543 
As very little is known about these methods by fruit growers, a few 
directions will prove useful, together with more detailed information 
regarding the process of fumigation and the making and handling 
of the gas-tight tents. 
WHAT AND WHEN TO FUMIGATE. 
Fumigation by means of hydrocyanic or prussic acid gas is 
successfully used in the treatment of insect pests ; it has little or no 
effect on blights of fungoid origin. Insects which can be more 
readily attacked are scales, red spider, miles, and aplides. Trees 
and plants can be fumigated at any season of the year. In the 
winter time deciduous trees can, without injury, be fumigated 
at any time of the day ; they can also, when dormant, stand heavier 
doses of gas, as well as a longer period under the tent. Citrus trees 
require more careful treatment, and should only be fumigated on 
dull mornings or afternoons, or in the evening by moonlight. 
In the summer, when the trees are of active growth, they should 
only be fumigated late in the afternoon or at night. 
The above sketches of bell tents Nos. 0, 1, 2, and 3, show dimen- 
sions for cutting widths and tops. One inch is the width allowed 
for allseams. All measurements are given in feet and inches. No. 
0 covers trees 44 feet diameter by 5 feet high ; No. 1 covers trees 
63 feet diameter by 7 feet high ; No. 2 covers trees 8 feet diameter 
by 11 feet high ; No. 3 covers trees 10} feet diameter by 12 feet 
high. This diagram is taken from Mr. A. Benson’s paper in the 
Queensland Agricultural Journal. 
CAUTION TO OPERATORS. 
Those using the process of fumigation for the treatment of scaly 
trees should bear in mind that they are handling, probably, the most 
insiduous and deadly of poisons. 
The gas inhaled in a close chamber produces sudden death ; 
when largely diluted with air it is harmless. Thousands of thou- 
sands of trees are now-a-days fumigated every year, and accidents 
are rare. With proper precautions there is no danger whatever. 
Unless handling small tents covering trees 5ft. or 6ft. high, 
not less than two men should operate. 
Not only is the hydrocyanic acid gas highly poisonous, but the 
ingredients or chemicals used in its production are also dangerous 
poisons. These ingredients are: 1° potassium-cyanide, of which a 
piece of the size of a grain of wheat would prove fatal to an adult 
or an animal ; 2° sulphuric acid or oil of vitriol, which is eminently 
corrosive, and every precaution should be taken to guard against 
its spurting on the face, hands, or clothes. 
When operating, hold your breath when dropping the cyanide 
into the acid, and also when removing the tent and uncovering the 
tree. See that the tents are always gas tight. Should the acid 
accidentally spurt on your hands or face, wash at once in water. 
