622 FUMIGATING 



Black-ants. These are sometimes very troublesome in a 

 garden, undermining roads, lawns, etc. According to the "Jamaica 

 Bulletin" nothing has been so successful in expelling these as a 

 solution of bitterwood (See quassia under Insecticides). 



FUMIGATING 



Destroying insect-pests by means of fumes of poisonous gas, 

 tobacco smoke, etc., is commonly adopted wherever plants are 

 grown in closed structures, and also in the fields where fruit-grow- 

 ing is practised on systematic lines. For cheapness, efficiency and 

 facility of application, the hydrocyanic gas process of fumigating 

 has been found to be the most satisfactory yet discovered. It is 

 extensively practised in America for orchards as well as for general 

 nursery stock, more especially against scale-insects, which are 

 difficult to destroy by other means. The gas is a deadly poison, 

 and the greatest care is needed in using it. It is generated from 

 cyanide of potassium (or sometimes sodium cyanide) and sulphuric 

 acid, and is fatal to insect or animal life by inhalation. When 

 applied to trees or shrubs in the open, special collapsible tents are 

 used for the purpose of enclosing these. Small or movable plants 

 may be treated in any enclosure, provided it is sufficiently air- 

 tight. An ordinary wardian case with a capacity of about 1\ cubic 

 feet is used for the purpose at Peradeniya, the proportions recom- 

 mended being: \ oz. cyanide of potassium (90%), J oz. sulphuric 

 acid, and \ oz. water. Place the water in a small earthenware 

 bowl; add the acid; drop in the cyanide, and close the case imme- 

 diately, stopping up all crevices with wet clay to prevent the gas 

 escaping. After the expiration of half an hour, open the case and 

 leave it for several hours. The principle is the same when the 

 process is applied on a larger scale. When fumigating plant- 

 houses, the cyanide is usually \vrapped in a small suspended paper 

 bag, which is dropped into the acid and water by means of a string 

 passing through a trap-door and released from outside. The pro- 

 per amount of cyanide to be used varies according to the nature 

 of the pest and plants to be treated, but the proportions, as above 

 stated, should always be approximately the same. Experienced 

 men recommend four- fifths of a grain of cyanide for every cubic 

 foot of free space. It is considered by some that the water should 

 be boiling when the acid is added (the cyanide being then dropped 

 into it), but this does not appear to be necessary. An essential 

 condition in any method of fumigating is that, contrary to 



