22G WALL'S MANUAL 



taste, and is about one and a half times heavier than 

 air. It exists abundantly in the mineral crust of the 

 earth, hence called fixed air ; and is found also in the 

 atmosphere in a pure state. It is found in lime 

 stone to the extent of forty-four per cent, of its 

 weight, and is best obtained by the action of muriatic 

 acid upon powdered marble. 



Any strong acid will do. A cubic inch of marble 

 will yield four gallons of gas. 



Properties of Carbonic Acid It Extinguishes Fire. 

 A candle dipped into it goes out at once, and if 

 poured upon a flame it quenches it as quickly as 

 water. It is the foul air in wells; hence no one 

 should venture into a well before testing whether 

 carbonic acid gas is present or not. A candle let 

 down in the well is a good test : if extinguished the 

 gas is present, if it burns as usual there is no danger. 



Sources of Carbonic Acid. Carbonic acid is pro- 

 duced very abundantly in nature. The burning of 

 wood (which always contains carbon) in the open air 

 yields it in vast quantities. The combustion of one 

 bushel of charcoal will produce two thousand five 

 hundred gallons of this gas. It is formed within the 

 bodies of all animals, by the union of the oxygen of 

 the atmosphere with the carbon contained in the 

 system ; it escapes through the lungs, by respiration, 

 into the -air. Each adult man exhales about one 

 hundred and forty gallons per day. [Davy. 



The test of carbonic acid is clear lime water, 

 which it turns milky, by forming insoluble carbonate 

 pf lime. To prove that it is the product of both com- 

 bustion and respiration, invert an empty jar over a 



