30 LESSONS ON CHEMISTRY. 



an iron vessel, the volatile gases pass away, and in the vessel 

 remains a black substance, the carbon of the coal. 



22. When a piece of wood, or common charcoal, is burned 

 in a vessel of oxygen gas, or with free exposure to the air, 

 as in an open fire, it almost entirely disappears, and merely 

 a small quantity of ash is left. In both cases, the carbon 

 which they contain enters into chemical combination with 

 oxygen, and the result of this union is the gaseous compound 

 carbonic acid, which I have mentioned is one of the ingre- 

 dients of the atmosphere. 



23. If we place in a bottle a few pieces of common 

 limestone, and pour over them some spirits of salts (muri- 

 atic acid) or common vinegar, a bubbling up of the liquid 

 will be produced by the escape of a gas from the stone; 

 but if we repeat this experiment with pieces of hmestone 

 from the same quarry after they have been burned in the 

 kiln, neither spirits of salts nor vinegar will produce any 

 escape of gas. If, however, we take a small quantity of the 

 same bunied limestone, after it has remained some weeks 

 exposed to the air, spread over your fields, and treat it in the 

 same manner, it seems to have recovered its original quali- 

 ties, and a copious evolution of gas takes place, which, when 

 examined by the chemist, is found to be identical with the 

 gas which is locked up in combination with lime in the lime- 

 stone rock, and also with the gas produced when charcoal is 

 burned in the air or in oxygen gas.* 



* To procure Carbonic acid we proceed as described above. The gas 

 however, being soluble in water, must not be collected over the trough ; 

 but, as it is considerably heavier than atmospheric air, we can readily 

 fill bottles with it, by a process exactly the reverse of that described 

 for collecting ammonia, thus, instead of directing the tube of the flask 

 vpwards to the bottom of an inverted receiver, we make it pass down- 

 wards to the bottom of a bottle standing in its usual position. The 

 heavy gas settles down to the bottom of the receiver, and displaces the 

 lighter atmospheric air which flows from the mouth of the bottle. We 

 may discover that all common air has been expelled by bringing a 

 lighted splinter of wood near the mouth of the bottle, when it will be 

 extinguished. Carbonic acid consists of 6 parts of carbon and 16 parts 

 of oxygen ; and, though the former of these is an inflammable sub- 

 stance, and the latter a gas remarkable for its power of supporting com- 

 bustion, when chemically combined in the above proportions, they pro- 

 duce a compound which immediately extinguishes flame. The teacher 

 should fill several bottles with the gas, and illustrate its properties. 



a. It possesses acid properties. — When the tube from which the gas 

 is escaping is made to descend into a glass containing some of the bluv? 



