Nov. 1, 1899. J THE TROPICAL AGEICULTUEIST. 
29d 
' Absence of Sunlight necessary. ~.The originators of 
the fumigation process observed that the gas was 
most efficacious, and that less injary I'esulted to 
the foliage when the operations were "performed at 
night than when they were carried on in sunlight. 
Jt is said that chemical changes are produced in 
the gas by the action of sunlight, and that the 
resulting gases are more injurious to the plant life 
and less to animal than hydrocyanic acid gas. 
Whether or not these theories are correct is of 
small practical impo'rtance, for the foliage of a tree 
will suiier serious injury if the tree is left covered 
with an air-tight oiled tent for half an hour in 
sunlight, without the gas being present. Having 
ascertained this fact by experience, the foreman in 
charge of the Board's outfit refrained from covering 
trees until the sun had sunk from sight on any 
but cool, dull days. Ihe great majority of the trees 
treated have been fumigated after sunset. The ideal 
night for fumigating is quiet, cool, and moonlight, 
and without dew.' 
It is evident, from the above that the period 
available for this process is somewhat limited, 
ilowever, when only a few trees have to be treated, 
the hour immediately preceding nightfall will be 
ample for the purpose. I have personally found no 
ill effects following the operation when performed 
on dull, cloudy days, when the sun is entirely 
obscured. 
Although hydrocyanic acid gas will certainly kill 
every insect — and even their eggs — if used in suffi- 
cient strength and for a sufficient length of time, 
both the necessary strength and time will be found 
to vary with different species of insects, and must 
be madii the subject of careful experiment. I find 
that Ortlteyia insignis is a very difficult insect to 
kill, and requires a double strength of gas, con- 
tinued for fully three-quarters of an hour. 
Mr. D. W. Coquillet, one of the first to employ 
this process, gives the following directions for making 
an air-tight tent : * — ' The material commonly used 
in the construction of the tent is what is known as 
blue or brown drilling. A few persons have used 
ducking instead of drilling, but this is much inferior 
to the latter; in the ducking the threads extend 
only lengthwise and crosswise, whereas in the drilling 
they also extend diagonally — this belonging to 
the" class of goods to which our merchants apply 
the term ''twilled'' — and for this reason the drilling 
is both stronger and closer' in texture than the 
ducking. 
' After the tent ia sewed up it is given a coat of 
black paint, as it has been ascertained that 
tents treated in this manner last longer than those 
which have been simply oiled with linseed oil. Some 
persons mix a small quantity of soap-suds with the 
paint in order to render the latter more pliable 
when dry, and therefore less liable to crack. Instead 
of thus painting the tent some persons simply give 
it a coating of size. Sometimes a small quantity 
of whiting or chalk is added to this sizing, with or 
without the addition of lampblack. A few make 
use of the mucilaginous juice of the cemmon cactus 
(Opuntia Engehnanni) for this purpose. To obtain 
this, the cactus leaves or stems are cut or broken 
up into pieces, thrown into a barrel, and covered 
with water after which they are allowed to soak 
for three or four days. The liquid portion is 
then drawn off, and is ready for use without further 
preparation. Tents which I saw that had been pre- 
pared with this substance were to all appearances 
as air-tight and pliable as when prepared in any 
other manner.' 
For the oiling, Mr. Lonuabury recommends a 
mixture of four parts boiled linseed oil to one part 
turpentine. The cloth should be first well wetted 
with water, and the mixture spread lightly over 
the surface with a brush. A thin coating is found 
to be sufficient. Mr. Lounsbury has since informed 
me that he now uses, with completely satisfactory 
* U S. Department of Ai;riculture (Division of 
flatomology). Bidlctia, No. 23. 
results, tents made of cloth merely shrunk in water, 
without any subsequent oiling. Such tents are, of 
course, much lighter and more easy to manipulate. 
Mr. Coquillet gives the annexed table, showing 
the quantities of chemicals reauired for different- 
sized trees. 
Height Diameter of "Water. Sulphuric Potassium 
of tree, tree top. acid. cyanide. 
Feet, 
Feet. 
Fluid oz 
Fluid oz. 
OZ. 
6 
4 
§ 
i 
8 
10 
6 
2 
1 
1 
8 
10 
4§ 
2i 
2i 
12 
8 
4 
4 
12 
14 
16 
8 
8 
11 
10 
10 
5 
6 
14 
14 
19 
9J 
9i 
16 
12 
16 
8 
8 
16 
16 
29 
Hi 
Hi 
18 
14 
26 
13 
13 
• 20 
16 
36 
18 
18 
22 
18 
52 
26 
26 
21 
20 
66 
33 
S3 
Mr. Lounsbury, after practical experience at the 
Cape, publishes the following figures, from which it 
appears that he found smaller quantities sufficient. 
This is doubtless, due to difference in purity of the 
chemicals. Mr. Lounsbury was working with cyanide 
of 98 to 100 per cent, purity, while Mr. Coquillet 
was using cyanide of only 33 to 58 per cent. It ii 
therefore important to know the exact amount of 
pure potassium cyanide in the particular brand 
employed. 
Height. 
Diameter. 
"Water. 
Acid. 
Cyanide. 
Space 
enclosed. 
Feet. 
Feet. 
Fluid oz. 
Fluid oz. 
oz. 
Cubic feet. 
4 
3 
1 
'I 
i 
4 
25 
6 
4 
i 
i 
65 
8 
5 
1 
4 
HO 
8 
6 
14 
2 
200 
10 
6 
2 
1 
255 
10 
8 
3 
li 
n 
435 
12 
8 
34 
li 
535 
12 
10 
54 
2i 
2i 
815 
14 
8 
44 
2i 
2i 
635 
14 
10 
6i 
3i 
3i 
970 
14 
12 
y 
44 
4» 
1355 
16 
10 
3i 
31 
1130 
16 
12 
104 
5i 
51 
1.585 
16 
14 
14 
7 
7 
2105 
18 
12 
12 
6 
6 
1810 
18 
14 
16 
8 
8 
2415 
18 
16 
20 
10 
10 
3085 ■ 
20 
14 
18 
9 
9 
2720 
20 
16 
23 
114 
Hi 
8485 
20 
18 
29 
144 
14i 
4325 
22 
18 
32 
16 
16 
4835 
22 
20 
39 
194 
194 
5865 
24 
20 
43 
214 
2l4 
6500 
The gas treatment has been largely used in com- 
bating scale insects (Particularly Aspidiottis aurantii) 
on orange trees. It will be found the most effectual 
method for exterminating Orthezia insignis, or any 
other insect, upon individual trees. 
Soap and Soapy Emulsions. 
Soap by itself has considerable insecticidal pro- 
perties. In fact, in many popular mixtures, it ia 
extremely probable that the soap is the most effi- 
cacious ingredient. It acts by asphixiation, forming 
an impervious film over the breathing pores of the 
insects. 
"Whale-oil soaps' are found to be the best for the 
purpose. In Insect Life, vol. vii. p. 369, the follow- 
ing conclusions are drawn from numerous experi- 
ments upon trees infested with the San Jose scale 
( Asi^idiotus pcrniciosus) in America ; — ' Soap washes 
