EXPERIMENTS 



26l 



peaty and of alkaline soils ; test each with moistened litmus paper. 



15. Absorption of Gases. — Put 50 grams of soil into a wide- 

 mouthed bottle, add 50 cc. of water and 1 cc. strong ammonia. 

 Note the odor. Cork the bottle, shake, and after twenty-four 

 hours again observe the odor. 



16. Insoluble and Soluble Products of Soil. — Digest in a covered 

 beaker 10 grams of soil with 100 cc. hydrochloric acid (50 cc. 

 strong hydrochloric acid and 50 cc. water). After two hours' diges- 

 tion, cool and filter, using 25 cc. water to wash the acid from the 

 insoluble residue. Note the quantity and appearance of the insol- 

 uble matter. To one-half the filtrate add ammonia until alkaline. 

 What is the precipitate ? Remove it by filtering, and to this second 

 filtrate add ammonium oxalate. What is the precipitate ? 

 Evaporate the remainder of the original filtrate nearly to 

 dryness. Add 20 cc. water, 3 cc. nitric acid, and 5 cc. of 

 ammonium molybdate. After shaking the test-tube con- 

 taining the mixture, it is placed in a beaker of water and 

 heated to about 65 ° C. What is the yellow precipitate ? 



17. Testing Soils for Combined Carbon Dioxide. — One 

 gram of soil is placed in a test-tube (Fig. 35) and 5 cc. of 

 water and 3 cc. of hydrochloric acid added. A small 

 looped tube a, containing a drop of lime-water, is then 

 inserted into the test-tube. The test-tube is warmed. 

 Observe the precipitate formed in the loop. What is it ? 



18. Humus from Soils. — Five grams of soil are placed 

 in a glass-stoppered bottle, 100 cc. water and 3 cc. hydro- 

 chloric acid added. After shaking, the contents of the 

 bottle are left twenty-four hours to subside. The acid 

 is then poured off and 100 cc. of water added. The soil 

 is left until the next day, when the water is poured off and 

 100 cc. of water and 5 cc. of ammonia are added. After 

 shaking and allowing a little time for the .soil to settle, the ammo- 

 nia solution is filtered off. 



To a portion of the filtrate add hydrochloric acid until the solu- 

 tion is just acid. Observe the precipitate. Evaporate another por- 

 tion of the solution to dryness. What is the black residue ? 



a 



6 



Fig- 35- 



