78 THE EEASON WHY. 



" Unto thee, O God, do we give thanks : for that thy name is near thy wondrous 

 works declare." PSAXM 



Also, as currents of air fly towards the fire, elevated fire-places 

 cause drafts about the persons of the inmates to a much greater 

 extent than they would if they were lower down. 



304. Why, if a piece of paper be laid with its flat surface 

 upon the fire, will it " char" but not ignite? 



Because, as in the case of the proper candle-extinguisher, the 

 carbonic acid gas accumulating beneath it prevents its igniting. 



305. Why, if you direct a current of air towards the paper, 

 will it burst into a Haze ? 



Because the carbonic acid gas is displaced by a current of air 

 containing oxygen. 



306. Why does water extinguish fire ? 



Became it saturates the fuel, and prevents the gases thereof 

 from combining with the oxygen of the air. 



307. As water contains oxygen, tvhy does not the oxygen of 

 the water support the fire ? 



Because the affinity between the hydrogen and oxygen of the 

 water is so strong that fire cannot separate them. 



"Water may be decomposed by heat, as will be hereafter explained. But the 

 heat of an ordinary fire is insufficient. There is, however, some reason for 

 believing that, in cases of very large fires, such as the accidental burning of 

 houses, &c., when the supply of water thrown upon the fire is very deficient, 

 the water does become decomposed, and add to the fury of the flames. 



308. Why does the blacksmith sprinkle water upon the 

 coals of his forge? 



The blacksmith uses small coals because the small pieces thereof 

 are more easily ignited than large lumps would be, and they convey 

 heat better by completely surrounding the articles put into the fire. 

 He sprinkles water on the coal dust to hold its particles toaether 

 by cohesion, until the heat forms it into a cake. A strong blast of 

 hot hair drives the vapour of the water away, and leaves a porous 

 mass to the action of the fire. 



309. Why, when the blacksmith thrusts a heated iron into 

 a tankard of water, do we recognise a peculiar smell ? 



