HYDROCYANIC ACID GAS 83 



In fumigating a house, or a part of a house, the materials are com- 

 bined in the same manner as above, but the proportions to use are 

 1 ounce of cyanide, 1 ounce of sulphuric acid, and 3 ounces of 

 water to each 100 cubic feet. All cracks should be sealed or stopped 

 up. Gummed paper is useful for this purpose. After the fumigation 

 is complete, the house must be aired out by opening the windows 

 from the outside. Fumigation of dwellings ought never to be 

 attempted unless one thoroughly understands the process and the 

 necessary precautions. 



In greenhouses the amount of material to use cannot definitely be 

 specified in advance, and ought always to be ascertained by careful 

 preliminary trial. Different plants will withstand varying amounts 

 of the fumigant, and much depends on the tightness of the house. 



It is best to begin with a dose of | to ^ ounce of cyanide to the thou- 

 sand cubic feet, continuing the treatment for about 2 hours, at once 

 airing the house and observing results. If the insects are not all 

 killed, and the plants are uninjured, the dose may be made a little 

 heavier. 



Fumigation in greenhouses must aways be done at night, and the 

 leaf surfaces must be dry. The house may be aired out late the same 

 night or early the next morning, before the sun is hot. 



Greenhouse fumigation is of special value against mealy bugs, 

 white fly, and violet aphis, because other possible treatments are in- 

 jurious to the plants or ineffective. It is not successful against scale 

 insects or red spider. 



When greenhouses are cleared of plants between crops, they should 

 be thoroughly fumigated, using the cyanide at the rate of 5 to 8 ounces 

 to the thousand cubic feet and continuing the treatment over night. 

 Valuable protection will thus be secured for the succeeding crop. 



Fumigation with Tobacco 



For the control of most plant lice in greenhouses, fumigation with 

 tobacco is a common method. This cannot be employed in houses 

 containing violets, since the fumes will spot the leaves. 



