VENTILATION 177 



The headaches and disagreeable feelings produced by breathing 

 air in crowded rooms are due to the overheating, to the moisture of 

 the air, and to the disagreeable odors, and not to the carbon dioxide. 



Tests to Determine Conditions of the Air. Air can best be 

 tested for its fitness to breathe by the sense of smell. However, 

 the sense of smell is fatigued very rapidly, and it is necessary for 

 one to come from fresh air in order to make a reliable test. Thus the 

 teacher and pupils, or members of the household, would be unable 

 to tell when the air was impure and unfit to breathe. Anyone 

 coming from out-of-doors would detect odors and unhealthful con- 

 ditions of the atmosphere. 



Why We Measure the Carbon Dioxide in the Room. The carbon 

 dioxide is measured in a room to determine the amount of carbon 

 dioxide which has been exhaled by people. It is not because the 

 carbon dioxide is poisonous, but because organic matter is exhaled 

 from the. lungs and the skin of people at the same time the carbon 

 dioxide is exhaled. By measuring the percentage of carbon dioxide 

 in the atmosphere it is easy to determine indirectly the relative 

 amount of contaminated or vitiated air, providing the carbon dioxide 

 was produced by respiration. 



Test for Amount of Carbon Dioxide (Dewing). One of the simplest tests 

 for CO 2 is to make up a test solution of 



2 or 3 drops of phenol phthalein solution; 

 1 c.c. of a saturated solution of lime water; 

 Sufficient water to make 100 c.c. of the solution. 



The water should have the phenolphthalein added and a few drops of lime 

 water (enough to produce slight discoloration before the cubic centimeter of 

 lime is added). 



Place 10 c.c. of the solution in a large test tube. Obtain a large size dowel 

 pin 12 inches long, graduate the stick by placing it in a graduate half full of 

 water, and notice how far the stick must be inserted to displace 10 c.c. of water. 

 Divide the stick from this point into 10 equal parts, each part representing a 

 cubic centimeter. Insert the stick into the test tube to the 10 c.c. point, which 

 will force out 10 c.c. of air, or 20 c.c. of air if the test tube is long enough and 

 the stick has been graduated to show 20 c.c. 



As the graduated stick is removed, the air of the room enters the test tube. 

 Shake the air thoroughly into the test liquid. Repeat, removing the air and 

 allowing new air to enter by means of the graduated stick. Shake the test 

 tube each time until the test solution has lost its color, or has returned to the 



