THE EEASON WHY. ^77 



' Who liath laid the measures thereof, if thou knowest V or who hath stretched 

 the line upon it? 



It exists in various natural bodies in which carbon and oxygen 

 are combined ; it is evolved by the decomposition of numerous 

 bodies called carbonates, in which carbon is united with a particular 

 base, such as the carbonate of lime, the carbonate of iron, the 

 carbonate of copper, &c. It is_ also evolved by the processes of 

 fermentation, by the breathing of animals, the combustion of fuel, 

 and the functions of plants. Carbonic acid also exists in various 

 ^caters. 



Carbonic acid is found most largely in solid combinations with 

 other bodies : it forms 44-100lhs of all limestones and marbles, and 

 it exists in smaller quantity, combined with other earths, and with 

 metallic oxides. 



800. What are the states in which <pure carbonic acid 

 exists ? 



Pure carbonic acid may exist in the solid, the liquid, or the 

 aeriform state. In the solid state it is produced only by artificial 

 means, and it is then a white crystalised body, in appearance like 

 snow ; in the liquid state it is a heavy colourless fluid ; in the 

 aeriform state it is a pungent, heavy, colourless gas, and is known 

 as carbonic acid gas. 



801. Why does bottled porter produce large volumes of 

 froth, much more than the bottle could contain ? 



Because, by the fermentive process, carbonic acid has been 

 developed in the porter, and is held in liquid solution; but it 

 always has a strong tendency to escape, and directly the pressure is 

 removed, it evolves into gas, by which it occupies much greater 

 space, and forces the porter in millions of small bubbles out of the 

 bottle. 



892. Why does soda-water effervesce ? 



Because carbonic acid gas is forced into the water by pressure. 

 Pressure alters the gas into a liquid, and directly the pressure 

 eeases, the liquid again evolves into gas. 



803, Why does spring water taste fresh and invigorating t 



Because it contains carloni; acid. 

 8* 



