2Q2 CHEMICAL INFLUENCES 



the degree of dissociation, there is a specific effect due to the chemical 

 structure, as is the case of nitrous, salicylic and hydrocyanic acids. 

 The same is true of alkalies. With metallic salts, the action will depend 

 mainly upon the metal in solution, but the electrolytic dissociation 

 is also of importance. NaCl will decrease the dissociation of mer- 

 curic chloride (HgC^) and decrease also its disinfectant power. Mer- 

 curic chloride dissolved in absolute alcohol is not dissociated. In 

 this case, it has almost no action upon bacteria. 



Acids are not commonly used as disinfectants, except in the house- 

 hold, but they play a certain role in nature. The common fruits con- 

 tain so much acid that bacteria cannot easily attack them; the decay- 

 ing of fruit is almost exclusively due to molds which have a preference 

 for acid media. The acid in the stomach of man and animals plays an 

 important role as a sterilizing agent for the food. Many microorgan- 

 isms are killed in the stomach. In the household, the natural 

 acidity of fruit helps in keeping canned fruit, preserves and jellies. 

 Especially in heating, the acid together with the high temperature 

 has a very strong germicidal effect. Vinegar is often used to pre- 

 serve fruit and vegetables; in some parts of the country, meat is kept 

 in buttermilk. Benzoic and salicylic acids are often used in the pres- 

 ervation of fruit and vegetables. Their poisonous influence is not 

 so much due to the acid reaction but to the specific chemical character 

 of these compounds. 



Of the alkalies, only one is used extensively, namely, lime; quick- 

 lime (CaO) is considered a valuable disinfectant for excreta in privy 

 vaults; it is universally applied as a whitewash in stables, barns, 

 poultry houses and similar buildings. Quite commonly, it is used as 

 "milk of lime" (one part of slaked lime with four parts of water). 

 It should be kept in mind that the calcium oxide unites with the carbon 

 dioxide of the air and thus gradually loses its disinfecting power. 



Of the metallic salts, many are well-known germicides. The most 

 powerful disinfectant is mercuric chloride (HgCU) which is one of the 

 standard disinfectants. It is generally used in a dilution i : 1000 

 which is sufficient to kill all vegetative cells as well as spores in a few 

 minutes. Quite commonly, hydrochloric acid or salt is added, to 

 prevent coagulation or precipitation of slimy or albuminous matter 

 which would protect the enclosed bacteria from immediate contact 

 with the poison. The addition of hydrochloric acid or any chloride 



