162 Chemistry. [Lecture 29. 



elastic fluid, which being absorbed by water, 

 gives it a brisk acidulous taste, and is an in- 

 gredient in many, or rather most, of the spa 

 waters. Carbonic acid gas is about twice as 

 heavy as common air. Hence it may be received 

 in open vessels, unconfined by water, may be 

 poured into others like that fluid, and will with 

 equal certainty extinguish flame, and suffocate 

 animals immersed in it. 



The base of this acid is carbon, and from its 

 acid character it is to be inferred that the carbon 

 is combined with oxygen. Burning charcoal 

 affords much more than its own weight of it. 

 The test for its presence is clear lime-water, 

 from which it throws down the lime in the form 

 of a white curd, which is chalk, or carbonat of 

 lime. It is in this manner that stalactites are 

 formed. When water holding lime in solution 

 oozes in drops through the roof of a grotto or 

 cavern, where there is carbonic acid gas, it is 

 immediately seized by the gas, which uniting 

 with the lime forms a solid ring on the surface 

 of the drop where it is attached to the stone roof. 

 Another drop succeeding, another ring is pro- 

 duced upon the former. Thus in process of 

 time a slender tube is formed, generally full of 

 water, with a drop suspended from the end. The 

 tube, however, gradually fills up, and the water 

 then proceeding over the external surface, de- 

 posits its lime more quickly in the state of a car- 



