CARBON 



61 



passed off is a solution of a salt and water. From a mixture 

 of hydrochloric acid and marble are obtained a salt, water, 

 and carbon dioxide. 



A commercial use of carbon dioxide. If a lighted splinter 

 is thrust into a test tube containing carbon dioxide, it 

 is promptly extinguished, because carbon dioxide cannot 

 support combustion ; if a stream of carbon dioxide and water 

 falls upon a fire, it acts like a blanket, 

 covering the flames and extinguishing 

 them. The value of a fire extinguisher 

 depends upon the amount of carbon 

 dioxide and water which it can furnish. 

 One form of fire extinguisher consists 

 of a metal case (Fig. 32) containing a 

 solution of bicarbonate of soda and a 

 glass vessel half full of strong sulphuric 

 acid. As long as the extinguisher is 

 in an upright position, these substances 

 are kept separate, but when the ex- 

 tinguisher is inverted, the acid escapes 

 from the bottle, and mixes with the 

 soda solution. The mingling liquids in- 

 teract and liberate carbon dioxide. A part 

 of the gas thus liberated dissolves in the 

 water of the soda solution and escapes 

 from the tube with the outflowing liquid. 



Carbon. Although carbon dioxide is FlG .^_ Inside 

 very injurious to health, both of the sub- fire extinguisher. 



stances of which it is composed are necessary to life. Our 

 bodies, our bones and flesh in particular, are partly carbon, and 

 every animal, no matter how small or insignificant, contains 

 some carbon ; while the plants around us, the trees, the grass* 

 rhe flowers, contain a large quantity of it. 



