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Cyanide of Potash or Potassium Cyanide. This insecti- 

 cide can be obi ained by mixing potash with prussic acid. 

 h is an extremely poisonous substance, which lias in recenl 

 years come into greal prominence in connexion with the 

 fumigation of Living plants infested with scale insects In 

 many pails of the world fruit trees are fumigated regularly 

 for the control of insect pests, the trees being covered for 

 the purpose by means of tents of air-tight canvas to confine 

 the gas made from the potassium cyanide in proximity to 

 t he parts of the tree. 



In the West Indies, fumigation of trees has not become 

 a regular practice, chiefly on account of the expense of the 

 process, which is very large in proportion to the value of the 

 products of the trees. 



Imported plants are fumigated, according to law, before 

 being allowed entry to any colony for the prevention of the 

 introduction of insect pests. 



In using potassium cyanide for fumigating purposes, 

 hydrocyanic acid gas is produced by the action of sulphuric 

 acid and water on it, in the following proportions : 



Potassium cyanide 1 oz. 



Sulphuric acid lh oz. 



Water 2 J oz. 



These amounts are suitable for an enclosed space of 300 

 cubic; feet. 



Potassium cyanide can be used with good results for 

 treating many of the insects for which carbon bisulphide 

 has been suggested. The very poisonous nature of this 

 insecticide must be borne in mind, however, and onlv 

 responsible persons allowed to handle it. 



It is probable that food stuffs would not be injured or 

 rendered poisonous by being fumigated with potassium 

 cyanide, but many persons would very likely prefer not to 

 take the risk. 



Books, clothing, and grain, however, might safely be 

 treated with this material, if this is desired. 



Ants may be killed by pouring into the nest a solu- 

 tion made by dissolving 2' 07 " ^ potassium cyanide in 

 2 quarts of water. The dissolved poison penetrates the 

 soil, and gives off fumes which kill the insects. 



