332 SULPHUROUS ACID 



weak solution is useful in the treatment of chronic pruritus 

 of the tail. A few drops, given with Epsom salt and other 

 saline purgatives, diminish their disagreeable taste and 

 rather increase their activity. 



DOSES, etc. Of the medicinal acid horses take f3J- to 

 f 3ij. ; cattle, f 3ij. to f 3iv. ; sheep, f 3ss. to f 3j. ; pigs, H\v. 

 to H\xx. ; dogs, H\ij. to fl\x., repeated several times a day, 

 given freely diluted, and often conjoined with aromatics and 

 bitters. As an external astringent, ten to twenty drops of 

 medicinal acid are mixed with an ounce of water. 



SULPHUROUS ACID 



ACIDUM SULPHUROSTJM. An aqueous solution containing 

 6-4 per cent, hydrogen sulphite, H 2 SO 3 , corresponding 

 to 5 per cent, by weight of sulphurous anhydride, S0 2 . 

 (B.P.) Sulphurous anhydride may be prepared by 

 burning sulphur in air or oxygen, or by boiling sul- 

 phuric acid with carbon, mercury, or copper (B.P.). 



The aqueous solution is colourless, has a pungent sul- 

 phurous odour, reddens litmus, bleaches colouring matter, 

 leaves no residue when heated, and has the specific gravity 

 I" 025. It is distinguished by its odour ; from its salts it 

 is liberated by hydrochloric acid. 



ACTIONS. Sulphurous acid is antiseptic, disinfectant, 

 and deodorant, and is used as a parasiticide. Concen- 

 trated doses, whether in the gaseous or liquid state, are 

 irritant. 



GENERAL ACTIONS. Its value in medicine depends on its 

 affinity for oxygen or powerful reducing action, and its 

 arresting the growth of micro-organisms, and not mainly on 

 its acid properties. A solution of one part in 8000 of water 

 destroys diastase and pytalin ; but although smaller quan- 

 tities arrest the action of emulsin and myrosin, one part in 

 1317 is required to destroy pepsin. Developed bacteria are 

 killed by one part in 2000 of water ; but to prevent repro- 

 duction of the spores one part in 325 is needful. Christison 

 found that one-fifth of a cubic inch, diluted with 10,000 

 volumes of air, destroyed the leaves of plants in forty-eight 



