178 



GENERAL SCIENCE 



faint pink color it possessed before the last cubic centimeter of lime water was 

 added. 



The number of cubic centimeters of air required to discolor the liquid 

 gives us the percentage of CO 2 in the atmosphere. 



Air showing 10 parts or more of carbon dioxide is badly vitiated. 



Carbon dioxide forms a white precipitate in lime water; hence 

 this is used as a test for the presence of the gas. 



Fill a test tube half full of saturated lime water, and blow gently through a 

 piece of glass tubing into the water. What does this show regarding the 

 atmosphere we breathe out? Test the city gas for the presence of carbon 

 dioxide. 



Allow a candle to burn in a bottle until it goes out. Test for the presence 

 of CO 2 by pouring in a few teaspoonfuls of lime water and shaking the bottle 

 vigorously for a moment. 



Complete apparatus using the above method is sold by L. E. Knott, Boston, Mass. 

 The Standard Scientific Co. of New York City manufactures a very simple apparatus for 

 testing for CO2. 



Experiment to Show the Best Method of Ventilation. If you 

 observe the duct for incoming air and the one for outgoing air you 

 will see that they are on. the same side of the room, one at the 

 top and one at the bottom. 



Build a little box to represent a room, as shown in diagram 141. Place a 

 piece of glass in front of the box, and bore four holes on each side to represent 

 the ducts for incoming air and outgoing air, or the windows of a room. 



1. Light the candles, after stopping the holes with a cork stopper. The 

 candles will soon go out. Why? 



2. Relight the candles and remove one stopper from each side at the top, 

 A and C. The candles will burn for a short time, and then go out. Why? 



3. Remove the two stoppers at the bottom B and D, with the other holes 

 closed. The candles will go out after a short time. Why? 



