FUMIGATION AGAINST GRAIN WEEVILS 



have been only stupefied.) To obtain the desired humidity, air 

 was bubbled through bottles of sulphuric acid of the proper density, 

 the vapor pressure of water in sulphuric acid-water mixtures being 

 known for mixtures of various densities. In the less volatile com- 

 pounds, the quantity of the compound present in the jar in the form 

 of vapor was determined by passing a known volume of air over a 

 weighed quantity of the compound. The loss in weight (in grams) of the 

 compound divided by the quantity of air (in liters) gives the quantity 

 (in grams) of substance present in the form of vapor per liter of air. 



The following factors were used in calculating the results reported : 



Grams per liter X 62. 43=pounds per 1,000 cubic feet. 



Grams per literX \ -, ^rr=percentage concentration. 



gram-molecular weight 



Percentage concentration X gram-molecular weight X 0.02787 =pounds per 



1,000 cubic feet. 



1 cubic foot = 28.32 liters. 



1 kilogram = 2.20462 pounds. 



Assuming the vapor of a compound to be a perfect gas, the mole- 

 cular weight (in-grams) of this vaporized compound will occupy 22.4 

 liters under a pressure of 760 millimeters of mercury and at a tem- 

 perature of 0° C. For example, the molecular weight of chloroform 

 is approximately 119.4. Therefore, if 22.4 liters of space contains 

 119.4 grams of chloroform vapor (equivalent to 5.33 grams per liter), 

 the percentage concentration is 100. 



Since the tests were made at about the same temperature on com- 

 pounds differing greatly in vapor pressure, it follows that the more 

 volatile compounds were tested in high molar concentrations and 

 the slightly volatile compounds were tested in low molar concen- 

 trations, which, however, were the maximum concentrations of the 

 vapors possible at the temperature of the test. 



EFFECT OF VOLATILE ORGANIC COMPOUNDS ON WEEVILS 



The results of the fumigation of weevils in glass flasks at room 

 temperature (21° to 32° C.) are shown in Table 1. Table 2 gives 

 the formula, molecular weight, boiling point, and mhiimun lethal 

 concentration for each compound tested. 



Table 1. — Results of fumigation tests on weevils in glass flasks at room temperature 



(21° to 82° C.) 





Tem- 

 pera- 

 ture 



Fumigant 



Concentration 

 of fumigant 



Weevils killed after exposure 

 for 24 hours 



Test No. 



Molar 

 per- 

 cent- 

 age 



Pounds 

 per 

 1,000 



cu. ft. 



S. 

 oryza 



S. 

 gran- 

 arius 



Tribo- 

 lium 



Plodia 



Hydrocarbons: 

 311 



°C. 

 25.0 

 21.5 

 22.5 

 28.5 

 23.0 

 30.5 

 28.5 

 28.5 

 29.0 

 30.5 

 28.5 

 30.0 

 24.0 



28.5 





40.31 



14.73 



21.26 



1 .40 



13.00 



14.00 



13.00 



.90 



1.60 



3.80 



3.00 



1.40 



'.50 



,01 



78.76 



28.78 



41.54 



1.43 



30.48 



32.82 



28.29 



1.96 



3.48 



8.27 



7.70 



4.14 



1.79 



.or, 



P.ct. 



100 















100 



100 



100 







10 



100 



75 



60 



75 







P.ct. 



100 















100 



100 



100 







30 



100 



50 







25 



1) 



P.ct. 



100 















100 



100 



100 







80 



100 



100 











P.ct. 



343 



do 



do 





347.. 





94 



10 



83 





85 



139... 



do.... 



70 



35 



100 



130 . 



do 



do 



do 







133 







136 



70 



37 



80 



23 







14 



Naphthalene (25 per cent) 

 and carb6n tetrachlo- 

 ride (76 per cent). 



Anthracene 



25 



39 







1 Molecular weight of kerosene assumed to bo 128. 



2 Concentration of naphthalene only. 



