INSECTICIDES, FUNGICIDES AND DISINFECTANTS 221 



out pressure, spraying and by an oxidizing agent. The 

 last two are ordinarily used. When spraying is resorted to, 

 the compartment should be kept closed for at least twenty- 

 four hours. An ounce of formalin is required to each 

 100 cubic feet, therefore a room 10 feet square and 10 feet 

 high would require ten ounces. The formalin is sprayed 

 on sheets hung in the room. 



The gas is readily liberated by several chemicals, but the 

 use of potassium permanganate has found most favor. The 



FIG. 75. Making Bordeaux mixture. The two men pour together 

 the diluted lime milk and the bluestone solution into a barrel or 

 spray tank and stir well. (Bulletin 243, U. S. Dept. Agr.) 



proportion which is most effective seems to be 6 parts of 

 formalin to 5 parts of potassium permanganate. For dis- 

 infecting 1000 feet of space, 20 ounces of formalin and 16f 

 ounces of potassium permanganate are required. The crystals 

 of potassium permanganate may be placed on the bottom 

 of an ordinary dishpan and the formalin poured on quickly 

 in order that the person so engaged may make a rapid exit. 

 Some of the formaldehyde is oxidized to formic acid by the 

 permanganate and this generates heat enough to drive the 

 remainder out as a gas. The compartment should be kept 



