30 CIRCULAR 3 6 9, U. S. DEPARTMENT OF AGRICULTURE 



evaporating pan by .gravity or compressed air. If liquid hydrocyanic 

 acid or the ethylene oxide-carbon dioxide mixture is to be used, a 

 short piping system with one or more spray nozzles can be installed 

 (figs. 20, 21, and 27). 



USE OF FUMIGANTS SUITABLE ALSO FOR LARGE SPACES 



Hydrocyanic acid, chloropicrin, ethylene oxide-carbon dioxide 

 mixture, and the methyl formate-carbon dioxide mixtures are all 

 suitable for vault fumigation, and they can be used in the manner 

 described for the fumigation of large spaces. If hydrocyanic acid 

 is used, the pot or the discoid method is best adapted for vault fumi- 

 gation, since only small quantities of the chemical are used at one 

 time. Chloropicrin can be applied by pouring the dosage into the 

 evaporating pan or by forcing it in through a piping system with 

 compressed air. The ethylene oxide-carbon dioxide mixture and the 

 methyl formate-carbon dioxide mixtures are applied through a pip- 

 ing system and can be administered by connecting the cylinder to 

 the system (fig. 27) and opening the valve. If the cylinder is placed 

 on a platform scale, it is an easy matter to let in the quantity desired. 



USE OF OTHER FUMIGANTS 



Various other fumigants, not suitable for warehouse fumigation, 

 can also be used successfully for vault fumigation. These are car- 

 bon disulphide, ethylene oxide, ethylene dichloride-carbon tetrachlo- 

 ride, and carbon tetrachloride. 



CARBON DISULPHIDE 



Carbon disulphide is a colorless, volatile liquid, which boils at 

 114.8° F. On exposure to air it evaporates, forming a heavy vapor 

 that is very toxic to insects. 



It is applied by pouring the liquid into the evaporating pan of a 

 vault at the rate of about 5 pounds per 1,000 cubic feet of space. If 

 the vault is not tight, more fumigant should be used. It should not 

 be used at temperatures below 70° F., and the exposure should be at 

 least 12, and preferably 24 hours. 



The vapors of carbon disulphide, when mixed with air in certain 

 proportions, are highly inflammable and explosive ; hence this fumi- 

 gant should be used only where the fumigation vault is isolated from 

 other buildings, and where the fire hazard can be controlled. 



Mixtures of carbon disulphide with other chemicals, such as carbon 

 tetrachloride and sulphur dioxide, for the purpose of reducing the 

 fire hazard are now on the market. Although not absolutely nonin- 

 flammable, they can be used with comparative safety. Their efficacy 

 is directly proportional to the carbon disulphide content, and they 

 should be used accordingly. 



The vapors of carbon disulphide are poisonous to human beings if 

 breathed for an extended period. Exposure to light concentrations 

 may induce a feeling of giddiness, which, however, will quickly pass 

 off on coming out into the fresh air. Small quantities of carbon 

 disulphide can be handled without danger by the ordinary person, 

 although persons having any heart trouble should take little part 

 in its application. 



