CARBON AND SOME OF ITS COMPOUNDS 



289 



residue being known to be an oxide of a metal, so that they 

 consist of carbon dioxide and a metallic oxide. 



EXPT. 297. Heat copper carbonate, and observe the pro- 

 duction of black oxide of copper. 



This leads us to the idea that lime is also the oxide of a 

 metal, and this view is now known to be correct, the metal 

 being named calcium. Lime therefore is calcium oxide, CaO, 

 and chalk calcium carbonate, CaCO 3 . The action of carbon 

 dioxide upon lime-water may be written 



CaO + CO 2 = CaCO 3 , 

 and the decomposition of chalk by heat is given by the equation : 



CaC0 = 



CO 



Carbon Dioxide. We are now in a position to prepare larger 

 quantities of pure carbon dioxide, and to study its properties 

 more fully. 



EXPT. 298. In a flask fitted with cork thistle funnel, and 

 delivery tube (Fig. 136), place some chalk or marble (also a form 



FIG. 136. The Preparation of Carbon Dioxide. 



of calcium carbonate). Pour in some dilute hydrochloric acid, 

 and collect the gas over water as in the case of the preparation 

 of hydrogen. Collect three jars. 



Pass the gas through a solution of lime-water. Observe 

 the formation of the white precipitate which afterward dis- 

 appears. Boil the solution so obtained, and notice the 

 re-precipitation. 



In the first jar place a lighted taper. Observe the effect. 



