206 SHADE-TREES IN TOWNS AND CITIES 



washes to kill the cottony maple scale or the woolly maple 

 scale. 



Kerosene emulsion is one of the most common contact 

 insecticides. A 10 per cent, solution of kerosene in water 

 is the usual strength employed in spraying foliage with 

 safety. Kerosene and water alone do not emulsify, and if an 

 attempt is made to spray with only a mechanical mixture of 

 the oil and water, the chances are that neither pure oil nor 

 water is pumped at any one time. Soap is therefore added 

 to the oil in order to make an emulsion. 



The preparation is made as follows : 



Kerosene 2 gals. 



Soap lb. 



Water 1 gal. 



Dissolve the soap in hot water, add the kerosene and 

 churn thoroughly, or pump into itself till a creamy emulsion 

 is formed. This emulsion, diluted with from twelve to fif- 

 teen times its own bulk of water, is an excellent summer 

 remedy for plant lice and other soft-bodied insects that can 

 be reached with contact poisons. 



There are now soft soaps on the market by means of 

 which it is possible to emulsify kerosene with water without 

 heating any of the ingredients. The soap is dissolved in the 

 water and then the kerosene is added while the mixture is 

 being pumped into itself until an emulsion is formed. 



There are also many oil and petroleum preparations now 

 manufactured that are soluble in cold water and are ready 

 for use on mixing. A perfect emulsion is formed without 

 pumping, and no stirring is necessary while the mixture is 

 being applied. These miscible oils are rather expensive, 

 but have the advantage of being always ready for use. To 



