INSECTICIDES AND THEIR APPLICATION 159 



External Poisons 



The petroleum oils are among the most important of the 

 contact-killing insecticides. For general use kerosene is 

 the most convenient of these oils. As kerosene does not 

 mix with water, dilution with this liquid is not practicable. 

 It has been found, however, that kerosene may be safely 

 and effectively used, provided it is first emulsified with hot 

 soapsuds. This is generally accomplished by adding two 

 gallons of kerosene to one gallon of a solution made by dis- 

 solving half a pound of common hard soap in one gallon 

 of boiling water, and then churning the mixture by forcing 

 it back into the same vessel through a force pump. A 

 creamy emulsion will thus be formed. Before it is ap- 

 plied, this epiulsion is to be diluted with nine or ten parts 

 of water. It is better to use soft water or rain water for 

 the dilution. 



The undiluted emulsion may be kept for some time, stored 

 in a dark, cool place. When needed, the required amount 

 may be measured out and mixed with three or four parts 

 of boiling water, cold water being added to fill out the di- 

 lution. 



Kerosene emulsion is an excellent remedy for insects 

 that suck the sap of plants through pointed beaks, such as 

 the plant lice and the chinch bugs. It kills by contact, but 

 does not remain upon the plant in an effective condition. 

 It is applied in a fine spray. 



Various forms of crude petroleum have recently come 

 into use against scale insects. Some proprietary insecti- 

 cides contain heavy oils so treated as to mix readily with 

 water, so that they are very easy to spray upon dormant 

 trees. 



The lime-sulphur wash is one of the most efficient con- 



