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PRACTICE 15 



Determination of Humus in Soils. 



Weigh out five or ten grams of water-free soil, the amount taken 

 depending upon the amount of humus in the soil. Plase in filter and 

 leach out the lime and magnesia with dilute hydrochloric acid.* 

 When the lime is all leached out, as shown by testing the filtrate with 

 ammonia and ammonium oxalate, wash out the hydrochloric acid with 

 distilled water. Dry the soil and filter paper in an oven at 100° C. 

 and put in a wide-mouthed bottle, carefully measure and add 150 cc. 

 to 300 cc. of dilute ammonia, the amount depending upon the richness 

 of the soil in humus. Shake for about three hours. Filter. Evapor- 

 ate 50 cc. or 100 cc. of filtrate to dryness. Dry at 100° C, weigh, ignite 

 and weigh again. The loss in weight is the humus. Calculate from 

 the part evaporated the total amount of humus and express in percent 

 of the water-free soil. 



Of what benefit is a large amount of humus? 



If an acre seven inches of soil weighs 2,000,000 pounds, how many 

 tons of humus per acre in the soil with which you are working? 



•For the dilute dydrochloric acid use 25 oc HC1 sp. grr. 1.19 with 808 cc of distilled 

 water. For the ammonia 178 cc saturated ammonia with 422 00 of distilled water 



