EFFECT OF CHEMICAL ENVIRONMENT 141 



hydrochloric acid contains about ten times as many hydro- 

 gen ions as normal acetic acid. 



In a few acids either the anion or undissociated acid 

 molecule may also exert a disinfecting action. In some 

 this action is much more important than that of the hydro- 

 gen ion; for example, benzoic acid is a comparatively 

 weak acid and yet it has relatively high antiseptic or 

 disinfecting value. This is likewise true of salicylic acid 

 and related compounds. 



Alkalinity or Alkalies. — High alkalinity, that is, high 

 concentration of hydroxyl ions likewise exerts a destruc- 

 tive action upon microorganisms. Lime owes its value as 

 a disinfectant to this fact. Unslaked lime (calcium 

 oxide) in the presence of water becomes calcium hydrate 

 and when used in strong solutions, as in whitewash, it has 

 a marked disinfecting value. It is a valuable disinfectant 

 to mix with stools or body excreta in order to destroy 

 disease-producing bacteria. It should be noted, however, 

 that upon exposure to air calcium hydrate is gradually 

 converted into calcium carbonate which is no longer ger- 

 micidal. 



Some bacteria will grow in relatively alkaline solutions. 

 For example, the organism causing Asiatic cholera, the 

 Vibrio cholerce, will grow in much higher hydroxyl ion con- 

 centration, that is, in more alkaline solutions, than will 

 most other species of bacteria. Use is made of this fact 

 in isolating this organism from feces, the medium being 

 made so alkaline as to inhibit the growth of most other 

 nucroorganisms rendering the securing of this organism 

 in pure culture comparatively easy. 



Salts of the Heavy Metals. — The soluble salts of the 

 heavy metals are almost without exception more or less toxic 

 to bacteria. In practically all eases their efficiency as disin- 

 fectants depends upon the degree of ionization. Salts of 

 silver, mercury, and copper are of particular importance. 



