IN POPULAR CHEMISTRY. 77 



.9. What test should be employed before going down in 

 an old ivell or cellar ? 



A lighted candle should be lowered. If that is dimmed or 

 extinguished, it is not safe for one to descend. 



10. What causes the sparkle of wine and the foam of 

 beer? 



The CO 3 formed in the process of fermentation. 



11. What causes the cork to fly out of a catsup bottle ? 



The CO 3 which is produced when the catsup ferments. 



12. What physical principle does the solidification of 

 CO 2 illustrate ? 



That evaporation is a cooling process. A portion of the 

 liquid CO 3 turns to vapor, and thus abstracts so much heat 

 from the remainder as to freeze it. (See Popular Physics, p. 

 255.) 



13. Why does the division in the chimney shown in 

 Fig. 29 produce tivo currents ? 



For a few moments there is an uncertainty a condition of 

 unstable equilibrium. The heated air is tending to rise, and 

 the cold air tending to come in to supply its place. The situ- 

 ation of the candle in the jar determines the length of time 

 before the currents start. If the candle be placed on one side 

 of the jar, they will be established almost instantly. 



14. What causes the unpleasant odor of coal-gas? Is 

 it useful ? 



Impurities which it contains. Olefiant gas has a faint 

 sweetish odor, while carbonic oxide and hydrogen, when pure, 

 are inodorous. The disagreeable smell is due in part to acety- 

 lene (C 2 H 2 ). The unpleasant odor warns us of the presence of 

 coal-gas. 



15. irJiat causes the sparkling often seen in a gas- 

 light? 



Particles of solid taken up mechanically in the process of 

 purification, or otherwise. 



