193$.] Fumigation with Hydrocyanic Acid Gas. 497 



" strengths " being as above. The proportions can be reduced 

 or increased according to the space to be fumigated. Put very 

 generally the proportions may be stated thus : — The amount of 

 acid in fluid ounces to be one-half more than the cyanide, and 

 the water to be double the amount of acid. 



" It must be remembered that both the gas and the cyanide of 

 potassium are deadly poisons. The fumes must not be breathed. 

 The cyanide of potassium, wrapped say in a paper bag, is 

 lowered into the acid by a mechanical arrangement worked 

 from the outside. Or the apparatus may be arranged so that 

 the acid is poured into a jar containing the cyanide. 



" The process may also be applied in the case of green-houses. 



" At the end of an hour the tent or greenhouse should be 

 opened in such a way that the wind blows the fumes away from 

 the operator, and should be left to ventilate for half an hour 

 before the stock is removed." 



As the practice is not, perhaps, so largely adopted in this as 

 in some other countries, the following* summary of an article 

 by Mr. Claude Fuller, the Natal Government Entomologist 

 written for the guidance of those who wish to undertake 

 orchard fumigation with this gas, may be useful as supple- 

 menting the information given above. 



It is stated that although the treatment may not lead to the 

 entire eradication of some of the more persistent scale insects, 

 it appears to be the most economical and effective way of 

 dealing with them. In the case of mussel scale it is recom- 

 mended that the fumigation should be followed by spraying, as 

 the gas, whilst killing the live insects, cannot be relied upon to 

 destroy all the eggs, so that the trees may again become 

 infested. 



Fumigation is effected by first covering the trees with com- 

 paratively air-tight canvas covers, and exposing them to the 

 fumes of hydrocyanic acid gas. The materials required consist 

 of covers for the trees, the necessary chemicals, jars, measures, 

 &c. The covers should be of light, durable material, sufficiently 

 gas-tight, the most suitable probably being canvas. Eight -ounce 

 duck canvas is recommended. There are three types of covers i 



* Natal Agricultural Journal, July 28th, 1905. 



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