IN CHEMISTRY. 105 



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 com- 

 bination with the fuel. " Thus hydrogen in burning takes 

 up three times as much O,as C does, and hence gives off 

 three times as much heat." YOUMANS. 



2 1. Why does blowing on afire kindle it, and on a lighted 

 lamp extinguish it ? 



(See Key, page 50, Question 6.) 



22. Why can we not ignite hard coal with a match ? 

 Because it is a good conductor of heat. 



23. What causes the dripping of a stove-pipe ? 



The condensation of the water formed in the combus- 

 tion of the fuel. 



24. Why will an excess of coal put out afire ? 



Because it will absorb the heat, and thus reduce the 

 temperature of the fire below the combining point of C 

 andO. 



25. Why do not stones burn as well as wood? 

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



26. Why does not hemlock make good coals ? 



Because (i) of its lack of C, and (2) its porous struc- 

 ture. 



27. 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 



