14 PRELIMINARY EXPERIMENTS 



carbon dioxide, giving its color, taste, smell, test, weight, 

 and effect on burning. 



Note. The weight of carbon dioxide and its power to put out 

 fire are well shown by filling a large wide-mouth bottle with the gas 

 and then pouring it into an inclined trough in the bottom of which 

 several short bits of lighted candle have been placed. The gas 

 will flow down, and, as it meets the candles, will extinguish them one 

 by one. 



Another device may be made by placing bottles of equal weight 

 in opposite pans of an ordinary balance. When they are exactly 

 counterpoised, hold the delivery tube of a flask over one of the 

 bottles, and the greater weight of the carbon dioxide will imme- 

 diately cause it to sink. 



Query. What causes limewater to become covered with 

 a scum of white substance whenever it is exposed for some 

 time to the air? 



What are some of the sources of carbon dioxide in the 

 atmosphere? Explain the construction of a chemical 

 fire extinguisher. On what properties of carbon dioxide 

 does it depend? 



Before going down into a deep well, how would you test 

 the air to find out whether there is carbon dioxide present ? 

 If present, how can it be removed before you go down 

 into the well ? 



Why are the laws so strict regarding ventilation of schools ? 



4. HYDROGEN 



Object. To prepare hydrogen and to learn some of Us 

 properties. 



Apparatus. Some granulated zinc or zinc scraps, dilute sul- 

 phuric acid (1 part acid poured into 5 parts of water), test tubes, 

 Argand lamp chimney, ,and a flask fitted as in Figure 3. 



