NITROGEN AND ITS USES 119 



very important use which has been discovered only within the 

 last few years. Peas, beans, lentils, alfalfa, and a few other 

 crops have on their roots bacteria which possess the power of 

 absorbing the nitrogen from the air, and combining it with the 

 oxygen and some of the salts of the earth to form nitrates. 

 These nitrates are very valuable as plant foods. If there has 

 been a crop of this kind in a field, there is always an excess of 

 bacteria left in the ground. These bacteria go on producing 

 the nitrates from the air, and make the soil very rich. Thus 

 we know that nitrogen is used indirectly by plants, and that 

 these have a never failing source of plant food. 



References : 



1. 1103 : 7-8. Nitrogen in the Atmosphere. 



2. 1304 : 229. Nitrogen in the Atmosphere. 



3. 1407 : 233-235. Nitrogen in Relation to Plants. 



4. 1503 : 94-95. Relation of Bacteria to Nitrogen. 



5. 1601 : 110-112. Importance of Nitrogen in Plant Life. 



6. 1605 : 116-122. The Sources and Losses of Soil Nitrogen. 



7. 1702 : 44-45. Properties and Importance of Nitrogen. 



8. 1703 : 107-109. Nitrogen and the Atmosphere. 



9. 1710:6. Nitrogen. 



a. 1602:45-48. Clover and Other Plants take Nitrogen 



from the Air. 



b. 1603 : 33-35. The Root Tubercles. 



c. 1612 : 125-128. Nitrification of the Soils. 



d. 1701 : 78-80. Nitrogen and its Properties. 



e. 1706 : 61-64. The Atmosphere and Nitrogen. 



Experiment 46. To Prepare Nitrogen. 



Apparatus: The same as in Experiment 3. 



Materials: Ammonium nitrite. 



a. Place a teaspoonful of ammonium nitrite in the test 

 tube, add twice the volume of water, and then follow the direc- 

 tions as given in Experiment 3. 



