8o ORGANIC AGRICULTURAL CHEMISTRY 



Citric Acid 



This is the third hydroxy acid which is found in nature in 

 acid fruits. It is especially abundant in fruits of the citrous 

 family, lemons, oranges, limes, etc., and is present in as much as 

 6 per cent of the juice. It is also produced by a fermentation 

 of glucose. It is a solid crystalline compound easily soluble in 

 water. The constitution of citric acid is as follows : 



CH2-COOH 



C(OH)COOH 



I 

 CH2-COOH 



Citric acid 



It is thus a mono-hydroxy-tri-carboxy acid, and is tribasic. 



Some of the salts of citric acid have important uses. Agri- 

 culturally one salt is of importance in a scientific way. A 

 neutral solution of ammonium citrate of approximately 20 

 per cent strength is used in fertilizer and soil analysis as a sol- 

 vent for the dicalcium or reverted calcium phosphate, the 

 phosphoric acid salt which is insoluble in water and yet 

 seems to be available to plants. Magnesium citrate is used in 

 medicine, and ferric-ammonium citrate is used in making blue 

 print photographic paper. 



EXPERIMENT STUDY XVII 



Lactic, Malic, Tartaric, Citric Acids 



(i) (a) Examine samples of lactic, malic, tartaric and citric acids. 

 {h) Test acidity toward phenolphthalein indicator, {c) Heat a few 

 grams of tartaric acid or a salt of tartaric acid with sulphuric acid in 

 a test tube. Note the odor of burnt sugar, {d) Prepare a little 

 ammoniacal silver nitrate (silver nitrate and just enough NH4OH to 

 dissolve the precipitate first formed). To this add a few drops of 

 tartaric acid or a tartrate and warm. Note reduction of silver nitrate 

 to metallic silver. 



