66 



PURE AIR 



Let us now try an experiment to show how to ventilate 

 properly as a basis for home study. 



Experiment. To demonstrate the principles involved in ventilation. 

 Materials: A ventilation box. This is to be about 20 inches tall, 2 feet 

 long, and 4 inches thick, having one of its large surfaces of glass. Either 

 the front or back should be grooved to facilitate opening. A slanting 



shelf one inch wide runs 

 from one lower corner 

 nearly to the opposite 

 upper corner. One-inch 

 holes are bored in the 

 sides and top as sug- 

 gested by the letters A 

 to F in the diagram. 

 Corks are used to close 

 these holes. Three small 

 candles are placed on 

 the diagonal shelf 

 equally spaced so that 

 they are at different 

 levels. 



Method and Results: (i) Light the three candles. Close all the open- 

 ings. Which candle goes out first? Explain why. (2) Light the 

 candles. Open holes B and C. Test currents of air by holding 

 smoking joss stick or rolled paper at the openings. Result? (3) Re- 

 peat (2), using holes A and D open. (4) Repeat, using D and C open. 

 (5) Repeat, using A and B open. (6) Repeat, using E and F open. 

 Conclusions: What facts about circulation of air are shown by the experi- 

 ments? What facts about changes in air due to burning substances? 

 What facts are indicated which will be helpful in planning circulation 

 of air in our homes? What conditions found in the experiment are 

 not duplicated in a room where we wish to apply the principles of 

 ventilation? In what particulars can we apply the results found here 

 to ventilation of rooms where people are congregated? Is ventilation 

 needed for any other reason than the fact that a part of the oxygen 

 of the air has been consumed? 



Dust and its dangers. Not very many years ago an 

 eminent New York physician wrote a book entitled " Dust 



A ventilation box. 



