498 Fumigation with Hydrocyanic Acid Gas. [nov., 



sheets, tents, and box covers. The first are octagonal in form,, 

 and can be further enlarged by sewing on a " skirt " round the 

 edge. These can be easily lifted over small trees up to six or 

 seven feet in height, above which a hoisting apparatus must be 

 used. Tent covers may be used for trees up to 13 feet in 

 height. They take the form of dome-shaped tents, the mouth 

 of which is kept open by a ring of gas-piping passed through 

 canvas loops, and they can be quickly lifted over and removed 

 from 8 to 13-ft. trees by a couple of men. Box covers are 

 made to any convenient size by covering a wooden framework 

 with canvas or calico ; the latter material should be painted or 

 oiled to make it sufficiently gas-tight. They are especially 

 adapted for small trees and bushes. 



The potassium cyanide may be used in lumps about the size 

 of cube sugar, and placed in a china basin or glazed earthen- 

 ware bowl. It should be placed well under the cover, after 

 which water and commercial sulphuric acid are added. It is 

 recommended that equal weights of cyanide and acid should be 

 used, and twice as much water as acid, i.e., one part of cyanide, 

 'one part of acid, two parts of water. The cyanide should be of 

 98 per cent, purity. As soon as the acid is added the side of 

 the cover must be quickly lowered and made tight, in order that 

 the gas may not escape. 



The time of exposure for small trees is put at 30 minutes, 

 and for trees over 10 feet from 40 to 45 minutes. Under no 

 circumstances should the cover be removed until 30 minutes 

 have elapsed. As to the quantities of acid and cyanide used in* 

 generating the gas, trees 6 feet high and 4 feet in diameter 

 when covered, enclose 65 cubic feet of space, and for such trees; 

 -J oz. each of cyanide and acid and 1 oz. of water may be used. 

 For trees 8 feet by 6 feet the space is roughiy 200 cubic feet,, 

 and the quantities should be oz. each of cyanide and acid,, 

 and 3 oz. of water. 



The potassium cyanide, being very poisonous, should be kept 

 in tightly stoppered bottles and labelled Poison, whilst the gas 

 as generated must on no account be breathed. Fumigation 

 - should not be carried out in a high wind, nor when the trees are 

 wet, but otherwise can be done at any season of the year, most, 

 opportunely perhaps directly the crop is removed. 



