VENTILATION 1 73 



inches of water forced out of the bottle. Covering the paper with shellac will 

 fasten the scale firmly to the bottle. 



A gallon contains 231 cubic inches. 



A cubic centimeter contains .061 cubic inch. 



Need of Ventilation. All authorities agree on the necessity of 

 ventilation, but not all agree as to the reason why air must be 

 constantly changed. Some have believed that carbon dioxide made 

 the air impure. This is not generally accepted to-day. Others 

 feel that the air becomes heated by the presence of people in a 

 limited or confined space. They are forced to take shorter breaths, 

 and the general activity of the body decreases. 



Another reason given for ventilation is that noxious gases called 

 anthrotoxins are given off which, if breathed in large quantities, 

 have poisonous effects on people. 



All agree, however, that large quantities of fresh air are neces- 

 sary to produce the right kind of activity for mind and body. 



To prevent the air from becoming impure, each person requires 

 about 2000 cubic feet of fresh air each hour. 



Children at different ages require different amounts of air. 

 In the primary grades each child should get about 2000 cubic feet 

 of air per hour, and in the grammar grades from 2500 to 3000 cubic 

 feet of air. The children do not breathe all the air, but each child 

 vitiates this amount and renders it unfit to breathe. 



It is possible, as far as the amount of oxygen in exhaled air 

 is concerned, that air be reinhaled, since the lungs contain a 

 large percentage of C02, and pupils could get along on a smaller 

 amount of air. But the rule should be definitely fixed in mind that 

 fresh air is " Nature's Greatest Remedy " for keeping us well, and 

 the nearer the percentage of C02 in the air of the room approaches 

 to that out-of-doors, the nearer we are living as nature intended. 



Different Amounts of Oxygen in the Air. It is necessary to 

 ventilate a room because the inhaling of air which has already 

 been exhaled exerts an unhealthy influence on the human organ- 

 ism. Normal air contains about 21 per cent oxygen. A candle 

 is extinguished in air containing less than 17 per cent but the 

 percentage can be reduced to about 14 per cent without any 

 apparent effect on the body. If the proportion is reduced to 12 



