28 MANUAL OF GENEEAL AGEICULTUEE. 



solve one gram of solid phosphoric acid in 200 c.c. of 

 water. 



Molybdate of ammonia. Add ten grams of ammo- 

 nium molybdate to 25 c.c. distilled water ; then add 15 c.c. 

 of strong chemically pure ammonium hydroxid and 150 

 grams chemically pure nitric acid. Keep warm and if a 

 yellow precipitate appears, pour off the clear liquid for 

 use ; if not the liquid is ready for use. 



A saturated solution of oxalate of ammonia. Fill a 

 bottle y^ full of ammonia oxalate, then fill with water and 

 allow to stand until saturated or for several hours. 



1.7% solution of nitrate of silver. Add 1.7 grams of 

 silver nitrate to 100 c.c. of distilled water. 



Ten per cent solution of barium chlorid. Add 10 

 grams of barium chlorid to 100 c.c. of water. 



Ten per cent solution of ammonium chlorid. Add 10 

 grams of ammonium chlorid to 100 c.c. water. 



27. DETERMINATION OF NITROGEN. 



Materials: 10% caustic potash solution, rubber 

 pestle made by placing a one-hole stopper on the end of a 

 stirring rod, mortar, test tube. 



Pulverize the soil with the rubber pestle. Place 7 

 grams in a test tube and add 20 c.c. of caustic potash solu- 

 tion. Boil from ten to fifteen seconds, then allow the 

 heavier portion to settle. The humus is dissolved and the 

 density of the color of the solution is an indication of ade- 

 quacy or inadequacy. A dense black, non-translucent 

 solution shows the presence of at least one per cent of 

 humus in the soil. A deep brown translucent color indi- 

 cates the presence of about one-half of one per cent of 

 humus. A light brown color clearly indicates a deficiency 

 of humus. 



The test tells us about the humus only, but in all ex- 

 cept very arid regions the humus content is an accurate 

 index of the nitrogen content, hence the test is of prac- 

 tical value. 



