LEAKAGE OF GAS DURING OPERATIONS. 47 



GENERAL CONSIDERATIONS. 

 LEAKAGE OF GAS DURING OPERATIONS. 



One of the most important questions relating to the proper dosage 

 in fumigation is that of the leakage of gas through the tent; in fact, 

 the dosage depends directly upon the leakage. To measure with 

 accuracy the amount of gas which escapes through tenting fabrics 

 of various grades during a given length of time, or the rapidity with 

 which the gas within the tent is diluted under different conditions, 

 is a difficult problem. In this work, as far as we have progressed, no 

 attempt has been made to measure directly with instruments the 

 rapidity with which the gas is diluted, but rather to measure it indi- 

 rectly and roughly through determining the eflfect on insects by using 

 different durations of exposure. The easiest and most practical 

 method of determining the influence of leakage is by fumigating 

 trees of the same size, in which all factors affecting the results are 

 identical with the exception of the length of exposure. 



There is, however, one consideration of value relative to the leak- 

 age of gas, which it is c^uite necessary to understand in successfully 

 fumigating an orchard containing trees of a wide range of size. In 

 geometrical figures which approximate in shape a citrus tree, the 

 volume decreases at a more rapid rate than does the surface area. 

 In order to bring out the relation of this fact to orchard fumigation, 

 the following table has been prepared : 



Table VIL — Leakage of gas from tents covering trees of different dimensions. 



" The comparison here and in the discussion which follows is between square feet of surface and cubic 

 feet of volume. 



Taking the first tree, 20 feet around by 12 feet over, representing a 

 volume of 99 cubic feet and an exposed surface area of 85 sc^uare 

 feet, the ratio of leakage surface to volume is 86 : 100. For each cubic 

 foot of volume within that 20 by 12 tree there is 0.86 square foot 

 of leakage surface in the tent. The tree 40 by 28 feet has 0.4 sc^uare 

 foot of leakage surface for each cubic foot in the tent, wdiile a tree 

 70 by 54 has but 0.22 square foot of leakage surface to each cubic 

 foot within. Suppose that these tented trees were charged with 

 gas and that all the gas were to escape through the tent. In the 



