Acidum Citricum, B.P. Citric Acid.

C6H8O7, H2O = 210.08.

Citric acid, C3H40H(COOH)3, H2O, is prepared from the juice of lemons and other fruits produced by species of Citrus. It should contain about 99.5 per cent. of pure citric acid. It is also official in the U.S.P. The acid occurs in colourless prismatic crystals, which are efflorescent in warm, dry air, and deliquescent (become liquid) in moist air. An 8 per cent. aqueous solution of the acid corresponds in strength to average samples of lemon juice. The presence of tartaric acid as an impurity may be detected by heating 0.5 gramme with 5 mils of sulphuric acid in a test tube suspended in boiling water for thirty minutes, when a more or less intense blackish-brown colour is evident.

Soluble in water (10 in 6), alcohol (2 in 3), glycerin (1 in 2).

Action and Uses.—Citric acid is partly absorbed from the alimentary canal, and this portion is decomposed, being excreted by the kidneys in the form of sodium carbonate. It is used in dilute solution, or in the form of lemon or lime juice, as a refrigerant drink in fevers, also as a prophylactic and cure in scurvy. Citric acid in large excess decreases the coagulability of the blood owing to its affinity for calcium, with which it forms a non-ionisable compound. It is given with this object every second or third day to typhoid fever patients on a milk diet, in the hope of reducing the liability to thrombosis. The alkali citrates increase the secretion of the urine and render it less acid. For the administration of citric acid in the free state either Succus Limonis or Syrupus Acidi Citrici, may be used. It is commonly administered in effervescing mixtures, in which the citric acid is directed to be added in the form of a powder, or solution, to an alkaline mixture. Draughts prepared with a slight excess of acid are more agreeable, but the following are the proportions necessary to form neutral mixtures:

Citric Acid, 10, will neutralise
. . Ammonium Carbonate, B.P. about 7 ½
Magnesium Carbonate, B.P. " 7
Potassium Bicarbonate " 14 ¼
Potassium Carbonate (Anhydrous) " 10
Potassium Carbonate (Commercial, K2CO3.1 ½ H2O) " 11 ¾
Sodium Bicarbonate " 12
Sodium Carbonate (Anhydrous) " 7 ½
Sodium Carbonate (Na2CO3 10H2O) " 20 ½

Citric acid is incompatible with alkalies, carbonates, benzoates, salicylates and potassium tartrate.

Dose.—3 to 12 decigrams (5 to 20 grains).


Syrupus Acidi Citrici, B.P.C.—SYRUP OF CITRIC ACID.
Citric acid, 3; tincture of lemon, 3; syrup, sufficient to produce 100.
Syrupus Acidi Citrici, U.S.P.—SYRUP OF CITRIC ACID, U.S.P.
Citric acid, 1 distilled water, 1; tincture of fresh lemon peel (1 in 2, alcohol, 95 per cent.), 1; syrup, sufficient to produce 100.

The British Pharmaceutical Codex, 1911, was published by direction of the Council of the Pharmaceutical Society of Great Britain.