DISINFECTANTS 89 



faces. This suggests a chemical rather than a physical 

 effect, perhaps the formation of a peroxide. But the 

 amounts of hydrogen peroxide formed on metal sur- 

 faces in water by oxygen are far too small to explain 

 the oligodynamic action. However, a combined action 

 of peroxide and metal ions may be sutficient to kill 

 bacteria. Dittmar, Baldwin and Miller (1930) had ob- 

 served that the lethal action of hydrogen peroxide is 

 speeded up nearly 100 times by the presence of 0.1 mil- 

 limoles of Cu++ and Fe+++ ions. With 6 mg. Cu++ per 

 liter. Staph, aureus was killed in 10 minutes by 0.025% 

 H2O2, and in 30 minutes by 0.008% H,0.. 



The use of silver surfaces has been proposed to ster- 

 ilize water and even milk. Bechliold (1918) coated 

 particles of coal and sand with a thin layer of silver and 

 used them for the sterilization of water. Krause and 

 Bergmann (1928) produced the so-called ''katadyn" by 

 turning molten silver into a fine foam. The crushed 

 solidified foam bubbles are claimed to disinfect water 

 upon contact. The results obtained with milk, however, 

 are not very encouraging. 



Colloidal silver differs from these silver preparations 

 only in having a much larger surface. No records could 

 be found which would throw light on the important 

 question whether oxygen is necessary for the disinfec- 

 tion by colloidal silver preparations. 



4. The Alcohols. Of the aliphatic alcohols, 

 only ethyl alcohol is used as a disinfectant, and it is 

 rather weak. Its strongest action is at a concentration 

 of 70%. Absolute alcohol is less effective because it is 

 dehydrating, and proteins without moisture are not 

 easily denatured. 



The rate of denaturation of different native proteins 

 by ethyl alcohol varies greatly. Some enzymes lose 

 their activity in alcoholic solutions rather slowly. 



A surprisingly high concentration exponent was 

 found by Tilley for ethyl alcohol (Table 15). 



