Grade. 

 Date. . 



(78) EXERCISE 30 



Testing Soils for Acidity 



Purpose. — There are three common tests for soil acidity. Any one of these 

 should furnish fair evidence as to the need of the soil for lime. An agree- 

 ment of the three tests should furnish conclusive evidence regarding the 

 condition of the soil. The purpose of this exercise is to familiarize the 

 student with the manipulation of these tests. 



Samples of the surface soil and subsoil of a soil well stocked with lime and 

 samples of acid soils should be supplied. Acid phosphate, lime, fresh 

 muck, wood ashes, silage, and horse manure also may be tested. 



I. Litmus Paper Test. — Take a tumbler with a smooth bottom. By means 



of forceps or the tips of the fingers select two pieces of litmus paper, one 

 blue and the other neutral, and drop into the tumbler. Then cut a disk 

 of filter paper and place in the bottom of the tumbler over the litmus 

 paper. On top of this place two or three tablespoonfuls of the moist 

 soil to be tested. If the soil is not moist enough add a small amount of 

 rain or distilled water. Take a handful of the same soil and squeeze into 

 a ball. Break the ball and in the center insert a piece of blue litmus 

 paper. With both of these tests, if the soil is acid, the litmus paper should 

 show a decided pink. 



II. Ammonia Test. — Take two tumblers and fill each about three-quarters 



full of distilled or rain water. To the first add a few drops of common 

 ammonia. Then into each tumbler stir a tablespoonful of the soil to 

 be tested, being careful to use two spoons and keep each in its respec- 

 tive glass. Stir the contents of each glass thoroughly for three or four 

 minutes and set aside for a few hours. At the end of that time examine 

 the contents of each glass. If the soil needs lime the water standing 

 above the soil in the glass in Avhich the ammonia has been added will 

 have a dark, reddish-brown or black appearance, while the water in 

 the other glass will be very nearly clear. On the other hand, if the soil 

 is well stocked with carbonates of lime or magnesia, the soil water 

 in both glasses will be entirely clear. 



III. Hydrochloric Acid Test. — Place a small quantity of soil in an evaporating 

 dish and pour on this three or four drops of hydrochloric acid. If bubbles 

 escape it is a sign that there is an abundance of carbonates. If there 

 is no effervescence the soil lacks carbonates and is probably acid. 



