HALOGENS 635 



laboratory cultures, but in practice need to be used in 

 excess proportionate to the amount of organic matter 

 which may be present. Thus, for instance, a 1 per cent, 

 solution of hypochlorite of soda mixed with an equal 

 volume of urine loses the whole of its available chlorine 

 almost immediately, and becomes inert as a germicide. 

 Where the amount of organic matter is small, and the 

 objects are not likely to be injured, the hypochlorites are 

 among the best of known disinfectants, provided they 

 are used fresh. The slow addition of hydrochloric acid, 

 yielding nascent chlorine, increases the activity of a hypo- 

 chlorite considerably. A solution of iodine is now used 

 for skin disinfection in surgical practice. Iodine trichloride 

 is a powerful disinfectant, of which the use has been 

 suggested, among other purposes, for the sterilisation of 

 water. Nessfield has suggested the use of chlorine for 

 sterilising water on the large scale, and iodine for the 

 same purpose on the small scale (p. 599). Chloride of 

 lime or other hypochlorite may be used for sterilising water 

 on the large scale (p. 600). 



Other inorganic substances. Solutions of salts of mercury 

 exercise a powerful disinfectant action in proportion to 

 the amount of dissolved metal which they contain. The 

 most commonly used is the perchloride (corrosive sub- 

 limate). Apart from its extremely poisonous character, 

 it has the disadvantage of forming with albuminoid sub- 

 stances both insoluble and soluble compounds of little or 

 no germicidal value, sulphuretted hydrogen converts it 

 into the insoluble and inert sulphide, and it acts on some 

 metals. The addition of acids or salts (e.g. hydrochloric 

 or tartaric acid or sodium or ammonium chloride) prevents 

 or largely reduces the formation of insoluble compounds ; 

 but it does not prevent the reactions resulting in soluble 

 substances, it may reduce the germicidal power, and the 

 action of perchloride in the presence of albuminoids is 



