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 2/3 oz. of potassium cyanide, or 1/2 oz. of sodium cyanide, should be used to every 1000 cub. ft. of 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 considered better to use than potassium cyanide, as it dissolves more readily and, taking weight for weight, liberates 30 per cent more gas.

Diagram showing Method of Fumigating with Hydrocyanic Gas.

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

F, Fan suspended from roof. F', String ing. C, Tray with cyanide. C', Movable owl containing sulphuric acid and water. ig all three ingredients, and gas generating.

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