6 
so that in case of breakage the work can be continued with 
little interruption. The length of the shifting poles should be 
about 2 feet more than the height of the average trees, and the small 
end should be about 14 inches in diameter. The poles for derricks 
should be about 3 or 4 feet more in length than the height of the 
average tree, and when ready for use should be between 3 and 4 
inches in diameter at the base and between 2 and 3 inches in diam- 
eter at the top. The method of attaching the crosspieces and braces 
is described and illustrated in Bulletin 76 of this Bureau. If ordinary 
three-eighths or one-half inch bolts are at hand, a pair of derricks can 
be prepared for use in less than half an hour, and this need not there- 
fore be considered a necessary part of the early perparations for 
fumigation. Cypress poles should be seasoned in a barn or packing 
house, or if out of doors they should be in the shade. Straight poles, 
while being seasoned, should be so supported as to prevent bending 
or warping. If, after cutting, a pole is found to be crooked, it may 
perhaps be made practically straight by the proper arrangement of 
the supports when seasoning. 
GENERATORS OR CROCKS. 
In generating the gas earthenware crocks are used. In general, 
trees 5 to 8 feet high will require crocks of 14 gallons capacity; trees 
9 to 12 feet high, crocks of 2 gallons capacity; trees 13 to 16 feet high, 
crocks of 4 gallons capacity; trees 17 to 20 feet high, crocks of 4 or 5 
gallons capacity; and trees 21 to 30 feet high, crocks of 5 or 6 gallons 
capacity. For trees up to about 18 feet in height one crock will be 
needed for each tent, but for larger trees two crocks should be used, 
dividing the dosage into two equal parts. Crocks with straight sides 
can be used with more cyanid for each gallon of capacity than crocks 
which narrow at the top, and it is to the former style rather than to 
the latter that the preceding statements refer. 
The foregoing directions should enable anyone preparing to fumi- 
gate to determine the actual number and sizes which will be needed. 
It is always advisable to have several extra crocks at hand, so that 
delays will be avoided in case of breakage. 
Crocks of more than 2 gallons capacity can not be readily obtained 
as a rule and frequently even the smaller sizes can not be obtained 
of local dealers in sufficient numbers to equip a large outfit. It is 
important, therefore, that orders for crocks be placed as soon as 
possible when preparing to fumigate. As the tops or covers are not 
needed, dealers should take this into consideration in quoting prices. 
When not purchased of local dealers and no allowance is made in the 
price on account of the covers of the crocks, instructions should be 
given not to include the covers in the shipment, in order to avoid 
unnecessary freight or express charges. 
[Cir. 111] 
