ACTION OF ORGANIC ACIDS UPON SOILS 7 1 



ash and phosphoric acid soluble in dilute organic 

 acids ; soils which are deficient in these elements usu- 

 ally contain less than o.oi per cent. 



The action of a single organic acid of specific 

 strength cannot be taken as the measure of fertility 

 for all soils and crops alike, because different plants 

 do not have the same amount or kind of organic acid 

 in the sap. Of the various organic acids, citric pos- 

 sesses the greatest solvent action upon lime, magnesia, 

 and phosphoric acid, while oxalic has the strong- 

 est solvent action upon the silicates. Tartaric acid 

 appears to be less active as a solvent than either citric 

 or oxalic acid. The combined use of dilute organic 

 acids, as citric, with hydrochloric acid (sp. gr. 1.115), 

 will generally give an accurate idea of the character 

 of a soil. . A fifth-normal solution of hydrochloric acid 

 has also been proposed as a measure of the soil's active 

 phosphoric acid, and has given satisfactory results. 24 



The use of dilute organic acids renders it possible 

 to detect small amounts of readily soluble phosphoric 

 acid and potash. It has been stated that when a soil 

 has been manured a few years with a phosphate fer- 

 tilizer and brought into good condition as to avail- 

 able phosphoric acid, a chemical analysis will fail to 

 detect any difference in the soil before or after the 

 treatment with fertilizer. In the case of hydrochloric 

 acid as a solvent, this is true because an acre of soil 

 to the depth of one foot weighs about 3,500,000 Ibs. 

 and 500 pounds of phosphoric acid would increase the 

 total amount of phosphoric acid about 0.015 per cent. 

 When a dilute organic acid is used, only the more 



