176 



GENERAL SCIENCE 



FIG. 139. 



Board arranged 



in window. 



necessary to readjust the windows. No one could adjust the 

 windows in the morning and expect sufficient fresh air to 

 enter later in the day. The greater the difference 

 in pressure between the outside and the inside 

 of a building the less the windows need to be 

 opened. 



Passage of Air through the Substance of Walls. 

 A small amount of air passes through the materials 

 from which walls are made. More air passes through 

 when the difference in pressure is great between 

 the outside and inside of the house. From 30 to 80 

 cubic feet of air per square foot per hour will pass 

 through ordinary flooring for a difference in pressure 

 of 1 pound per square foot. The amount of air 

 which will pass through an ordinary brick wall for 

 the same pressure and time will be about 48 cubic feet. 



Carbon Dioxide not Injurious. It has been definitely proved 

 that carbon dioxide in the air is not injurious. People have worked 

 for many years in mineral water factories or in breweries, breathing 

 air which contains a relatively large proportion of carbon dioxide, with- 

 out suffering any ill effects. Carbon dioxide breathed within certain 

 very wide limits, up to 300 parts in 10,000 parts of air, appears to 

 make very little difference. The reason for this is that the presence 

 of carbon dioxide in the blood excites the breathing centers, and auto- 

 matically causes the breathing to be deeper and stronger, resulting 

 in the quantity of carbon dioxide in the blood remaining constant. 

 Effects of Carbon Dioxide on the Body. Although carbon 

 dioxide is not considered dangerous in the air, carbon dioxide 

 exhaled from the lungs with other substances seems to pro- 

 duce some ill effects on the body, according to some investigators. 

 Certain amounts cause drowsiness and mental dullness. Long ex- 

 posure to such an atmosphere causes paleness. This is because of 

 decrease in the amount of oxygen necessary to maintain life, and 

 the vitiating of the atmosphere. 



The " Choke Damp "Jfound in mines is carbon dioxide. Often 

 large quantities collect in wells. Before cleaning a well, lanterns 

 are usually lowered into the well to test for its presence. 



