CARBON AND CARBONIC ANHYDRIDE. 85 



the bent tube, and so can be collected in jars in the pneu- 

 matic cistern. The explanation is this : The chalk and mar- 

 ble are two forms of the same substance, calcium carbon- 

 ate, which contains carbonic anhydride united to the oxide 

 of calcium, commonly called lime. Now the hydrochloric 

 acid decomposes the calcium carbonate, forming water, the 

 gaseous carbonic anhydride, and a new body, calcium chlo- 

 ride, which remains dissolved in the water. We do not see 

 the water formed, for it mixes with that in the flask ; nor 

 do we see the calcium chloride, for it is very soluble, and 

 remains in the water ; we can easily prove it is there, how- 

 ever, by evaporating the watery solution, when we will ob- 

 tain a white solid mass. The carbonic anhydride set free 

 is seen as it bubbles up through the water. Expressing 

 this in symbols, we write thus : 



,, ., Hydrochloric Calcinm \xr^ a Carbonic 



Marble - ' acid. chloride. Water * anhydride. 



CaCO 3 + 2HC1 = CaCl 3 + HsO + CO a 



Sodium carbonate, potassium carbonate, or any other car- 

 bonate, will serve equally well; so, also, sulphuric or nitric 

 acid may be used instead of hydrochloric. 



104. Properties of Car- 

 bonic Anhydride. This 

 gas is, like air, transparent 

 and without color. It has 

 a slightly acid and agreea- 

 ble taste. Its specific grav- 

 ity is 1.527 that is, it is 

 about one and a half times 

 as heavy as air. Because it 

 is so much heavier than air 

 it can be collected by dis- Fi s- 22 - 



placement, as it is termed. This is represented in Fig. 22. 

 The gas produced in the flask passes over in the tube and 



