AEOUT COMMON WATER. 839 



heard and read, that our feet were plunged in a stream 

 of heavy carbonic acid flowing along the bottom of the 

 cave. The poor little dog, much against its will, was 

 brought into the grotto. The stream of carbonic acid 

 was not deep enough to cover the animal ; its master, 

 accordingly, pressed its head under the suffocating gas. 

 It struggled for a time, but soon became motionless 

 apparently lifeless. Taken into the air outside, 

 through a series of convulsions painful to look upon, 

 it returned to life. 



The experiment is a barbarous one, and ought not 

 to be tolerated. There are many ways of satisfying 

 the curious, without cruelty to the dog, I made the 

 following experiment, which seemed to surprise the by- 

 standers. Placing a burning candle near the bottom 

 of my hat, in the open air outside the cave, I borrowed 

 a cap, and by means of it ladled up the heavy gas. 

 Pouring it from the cap into the hat, the light was 

 quenched as effectually as if water had been poured 

 upon it. Made with glass jars instead of hats, this is a 

 familiar laboratory experiment. 



We must now proceed slowly forward, making our 

 footing sure as we advance. Lime is sparingly soluble 

 in water, giving it a strong acrid taste. Lime-water 

 is as clear as ordinary water ; the eye discerns no differ- 

 ence between them. And now I want to point out to 

 you one of the ways in which the carbonate of lime, 

 which we have been speaking of, may be formed. 



I suppose you to have before you a tumbler, or 

 beaker, filled with clear lime-water. By means of a 

 pair of bellows, to the nozzle of which a glass tube is 

 attached, you can cause pure air to bubble through the 

 lime-water. It continues clear. You have been just 

 iformed that the breath exhaled from the lungs con- 

 tains carbonic acid, and if this acid be brought into 



