Materials and Formulas. 



149 



insects. His experiments began in September, 1886, in the 

 orange grove of J. W. Wolfskill, of Los Angeles, Cal. Its 

 use has been followed by such good results that all other gases 

 have been abandoned in treating these pests. The gas is pre- 

 pared by using 



Cyanide of potassium, 60 per cent 1 ounce. 



Commercial sulphuric acid 1 fluid ounce. 



Water 3 " ounces. 



Potassium cyanide of 90 per cent has also given excellent 

 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 cya- 

 nide of potassium is dropped in, and the tent immediately 

 closed. The gas is exceedingly poisonous, and should not be 

 inhaled. The amount formed with the above materials is suffi- 

 cient for a confined space containing 150 cubic feet. It is safer 

 to use the gas upon dormant trees, and during cool weather or at 

 night, since trees are more easily injured during a high tempera- 

 ture. The treated parts should remain covered about an hour. 



" The following table, giving height of trees and the propor- 

 tions of chemicals and water, will be found suitable for districts 

 in the interior or beyond ten miles in a direct line from the sea- 

 coast : 



