44: THE EEASON WHY. 



; I will praise thee, O Lord, with my whole heart ; I will show forth ll.y 

 marvellous work." PSA.LM ix. 



Because, the fire being slow, the temperature is not high enough 

 to ignite the gas. 



98. What is the gas which escapes from the coals ? 

 Carburetted hydrogen. 



99. Why, if we light a piece of paper, and lay it where the 

 gas is escaping from the coals, will it burst into flame ? 



Because the lighted paper gives a heat sufficient to ignite the gas ; 

 and because also hydrogen requires the contact of flame to ignite it. 



100. Why, when the coals have become heated, will the 

 hydrogen burst into flame ? 



Because the carbon of the coals, and the oxygen of the air, have 

 begun to combine, and have greatly increased the heat, and have 

 produced a rapid combustion, so nearly allied, to flame, that it 

 ignites the hydrogen. 



101. What temperature is required to produce flame ? 

 That depends upon the nature of the combustible you desire to 



burn. Finely divided phosphorous and phosphorated hydrogen will 

 take fire at a temperature of 60 deg. or 70 deg. ; solid phos- 

 phorous at 140 deg. ; sulphur at 500 deg. ; hydrogen and car- 

 bonic oxide at 1,000 deg. (red heat) ; coal gas, ether, turpentine, 

 alcohol, tallow, and wood, at about 2,000 deg. (incipient white 

 heat). When once inflamed they will continue to burn, and will 

 maintain a very high temperature. 



102. What is smoJce ? 



Smoke consists of small particles of carbon of hydrogen gas, and 

 other volatile matters, which are driven off by heat and carried up 

 the chimney. 



103. Is it not a waste of fuel to allow this matter to escape? 

 It is, as it might all be burnt up by better management, 



104. How may the waste be avoided? 



By putting on only a little coals at a time, so that the heat of the 

 fire shall be sufficient to consume these volatile matters as tuey 

 escape. 



