28 CARBONIC ACID GAS. 



SECTION il. CARBONIC ACID, ITS SOURCES AND PRINCIPAL 

 PROPERTIES. 



One of the most important of these combinations is 

 known to chemists as carbonic acid gas. This gas is 

 very abundant in nature, and combines with many 

 solid substances, forming what are called carbonates. 



a. Common limestone is a carbonate of lime; and 

 if muriatic acid be poured upon it, a violent efferves- 

 cence takes place, caused by the escape of this gas. 



b. So in the common soda powers, the soda is a 

 carbonate of soda; and when tartaric acid is added, a 

 violent effervescence ensues, as all have often seen. 

 This too results from the escape of carbonic acid gas. 



c. It causes the froth on beer, and on the surface of 

 all fermenting liquids. 



It is easily collected in glass receivers over water, 

 in the same way as heretofore described. Pouring 

 muriatic acid upon common limestone powdered, or 

 upon carbonate of soda, is a convenient and cheap 

 method of obtaining this gas. If it be done in a tall 

 glass or wide-mouthed bottle, the gas will rise and 

 fill the bottle, so that its properties may be examined. 



1. The first thing apparent will be, that a lighted 

 taper plunged into the bottle is instantly extinguished; 

 thus showing that the gas neither inflames itself, nor 

 supports combustion. 



2. It will be perceived that carbonic acid gas is 

 heavier than common air. It does not rise and mingle 

 with the air, but fills the vessel like water. The taper 

 will burn freely until it reaches its surface, and for a 

 moment even after the lower part of the flame is im- 

 mersed. When the vessel is full, the gas, in place of 

 rising, flows over the edge and downward as water 

 would do. It may be poured from a vessel upon a 

 candle or tai)er so as to extinguish it, provided that 



