282 MATERIA MEDIC A AND THERAPEUTICS. 



From Acidum Benzoicum are prepared : 



a. Tinctura Camphorae Composita. 2 gr. to 1 fl.oz. 



b. Tinctura Opii Ammoniata. 9 gr. to 1 fl.oz. See Opium. 



From Acidum Benzoicum is made : 



Ammonia Benzoas. NH 4 C 7 H R O g . Colourless laminar crystals 

 with the fragrant odour of benzoic acid, made by 

 dissolving benzoic acid in solution of ammonia and water, 

 evaporating and crystallising. Soluble in 5 of water ; in 

 18 of rectified spirit. Sublimes without residue. Incom- 

 patibles. Persalts of iron, liquor potassse, and acids. 

 Dose, 10 to 20 gr. 



ACTION AND USES. 

 1. IMMEDIATE LOCAL ACTION AND USES. 



Externally. Benzoin and its preparations are antiseptic 

 and disinfectant, and at the same time slightly stimulant to the 

 vessels. The compound tincture, or " Friar's Balsam," has 

 been long used as an application to ulcers and foul wounds, 

 and also to promote the healing of freshly incised wounds. 



Internally. Benzoin and its acid cause sneezing and 

 coughing when inhaled or applied in the solid form to the 

 nose ; much diluted with watery vapour, they are mild stimu- 

 lants. The compound tincture is thus a useful substance for 

 inhalation or spray in many laryngeal diseases; and benzoic 

 acid has been applied direct to the affected surface in diphtheria, 

 where it acts also as a disinfectant. 



Taken by the mouth, benzoic acid causes slight heat and 

 irritation in the region of the stomach ; the ammonia salt is 

 much less irritant, and can be given in larger doses. 



2. ACTION IN THE BLOOD AND USES. 



Benzoin and benzoic acid enter the blood in the form of 

 benzoate of sodium, and here, as well as in the kidneys, this 

 acid is partly converted into hippuric acid by combination with 

 a molecule of glycocoU, thus : C 7 H 6 O 2 -f C 2 H 5 N0 2 (glycocoU) 

 = C 9 H 9 N0 3 (hippuric acid) + H 2 0. The exact source of the 

 glycocoll is still obscure. It is not derived from the urea or 

 uric acid, as was once suggested ; and the use of benzoic acid 

 to take up and carry out by the urine excess of urea in uraemia, 

 or excess of uric acid in gout, is erroneous in theory, as it has 

 failed in practice. 



