DURATION OF EXPOSURE. If) 
present system, whereas an hour is supposed to be the length of 
exposure throughout. Thus it' fifty minutes is found to give as 
satisfactory results as an hour, it would be poor policy to reduce the 
general exposure to this basis, inasmuch as with a general exposure 
of one hour some trees are already receiving but little more than fifty 
minutes. 
As a rule, very little gas remains under the tent at the expiration of 
one hour. The amount is usually so small that the mortality among 
the scale-insects could he hut slightly increased by greatly lengthen- 
ing the exposure. \ arious authorities have recommended two hours 
or more as the duration of exposure, and it i> possible that these long 
exposures would produce slightly better results than an exposure <>!' 
one hour. 
From the standpoint of the fruit grower, who requires the best 
results at the least possible expense, the item of time is highly impor- 
tant. The question which must be considered is whether it i> more 
advantageous to sacrifice time or cyanid. No doubt it is cheaper to 
sacrifice time up to a certain point, hut beyond this it is cheaper to 
sacrifice cyanid. As previously stated, the mortality among scale- 
insects, when a two-hour exposure i> employed, might he slightly 
greater than at one hour. Before advising a two-hour exposure, 
however, we must determine whether or not it would he more eco- 
nomical to employ an exposure of one hour and use sufficient cyanid to 
accomplish the same results secured by the longer time. Fumigators 
are usually paid by the hour. Where tents are left on the trees two 
hours, with the same number of tents the cost for labor is exactly 
twice that for one hour. From 4 to 6 men, at an average wage of :;.", 
cents per hour, are used on an outfit (infrequently 3), making the 
hourly cost for labor from SI. 40 to $2.10. This would purchase from 
5 to 7 pounds of cyanid/' Under these circumstances, if we can 
obtain as good results in an hour by using 5 to 7 pounds more of 
cyanid — or a smaller amount, according to the number of men in the 
outfit — it would be more economical in the (Mid to use the additional 
cyanid and expose for the shorter time. The writer's own held 
experience Leads him to believe that as good results can be accom- 
plished in one hour as in two hours by using an amount of cyanid 
costing far less than would the extra hour's labor. 
It will be seen that the question before the fumigator is not simply 
one of using that length of exposure which will produce the best 
results, but that which will at the same time be most economical. 
From field experience and other considerations the writer is led to 
believe that this will be between (il'ty minutes and one and one-half 
hours. 
a Cyanid i- here considered as including acid, both costing aboul 28 cents per pound. 
