73 
between the two trees, removing from the one and at the same time 
getting almost in position to lower upon another by a quick adjust- 
ment of the angle of the gaff, it requiring less than eight minutes to 
cover a tree from this position. The apparatus requires four men, 
-one of whom may be the fumigator if his chemicals have been weighed 
out beforehand. A gang of four can operate about four tents or two 
derricks. This gives forty minutes to the tree and allows ten minutes 
for shifting of each tent. In order to realize this expeditiousness in 
practice all apparatus must be in perfect working order and repair 
and the men trained to handling it. The results secured in my prae- 
tice satisfied me that this would be a reasonable estimate, for it was 
done often enough in this time with our then imperfected apparatus 
to justify such a conclusion. 
Some determinations made by Professor Miller, of the chemical 
department, are of interest and importance. He found that 1 ounce 
of sulphuric acid and 1 ounce of water, mixed and cold, when added 
to 1 ounce potassium cyanide yielded 428.4 cubic inches of gas; that 1 
ounce of sulphuric acid and 1 ounce of water, mixed and added imme- 
diately while warm to 1 ounce of potassium cyanide, yielded 467.9 
cubic inches of gas, greater by a little more than 9 per cent than with 
a cold mixture of water and acid. Mixing the acid and water, there- 
fore, only as used means a saving of 6 or 7 cents per tree on large 
trees requiring 2 pounds of cyanide. He further determined that a 
greater proportion of acid did not materially alter the result, and that 
ammonia seems not to be formed immediately after the reaction under 
laboratory conditions. 
A number of experiments were made with citrus twigs, orange, 
lemon, pomelo, etc., infested with white fly, to determine the suscepti- 
bility of the insect to the gas, dose of chemicals to use, length of time 
necessary, and most favorable temperature for treatment, influence 
of moisture present upon the leaves when fumigated, ete. 
It was found that in its larval and pupal stages the insect was very 
readily killed by much lighter doses of gas than are commonly used 
against the black seale in California; in fact, the field practice with 
tents demonstrated that the dose could be reduced about one-half; 
that the time should be about forty minutes; the variation in tem- 
perature ordinarily encountered in Florida seems to be a neglectable 
factor; moisture did not seem to interfere greatly with the efficieney 
of the work unless the leaves were almost dripping, when it became a 
factor of much disturbanee, though not so great as I had thought 
probable. 
Trees were fumigated in the field in warm sunshine at all hours of the 
day, in cloudy weather, and at night. But little injury to trees or foli- 
age was observed if fumigated at night, during cloudy weather, early in 
the morning, or latein the evening. Trees fumigated after 9 a. m. and 
