SMOKE. 59 



A. Because they very readily ferment, 

 and (during fermentation) throw off ex- 

 ceedingly inflammable gases. 



(N. B. Lamp-black mixed with linseed oil is more liable 

 to spontaneous combustion, than anything that servants 

 handle.) 



CHAPTER IV. 



SMOKE. 



Q. Why does SMOKE ASCEND the chimney ? 



A. As the air of the room passes 

 over the fire, it becomes heated; and 

 (being thus made lighter,) ascends the 

 chimney, carrying the smoke with it. 



What is SMOKE ? 



A. Small particles of carbon, separa- 

 ted by combustion from the fuel, but not 

 consumed. 



Q. Wliy do SMOKE and steam CUBL, as they 

 ascend ? 



A. Because they are moved in a right 

 line, and then pushed on all sides ; and 

 this forces them into a circular motion. 



