54 BURNING OR OXIDATION 



curs in large quantities, it is dangerous to health, because it 

 interferes with normal breathing, lessening the escape of 

 waste matter through the breath and preventing the access 

 to the lungs of the oxygen necessary for life. Carbon diox- 

 ide is not poisonous, but it cuts off the supply of oxygen, just 

 as water cuts it off from a drowning man. 



Since every man, woman, and child constantly breathes 

 forth carbon dioxide, the danger in overcrowded rooms is 

 great, and proper ventilation is of vital importance. 



47. Ventilation. In estimating the quantity of air neces- 

 sary to keep a room well aired, we must take into account 

 the number of lights (electric lights do not count) to be 

 used, and the number of people to occupy the room. The 

 average house should provide at the minimum 600 cubic feet 

 of space for each person, and in addition, arrangements for 

 allowing 300 cubic feet of fresh air to enter every hour. 



In houses which have not a ventilating system, the air 

 should be kept fresh by intelligent action in the opening of 

 doors and windows ; and since relatively few houses are 

 equipped with a satisfactory system, the following sugges- 

 tions relative to intelligent ventilation are offered. 



1. Avoid drafts in ventilation. 



2. Ventilate on the sheltered side of the house. If the 

 wind is blowing from the north, open south windows. 



48. What Becomes of the Carbon Dioxide. When we re- 

 flect that carbon dioxide is constantly being supplied to the 

 atmosphere and that it is injurious to health, the question 

 naturally arises as to how the air remains free enough of the 

 gas to support life. This is largely because carbon dioxide 

 is an essential food of plants. Through their leaves plants 

 absorb it from the atmosphere, and by a wonderful process 

 break it up into its component parts, oxygen and carbon. 

 They reject the oxygen, which passes back to the air, but they 



