218 WATER, HEAT, AIR, AND LIGHT IN THE HOUSE 



prevent our getting control of the "Great White Plague," as consump- 

 tion is called, in civilized communities. Many healthy persons, 

 realizing that their daily work gives them too little time in the open 

 air, sleep out-of-doors, even in winter. They do this, not only without 

 injury, but with great gain in health and vigor. 



247. Methods of Ventilation. It has been calculated 

 that during one hour a healthy man will make about 

 4,000 cubic feet of air unfit for breathing. This is the 

 vclume of a room 20 x 20 x 10 feet. Of course rooms are 

 not air-tight; hence all this air need not be forced into a 

 room artificially. The Massachusetts law provides that 

 at least 1,800 cubic feet of fresh air shall be furnished each 

 pupil each hour he is in school. If the amount of air 

 furnished to a schoolroom is below this, somebody ought 

 to take steps to get better ventilation. 



Recent experiments show that the air of houses becomes 

 unfit to breathe, not so much because it contains im- 

 purities, as because it is stagnant. Slightly impure air, 

 if in motion, is better than highly pure air that is not 

 moving. In other words, the greatest need is circulation 

 of air. 



Where steam or electric power can be obtained, as in city build- 

 ings, and in factories, heating and ventilation are often carried out- 

 together. One method of such forced ventilation is to drive warm, 

 fresh air into the building by means of rotary fans, while the im- 

 pure air escapes through openings made in the walls and ceilings. 

 Another method is to remove the impure air by fans, and to admit 

 fresh, warm air through many small openings near the floor. Drafts 

 are thus prevented. The air is usually warmed by steam coils in the 

 basement. 



The means of ventilation may also be used to cool buildings in sum- 

 mer, if the fresh air is first passed over ice. 



