366 DISINFECTION 



Disinfectants. A true disinfectant is a substance which destroys 

 the organisms (and their spores) which produce putrefaction or disease. 

 An antiseptic, on the other hand, is a substance which prevents their 

 growth, though it may or may not destroy them. A deodoriser is a 

 body which absorbs or destroys the evil-smelling gases which are 

 evolved during processes of decay. 



Disinfectants act in various ways and it is impossible to exactly cor- 

 relate their germicidal action with their chemical or physical properties. 



Rideal x classifies their action thus : 



1. Free acids or salts of acid reaction retard the growth of most 

 bacteria 



2. Albumin is precipitated by soluble salts of many heavy metals, 

 e.g., mercury, copper. Such salts probably act by coagulating the 

 protoplasm in the organisms. 



3. By combining with such metals, or in ether ways, e.g., by con- 

 tact with charcoal, the food of bacteria may be rendered insoluble and 

 the organisms are thus starved. 



4. Reducing agents, e.g., sulphites and ferrous salts, remove oxygen 

 and so destroy aerobic organisms. 



5. Oxidising agents, e.g., chlorine, ozone, hydrogen peroxide and 

 permanganates, destroy by oxidation both the bacteria and their food. 

 These are the most nearly perfect disinfectants. 



6. Some easily reducible metallic salts are assimilated by the 

 bacteria, with the deposition of the metals within their tissues. This 

 deposition, when it becomes great enough, kills the organisms. This 

 happens with salts of gold and silver. In some cases, very minute 

 quantities of these poisons promote the growth of the same organisms 

 which larger doses quickly destroy. 



7. Some substances which are germicides act in a manner which 

 can only be described as physiological and not chemical. To this class 

 belong boric acid and the berates and many of the aromatic com- 

 pounds. 



The number of substances which have been used as disinfectants 

 is very great and is constantly being increased. 



Among them, the following may be mentioned : 



Chlorine, which is used as the free element, as hypochlorous acid, 

 and as hydrochloric acid. 



Bromine and iodine. The former has some advantages because of 

 its being liquid and is now sufficiently cheap to permit of its use ; the 

 latter is less convenient and too costly for general purposes. They 

 .act, like chlorine, best in the presence of moisture. Iodine trichloride, 

 IC1 3 , has also been highly recommended. 



Hydrofluoric acid, HF, and especially hydrofluosilicic acid, H.,SiF G , 

 and the silicofluorides, are highly antiseptic. 



"Salufer" is a patented disinfectant, the basis of which is silico- 

 fluoride of sodium, Na 2 SiF (i . The use of hydrofluosilicic acid as a 

 preventative of the decay of farm-yard manure has already been alluded 

 to. Fluorides are also employed to prevent undesirable fermentations 

 in breweries, 



1 Disinfection and Disinfectants, 1893, 145. 



