DIBASIC AND TRIBASIC ORGANIC ACIDS. 337 



obtained from the juice of lemons by saturating it with calcium car- 

 bonate and decomposing by sulphuric acid the calcium citrate thus 

 formed. (100 parts of lemons yield about 5 parts of the acid.) It 

 forms colorless crystals, easily soluble in water. 



Analytical reactions. 

 (Potassium citrate, K 3 C 6 H 5 O 7 , may be used.) 



1. Neutral solutions of citrates yield with calcium chloride on 

 boiling (not in the cold) a white precipitate of calcium citrate, which 

 is insoluble in potassium hydroxide, but soluble in cupric chloride. 



2. Neutral solutions of citrates are precipitated white by silver 

 nitrate. The precipitate does not blacken on boiling, as in the case 

 of tartrates. 



3. A neutral or alkaline solution of a citrate to which a few drops 

 of a solution of potassium permanganate have been added, becomes 

 green or reddish-green. Tartrates decolorize permanganate. 



Citrates. Potassium citrate, K 3 C 6 H 5 O 7 .H 2 O, Lithium citrate, 

 Li 3 C 6 H 5 O 7 , and Magnesium citrate, Mg 3 (C 6 H 5 O 7 ) 2 .14HO 2 , are color- 

 less substances, easily soluble in water and obtained by dissolving 

 the carbonates in citric acid. 



The effervescent citrates of potassium, lithium, and magnesium, are granulated 

 mixtures of citric acid with potassium bicarbonate, lithium carbonate, and 

 magnesium carbonate respectively ; sugar is added to all, and some sodium 

 bicarbonate to the two last preparations. 



The official solution of magnesium citrate is made by dissolving magnesium 

 carbonate in an excess of citric acid solution to which some syrup is added, 

 and dropping into this mixture, which should be contained in a strong bottle, 

 potassium bicarbonate. The bottle is immediately closed with a cork in order 

 to retain the liberated carbon dioxide. 



Bismuth citrate, BiC 6 H 5 O 7 , is obtained by boiling a solution of citric acid 

 with bismuth nitrate, when the latter is gradually converted into citrate whilst 

 nitric acid is set free ; the insoluble bismuth citrate is collected, washed, and 

 dried ; it forms a white, amorphous powder, which is insoluble in water, but 

 soluble in water of ammonia. 



Bismuth ammonium citrate is a scale compound obtained by dissolving bismuth 

 citrate in water of ammonia and evaporating the solution at a low temperature. 



Ferric citrate, Ferri citras. Obtained in transparent, red scales, by dissolving 

 ferric hydroxide in citric acid and evaporating the solution as mentioned here- 

 tofore. By mixing solution of ferric citrate with either water of ammonia, or 

 quinine, strychnine, sodium phosphate, or sodium pyrophosphate, evaporating 

 to the consistence of syrup and drying on glass plates, the following scale com- 

 pounds are obtained respectively : Iron and ammonium citrate, iron and quinine 



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