SUBSTANCES PRODUCED IN BREATHING AND BURNING 19 



Now put the mouth of the bottle under water, and remove 

 the paper. Why does not the water fall out? How tall might 

 the bottle be, and yet remain full of water when inverted in 

 water? 



Through a glass tube blow your breath (see Fig. 37, 45, of 

 the text), and catch the gas bubbles by the displacement of the 

 water in the bottle. When the bottle is full, slip the wet piece 

 of paper under it, hold the wet paper tightly against the 

 bottle's mouth, and set the bottle upright on the table. Put 

 into the bottle of gas a lighted splinter or match. Does the 

 gas take fire? Does the splinter (or match) continue to burn 

 in the gas? 



6. In a similar way fill a test tube with water, and then fill 

 the tube, by water displacement, with illuminating gas. Get 

 the gas from a tube connected with the gas outlet. Carefully 

 light the test tube of gas. 



EXERCISE 15 

 SUBSTANCES PRODUCED IN BREATHING AND BURNING 



Apparatus and Materials.^- An acid (vinegar or hydrochloric acid), 

 test tubes, limewater, glass tube, wide-mouth bottle, cardboard cover, 

 splinter, candle, wire for a holder, marble or soda. 



a. Prepare some carbon dioxide in a test tube by adding an 

 acid, such as vinegar or dilute hydrochloric acid, to some marble 

 or soda that is in the test tube. Hold the mouth of the test 

 tube over the mouth of another test tube as if you were going to 

 pour a liquid from the one into the other, but do not actually 

 pour any of the liquid. The invisible gas carbon dioxide is thus 

 poured over. 



Add to the test tube that now contains carbon dioxide about 

 5 cu. cm. of limewater, close the test tube with the thumb, and 

 shake the tube, so that the gas is mixed with the liquid. What 



