INSECTICIDES AND FUNGICIDES: FUMIGATION 57 



denatured alcohol to insure burning : then light the sulfur and keep the 

 place tightly closed for 24 to 48 hr.; then air thoroughly. 



Hydrocyanic -acid Gas (HCN). This is one of the most powerful and 

 dangerous gases known, and persons having had no training in its use are 

 advised not to try it. It is produced by the addition of sodium or potas- 

 sium cyanid to sulf uric acid which has been diluted with water. Formerly, 

 potassium cyanid was used almost entirely but now the sodium cyanid has 

 taken its place. Care should be taken that the cyanid is of good quality 

 and (at least for use with plants) contains no chlorine. If potassium 

 cyanid is used it should contain 38 per cent of cyanogen : if sodium cyanid, 

 51 to 52 per cent. The sulf uric acid should have a specific gravity of 1.83 

 and be free of any nitric acid. 



Hydrocyanic-acid gas can be used to advantage in the following ways: 



(a) For household and storehouse pests and for fumigating bales of 

 imported cotton. 



(6) For greenhouse insects. 



(c) For insects on dormant nursery stock. 



(d) For insects on citrus trees. 



For the first class, an ounce of sodium cyanid for every 100 cu. ft. of 

 space is used, and at least 2 hr. of fumigation is necessary. 



For greenhouse insects the dose is J^ to % oz. of sodium cyanid for 

 every 1,000 cu. ft., with a fumigation period of % to 1 hr. This treatment, 

 at a temperature of about 65F. and a low percentage of atmospheric 

 moisture, should be given only after dark. Some of the more delicate 

 varieties of plants may be somewhat injured by this, but in all probability 

 much less than by the continued attacks of the insects. The plants 

 should be dry (not watered recently) at the time of treatment. 



Dormant nursery stock should be treated with % to 1 oz. of sodium 

 cyanid for every 100 cu. ft., for 1 hr. The stock should not be wet nor 

 very closely packed. 



For the fumigation of citrus trees during their dormant or most 

 nearly dormant season (October to January) Y to \Y oz. of sodium cya- 

 nid should be used for every 100 cu. ft. of space for a period of ^ to 1 hr. 

 The value of good citrus trees is such that gas-tight tents are made and 

 used for fumigating them. 



In using potassium cyanid, one-fourth more should be taken as the 

 dose than indicated above. 



Before treating any place to be fumigated, determine the number of 

 cubic feet in the place and weigh out the proper amount of cyanid. Tak- 

 ing this quantity as the unit from which to determine the amounts of 

 sulf uric acid and water for this dose, measure out 1J^ times as much of 

 the acid in fluid ounces and twice as much water, also in fluid ounces. 

 Thus if the space to be fumigated calls for 4J^ oz. (by weight) of the 

 cyanid, 6% fl. oz. of the acid, and 9 fl. oz. of water will constitute the 



