Methods of Control 397 



Mixing the Chemicals. The chemicals should be 

 mixed as follows : For each ounce of sodium cyanid 

 use ii/2 fluid ounces of sulphuric acid and 2 fluid 

 ounces of water. The water is first placed in the 

 generators, then the sulphuric acid. The cyanid is 

 then dropped into the warm acid, and the manipula- 

 tor must at once leave the greenhouse and shut the 

 door tightly behind him. 



Short exposure with a greater strength of gas is 

 more desirable than overnight exposure with a 

 weaker gas. Better results are obtained when the 

 fumigation lasts about two hours. After fumigation 

 the house is opened at the top or at the side doors 

 to allow the escape of the gas. During cold weather 

 the ventilators should be opened for a short time 

 only at several intervals. 



It is not advisable to fumigate if the house tem- 

 perature is below 52 degrees F. or above 70 degrees 

 F. As already stated, fumigation should never be 

 done while the sun shines. Hydrocyanic acid gas 

 is soluble in water. It is, therefore, evident that 

 neither the plants nor the benches should be wetted 

 before fumigation. 



Don'ts in Fumigation 



The following don'ts laid down by Sasscer and 

 Borden will be of value to the greenhouse man : 



"Do not guess the amount of chemicals to be em- 

 ployed or the cubic contents of the house. 



