farmers' bulletin 880. 



Table I. — Amounts of cyanid and nuinber of fumigations sufficient to destroy various 

 greenhouse pests. 



1 For the most part aphids can be controlled with one-half ounce of sodium cyanid per 1,000 cubic 

 feet, although there are a few species which are quite resistant to this gas and not so readily killed. 

 ^ The ereenhouse < >rthezia and mealybugs around the roots of plants are very difficult to kill, and this 

 1 is recommended only for those occurring above the soil. 



CHEMICAL FORMULA TO BE EMPLOYED. 



The chemicals ^ should be mixed in the followino; proportions: For 

 each ounce of sodium cyanid use 1 ^ fluid ounces of sidphuric acid and 

 2 fluid ounces of water. 



MIXING THE CHEMICALS. 



After the generators have been distributed throughout the green- 

 house, and before the chemicals have been mixed, the cyanid should 

 be weighed accurately and the proper amount for each generator 

 placed in a paper bag near the generator. The chemicals should be 

 mixed invariably in the following manner: Fii-st, measm"e and place 

 in each generator the amomit of water required; second, measm'o and 

 place in each generator the amomit of sulphuric acid required; 

 third, drop the cyanid into the diluted warm acid in each gen- 

 erator, immediately leave the greenhouse, and post a danger sign 

 on the closed door. The cyanid should be dropped gently from the 

 bag, not thrown, into the generators, and the operator should begin 

 at the generator farthest from the door and work toward the door. 

 In case there are two rows of generators the cyanid should be dropped 

 simultaneously by two operators. As little time as possible should 

 elapse between the addition of the acid and the addition of the 

 cyanid, as the heat which is liberated by the mixmg of the acid 

 and water assists in the generation of the gas. 



' If potassium cyanid is used in place nf sodium cyanid, the formula should be as follow;: For each ounce 

 of 98 to 99 per cent potassium cyanid containing 38.4 per cent cyanogen use 1 ounce of sulphuric arid and 

 3 ounces of water. The yield from 1 ounce of high-grade sodium cyanid is equivalent to the yield from 

 IJ ounces of high-grade potassium cvanid. 



