496 Fumigation with Hydrocyanic Acid Gas. [nov., 



the soil, walls, glass, &c. should be thoroughly drenched with a 

 solution of i lb. of sulphate of copper dissolved in 25 gallons 

 of water. This dressing should be applied during the winter 

 before the leaf-buds begin to swell, otherwise the foliage will be 

 destroyed. 



The use of hydrocyanic acid gas for fumigating young fruit 



trees has been recommended during the past few years, and its 



value as a remedy for mussel scale is well 



Fumigation with known. In the Board's Leaflet No. 34, " The 

 Hydrocyanic . , 



Acid Gas. Woolly Aphis," the suggestion is made 



in reference to young apple and pear trees 



that all nursery stock should be fumigated with hydrocyanic 



acid gas, and thus thoroughly cleared of all insect pests before 



planting. In some countries, e.g., British Columbia, New 



Zealand and Cape Colony, the fumigation of imported plants 



is required by law. 



'Full directions as to the method of treatment are given in 



Leaflet No. 107, from which the following extract may be 



quoted : — 



" The bushes or young trees should be placed in an air-tight 

 box or canvas tent of known capacity and subjected to the 

 fumes of hydrocyanic acid gas for one hour. Large numbers 

 can be treated at once at little expense. After the stock is 

 stacked under the tent or in the box a glazed earthenware jar 

 (never a tin or iron vessel) should be placed on the floor and 

 then water poured into it. Sulphuric acid is added to the water 

 and cyanide of potassium allowed to fall into the jar. 



" The acid used should have a specific gravity of not less than 

 1-83, and the cyanide should be of 98 per cent, purity. The 

 proportions to be used, even with these standard materials, will 

 vary according to the character of the season, the strength of the 

 plants to be treated, and whether the plants are dormant or 

 active, evergreen or deciduous, &c. 



" For 150 to 200 cubic feet of air space the following general 

 formula may, however, be given : — 1 oz. of potassium cyanide, 

 i\ fluid oz. of sulphuric acid, and 3 to 4 oz. of water, the 



