220 CHEMISTRY OF FARM PRACTICE 



odor to bleaching powder. It should be kept in sealed con- 

 tainers. Chlorinated lime is prepared for use by mixing in 

 the proportion of 6 ounces of the powder to each gallon of 

 water. It is largely used for the disinfection of refuse, 

 stock-pens, or cars, and is the most efficient disinfectant. 

 It has a bleaching effect on fabrics when there is need of 

 concentrated effect; the chlorinated lime may be treated 

 with dilute acid. 



Formaldehyde. Formaldehyde (HCHO) is commonly 

 purchased under the name formalin, which is a solution con- 

 taining about 40 per cent formaldehyde. It may be used 

 for disinfecting purposes either as a liquid or as a gas. A 

 5 per cent solution of formalin is considered to be superior 

 to carbolic acid of the same strength, as a disinfectant. 

 Formaldehyde is peculiarly effective as a disinfectant, as it is 

 an unstable compound which on the one hand is easily re- 

 duced to methyl alcohol by the addition of hydrogen or of 

 reducing agents, which it abstracts from the organism which 

 needs disinfection, and on the other hand, it is easily oxidized 

 into formic acid by the addition of oxygen, which it takes from 

 the substance to be disinfected in either case sterilizing the 

 infecting material. 



These opposing actions are represented by the following 

 equations : 



HCHO + Ho CH.jOH 



Formaldehyde Methyl alcohol 



HCHO+O = HCOOH 



Formaldehyde Formic acid 



When disinfecting with gaseous formaldehyde, it is neces- 

 sary to close tightly the place to be disinfected in order that 

 the concentrated gas may be in contact with the infected 

 material for some time and the temperature should be warm. 

 The gas may be produced from formalin in several ways, 

 but the chemical means are usually most convenient. The 

 various methods are: heating under pressure, heating with- 



