58 DESTRUCTION OF BACTERIA BY CHEMICALS 



Formaldehyde. This is a gas, but is most commonly 

 seen as a solution ordinarily known under its trade 

 name formalin. This contains from 35 to 40 per cent, 

 of the gas and also some wood alcohol. The gas has 

 an affinity for many organic substances, among them 

 some of the dyes, but fabrics are not affected. Of the 

 metals, iron and steel are attacked after long exposure 

 in the presence of moisture. By reason of its affinity 

 for organic substances it is a good deodorizer and 

 disinfectant chiefly because it forms new insoluble 

 odorless compounds. 



It is not very irritant when taken into the stomach, 

 but its vapors cause considerable annoyance in the eyes, 

 nose, and mouth. The lower animals resist it consider- 

 ably, but insects are not affected. - It is more effective 

 in the presence of moisture and when the temperature 

 is high, up to 120 F. If these conditions cannot be 

 obtained the exposure must be longer. Two and one- 

 half per cent, by volume of the aqueous solution or 

 1 per cent, by volume of gas are sufficient to destroy 

 fresh virulent cultures of the common non-spore-bearing 

 bacteria in a few minutes. 



PRACTICAL APPLICATION OF DISINFECTION. 



Stock Solutions. As given by Park these can be 

 made as follows: 6 ounces of carbolic acid in 1 gallon 

 of hot water this is about a 5 per cent, solution. It 

 is milky at first and must be stirred thoroughly. The 

 addition of a small amount of glycerin keeps the 

 carbolic acid in solution and probably assists in disin- 



