Insect Pests 



169 



houses. These fumes are fatal to insect pests of all kinds, and if properly 

 applied are harmless to almost every plant. It is not wise, however, for 

 the gardeners to remain long after the lamps are lighted. 



Cyaniding". Of recent years other methods of vaporizing have been 

 introduced, the best known perhaps being that known as the cyanide 

 process, in which hydrocyanic acid gas is diffused to kill mealy-bug, scale 

 insects, and others. This gas is generated by mixing potassium or sodium 

 cyanide, sulphuric acid, and water in various proportions. For Vines in 

 leaf, and other plants, it is recommended that not more than f oz. of 

 potassium cyanide, or | oz. of sodium cyanide, should be used to every 



Fig. 91. Diagram showing Method of Fumigating with Hydrocyanic Gas 



Line 11, for 100 cub. ft. read 1000 cub. ft. 



P, Fan suspended from roof. F^ String 

 ing. c, Tray with cyanide, (f, Movable 

 owl containing sulphuric acid and water. 

 ig all three ingredients, and gas generating. 



lOOGeub. ft. ot" space. To every ounce or cyanide use 1 oz. of sulphuric 

 acid and 4 oz. of water. The sulphuric acid and water are mixed slowly 

 together, and then the cyanide is dropped into the liquid, and the poisonous 

 gas, which is fatal to men and most animals, is rapidly generated and is 

 best diffused by using a fan as shown in the diagram (fig. 91). Great 

 care must therefore be exercised if these dangerous materials are used to 

 vaporize planthouses. Even if the fumes are inhaled for a few seconds 

 they may prove fatal. By using proper cyaniding apparatus, however, 

 there is practically no danger in the hands of competent operators. The 

 accompanying diagram will give one an excellent idea how a planthouse 

 should be vaporized with hydrocyanic acid gas. Sodium cyanide is con- 

 sidered better to use than potassium cyanide, as it dissolves more readily 

 and, taking weight for weight, liberates 30 per cent more gas. 



Outdoor Pests. These are far more numerous than those afflicting 

 plants under glass. There is scarcely a fruit or vegetable, flower, tree, 



