FUMIGATION. 159 



CHAPTER LXXI. 



EUMIGATION. 



{^Hydrocyanic-gas Treatment.) 



" Dr. Coquillet was the first to suggest and use this 

 gas for the destruction of scale insects. His experiments, 

 according to Professor Lodeman, began in September, 

 1886, in the orange grove of J. W. Wolfskill, of Los 

 Angeles, California. Its use has been followed by such 

 good results that all other gases have been abandoned in 

 treating these pests. 



" The gas is prepared by using — 



Cyanide of Potassium, 60 per cent., 1 ounce. 

 Commercial Sulphuric Acid, 1 fluid ounce. 

 Water, 3 fluid ounces. 



" Potassium cyanide of 90 per cent, has also given excel- 

 lent results. The water is first placed in an open glazed 

 vessel, and then the acid is added. When the parts to be 

 treated are all covered the diluted acid is placed under 

 the tent, the cyanide of potassium is dropped in, and the 

 tent immediately closed. Thegas is exceedingly poisonous, 

 and should not be inhaled. The amount formed with the 

 above materials is sufficient for a confined space contain- 

 ing 150 cubic feet. It is safer to use the gas upon dor- 

 mant trees and during cool weather or at night, since 

 trees are more easily injured during a high temperature ; 

 treated parts should remain covered about an hour, and 

 to work the thing properly several tents should be in 

 use at once ; this to prevent loss of time on the part of 

 those engaged in the operation of fumigation. The fol- 

 lowing table, giving height of trees and the proportions 



