18 



FUMIGATION INVESTIGATIONS IN CALIFOENIA. 



threads twisted hard and woven fairly close. This double-twisted 

 material is heavier and much stronger than the special drill, but not 

 so closely woven; consequently it is somewhat more porous. In 

 field work the special drill will adapt itself more closely to the 

 irregularities of the ground than the army duck, and particularly if 

 the tents become damp. The special 6i-ounce drill is generally con- 

 sidered the best 

 obtainable for use 

 in all fumigation 

 tents up to 45 

 feet standard size. 

 Special 8-ounce 

 army duck is rec- 

 ommended for 

 use in tents of 

 larger size. Prob- 

 ably the most sat- 

 isfactory method 

 of making large 

 tents is to have 

 the center of spe- 

 cial duck and the 

 sides of special 

 drill. This dis- 

 tributes the heavy material at the points of greatest wear, while the 

 drill makes the tent much lighter and more flexible. 



Fig. 8.— Tray commonly used for carrying the chemicals of fumigation 

 from tree to tree. Cans above contain cyanid; pitchers below contain 

 acid. (Original.) 



POINTS ON PROCEDURE. 



The number of men making up an outfit varies from three to six. 

 In San Bernardino County most of the outfits consist of six men ; else- 

 where they more commonly consist of four. 



In estimating the dosage, the usual method is to make the estimate 

 before the trees are covered with a tent. Sometimes this scheduling 

 is done in the daytime, sometimes by night. The schedule for a row 

 of trees to be fumigated having been given, either one of two methods 

 of procedure is followed. In the first and more common method the 

 dosage of cyanid and acid for each tree of the row is measured out 

 into small cans and pitchers, which are placed in a tray after the man- 

 ner shown in figure 8. When ready for use this tray is carried from 

 one tree to the next down the row (fig. 9). Frequently two trays are 

 necessary to carry the material required for the entire row or set of 

 trees. The w^ater is carried in a pail and measured at each tree. 

 The receptacles in wdiich the gas is generated consist of earthenware 

 jars holding IJ to 2 gallons, having the handle on the side (fig. 10). 

 If dosages in excess of 16 ounces are used in a IJ-gallon generator or 



