ACID SOILS AND ALKALI SOILS 123 



Treat another small portion of this soil in the same way, using 

 a neutral potassium nitrate solution instead of distilled water. 



Observe the rate of change of color of the litmus paper with and 

 without potassium ni- 

 trate. n & 



Exercise III. 

 Litmus paper test. 



Materials. — Same 

 as Exercise II. 



Procedure. — Test 

 a number of different Fig. 21. — Procedure in the litmus paper test, 

 soils. The students («) small evaporating dish, (6) soil worked to a 

 should be encouraged *^ n P aste w * tn P ure water or a neutral potassium 



, . , . . nitrate solution, (c) the litmus paper in position, 



to bring m their own wit h one end free for comparison, 

 samples. Note whether 



there appears to be a difference in degree of acidity of these soils 

 as indicated by the quickness with which the litmus paper turns red 

 and the shade of red produced. 



Exercise IV. — Test for soil carbonates. 



Materials. — Soil, evaporating dish, dilute hydrochloric acid. 



Procedure. — Treat a small portion of the soil to be tested with 

 dilute hydrochloric acid. Effervescence indicates the presence of 

 carbonates. A soil so reacting needs no lime. If no reaction oc- 

 curs, test with litmus paper, as the soil may be alkaline, neutral 

 or acid. 



Exercise V. — Ammonia test for acidity. 



Materials. — Soil, 8 oz. bottle, concentrated ammonia. 



Procedure. — Place about 25 grams of soil in an 8 oz. bottle and 

 add 10 c.c. of ammonia. Fill two-thirds full with distilled or rain 

 water. Shake well and allow to stand overnight. A darkening 

 of the supernatant liquid is an indication of the lack of lime. 



This method is not a quantitative one because the degree of 

 darkening of the liquid depends on the amount of organic matter 

 present rather than the degree of acidity. 



Exercise VI. — Zinc sulfide test for acidity. (See Fig. 22.) 



Materials. — Soil, 250 to 300 c.c. Erlenmeyer flask, tripod and 

 wire gauze, flame, calcium chloride-zinc sulfide solution, lead ace- 

 tate paper. 



The calcium chloride-zinc sulfide reagent is made up as follows : 

 50 grams of neutral calcium chloride plus 5 grams of zinc sulfide 



