368 DISINFECTANTS 



t3 be brought into actual contact with the substance to be oxidised. 

 All oxidisable matter, e.g., nitrites, ferrous salts and organic matter, is 

 first attacked, before the micro-organisms are affected. 



These substances form the active ingredients in "Condy's fluid". 



Zinc chloride, ZnCL,, a djliquescent and caustic white solid, very 

 soluble in water, is a powerful disinfectant. A solution containing 

 about 50 per cent of zinc chloride constitutes "Burnett's disinfecting 

 fluid". A more dilute solution is often used in surgery as an anti- 

 septic. 



Carbolic acid, phenol, C H 5 OH, and its homologues, e.g., cresol, 

 C H 4 (CH 3 ).OH, have long been used as antiseptics and disinfectants. 



They are obtained from coal-tar or from the tar produced by the 

 distillation of wood. 



These substances are poisonous in large quantities and when un- 

 diluted are caustic and generally deliquescent. They are only slightly 

 soluble in water, but by the action of alkalies they yield salt-like 

 bodies "carbolates" or "phenates" which are readily soluble and 

 easily d3composed by acids, even by carbonic acid, yielding again the 

 free phenol. 



Many disinfectants consist of lime or magnesia containing about 

 15 per cent of phenol. Such powders gradually lose their phenol on 

 exposure to air. Pure phenol is a colourless crystalline body, melting 

 at 41 and boiling at 182. With a little water it liquefies, forming a 

 fluid hydrate, which, however, is only soluble in about fifteen times 

 its weight of water. 



Phenol is decidedly antiseptic, but recently, doubts have been ex- 

 pressed as to its disinfectant powers. Certain pathogenic organisms 

 are very resistant to phenol, e.g., the typhoid bacillus can be separated 

 from many other micro-organisms by taking advantage of its power of 

 growing in carbolised nutrients. 



Phenol is a violent plant poison, and a very dilute solution will 

 prevent the germination of seeds. It is sometimes used as a weed 

 destroyer. 



Many of the "disinfecting powders" of commerce consist essenti- 

 ally of an indifferent powder, e.g., silicates or even silica, containing 

 about 15 per cent of carbolic acid. They are often coloured pink. 

 Sometimes calcium sulphite is also present. 



Creasote or creosote is a mixture of cresol, C (5 H 4 (CH 3 )OH, xylenol, 

 C 6 H 3 (CH 3 ).jOH, and other higher members of the series ; about 1 or 

 2 per cent of phenol is usually present. It is colourless when fresh, 

 but soon darkens. It possesses good antiseptic powers and is thought 

 to be preferable to phenol. It is used in the preservation of timber. 



Many preparations containing cresols are in use as disinfectants. 

 Lysol is obtained by mixing tar-oils (chiefly cresol) with fat and 

 saponifying with potash. It is soluble in water and is apparently an 

 excellent antiseptic. 



Wood creosote is a more powerful disinfectant than that from 

 coal-tar. In addition to cresol and phenol it contains guaiacol, 

 C 6 H 4 (OCH 3 )OH, and creosol, C 6 H 3 (CH 3 )(OCH 3 ).OH. Wood creasote 

 is very poisonous both to animals and plants. 



