion. It is slightly soluble in 

 water, the solution acting as a 

 weak acid and turning blue litmus 

 to a port wine colour, different 

 from the red produced by strong 

 acids. 



The solution of the gas may in 



fact be regarded as containing an acid, carbonic acid, of composi- 

 tion H 2 CO 3 (thus, CO 2 + H 2 O = H 2 CO 3 ), from which the carbonates 

 are derived. 



The formation of the white precipitate with lime-water has 

 been shown to be due to the formation of calcium carbonate. 

 Its disappearance is usually explained by the statement that the 

 calcium carbonate is soluble in a solution of carbon dioxide, 

 although insoluble in pure water, and is hence re -precipitated 

 when the gas is boiled away. The true explanation most 

 probably is that really a new compound is formed from the 

 calcium carbonate and the carbonic acid, viz., CaH 2 C 2 O 6 , hydrogen 

 calcium carbonate, which is soluble in water, and which decom- 

 poses when heated, again forming chalk. 



Uses of Carbon Dioxide. The fact that carbon dioxide is a 

 non-supporter of combustion is made use of in many forms of 

 chemical fire extinguishers, which are generally solutions which 

 on heating evolve carbon dioxide in which the burning cannot 

 take place and is therefore extinguished. 



The solubility of carbon dioxide in water is increased by pres- 

 sure, and the sparkling nature of the various aerated waters is 

 due to the carbon dioxide with which they have been charged at 

 high pressures, and which escapes when the pressure is reduced 

 to that of the atmosphere by the opening of the bottle. It is 



