204: SCIENCE OF COMMON THINGS. 



What Is ventilation ? Warming and ventilation of buildings. 



PART VI. 



.VENTILATION AND WARMING, COMBUSTION, 

 RESPIRATION, AND NUTRITION. 



CHAPTEK I. 



WARMING AND VENTILATION. 



1354 What is ventilation f 



Ventilation is the act or operation of causing air to 

 pass through any place, for the purpose of expelling 

 impure air and dissipating noxious vapors. 



1355 What is the theoretical perfection of ventilation ? 



To render it impossible for any portion of air to be 

 breathed twice in the same building. 



1356 Upon what principle does the whole process of warming and ven- 

 tilating buildings depend ? 



Upon the expansion and contraction of air, or, in 

 other words, upon the fact that air which has been 

 heated and expanded ascends, and air w r hich has been 

 deprived of heat, or has become contracted, descends. 



1357 f Is there an upward current of air always 

 rising from heated substances f 



There is ; air made lighter by heat 

 ascends through colder strata, as a cork 

 (put at the bottom of a basin of water) 

 rises to the surface. 



135S What simple experiment shows the exist* 

 ence of this upward current in an ordinary stove f 



If we attach to the side of a heated 

 stovepipe a wire on which a piece of 

 paper cut in the form of a spiral may 



