78 ANSWERS TO PRACTICAL QUESTIONS 



16. Why does H in burning give out more heat 

 than C? 



1 Ib. of H burned in O emits heat sufficient to melt 315.2 

 Ibs. of ice ; and 12 Ibs. of carbon converted into CO 2 enough to 

 melt 700 Ibs. of ice. (This subject is quite fully treated in 

 Miller's Chemical Physics, page 294, et seq.) The cause is not 

 as yet fully determined, although it is perhaps safe to say that 

 in ordinary combustion the heat depends on the amount of O 

 which enters into combination with the fuel. 



1 7. Wiiy do not stones burn as well as ivood ? 



Because they are already burned, i.e., combined with O. 



18. Why does not hemlock make good coals? 



Because (1) of its lack of C, and (2) its porous structure. 



19. What adaptation of chemical affinities is shown in 

 a light ? 



If O had the same affinity for C that it has for H, they 

 would be consumed at once, with little light. The fact that 

 the H burns first, and thus heats up to the luminous point the 

 particles of C as they float outward to the air, causes the illu- 

 minating power of the hydro-carbons. 



20. Why does snuffing a candle brighten the flame ? 



Because it removes the charred wick, which diminishes the 

 heat of the flame by both conduction and radiation. 



21. Wliy is the flame of a candle red or yellow, and 

 that of a kerosene oil-lamp white ? 



(See Popular Physics, p. 243). 



The heat of a candle-flame is much less than that of kero- 

 sene, and thus the colors characteristic of a lower temperature 

 are produced. 



22. Why does a street gas-light burn blue on a ivindy 

 night ? Is the light then as intense ? The heat ? 



O is mingled with the flame in sufficient quantities to burn 

 the H and C simultaneously. Thereby the heat is increased, 



