DISINFECTION 357 



and are used in solutions containing from 1 to 3 per cent, 

 of the agent. They are less corrosive and less poisonous 

 than phenol, and can be used as a dip for the destruction 

 of insects on animals. They are usually composed of the 

 creosote oil and soap, and when mixed with water form a 

 milky emulsion that is very permanent. They can be em- 

 ployed in widely varying concentrations, and their action 

 is. as a rule, not greatly impaired by the presence of or- 

 ganic malter. Only soft or rain water should be used to 

 dilute the coal-tar disinfectants, because the salts present 

 in hard water may materially reduce the disinfecting action. 

 They are undoubtedly the best class of disinfectants for 

 common use on the farm, especially in the treatment of 

 animals. 



Formaldehyde. This important disinfectant is sold in 

 the form of a 40 per cent, solution of the gas dissolved in 

 water, and is usually called formalin. Its widest use on the 

 farm is in the disinfection of closed spaces by setting free 

 the iias from the liquid, as will be described later, and for 

 the destruction of smut on seed grains and scab on seed 

 potai 



Corrosive sublimate. This compound, frequently known 

 as bichloritli <>\ mercury, is one of the strongest disinfect- 

 ants known. Its disadvantages are its poisonous properties 

 and its greatly decreased action in the presence of organic 

 matter such as manure. It also has a corrosive action on 

 metals, and is irritating to the tissues. It can be used to 

 advantage in many places as a wash or as a spray on walls. 

 For this purpose it is used in a one to one thousand solu- 

 tion, or one ounce of the salt to eight gallons of water. 



Sulphur. When sulphur is burned, irritating fumes are 

 formed. When moisture is present in the air, sulphurous 

 acid is formed which possesses a considerable disinfecting 

 action. It is used in the place of formaldehyde as a gaseous 



