20 PRACTICAL AGRICULTURAL CHEMISTRY [50-51 



WATER 



50. Water differs chemically from air in being a compound 

 of the two gases oxygen and hydrogen, whereas air was seen 

 to be a mixture of the gases nitrogen and oxygen. 



The properties of oxygen have been already described 

 (30-34). The preparation and properties of hydrogen are 

 described below. 



Preparation and Properties of Hydrogen 



51. Fit up the apparatus for this experiment as shown in 

 fig. 21. Place a handful of granulated zinc at the bottom of 



Fig. 21 



the Woulffe's bottle and pour sufficient water down the thistle- 

 funnel to cover the zinc. Now add some strong hydro- 

 chloric acid, when a brisk effervescence will ensue. Do not 

 collect the first portion of gas, but after it has been in action 

 for two or three minutes fill a test-tube with water, invert it 

 in the water, and allow the gas to pass into it. When it is 

 full of gas close it with your thumb and bring it close to a 

 lighted burner. Remove your thumb and apply the light to 

 the tube. If the gas be pure it will burn steadily ; if it con- 

 tain air it will explode with a sharp squeak. Continue 



