The Effect of Chemicals on Microorganisms 203 



4. Copper Salts are much better algicides than bactericides. 

 Suggestions have been made that copper sulphate be added to 

 water suppHes to serve the double purpose of inhibiting the growth 

 of algae and of killing bacteria. Since we know little about the 

 cumulative effects of ingested copper and other metals in small 

 amounts over a long period of time, it seems wise to adhere to the 

 tested technics, especially chlorination, for treating public supplies 

 of drinking water. 



THE HALOGEN COMPOUNDS 

 The electro-negative substances, chlorine, bromine, fluorine, 

 and iodine, are not found in a free state in nature; they are much 

 too active and readily combine with many other substances. 



1. Chlorine. Phenol is often considered by the layman to be a 

 rather powerful disinfectant, probably because it has "that hospital 

 smell." But free chlorine has a bactericidal power up to two 

 hundred times that of phenol, because the halogen is a strong 

 oxidizing agent and its ions are quite toxic for protoplasm. The 

 firmness with which the chlorine is bound to other substances or 

 elements determines how eftective the chlorine is going to be in 

 killing germs. Sodium chloride (table salt) is a tight combination 

 of sodium and chlorine (NaCl), and no measurable germicidal 

 effect of this compound of chlorine can be registered. Loosely- 

 bound chlorine, such as that found in calcium hypochlorite, can be 

 active in killing organisms. Upon prolonged storage, however, 

 these loosely bound compounds lose their active principle, and a 

 false sense of gennicidal activity may result from their use. 

 Chlorine can combine directly with protein in a process called 

 clilorination, or it may act by oxidation. In either case, the living 

 cell's normal protoplasmic balance is disrupted and the cell 

 eventually dies. Liquid chlorine has largely replaced hypochlorite 

 in treating water supplies, and this purified liquid chlorine adds 

 no inert matter to the water supply. But for smaller operations, 

 it is safer to handle the hypochlorite. 



Calcium hypochlorite, also known by the names of chloride of 

 lime, hypo, bleaching powder, or bleach, is widely used in sanita- 



