SOII, DEFICIENCIES 253 



Indifferent to Lime. Blackberries, millet, potatoes, rasp- 

 berries, rye, and red top grass. 



Injured by Lime. Cranberries, cowpeas, sheep sorrell, lupine, 

 serradilla, and watermelon. 



In these experiments, it will be noted that the plants were sup- 

 plied with an abundance of phosphoric acid, potash, and nitrogen. 

 Such being the case, the beneficial effect of the lime could not be 

 to render potash or phosphoric acid available. Other experi- 

 ments showed that caustic magnesia, or sodium carbonate also 

 had a good effect. These substances would also neutralize acidity. 



Detection of Soil Acidity. The most satisfactory method of 

 ascertaining whether a soil needs lime is to determine the gain in 

 crop by its application. It does not necessarily follow that a soil 

 which responds to lime is acid. 



The tests for acidity used at present are as follows: 



1. The Litmus Test. 1 The soil is moistened with water and 

 brought in contact with blue litmus paper. If acid, the litmus 

 turns red. Carbonic acid also reddens litmus, but to a less degree 

 that, an acid soil. 



2. Ammonia Test. 2 The soil is treated with ammonia water, 

 and if the liquid assumes a dark brown or black appearance, the 

 soil may be acid. This test applies only where the acidity is due 

 in a considerable measure to acid organic substances, and may 

 not apply to all sections of the country. 



3. Salt Method?. The soil is shaken with a solution of potas- 

 sium nitrate and the solution, after being boiled to remove car- 

 bonic acid, titrated with caustic soda and phenolphthalein. Part 

 of the acidity is due to formation of aluminium and iron chlorides, 

 which are decomposed in the titration. 



4. Lime Water Method. 4 The soil is treated with standard 

 lime water, evaporated, taken up with water, and the nitrate tested 

 by evaporating it nearly to dryness with a few drops of 

 phenolphthalein. If the phenolphthalein indicator becomes pink, 



1 See Circular No. 71, Bureau of Plant Industry. 



2 Bulletin 62, Rhode Island Exp. Sta. 



3 Proceedings Association Off. Agr. Chem., 1902. 



4 Jour. Am. Chem. Soc., 1902, p. 120. 



