TESTS FOR ACIDITY 



present, and this may give a wrong impres- 

 sion to the operator. Another objection to 

 the use of litmus is that the degree of 

 acidity is not accurately indicated, and 

 therefore the farmer is sometimes at a loss 

 to know just how much lime should be 

 applied to make soil conditions favorable 

 for growing crops. 



A More Accurate Method. Within the 

 last few years improved methods for deter- 

 mining the presence of acidity in soil have 

 been developed. Some of these are suitable 

 only for the chemist jvith his complete 

 laboratory equipment, while others are 

 more simple and can be used by anyone 

 willing to exercise reasonable care. 



One of the simplest and most accurate 

 tests to date is that devised by Professor E. 

 Truog of the agricultural experiment sta- 

 tion of the University of Wisconsin. This 

 test not only detects positively the presence 

 of soil acidity, but also gives definite in- 

 formation as to the degree of acidity. The 

 test is based upon the principle that when 

 zinc sulfid comes in contact with the acid, 

 hydrogen sulfid gas is formed, and when 

 this gas comes in contact with lead acetate, 

 lead sulfid, a black chemical, is formed. 



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